Discussion: Impactful Experiences

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1 Understanding Human Development: Approaches and Theories

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Learning Objectives 1.1 Outline five principles of the lifespan developmental perspective. 1.2 Discuss three theoretical controversies about human development. 1.3 Summarize five theoretical perspectives on human development. 1.4 Describe the methods used in studying human development, including types of data and designs. 1.5 Discuss the responsibility of researchers to their participants and how they may protect them.

Digital Resources

Resilience: It Takes a Village

Poverty and Brain Development

Second Couplehood in Late Adulthood

Nature and Nurture

Educational Aspirations

Sociocultural Influences on Development: Desegregation

Children of Katrina: Longitudinal Research

Childhood Exposure to Lead

Voluntary Participation in HIV Research

Master these learning objectives with multimedia resources available at edge.sagepub.com/kuthertopical and Lives in Context video cases available in the interactive eBook.

Think back over your lifetime. How have you grown and changed through the years? Do your parents describe you as a happy baby? Were you fussy? Do you remember your first day of kindergarten? What are some of your most vivid childhood memories? Did you begin puberty early, late, or was your development similar to others your age? Were your adolescent years a stressful time? What types of changes do you expect to undergo in your adult years? Where will you live? Will you have a spouse? Will you have children? What career will you choose? How might these life choices and circumstances influence how you age and your perspective in older adulthood? Will your personality remain the same or change over time? In short, how will you change over the course of your lifespan?

What is Lifespan Human Development? This is a book about lifespan human development—the ways in which people grow, change, and stay the same throughout their lives, from conception to death. When people use the term development, they often mean the transformation from infant to adult. However, development does not end with adulthood. We continue to change in predictable ways throughout our lifetime, even into old age. Developmental scientists study human development. They seek to understand lifetime patterns of change.

lifespan human development An approach to studying human development that examines ways in which individuals grow, change, and stay the same throughout their lives, from conception to death.

Table 1.1 illustrates the many phases of life that we progress through from conception to death. Each phase of life may have a different label and set of developmental tasks, but all have value. The changes that we undergo during infancy influence how we experience later changes, such as those during adolescence and beyond. This is true for all ages in life. Each phase of life is important and accompanied by its own demands and opportunities.

Change is the most obvious indicator of development. The muscle strength and coordination needed to play sports increases over childhood and adolescence, peaks in early adulthood, and begins to decline thereafter,

declining more rapidly from middle to late adulthood. Similarly, children’s capacity to learn and perform cognitive tasks increases as they progress from infancy through adolescence, and adults typically experience a decline in the speed of cognitive processing. However, there also are ways in which we change little over our lifetimes. Some personality traits, for example, are highly stable over the lifespan, so that we remain largely the “same person” into old age (McCrae, 2002; Roberts & Caspi, 2003; Wortman, Lucas, & Donnellan, 2012).

Table 1.1 Ages in Human Development Table 1.1 Ages in Human Development

Life Stage Approximate

Age Range Description

Prenatal Conception to birth

Shortly after conception, a single- celled organism grows and multiplies. This is the most rapid period of physical development in the lifespan as basic body structures and organs form and grow. The fetus hears, responds to sensory stimuli (such as the sound of its mother’s voice), learns, remembers, and begins the process of adjusting to life after birth.

Infancy and toddlerhood

Birth to 2 years

The newborn is equipped with senses that help it to learn about the world. Environmental influences stimulate the brain to grow more complex, and the child interacts with her environment, shaping it. Physical growth occurs as well as the development of motor, perceptual, and intellectual skills. Children show advances in language comprehension and use, problem solving, self- awareness, and emotional control. They become more independent and

interested in interacting with other children and form bonds with parents and others.

Early childhood

2 to 6 years

Children grow steadily over these years of play prior to beginning elementary school. Children’s muscles strengthen, and they become better at controlling and coordinating their bodies. Children’s bodies become more slender and adultlike in proportions. Memory, language, and imagination improve. Children become more independent and better able to regulate their emotions as well as develop a sense of right and wrong. Children become more aware of their own characteristics and feelings. Family remains children’s primary social tie, but other children become more important and new ties to peers are established.

Middle childhood 6 to 11 years

Growth slows, and health tends to be better in middle childhood than at any other time during the lifespan. Strength and athletic ability increase dramatically. Children show improvements in their ability to reason, remember, read, and use arithmetic. As children advance cognitively and gain social experience, they understand themselves and think about moral issues in more complex ways as compared with younger children. As friendships develop, peers and group memberships become more important

Adolescents’ bodies grow rapidly.

Adolescence 11 to 18 years

They become physically and sexually mature. Though some immature thinking persists, adolescents can reason in sophisticated and adultlike ways. Adolescents are driven to learn about themselves and begin the process of discovering who they are, apart from their parents. Most adolescents retain good relationships with parents, but peer groups increase in importance. Adolescents and their peers influence each other reciprocally. It is through adolescents’ interactions with family and peers that they begin to establish a sense of who they are.

Early adulthood

18 to 40 years

In early adulthood, physical condition peaks and then shows slight declines with time. Lifestyle choices, such as smoking, diet, and physical activity, play a large role in influencing health. As they enter early adulthood, young adults experience

a great many changes, such as moving out of the family home, going to college, establishing mature romantic relationships, and beginning careers. Young adults’ understanding of themselves is complex and shifts as they experience life changes and take on new responsibilities and new roles. Young adults make and carry out decisions regarding career, lifestyle, and intimate relationships. Most young adults join the workforce, marry or establish a long-term bond with a spouse, and become parents. The timing of these transitions varies, but most fully enter adult roles by the

mid-20s. Some developmental scientists define a transitional period between adolescence and early adulthood, referred to as emerging adulthood, which represents the period between completing secondary education and adopting adult roles, such as work and family. Emerging adulthood spans ages 18 to 25, or even as late as age 29; however, not all young people experience a period of emerging adulthood as not all are embedded in contexts that permit a gradual transition to adulthood.

Middle adulthood

40 to 65 years

In middle adulthood, people begin to notice changes in their vision, hearing, physical stamina, and sexuality. Basic mental abilities, expertise, and practical problem- solving skills peak. Career changes and family transitions require that adults continue to refine their understandings of themselves. Some adults experience burnout and career changes while others enjoy successful leadership positions and increased earning power at the peak of their careers. Stress stems from assisting children to become independent, adapting to an empty nest, and assisting elderly parents with their health and personal needs.

Most older adults remain healthy and active despite physical declines. Reaction time slows, and most older adults show decline in some aspects of memory and intelligence, but an increase in expertise and wisdom compensates for losses. Most older

Late adulthood

65 years and beyond

adult friendships are old friendships, and these tend to be very close and a source of support. At the same time, older adults are less likely to form new friendships than at other times in life. They face adjustments to retirement, confront decreased physical health and strength, cope with personal losses (such as the death of a loved one), think about impending death, and search for meaning in their lives.

Death

Death itself is a process. Regardless of whether it is sudden and unexpected, the result of a lengthy illness, or simply old age, death entails the stopping of heartbeat, circulation, breathing, and brain activity. A person’s death causes changes in his or her social context— family members and friends must adjust to and accept the loss.

Lifespan human development can be described by several principles. As discussed in the following sections, development is: (1) multidimensional, (2) multidirectional, (3) plastic, (4) influenced by multiple contexts, and (5) multidisciplinary (Baltes & Carstensen, 2003; Baltes, Lindenberger, & Staudinger, 1998; Baltes, 1997).

Development Is Multidimensional Physical changes such as body growth are the most obvious forms of development. Not only do our bodies change, but so do our minds, the ways in which we show emotion, and our social relationships. In this way, development is multidimensional: It entails changes in many areas of development, including the physical, the cognitive, and the socioemotional (Baltes et al., 1998; Baltes, 1997; Staudinger & Lindenberger, 2003). Physical development refers to body maturation and growth, including body size, proportion, appearance, health, and perceptual abilities.

Cognitive development refers to the maturation of thought processes and the tools that we use to obtain knowledge, become aware of the world around us, and solve problems. Socioemotional development includes changes in personality, emotions, views of oneself, social skills, and interpersonal relationships with family and friends. Each of these areas of development overlap and interact. With advances in cognitive development, for example, a child may become better able to take her best friend’s point of view, which in turn influences her socioemotional development as she becomes more empathetic and sensitive to her friend’s needs and develops a more mature friendship. Figure 1.1 illustrates these three areas of development and how they interact.

physical development Body maturation, including body size, proportion, appearance, health, and perceptual abilities.

cognitive development Maturation of mental processes and tools individuals use to obtain knowledge, think, and solve problems.

socioemotional development Maturation of social and emotional functioning, which includes changes in personality, emotions, personal perceptions, social skills, and interpersonal relationships.

Figure 1.1: Multidimensional Nature of Development

Advances in physical, cognitive, and socioemotional development interact, permitting children to play sports, learn more efficiently, and develop close friendships.

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Development Is Multidirectional Development is commonly described as a series of improvements in performance and functioning, but in fact development is multidirectional, meaning that it consists of both gains and losses, growth and decline, throughout the lifespan (Baltes et al., 1998; Baltes, 1997; Staudinger & Lindenberger, 2003). For example, we are born with a stepping reflex, an innate involuntary response in which infants make step-like movements when held upright over a table, bed, or hard horizontal surface (for more on infant reflexes, see Chapter 4). Over the first year, infants gain new motor skills and the stepping reflex disappears (Thelen, Fisher, & Ridley- Johnson, 2002). As another example of multidirectionality, in older adulthood people’s social networks narrow and they have fewer friends; however, their relationships become more significant and meaningful (Carstensen & Mikels, 2005). Throughout life there is a shifting balance between gains and improvements in performance (common early in life) and losses and declines in performance (common late in life; Baltes & Carstensen, 2003). At all ages, however, individuals can compensate for losses by improving existing skills and developing new ones (Boker, 2013; Freund & Baltes, 2007). For example, though the speed at which people think tends to slow in older adulthood, increases in knowledge and experience enable older adults to compensate for the loss of speed, so that they generally retain their ability to complete day-to-day tasks and solve everyday problems (Bluck & Gluck, 2004; Hess, Leclerc, Swaim, & Weatherbee, 2009; Margrett, Allaire, Johnson, Daugherty, & Weatherbee, 2010). Outside of our awareness, the brain naturally adapts to a lifetime of sensory experiences in order to portray the world around us efficiently and accurately as we age well into older adulthood (Moran, Symmonds, Dolan, & Friston, 2014).

Development Is Plastic Development is characterized by plasticity: It is malleable or changeable. Frequently the brain and body can compensate for illness and injury. Children who are injured and experience brain damage may show resilience as other parts of the brain take on new functions. The plastic nature of human development allows people to modify their traits,

capacities, and behavior throughout life (Baltes et al., 1998; Baltes, 1997; Staudinger & Lindenberger, 2003). For example, older adults who have experienced a decline in balance and muscle strength can regain and improve these capabilities through exercise (McAuley et al., 2013). Plasticity generally tends to decline as we age, but it does not disappear entirely. Short instruction, for instance, can enhance the memory capacities of very old adults, but less so than younger adults (Singer, Lindenberger, & Baltes, 2003). Thus, memory plasticity is preserved, but to a reduced degree, in very old age. Plasticity makes it possible for individuals to adjust to change and to demonstrate resilience, which is the capacity to adapt effectively to adverse contexts and circumstances (Luthar et al., 2015; Masten, 2016).

plasticity A characteristic of development that refers to malleability, or openness to change in response to experience.

resilience The ability to adapt to serious adversity.

Some plasticity is retained throughout life. Practicing athletic activities can help older adults rebuild muscle and improve balance.

Reuters/Mike Blake

Development Is Influenced by Multiple Contexts In its simplest terms, context refers to where and when a person develops. Context includes aspects of the physical and social environment such as family, neighborhood, country, culture, and historical time period. Context also includes intangible factors, characteristics that are not visible to the

naked eye, such as values, customs, and ideals. Culture is a particularly important context that influences us, as illustrated in Cultural Influences on Development: Defining Culture.

context Unique conditions in which a person develops, including aspects of the physical and social environment such as family, neighborhood, culture, and historical time period.

In order to understand a given individual’s development, we must look to his or her context. For example, consider the context in which you were raised. Where did you grow up? City? Suburb? Rural area? What was your neighborhood like? Were you encouraged to be assertive and actively question the adults around you, or were you expected to be quiet and avoid confrontation? How large a part was religion in your family’s life? How did religious values shape your parent’s child-rearing practices and your own values? How did your family’s economic status affect your development?

An important context that influences our development is the time period in which we live. Some contextual influences are tied to particular historical eras and explain why a generation of people born at the same time, called a cohort, are similar in ways that people born at other times are different. History-graded influences include wars, epidemics, and economic shifts such as periods of depression or prosperity (Baltes, 1987). These influences shape our development and our views of the world—and set cohorts apart from one another. Adults who came of age during the Great Depression and World War II are similar in some ways that make them different from later cohorts; for example, they tend to have particularly strong views on the importance of the family, civic mindedness, and social connection (Rogler, 2002). Age-graded influences, those tied to chronological age, such as the age at which the average person enters school, reaches puberty, graduates from high school, gets married, or has children, are also shaped by context as the normative age of each of these events has shifted over the last few generations (Baltes, 1987).

cohort A generation of people born at the same time, influenced by the same historical and cultural conditions.

What roles have larger historical events played in your development? For example, consider Hurricane Sandy of October 2012, the second costliest hurricane in U.S. history, which affected 24 states, including the entire eastern seaboard, with flooding, downed power lines, and many destroyed homes. Historical events include the terrorist attacks of September 11, 2001; the election of the first African American president of the United States in 2008; and the school shooting in Newtown, Connecticut in 2012. How have historical events influenced you and those around you? Can you identify ways in which your cohort differs from your parents’ cohort because of historical events?

Developmental Science Is Multidisciplinary To say that people are complex is an understatement. Scientists who study lifespan human development attempt to understand people’s bodies, minds, and social worlds. The contributions of many disciplines are needed to understand how people grow, think, and interact with their world. Psychologists, sociologists, anthropologists, biologists, neuroscientists, and medical researchers all conduct research that is relevant to understanding aspects of human development. For example, consider cognitive development. Children’s performance on cognitive measures, such as problem solving, are influenced by their physical health and nutrition (Anjos et al., 2013), interactions with peers (Fawcett & Garton, 2005; Holmes, Kim-Spoon, & Deater-Deckard, 2016), and neurological development (Ullman, Almeida, & Klingberg, 2014)— findings from the fields of medicine, psychology, and neuroscience, respectively. In order to understand how people develop at all periods in life, developmental scientists must combine insights from all of these disciplines.

Cultural Influences on Development

Defining Culture

Cultural influences on development are illustrated by the many ethnic communities that comprise most U.S. cities. What subcultures and neighborhoods can you identify in your community?

Reuters/Lucy Nicholson

A large and influential part of our context is culture, which is the set of customs, knowledge, attitudes, and values that are shared by members of a group and are learned early in life through interactions with group members (Hofstede, 2001). Most classic theories and research on human development are based on Western samples, and developmental researchers once believed that the processes of human development were universal. Early studies of culture and human development took the form of cross-cultural research, comparing individuals and groups from different cultures to examine how these universal processes worked in different contexts (Gardiner & Kosmitzki, 2002).

More recently we have learned that the cultural context in which individuals live influences the timing and expression of many aspects of development (Gardiner & Kosmitzki, 2002). For example, the average age that infants begin to walk varies with cultural context. In Uganda, infants begin to walk at about 10 months of age, in France at about 15 months, and the United States at about 12 months. These differences are influenced by parenting practices that vary by culture. African parents tend to handle infants in ways that stimulate walking, by playing games that allow infants to practice jumping and walking skills (Hopkins & Westra, 1989; Super, 1981). Developmental researchers have argued that because much of the research in human development has focused on individuals from Western industrialized societies, there is a danger of defining typical development in Western samples as the norm, which can lead to narrow views of human development that do not take into account the variety of contexts in which people live. At the extreme, differences in human development within other cultural groups might be viewed as abnormal (Rogoff & Morelli, 1989). Some argue that cross-cultural research that compares the development of people from different cultures in order to understand universals in development is misguided because norms vary by cultural context (Schweder et al.,

1998).

There is a growing trend favoring cultural research, which examines how culture influences development, over cross-cultural research, which simply examines differences among cultures (Schweder et al., 1998). From a cultural research perspective, culture influences our development because it contributes to the context in which we are embedded, transmitting values, attitudes, and beliefs that shape our thoughts, beliefs, and behaviors (Cole, 1999). The shift toward cultural research permits the examination of the multiple cultures that exist within a society. For example, North American culture is not homogenous; many subcultures exist, defined by factors such as ethnicity (e.g., African American, Asian American), religion (e.g., Christian, Muslim), geography (e.g., southern, Midwestern), and others, as well as combinations of these factors. Instead of looking for universal similarities in development, cultural research in human development aims to document diversity and understand how the historical and cultural context in which we live influences development throughout our lifetime (Schweder et al., 1998).

What Do You Think? 1. How would you describe North American culture? Can you

identify aspects of North American culture that describe most, if not all, people who live there? Are there aspects of culture in which people or subgroups of people differ?

2. What subcultures can you identify in your own neighborhood, state, or region of the country? What characterizes each of these subcultures?

3. Consider your own experience. With which culture or subculture do you identify? How much of a role do you think your cultural membership has had in your own development?

culture A set of customs, knowledge, attitudes, and values shared by a group of people and learned through interactions with group members.

The field of lifespan human development studies the ways in which people grow, change, and stay the same throughout their lives. Human

development is complex. We change in multiple ways, show gains and losses over time, and retain the ability to change over our lifespan. The context in which we live influences who we become. Developmental science incorporates research from multiple disciplines.

Thinking in Context 1.1

1. Describe your own development. In what ways have you changed over your lifetime? What characteristics have remained the same?

2. Lifespan human development is multidimensional, multidirectional, plastic, and influenced by multiple contexts. Consider your own experience and provide examples from your life that illustrate the multidimensional nature of your own development. Can you do the same for multidirectionality and for plasticity? How does the context in which you were raised and live influence your development?

3. Compare the historical context in which you, your parents, and your grandparents were raised. How did historical and societal influences affect your grandparents’ development, their world view, and their child-rearing strategies? What about your parents? How might historical influences affect your own development, world view, and perspective on parenting?

Basic Issues in Lifespan Human Development Developmental scientists agree that people change throughout life and show increases in some capacities and decreases in others from conception to death. Yet, how development proceeds, the specific changes that occur, and the causes of change are debated. Developmental scientists’ explanations of how people grow and change over their lives are influenced by their perspectives on three basic issues, or fundamental questions, about human development:

1. Do people remain largely the same over time, or do they change dramatically?

2. What role do people play in their own development? How much are they influenced by their surroundings, and how much do they

influence their surroundings? 3. To what extent is development a function of inborn genetic

endowments, as compared with the environment in which individuals live?

The following sections examine each of these questions.

Continuities and Discontinuities in Development Do children slowly grow into adults, steadily gain more knowledge and experience, and become better at reasoning? Or do children grow in spurts, showing sudden and large gains in knowledge and reasoning capacities? In other words, in what ways is developmental change continuous, characterized by slow and gradual change, or discontinuous, characterized by abrupt change? As shown in Figure 1.2, a discontinuous view of development emphasizes sudden transformation in abilities and capacities whereas a continuous view emphasizes the gradual and steady changes that occur. Scientists who argue that development is continuous in nature point to slow and cumulative changes we experience in the amount or degree of skills, such as a child slowly gaining experience, expanding his or her vocabulary, and becoming quicker at problem solving, or a middle-aged adult experiencing gradual losses of muscle and strength. The discontinuous view of development describes the changes we experience as large and abrupt, with individuals of various ages dramatically different from one another. For example, puberty quickly transforms children’s bodies into more adult-like adolescent bodies, infants’ understanding and capacity for language is fundamentally different from that of school-aged children, and children make leaps in their reasoning abilities over the course of childhood (Piek, Dawson, Smith, & Gasson, 2008). For example, children progress from believing that robotic dogs and other inanimate objects are alive to understanding that life is a biological process (Gelman & Opfer, 2002).

continuous development The view that development consists of gradual cumulative changes in existing skills and capacities.

discontinuous development The view that growth entails abrupt transformations in abilities and capacities in which new ways of interacting with the world emerge.

Figure 1.2: Continuous and Discontinuous Development

It was once believed that development was either continuous or discontinuous—that changes were either slow and gradual or sudden and dramatic—but not both. Today, developmental scientists agree that development includes both continuity and discontinuity (Kagan, 2008; Lerner, Agans, DeSouza, & Gasca, 2013; Miller, 2016). Whether a particular developmental change appears continuous or discontinuous depends on our point of view. For example, consider human growth. We often think of increases in height as a slow and steady process of simply getting taller with time; each month infants are taller than the prior month, illustrating continuous change. However, as shown in Figure 1.3, when researchers measured infants’ height every day they discovered that infants have growth days and non-growth days, days that they show rapid change in height interspersed with days in which there is no change in height, thus illustrating discontinuous change (Lampl, Johnson, Frongillo Jr., & Frongillo, 2001; Lampl, Veldhuis, & Johnson, 1992). In this example, monthly measurements of infant height suggest gradual increases, but daily measurements show spurts of growth, each lasting 24 hours or less. In this way, whether a given phenomenon, such as height, is described as continuous or discontinuous can vary. Most developmental scientists agree that some aspects of lifespan development are best described as continuous and others as discontinuous (Miller, 2016).

Figure 1.3: Infant Growth: A Continuous or Discontinuous Process?

Infants’ growth occurs in a random series of roughly 1-centimeter spurts in height that occur in 24 hours or less. The overall pattern of growth entails increases in height, but whether the growth appears to be continuous or discontinuous depends on our point of view.

Source: Figure 1 from Lampl, M., Veldhuis, J. D., & Johnson, M. L. 1992. Saltation and stasis: A model of human growth. Science, 258, 801–803. With permission from AAAS.

Individuals Are Active in Development Do people have a role in influencing how they change over their lifetimes? That is, are people active in influencing their own development? Taking an active role means that they interact with and influence the world around them, create experiences that lead to developmental change, and thereby influence how they themselves change over the lifespan. Alternatively, if individuals take a passive role in their development, they are shaped by, but do not influence, the world around them—including home and relationships with family, school, and neighborhood characteristics, such the availability of playgrounds or health care.

Infants naturally influence people and the world around them. What reactions might these two babies elicit?

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The prevailing view among developmental scientists is that people are active contributors to their own development. People are influenced by the physical and social contexts in which they live, but they also play a role in influencing their development by interacting with, and changing, those contexts. Even infants influence the world around them and construct their own development through their interactions. Consider an infant who smiles at each adult he sees; he influences his world because adults are likely to smile, use “baby talk,” and play with him in response. The infant brings adults into close contact, making one-on-one interactions and creating opportunities for learning. By engaging the world around them, thinking, being curious, and interacting with people, objects, and the world around them, individuals of all ages are “manufacturers of their own development” (Flavell, 1992, p. 998).

Nature and Nurture Influence Development Perhaps the most fundamental question about lifespan human development is: What is its cause? Why do people change in predictable ways over the course of their lifetimes? The answer to this question reflects perhaps the oldest and most heated debate within the field of human development: the nature-nurture issue. Is development caused by nature or nurture? Explanations that rely on nature point to inborn genetic endowments or heredity, maturational processes, and evolution as causes of developmental change. For example, most infants take their first steps at roughly the same age as other children, suggesting a maturational trend that supports the role of nature in development. An alternative explanation for developmental change is nurture, the view that individuals are molded by the physical and social environment in which they are raised, including the home, school, workplace, neighborhood, and society. From this perspective, although most begin to walk at about the same time, environmental conditions can

speed up or slow down the process. Infants who experience malnutrition may walk later than well-nourished infants, and—as mentioned in Cultural Influences on Development—those who are given practice making stepping or jumping movements may walk earlier (Sigman, 1995; Vereijken & Thelen, 1997; Worobey, 2014).

nature–nurture issue A debate within the field of human development regarding whether development is caused by nature (genetics or heredity) or nurture (the physical and social environment).

Although developmental scientists once attempted to determine whether nature or nurture influenced development, most now agree that both nature and nurture are important contributors (Grigorenko & Sternberg, 2003; Scarr & McCartney, 1983). As in the prior example, walking is heavily influenced by maturation (nature), but experiences and environmental conditions can influence the timing of a child’s first steps (nurture). Today developmental scientists attempt to determine how nature and nurture work together to influence how people grow and change throughout life (Anastasi, 1958; Crews, Gillette, Miller-Crews, & Gore, 2014; Rutter, 2012).

To review, there are three basic questions regarding lifespan human development:

1. Do people remain largely the same over time, showing continuity, or do they change dramatically, illustrating discontinuity?

2. What role do people play in their own development? How much are they influenced by their surroundings, and how much do they influence their surroundings? To what degree are they active or passive participants in their development?

3. To what extent is development a function of inborn genetic endowments, as compared with the environment in which individuals live?

Developmental scientists vary in their responses to these questions, as we will discover throughout this book. Different answers reflect different assumptions about the causes of development and different explanations for human development.

Thinking in Context 1.2

1. Can you identify ways in which you have changed very gradually over the years? Were there other times in which you showed abrupt change, such as physical growth, strength and coordination, thinking abilities, or social skills? In other words, in what ways is your development characterized by continuity? Discontinuity?

2. Are people active or passive participants in their development? What role did your physical and social environment play in your growth? In what ways, if any, did you take an active role in your own development?

3. How much of who you are today is a function of nature? Nurture?

Theoretical Perspectives on Human Development Human development researchers offer many theoretical explanations for the changes that occur over the lifetime. Over the past century, developmental scientists have learned much about how individuals progress from infants to children to adolescents, and to adults, as well as how they change throughout adulthood. Scientists explain their observations by constructing theories of human development. A theory is a way of organizing a set of observations or facts into a comprehensive explanation of how something works. Theories are important tools for compiling and interpreting the growing body of research in human development as well as determining gaps in our knowledge about a given phenomenon and making predictions about what is not yet known (Crain, 2011; Green & Piel, 2010; Miller, 2016).

theory An organized set of observations to describe, explain, and predict a phenomenon.

Effective theories generate specific hypotheses, or proposed explanations

for a given phenomenon, that can be tested by research. It is important to note that this testing seeks to find flaws in the hypothesis—not to “prove” that it is flawless. A good theory is one that is falsifiable, or capable of generating hypotheses that can be tested and, potentially, refuted. As scientists conduct research and learn more about a topic, they modify their theories. Updated theories often give rise to new questions and new research studies, whose findings may further modify theories.

hypothesis A proposed explanation for a phenomenon that can be tested.

The great body of research findings in the field of lifespan human development has been organized into several theoretical perspectives to explain how we change throughout our lives. Given the myriad ways in which we develop, theories vary in their explanatory focus and emphasis. For example, some theories examine personality development and others address changes in how individuals reason and solve problems. As the following sections illustrate, these theoretical perspectives vary greatly in how they account for the developmental changes that occur over the lifespan.

Sigmund Freud (1856–1939), the father of the psychoanalytic perspective, believed that much of our behavior is driven by unconscious impulses.

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Psychoanalytic Theories

Are there powerful forces within us that make us behave as we do? Are we pushed by inner drives? Psychoanalytic theories describe development and behavior as a result of the interplay of inner drives, memories, and conflicts we are unaware of and cannot control. These inner forces influence our behavior throughout our lives. Freud and Erikson are two key psychoanalytic theorists whose theories remain influential today.

psychoanalytic theory A perspective introduced by Freud that development and behavior is stagelike and influenced by inner drives, memories, and conflicts of which an individual is unaware and cannot control.

Freud’s Psychosexual Theory

Sigmund Freud (1856–1939), a Viennese physician, is credited as the father of the psychoanalytic perspective. Freud believed that much of our behavior is driven by unconscious impulses that are outside of our awareness. As shown in Table 1.2, Freud believed we progress through a series of psychosexual stages, periods in which unconscious drives are focused on different parts of the body, making stimulation to those parts a source of pleasure. How parents direct and gratify their children’s basic drives influences their personality development. Freud explained that the task for parents is to strike a balance between over- and under-gratifying a child’s needs at each stage in order to help the child develop a healthy personality with the capacity for mature relationships throughout life.

Table 1.2 Freud’s Psychosexual Stages Table 1.2 Freud’s Psychosexual Stages

Stage Approximate Age

Description

Oral 0 to 18

Basic drives focus on the mouth, tongue, and gums, whereby the infant obtains pleasure by feeding and sucking. Feeding and weaning are particularly important influences on personality development at

Oral months this time. Failure to meet oral needs can be shown in behaviors that center on the mouth, such as fingernail biting, overeating, smoking, or excessive drinking.

Anal 18 months to 3 years

Basic drives are oriented toward the anus, and the infant obtains pleasure by retaining or passing of bowel and bladder movements. Toilet training is an important influence on personality development. If caregivers are too demanding, pushing the child before he or she is ready, or if caregivers are too lax, children may develop issues of control such as a need to impose extreme order and cleanliness on their environment or extreme messiness and disorder.

Phallic 3 to 6 years

Basic drives shift to the genitals. The child develops a romantic desire for the opposite-sex parent and a sense of hostility and/or fear of the same-sex parent. The conflict between the child’s desires and fears arouses anxiety and discomfort. It is resolved by pushing the desires into the unconscious and spending time with the same-sex parent and adopting his or her behaviors and roles. It is through this process that children begin to become members of society by adopting societal expectations and values. Failure to resolve this conflict may result in guilt and a lack of conscience.

Latency 6 years to puberty

This is not a stage but a time of calm between stages when the child develops talents and skills and focuses on school, sports, and friendships.

Genital Puberty to adulthood

With the physical changes of early adolescence, the basic drives again become oriented toward the genitals. The person becomes concerned with developing mature adult sexual interests and sexual satisfaction in adult relationships throughout life.

Freud made many contributions to psychology, psychiatry, and Western thought. Many of his insights have stood up well to the test of time, such as the notion of unconscious processes that we are not aware of (Adolph & Berger, 2005; Bargh, 2013; Fonagy & Target, 2000). The idea that early experiences in the family are important contributors to development is also accepted by the general public, as is the role of emotions in development, both of which Freud espoused. However, Freud did not study children; his theory grew from his work with female psychotherapy patients. Because of its heavy emphasis on infant sexuality, Freud’s psychosexual stage framework, especially the phallic stage, is not widely accepted (Westen, 1998).

Freud’s theory has declined in popularity, partly because it cannot be directly tested and is therefore not supported by research (Crews, 1996). How are we to study unconscious drives when we are not aware of them? Only about 2% of today’s psychotherapists practice traditional Freudian psychoanalysis that emphasizes unconscious motivators of behavior because shorter and more behaviorally focused therapies have been found to be more effective at helping people (Leichsenring & Rabung, 2008; McDonald, 1998).

Erikson’s Psychosocial Theory

Erik Erikson (1902–1994) was influenced by Freud, but he placed less emphasis on instinctual drives as motivators of development and instead focused on the role of the social world, society, and culture in shaping development. Erikson posed a lifespan theory of development in which individuals progress through eight stages of psychosocial development that include changes in how they understand and interact with others, as well as changes in how they understand themselves and their roles as members of society (Erikson, 1950; see Table 1.3). Each stage presents a unique developmental task, which Erikson referred to as a crisis or conflict that must be resolved. How well individuals address the crisis determines their

must be resolved. How well individuals address the crisis determines their ability to deal with the demands made by the next stage of development.

Erik Erikson (1902–1994), shown with his wife and collaborator, Joan, posited that, throughout their lives, people progress through eight stages of psychosocial development.

Jon Erikson/Science Source

Regardless of their success in resolving a crisis of a given stage, individuals are driven by biological maturation and social expectations to the next psychosocial stage. No crisis is ever fully resolved, and unresolved crises are revisited throughout life. Although Erikson believed that it is never too late to resolve a crisis, resolving a crisis from a previous stage may become more challenging over time as people focus on current demands and the crises of their psychosocial stages.

Erikson’s psychosocial theory is well regarded as one of the first lifespan views of development. He took a positive view of development and included the role of society and culture by basing his theory on a broad range of cases including larger and more diverse samples than did Freud (Thomas, 2004). Erikson’s theory is criticized as difficult to test, but it has nonetheless sparked research on specific stages, most notably on the

and contribute to the next generation during middle adulthood (Crain, 2011; Miller, 2016). Because Erikson’s lifespan theory of development holds implications for every period of life, we will revisit his theory throughout this book at each period in the lifespan: infancy, childhood, adolescence, adulthood, and old age.

Table 1.3 Erikson’s Psychosocial Stages of Development Table 1.3 Erikson’s Psychosocial Stages of Development

Stage Approximate Age

Description

Trust vs. mistrust

Birth to 1 year

Infants learn to trust that others will fulfill their basic needs (nourishment, warmth, comfort) or to lack confidence that their needs will be met.

Autonomy vs. shame and doubt

1 to 3 years

Toddlers learn to be self-sufficient and independent through toilet training, feeding, walking, talking, and exploring, or they lack confidence in their own abilities and doubt themselves.

Initiative vs. guilt 3 to 6 years

Young children become inquisitive, ambitious, and eager for responsibility, or they experience overwhelming guilt for their curiosity and overstepping boundaries.

Industry vs. inferiority 6 to 12 years

Children learn to be hard working, competent, and productive by mastering new skills in school, friendships, and home life, or they experience difficulty, leading to feelings of inadequacy and incompetence.

Adolescents search for a sense of self

Identity vs. role confusion

Puberty to early adulthood

Adolescents search for a sense of self by experimenting with roles. They also look for answers to the question, “Who am I?” in terms of career, sexual, and political roles, or they remain confused about who they are and their place in the world.

Intimacy vs. isolation

Early adulthood

Young adults seek companionship and close relationship with another person, or they experience isolation and self- absorption due to difficulty developing intimate relationships and sharing with others.

Generativity vs. stagnation

Middle adulthood

Adults contribute to, establish, and guide the next generation through work, creative activities, and parenting, or they stagnate, remaining emotionally impoverished and concerned about themselves.

Integrity vs. despair

Late adulthood

Older adults look back at life to make sense of it, accept mistakes, and view life as meaningful and productive, or they feel despair over goals never reached and fear of death.

Behaviorist and Social Learning Theories In response to psychoanalytic theorists’ emphasis on the psyche as an invisible influence on development and behavior, some scientists pointed to the importance of studying observable behavior rather than thoughts and emotion, which cannot be seen or objectively verified. Theorists who study behaviorism examine only behavior that can be observed and believe that all behavior is influenced by the physical and social environment. For example, consider this famous quote from John Watson, an early founder of behaviorism:

behaviorism A theoretical approach that studies how observable behavior is controlled by the physical and social environment through conditioning.

Give me a dozen healthy infants, well formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select—doctor, lawyer, artist, merchant, chief, and yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors. (Watson, 1925, p. 82)

Ivan Pavlov (1849–1936) discovered classical conditioning when he noticed that dogs naturally salivate when they taste food, but they also salivate in response to various sights and sounds that they associate with food.

Sovfoto/Universal Images Group/Newscom

By controlling an infant’s physical and social environment, Watson believed he could control the child’s destiny. Behaviorist theory is also known as learning theory because it emphasizes how people and animals learn new behaviors as a function of their environment. As discussed in the following sections, classical and operant conditioning are two forms of behaviorist learning; social learning integrates elements of behaviorist theory and information processing theories.

Classical Conditioning

Classical conditioning is a form of learning in which the person or animal comes to associate environmental stimuli with physiological responses. Ivan Pavlov (1849–1936), a Russian physiologist, discovered classical conditioning when he noticed that dogs naturally salivate when they taste food, but they also salivate in response to various sights and sounds that occur before they taste food, such as their bowl clattering or their owner opening the food cupboard. Pavlov tested his observation by pairing the sound of a tone with the dog’s food; the dogs heard the tone, then received their food. Soon the tone itself began to elicit the dogs’ salivation. Through classical conditioning a neutral stimulus (in this example, the sound of the tone) comes to elicit a response originally produced by another stimulus (food). Many fears as well as emotional associations are the result of classical conditioning. For example, some children may fear a trip to the doctor’s office because they associate the doctor’s office with the discomfort they felt upon receiving a vaccination shot. Classical conditioning applies to physiological and emotional responses only, yet it is a cornerstone of psychological theory. (See Figure 1.4 for an example of classical conditioning in humans.) A second behaviorist theory accounts for voluntary, nonphysiological responses, as described in the following section.

classical conditioning A form of learning in which an environmental stimulus becomes associated with stimuli that elicit reflex responses.

Figure 1.4: Classical Conditioning in a Newborn

Classical conditioning has been observed in newborns, who naturally make sucking movements (unconditioned response) in response to sugar water (unconditioned stimulus). When stroking the forehead (neutral stimulus) is paired with sugar water, infants come to make sucking movements (conditioned response) in response to forehead strokes (conditioned stimulus).

Source: Lampl et al. (1992).

Operant Conditioning

Perhaps it is human nature to notice that the consequences of our behavior influence our future behavior. A teenager who arrives home after curfew and is greeted with a severe scolding may be less likely to return home late in the future. An employer who brings coffee and muffins to her staff on Monday morning and then notices that her employees are in good spirits and productive may be more likely to bring them snacks in the future. These two examples illustrate the basic tenet of B. F. Skinner’s (1905– 1990) theory of operant conditioning: Behavior becomes more or less probable depending on its consequences. We repeat behaviors that have pleasant outcomes and stop behaviors with unpleasant outcomes. Behaviorist ideas about operant conditioning and the nature of human behavior are woven into the fabric of North American culture and appear often in discussions of parenting (Rutherford, 2000). According to Skinner, a behavior followed by a rewarding or pleasant outcome, called reinforcement, will be more likely to recur, but one followed by an aversive or unpleasant outcome, called punishment, will be less likely to recur. Operant conditioning is a very important concept because it explains much of human behavior, including how we learn skills and habits.

operant conditioning A form of learning in which behavior increases or decreases based on environmental consequences.

reinforcement In operant conditioning, the process by which a behavior is followed by a desirable outcome increases the likelihood of a response.

punishment In operant conditioning, the process in which a behavior is followed by an aversive or unpleasant outcome that decreases the likelihood of a response.

Social Learning Theory

A common criticism of behaviorist theory is its overemphasis on the observable and neglect of internal influences on development and behavior (Miller, 2016). Albert Bandura (b. 1925) agreed that the physical and social environments are important, but he also advocated for the role of thought and emotion as contributors to development. According to Bandura’s social learning theory, people actively process information— they think and they feel emotion—and their thoughts and feelings influence their behavior. The physical and social environment influences our behavior through their influence on our thoughts and emotions. For example, the teenager who breaks his curfew and is met by upset parents may experience remorse, feeling bad about his actions, which may then make him less likely to come home late in the future. In this example, the social environment (a discussion with upset parents) influenced the teen’s thoughts and emotions (feeling bad for upsetting his parents), which then influenced the teen’s behavior (not breaking curfew in the future). In this way, our thoughts and emotions about the consequences of our behavior influence our future behavior. We do not need to experience punishment or reinforcement in order to change our behavior (Bandura, 2001). We can learn by thinking about the potential consequences of our actions.

social learning theory An approach that emphasizes the role of modeling and observational learning over people’s behavior in addition to reinforcement and punishment.

One of Bandura’s most enduring ideas about development is that people learn through observing and imitating models, which he referred to as observational learning (Bandura, Ross, & Ross, 1963; Bandura, 1986). People learn by watching others. This finding suggests that children who observe violence rewarded, such as a child grabbing (and successfully obtaining) another child’s toy, may imitate what they see and use aggressive means to take other children’s toys. People also learn by observing the consequences of others’ actions. A child observer might be less likely to imitate a child who takes another child’s toy if the aggressor is scolded by a teacher and placed in time out. Observational learning, learning by watching and imitating others around us, is one of the most powerful ways in which we learn.

observational learning Learning that occurs by watching and imitating models, as posited by social learning theory.

Another of Bandura’s contributions that has influenced the field of lifespan human development is the concept of reciprocal determinism, according to which individuals and the environment interact and influence each other (Bandura, 2011, 2012). In contrast with behaviorist theorists, Bandura viewed individuals as active in their development rather than passively molded by their physical and social environment. Individuals can influence and change their physical and social surroundings. Specifically, development is a result of interactions between the individual’s characteristics, his or her behavior, and the physical and social environment (see Figure 1.5).

reciprocal determinism A perspective positing that individuals and the environment interact and influence each other.

In a classic study conducted by Albert Bandura, children who observed an adult playing with a bobo doll toy roughly imitated those behaviors, suggesting that children learn through observation.

Albert Bandura

As an example, let us examine how characteristics of a given person might influence that person’s behavior and the surrounding social environment.

Suppose Isaac is an excitable person, and his excitability makes him quick to debate with others. This behavioral tendency, in turn, stimulates others around him to engage in debate. In addition to Isaac’s characteristics, his behavior (being quick to debate) also is influenced by the environment (e.g., being surrounded by smart people who enjoy debating) and influences the environment (e.g., people who enjoy debating are more likely to talk to Isaac, while people who avoid debating are less likely to talk to him). This is an example of the complex interplay between person, behavior, and physical and social environment that underlies much of what we will discuss throughout this book.

Figure 1.5: Bandura’s Model of Reciprocal Determinism

Behaviorist theories make important contributions to understanding lifespan human development. Classical and operant conditioning and social learning are powerful means of explaining human behavior at all ages. Concepts such as observational learning, reinforcement, and punishment hold implications for parents, teachers, and anyone who works with people. Moreover, social learning theory and reciprocal determinism offer a more complex explanation for development and behavior than do behaviorist theories. We will revisit these concepts throughout this book.

Cognitive Theories According to the lifespan developmental perspective, there are multiple domains of development. We grow and change in many ways over our lifetime. Whereas psychoanalytic theories examine inner influences on our personality and behavior, and behaviorist and social learning theories look to the environment as an influence on development, cognitive theorists examine the role of thought on behavior. Cognitive-developmental theory

and information processing theorists view cognition—thought—as essential in understanding people’s functioning across the lifespan.

Jean Piaget (1896–1980) believed that children’s drive to explore and understand the world around them propels them through four stages of cognitive development.

Bill Anderson / Science Source

Piaget’s Cognitive-Developmental Theory

Do infants think? How do children understand physical phenomena, such as whether a ball of modeling clay changes in mass when it is rolled into the shape of a hot dog? As the first scientist to systematically examine children’s thinking and reasoning, Swiss scholar Jean Piaget (1896–1980) believed that in order to understand children we must understand how they think because thinking influences all of behavior. Piaget founded the cognitive-developmental perspective on child development, which views children and adults as active explorers of their world, learning by interacting with the world around them, and organizing what they learn into cognitive schemas, or concepts, ideas, and ways of interacting on the world. In this way people contribute to their own cognitive development

because they are biologically driven to interact with others and through these interactions they construct and refine their own cognitive schemas.

cognitive-developmental perspective A perspective posited by Piaget that views individuals as active explorers of their world, learning by interacting with the world around them and describes cognitive development as progressing through stages.

schema A mental representation, such as concepts, ideas, and ways of interacting with the world.

Piaget proposed that children’s drive to explore and understand the world propels them through four stages of cognitive development. With each advancing stage, people create and use more sophisticated cognitive schemas so that they think, reason, and understand their world in more complex ways. As shown in Table 1.4, individuals move from understanding the world through their senses and motor skills, to a thought-based understanding, to viewing the world in logical but concrete terms, to viewing it in complex and abstract forms. Each stage corresponds to a different period in life. We will discuss each stage in further detail in Chapter 6.

Table 1.4 Piaget’s Stages of Cognitive Development Table 1.4 Piaget’s Stages of Cognitive Development

Stage Approximate Age

Description

Sensorimotor Birth to 2 years

Infants understand the world and think using only their senses and motor skills, by watching, listening, touching, and tasting.

Preoperational 2 to 6 years

Preschoolers are able to explore the world using their own thoughts as guides and develop the language skills to communicate their thoughts to others. Despite these advances,

their thinking is characterized by several errors in logic.

Concrete operational 7 to 11 years

School-aged children become able to solve everyday logic problems. Their thinking is not yet fully mature because they are able to apply their thinking only to problems that are tangible and tied to specific substances.

Formal operational

12 years to adulthood

Adolescents and adults can reason logically and abstractly about possibilities, imagined instances and events, and hypothetical concepts.

Piaget’s cognitive-developmental theory transformed the field of developmental psychology and remains one of the most widely cited developmental theories (Lourenco & Machado, 1996). It was the first to consider how infants and children think and to view people as active contributors to their development. Piaget’s concept of cognitive stages and the suggestion that children’s reasoning is limited by their stage holds implications for education—specifically the idea that effective instruction must match the child’s developmental level.

Some critics of cognitive-developmental theory argue that Piaget focused too heavily on cognition and ignored emotional and social factors in development (Broughton, 1981; Winegar & Valsiner, 1992). Others believe that Piaget neglected the influence of contextual factors by assuming that cognitive-developmental stages are universal, that all individuals everywhere progress through the stages in a sequence that does not vary (Lutz & Sternberg, 1999). Some cognitive theorists disagree with Piaget and argue that cognitive development is not a discontinuous, stage- like process; instead, it is a continuous process, as described in the following section.

Information Processing Theory

A developmental scientist presents a 5-year-old child with a puzzle in which a dog, cat, and mouse must find their way to a bone, piece of fish,

and hunk of cheese (Klahr, 1985). To solve the puzzle, the child must move all three animals to the appropriate locations. How will the child approach this task? Which item will she move first? What steps will she take? Will the child keep all three animals in mind? Will she remember the task and show what item goes with each animal? How quickly will the child respond? What strategies will she use? What factors influence whether and how quickly a child completes this task? Finally, how does the 5-year-old child’s process and performance differ from that of children older and younger than herself?

The problem described above illustrates the questions studied by developmental scientists who favor information processing theory, a perspective that views thinking as information processing and posits that the mind works in ways similar to a computer because information enters, is manipulated, stored, recalled, and used to solve problems (Halford & Andrews, 2011; Klahr, 1992). Unlike the theories we have discussed thus far, information processing theory is not one theory that is attributed to an individual theorist. Instead there are many information processing theories, and each emphasizes a different aspect of thinking. Some theories focus on how people perceive, focus on, and take in information. Others examine how people store information, create memories, and how they remember information. Still others examine problem solving—how people approach and solve problems in school, the workplace, and everyday life.

information processing theory A perspective that uses a computer analogy to describe how the mind receives information and manipulates, stores, recalls, and uses it to solve problems.

According to information processing theorists, we are born with the ability to process information. Our mind itself and its processes of noticing, taking in, manipulating, storing, and retrieving information does not show the radical changes that are associated with stage theories. Instead, from an information processing perspective, development is continuous and entails changes in the efficiency and speed with which we think. Maturation of the brain and nervous system contributes to changes in our information processing abilities, our tendency to become more efficient at processing information over the childhood years and to slow over the adult years (Kail, 2003; Luna, Garver, Urban, Lazar, & Sweeney, 2004). Experience

and interaction with others also contributes by helping us learn new ways of managing and manipulating information. Over the childhood years, we become better able to attend to and store information, and we operate on the information we have stored with a greater repertoire of strategies and greater efficiency.

Information processing theory offers a complex and detailed view of how we think, which permits scientists to make specific predictions about behavior and performance that can be tested in research studies. Information processing theory has generated a great many research studies and has garnered much empirical support (Halford & Andrews, 2011). Critics of the information processing perspective argue that a computer model cannot capture the complexity of the human mind and people’s unique cognitive abilities. In addition, findings from laboratory research may not extend to the everyday contexts in which people adapt to changing circumstances in contexts that pose great challenges to attention and require flexibility (Miller, 2009). Because findings from information processing research are fundamental to any discussion of cognitive development, we will explore the research in information processing as we discuss each age period throughout this book.

Sociocultural Systems Theory A major tenet of lifespan development is that people play an active role in their development by interacting with the world around them. Sociocultural systems theories emphasize the role of the sociocultural context in development. People of all ages are immersed in their social contexts; they are inseparable from the cultural beliefs and societal, neighborhood, and familial contexts in which they live. The origins of sociocultural systems theory lie with two theorists, Lev Vygotsky and Urie Bronfenbrenner.

Vygotsky’s Sociocultural Theory

Writing at the same time as Piaget, Russian scholar Lev Vygotsky (1896– 1934) offered a different perspective on development that emphasized the importance of culture. As illustrated in Cultural Influences on Development: Defining Culture, culture refers to the beliefs, values, customs and skills of a group. Vygotsky ’s (1978) sociocultural theory examines how culture is transmitted from one generation to the next

through social interaction. Children interact with adults and more experienced peers as they talk, play, and work alongside them. It is through these formal and informal social contacts that children learn about their culture and what it means to belong to it. By participating in cooperative dialogues and receiving guidance from adults and more expert peers, children adopt their culture’s perspectives and practices, learning to think and behave as members of their society (Rogoff, 2003, 2016). As children acquire their culture’s patterns of thought and behavior, they are able to apply these skills and ways of thinking to guide their own actions, thus requiring less assistance from adults and peers (Rogoff, Mosier, Mistry, & Göncü, 1993; Winsler, Carlton, & Barry, 2000).

sociocultural theory Vygotsky’s perspective that individuals acquire culturally relevant ways of thinking through social interactions with members of their culture.

Vygotsky’s sociocultural theory holds important implications for understanding cognitive development. Like Piaget, Vygotsky emphasized that children are active in their development by engaging with the world around them. However, Vygotsky also viewed cognitive development as a social process that relies on interactions with adults, more mature peers, and other members of society. Children engage their social world, and the social world shapes development by transmitting culturally relevant ways of thinking and acting. Vygotsky also argued that acquiring language is a particularly important milestone for children because it enables them to think in new ways and have more sophisticated dialogues with others in their culture, advancing their learning about culturally valued perspectives and activities (Vygotsky, 1962). We will revisit Vygotsky’s ideas about the roles of culture, language, and thought in Chapter 6.

Vygotsky’s sociocultural theory is an important addition to the field of lifespan human development because it is the first theory to emphasize the role of the cultural context in influencing people’s development throughout life. Critics argue that sociocultural theory overemphasizes the role of context, minimizes the role of individuals in their own development, and neglects the influence of genetic and biological factors (Wertsch, 1998). Another perspective on cognitive development, described below, refocuses attention on the individual.

Lev Vygotsky (1896–1934) emphasized the importance of culture in development. Children actively engage their social world, which transmits culturally relevant ways of thinking and acting that influence children’s thought and behavior.

SPUTNIK/Alamy

Bronfenbrenner’s Bioecological Systems Theory

Similar to other developmental theorists, Urie Bronfenbrenner (1917– 2005) believed that we are active in our development and interact with the world around us. Specifically, Bronfenbrenner’s bioecological systems theory poses that development is a result of the ongoing interactions among biological, cognitive, and psychological changes within the person and his or her changing context (Bronfenbrenner & Morris, 2006; Bronfenbrenner, 1979, 2005). Bronfenbrenner proposed that individuals are all embedded in, or surrounded by, a series of contexts: home, school, neighborhood, culture, and society. The bioecological systems theory offers a comprehensive perspective on the role of context as an influence on development. As shown in Figure 1.6, contexts are organized into a series of systems in which individuals are embedded and that interact with one another and the person to influence development.

bioecological systems theory A theory introduced by Bronfenbrenner that emphasizes the role of context in development, positing that contexts are organized into a series of systems in which individuals are embedded and that interact with one another and the person to influence development.

At the center of the bioecological model is the individual. The developing person’s genetic, psychological, socioemotional, and personality traits interact, influencing each other. For example, biological development, such as brain maturation, may influence cognitive development, which in turn might influence social development, such as a child’s understanding of friendship. Social development then may influence cognitive development, as children may learn activities or ideas from each other. In this way the various forms of development interact. The individual interacts with the contexts in which he or she is embedded, influencing and being influenced by them (Bronfenbrenner & Ceci, 1994; Bronfenbrenner & Morris, 2006).

The individual is embedded in the innermost level of context, the microsystem, which includes the immediate physical and social environment surrounding the person, such as family, peers, and school. The individual interacts with elements of the microsystem by, for example, developing relationships with peers in which peers influence the person and vice versa. Because the microsystem contains the developing person, it has an immediate and direct influence on his or her development. Peer relationships can influence a person’s sense of self-esteem, social skills, and emotional development.

microsystem In bioecological systems theory, the innermost level of context, which includes an individual’s immediate physical and social environment.

Figure 1.6: Bronfenbrenner’s Bioecological Model

Source: Adapted from Bronfenbrenner and Morris (2006).

Bronfenbrenner’s next level, the mesosystem, refers to the relations and interactions among microsystems, or connections among contexts. For example, experiences in the home (one microsystem) influence those at school (another microsystem); parents who encourage and provide support for reading will influence the child’s experiences in the classroom. Like the microsystem, the mesosystem has a direct influence on the individual because he or she is a participant in it.

mesosystem In bioecological systems theory, the relations and interactions among microsystems.

An important contribution of bioecological theory is the role of the exosystem, which consists of other settings in which the individual is not a participant but that nevertheless influence him or her. For example, a child typically does not participate in a parent’s work setting, yet the work setting has an indirect influence on the child because it affects the parent’s mood. The availability of funding for schools, another exosystem factor, indirectly affects children by influencing the availability of classroom resources. The exosystem is an important contribution to our understanding of development because the effects of outside factors trickle down and indirectly affect children and adults.

exosystem In bioecological systems theory, social settings in which an individual does not participate but has an indirect influence on development.

The macrosystem is the greater sociocultural context in which the microsystem, mesosystem and exosystem are embedded. It includes cultural values, legal and political practices, and other elements of the society at large. The macrosystem indirectly influences the child because it affects each of the other contextual levels. For example, cultural beliefs about the value of education (macrosystem) influence funding decisions made at national and local levels (exosystem), as well as what happens in the classroom and in the home (mesosystem and microsystem). Lives in Context: Sociohistorical Influences on Development illustrates how one element of the macrosystem, historical events, may influence development.

macrosystem In bioecological systems theory, the sociohistorical context—cultural values, laws, and cultural values—in which the microsystem, mesosystem, and exosystem are embedded, posing indirect influences on individuals.

A final element of the bioecological system is the chronosystem, which refers to how the bioecological system changes over time. As people grow

and change, they take on and let go of various roles. For example, graduating from college, getting married, and becoming a parent involve changes in roles and shifts in microsystems. These shifts in contexts, called ecological transitions, occur throughout life. The complexity of the bioecological model, the attention to patterns and interrelations among multiple determinants of development, is both a strength and weakness of the theory (Darling, 2007; Dixon & Lerner, 1999). Human development is complex, and only when we consider the multiple interacting influences within the individual and context will we gain insight into the processes and outcomes of developmental change. However, we can never measure and account for all of the potential influences on development at once. Therefore, it is difficult to devise research studies to test the validity of the bioecological model. Despite this, bioecological theory remains an important contribution toward explaining developmental change across the lifespan.

Lives in Context Video 1.1

Sociocultural Influences on Development: Desegregation

chronosystem In bioecological systems theory, refers to how the people and contexts change over time.

Ethology and Evolutionary Developmental Theory Why do infants bond to their parents? Are parents innately attuned to their infants? How might attachments between infants and parents contribute to infants’ development? Some theorists argue that parenting is innate and

has survival value. In 1859, Charles Darwin proposed his theory of evolution, explaining that all species adapt and evolve over time. Specifically, traits that enable a species to adapt, thrive, and mate tend to be passed to succeeding generations because they improve the likelihood of the individual’s and species’ survival. Ethology is the scientific study of the evolutionary history of behavior and its survival value (Dewsbury, 1992). Konrad Lorenz and Kiko Tinbergen, two European zoologists, observed animal species in their natural environments and noticed patterns of behavior that appeared to be inborn, emerged early in life, and ensured their survival. For example, shortly after birth, goslings imprint on their mothers, meaning that they bond to her and will follow her, thereby ensuring they stay close to the mother, get fed, and remain protected. Imprinting ensures the goslings’ survival. In order for imprinting to occur, the mother goose must be present immediately after the goslings hatch; mothers instinctively stay close to the nest so that their young may imprint and enhance their odds of surviving (Lorenz, 1952).

ethology A perspective that emphasizes the evolutionary basis of behavior and its adaptive value in ensuring survival of a species.

According to Bowlby (1969), humans also display biologically preprogrammed behaviors that have survival value and promote development. For example, caregivers naturally respond to infants’ cues. Crying, smiling, and grasping are inborn ways that infants get attention from caregivers, bringing them physical contact and ensuring that the infants will be safe and cared for. Many infant behaviors have adaptive significance because they meet infants’ needs and promote the formation of bonds with caregivers, ensuring that the caregivers will feel a strong desire and obligation to care for them (Bowlby, 1973). In this way innate biological drives and behaviors work together with experience to influence adaptation and ultimately an individual’s survival.

Are you—your abilities, personality, and competencies—a result of your genes and inborn influences? Or did the physical and social environment in which you were raised, your family, friends, and school make you who you are today? Evolutionary developmental scientists explain that these are the wrong questions to ask. Evolutionary developmental theory applies principles of evolution and scientific knowledge about the

interactive influence of genetic and environmental mechanisms to understand the changes people undergo throughout their lives. From this perspective, genes and context interact in an ever-changing way so that it is impossible to isolate the contributions of each to development (Gottesman & Hanson, 2005; Gottlieb, 2003; LaFreniere & MacDonald, 2013; Lickliter & Honeycutt, 2003). Although all of our traits and characteristics are influenced by genes, contextual factors influence the expression of genetic instructions, as illustrated by Figure 1.7. Contextual factors such as gravity, light, temperature, and moisture influence how genes are expressed and therefore how individuals develop (Gilbert, 2001; Meaney, 2010; Rutter, 2010). For example, in crocodiles, sex is determined by the temperature in which the organism develops. Eggs incubated at one range of temperatures produce male crocodiles and at another temperature produce female crocodiles (Gans & Crews, 1992).

evolutionary developmental theory A perspective that applies principles of evolution and scientific knowledge about the interactive influence of genetic and environmental mechanisms to understand the adaptive value of developmental changes that are experienced with age.

Lives in Context

Sociohistorical Influences on Development Sociohistorical influences, such as the Great Depression (1929–1939), contribute to cohort, or generational, differences in development.

Rolls Press/Popperfoto/Popperfoto/Getty Images

Historical events, such as wars, economic and natural disasters, and periods of social unrest, are contextual influences that shape our world and our development. Glen Elder (1999) illustrated the influence of historical events by examining the progress of two generations, or cohorts, of California-born Americans from childhood to adulthood. The Oakland Growth Study consisted of individuals born in 1920–1921 who were adolescents during the Great Depression. The Berkeley Guidance Study consisted of individuals born in 1928–1929 who were young children when their families experienced the economic losses of the Great Depression. The decades-long studies of these two cohorts, who were 8 years apart in age, demonstrated that they had very different experiences during their adolescent and early adult years. Influenced in part by the findings of these studies, Elder (2000) believed that the impact of historical events depends on when they occur in a person’s life.

For all participants of both studies, family roles and relationships changed in response to the economic adversity wrought by the Great Depression. As fathers lost jobs and income, more work was required of children, giving them opportunities to participate in helping their families. Mothers took on an increasingly important role in the family as income earners as well as authority figures. This upheaval of traditional gender roles was accompanied by an increase in family discord and conflicts.

The older, Oakland cohort were children during the affluent 1920s, a time of economic growth in California, and they experienced a prosperous and relatively stress-free childhood. But they entered adolescence during the Great Depression, a period of severe economic stress in which unemployment skyrocketed and people’s savings were depleted. As adolescents during the Great Depression, the Oakland cohort tended to behave responsibly and assist their families in coping. The boys often assumed jobs outside the home to aid financially

troubled families. Their activities outside the home enhanced their social independence and reduced their exposure to family stress. Girls spent more time at home caring for siblings and completing household chores as many mothers worked outside the home; they were exposed to greater amounts of family stress and showed poorer adjustment than did the boys.

The Berkeley children, the younger cohort, experienced the Great Depression during their vulnerable early childhood years. The children experienced economic scarcity and family discord early in life, at a time when they were very dependent on family. The Berkeley cohort entered adolescence during World War II, a period of additional economic and emotional stress from empty households (as both parents worked to support the war effort) and the military service and war trauma of older brothers. As adolescents, the Berkeley cohort (especially the boys) experienced greater emotional difficulties, more poor attitudes toward school, and less hope, self-direction, and confidence about their future than did the Oakland cohort (who were children during the prosperous 1920s).

However, the Berkeley cohort demonstrated resilience in adulthood, largely because of the influence of military service. Seventy percent of the males in the Berkeley sample served in the military during World War II. Military service appeared to offer the men several opportunities, such as to begin again and reconsider their lives, to travel, and access to the GI Bill of Rights, which enabled them to expand their education and acquire new skills after the war. These two cohorts of young people offer striking examples of how sociohistorical context influences development. Context always plays a role in development—not only in times of social upheaval, but every day and for every generation of people.

What Do You Think? 1. Consider the sociohistorical context in which you were raised.

What historical and societal events may have influenced you? What events have shaped your generation’s childhood and adolescence?

2. Consider the societal and cultural events that your parents may have experienced in childhood and adolescence. What technology was available? What historical events did they experience? What were the popular fads of their youth? What influence do you think these sociohistorical factors may have had on your parents’ development?

3. Compare the sociohistorical context in which you are

embedded today with that of your parents and grandparents at your age.

Figure 1.7: Interaction of Genetic and Environmental Factors

Development is influenced by the dynamic interplay of genetic and environmental factors. Genetic predispositions may influence how we experience environmental factors, and environmental factors may influence how genes are expressed.

Source: Picker (2005).

According to evolutionary developmental theory, genetic programs and biological predispositions interact with the physical and social environment to influence development and Darwinian natural selection determines what genes and traits are passed on to the next generation (Bjorklund & Pellegrini, 2000; Krebs, 2003; Lickliter & Honeycutt, 2003). People are viewed as active in their development, influencing their contexts (through their genetic characteristics and by choosing and interacting within settings), responding to the demands for adaptation posed by their contexts, and constantly interacting with and adapting to the

world around them. The relevance of both biological and contextual factors to human development is indisputable and most developmental scientists appreciate the contributions of evolutionary developmental theory (Frankenhuis, Panchanathan, & Clark Barrett, 2013; Gottlieb, Wahlsten, & Lickliter, 1998; Lickliter & Honeycutt, 2013). The ways in which biology and context interact and their influence on development changes over the course of the lifetime, as we will discuss throughout this book.

In summary, there are many theories of human development that offer complementary and contrasting views of how we change throughout our lifetimes. Psychoanalytic theories emphasize personality change—how unconscious forces shape people (Freud) and how sociocultural forces influence ego development (Erikson). Behaviorist and social learning theories point to the physical and social environment as a shaper of development and behavior, as well as the role of observation and imitation in learning. Other theories emphasize cognitive development. Piaget’s cognitive-developmental theory explains how individuals construct their own knowledge structures through interaction with the world, whereas Vygotsky emphasizes the role of sociocultural context in influencing thought. Information processing theories examine the ways in which attention, processing speed, and strategy use lead to advances in thinking and problem solving ability. Finally, Bronfenbrenner’s bioecological theory takes a comprehensive look at the many contextual systems in which people live and how people and their contexts interact. Table 1.5 provides an at-a-glance comparison of theories of human development.

Table 1.5 Comparing Theories of Human Development Table 1.5 Comparing Theories of Human Development

Continuity vs. Discontinuity

Active vs. Passive Individual

Nature vs. Nurture

Freud’s psychosexual Discontinuous

stages

Passive individuals are motivated

Greater emphasis on nature: People are driven by inborn drives, but the extent to which the

theory by inborn basic drives.

drives are satisfied influences developmental outcomes.

Erikson’s psychosocial theory

Discontinuous stages

Active individuals interact with their social world to resolve psychosocial tasks.

Both nature and nurture: Biological and social forces propel people through the stages and social and psychosocial influences determine the outcome of each stage.

Behaviorist theory

Continuous process of learning new behaviors

Passive individuals are shaped by their environment.

Nurture: Environmental influences shape behavior.

Bandura’s social learning theory

Continuous process of learning new behaviors

Individuals’ characteristics and behavior interact with the environment.

Both nature and nurture: Inborn characteristics and the physical and social environment influence behavior.

Both nature and nurture: An innate drive to

Piaget’s cognitive- developmental theory

Discontinuous stages, but also continuous process of seeking equilibration

Active individuals interact with the world to create their own schemas.

learn coupled with brain development leads people to interact with the world. Opportunities provided by the physical and social environment influence development.

Vygotsky’s sociocultural theory

Continuous interactions with others lead to developing new reasoning capacities and skills.

Active individuals interact with members of their culture.

Both nature and nurture: People learn through interactions with more skilled members of their culture; however, capacities are influenced by genes, brain development, and maturation.

Information processing theory

Continuous increase of skills and capacities

Active individuals attend to, process, and store information.

Both nature and nurture: People are born with processing capacities that develop through maturation and environmental influences.

Bronfenbrenner’s bioecological systems theory

Continuous: People constantly change through their interactions with the contexts in which they are embedded.

Active individuals interact with their contexts, being influenced by their contexts but also determining what kinds of physical and social environments are created and how they change.

Both nature and nurture: People’s inborn and biological characteristics interact with an ever changing context to influence behavior.

Ethology and evolutionary developmental theory

Both continuous and discontinuous: People gradually grow and change throughout life but there are sensitive periods during which specific experiences and developments must occur.

Active individuals interact with their physical and social environment.

Both nature and nurture: Genetic programs and biological predispositions interact with the physical and social environment to influence development, and Darwinian natural selection determines what genes and traits are passed on to the next generation.

Maria and Fernando have just given birth to their first child, a healthy baby boy. Like most new parents, Maria and Fernando are nervous and overwhelmed with their new responsibilities. Of utmost importance to them is that the baby develop a strong and secure bond to them. They want their baby to feel loved and to love them.

1. What advice would a psychoanalytic theorist give Maria and Fernando? Contrast psychoanalytic with behaviorist perspectives. How might a behaviorist theorist approach this question?

2. How might an evolutionary developmental theorist explain bonding between parents and infants? What advice might an evolutionary developmental theorist give to Maria and Fernando?

3. Considering bioecological systems theory, what microsystem and mesosystem factors influence the parent–child bond? What role might exosystem and macrosystem factors take?

Research in Human Development The many theories of lifespan human development differ in focus and explanation, but they all are the result of scientists’ attempts to organize observations of people at all ages. Developmental scientists conduct research studies to gather information and answer questions about how people grow and change over their lives. They devise theories to organize what they learn from research and to suggest new hypotheses to test in research studies. In turn, research findings are used to modify theories. By conducting multiple studies over time, developmental scientists refine their theories about lifespan human development and determine new questions to ask. Developmental science also finds significant influences in contexts, as discussed in Applying Developmental Science.

The Scientific Method Researchers employ the scientific method, a process of posing and answering questions by making careful and systematic observations and gathering information. The scientific method provides an organized way of formulating questions, finding answers, and communicating research discoveries. Its basic steps are as follows:

scientific method The process of forming and answering questions using systematic observations and gathering information.

1. Identify the research question or problem to be studied and formulate the hypothesis, or proposed explanation, to be tested.

2. Gather information to address the research question. 3. Summarize the information gathered and determine whether the

hypothesis is refuted, or shown to be false. 4. Interpret the summarized information, consider the findings in light of

prior research studies, and share findings with the scientific community and world at large.

In practice, the scientific method usually does not proceed in such a straightforward, linear fashion. Frequently research studies raise as many questions as they answer—and sometimes more. Unexpected findings can prompt new studies. For example, researchers may perform an experiment again (i.e., a replication) to see whether the results are the same as previous ones. Sometimes analyses reveal flaws in data collection methods or research design, prompting a revised study. Experts may also disagree on the interpretation of a study. Researchers may then conduct new studies to test new hypotheses and shed more light on a given topic. For all of these reasons, scientists often say the scientific method is “messy.”

Applying Developmental Science

The Importance of Context in Developmental Science Dutch children raised in Amsterdam are immersed in a different context than that of children reared in North America

Paulo Amorim /VWPics/Alamy

In its early years, the study of human development was based in laboratory research devoted to uncovering universal aspects of development by stripping away contextual influences (Wertlieb, 2003). This basic research was designed to examine universal processes that apply to all people, such as perceptual development (e.g., what visual skills are infants born with?).

As developmental scientists began apply their knowledge outside of laboratory settings, however, it became apparent that there are a great many individual differences in development.

Developmental scientists have since realized the importance of context. The field of applied developmental science has emerged, studying individuals within the contexts in which they live. This approach promotes the ability to understand the diverse range of patterns development takes throughout the life course (Lerner, 2010; Wertlieb, 2003).

applied developmental science A field that studies lifespan interactions between individuals and the contexts in which they live and applies research findings to real-world settings, such as to influence social policy and create interventions.

Research in human development is now directed toward understanding a variety of social problems and issues of immediate social relevance, such as the capacities of preterm infants, children’s ability to provide eyewitness testimony, adolescent sexual practices, and the impact of disability on the psychological and social adjustment of older adults and their adult children (Fisher, Busch-Rossnagel, Jopp, & Brown, 2013; Lerner, 2012). Applying developmental scientists study and make

Lerner, 2012). Applying developmental scientists study and make contributions to social policies on a issues that affect children, adolescents, adults, and their families, including environmental quality, health and health care delivery, violence, hunger and poor nutrition, school failure, and pervasive poverty (Tseng, 2012). Developmental scientists seek to enhance the life chances of diverse groups of individuals, families, and communities. Throughout this book you will be introduced to these and more issues studied by applying developmental scientists.

What Do You Think? 1. Identify three areas that you believe are in need of study or

intervention by developmental scientists. 2. What are some challenges faced by children, adolescents, or

adults that you believe should be studied and addressed?

Methods of Data Collection The basic challenge that scientists face in conducting research is determining what information is important and how to gather it. Scientists use the term data to refer to the information they collect. How can we gather data about children, adolescents, and adults? Should we simply talk with our participants? Watch them as they progress through their days? Hook them up to machines that measure physiological activity such as heart rate or brain waves? Developmental scientists use a variety of different methods, or measures, to collect information.

Self-Report Measures

Interviews and questionnaires are known as self-report measures because the person under study answers questions about his or her experiences, attitudes, opinions, beliefs, and behavior. Interviews can take place in person, over the phone, or over the Internet.

The open-ended interview is very flexible because the trained interviewer uses a conversational style that encourages the participant, or the person under study, to expand his or her responses. Interviewers may vary the order of questions, probe, and ask follow up questions based on responses. The scientist begins with a question and then follows up with prompts to

example of this is the Piagetian Clinical Interview, which requires specialized training to administer. Consider this dialogue between Piaget and a 5-year-old child:

open-ended interview A research method in which a researcher asks a participant questions using a flexible, conversational style and may vary the order of questions, probe, and ask follow-up questions based on the participant’s responses.

Where does the dream come from? I think you sleep so well that you dream. Does it come from us or from outside? From outside. What do we dream with? I don’t know. With the hands? With nothing? Yes, with nothing. When you are in bed and you dream, where is the dream? In my bed, under the blanket. I don’t really know. If it was in my stomach the bones would be in the way and I shouldn’t see it. Is the dream there when you sleep? Yes, it is in my bed beside me. Is the dream in your head? It is I that am in the dream; it isn’t in my head. When you dream, you don’t know you are in the bed. You know you are walking. You are in the dream. You are in bed, but you don’t know you are. (Piaget, 1929, pp. 97–98)

Open-ended interviews permit participants to explain their thoughts thoroughly and in their own way. This method also enables researchers to gather a large amount of information quickly. However, the flexibility of open-ended interviews poses a challenge: When questions are phrased differently for each person, responses may not capture real differences in how people think about a given topic and instead may reflect differences in how the questions were posed and followed up by the interviewer.

A structured interview poses the same set of questions to each participant in the same way, and therefore is less flexible than open-ended interviews. Because all participants receive the same set of questions, differences in

responses are more likely to reflect true differences among participants and not merely differences in the manner of interviewing. For example Evans, Milanak, Medeiros, and Ross (2002) used a structured interview to examine American children’s beliefs about magic. Children between the ages of 3 and 8 were asked the following set of questions:

structured interview A research method in which each participant is asked the same set of questions in the same way.

What is magic? Who can do magic? Is it possible to have special powers? Who has special powers? Does someone have to learn to do magic? Where have you seen magic? What are tricks? Who can do tricks? What is the difference between tricks and magic? How do wishes work? What does it mean to make a wish? Do wishes come true? Who makes wishes come true? What do you think about Santa Claus/the Tooth Fairy? What do you think about Monsters? (p. 49)

After compiling and analyzing the children’s responses as well as administering several cognitive tasks, Evans and colleagues concluded that even older children, who have the ability to think logically and perform concrete operations, may display magical beliefs.

A questionnaire, also called a survey, is a set of questions, typically multiple choice, that scientists compile and use to collect data from large samples of people. Questionnaires can be administered in person, online, or by telephone, e-mail, or postal mail. Questionnaires are popular data collection methods because they are easy to use and enable scientists to collect information from a large number of people quickly and inexpensively. Scientists who conduct research on sensitive topics, such as sexual interest and experience, often use questionnaires because they can easily be administered anonymously, protecting participants’ privacy by not including any identifying information on the survey. For example, the Monitoring the Future Study is an annual survey of 50,000 students in Grades 8, 10, and 12 that collects information about their behaviors, attitudes, and values concerning drug and alcohol use (Miech, Johnston,

O’Malley, Bachman, & Schulenberg, 2015). In this example, the survey permits scientists to gather an enormous amount of data yet its anonymity protects the adolescents from the consequences of sharing personal information that they may not otherwise reveal.

questionnaire A research method in which researchers use a survey or set of questions to collect data from large samples of people.

Despite their ease of use, self-report measures are not without challenges. Sometimes people give socially desirable answers: They respond in ways they would like themselves to be perceived or believe researchers desire. A college student completing a survey about cheating, for example, might choose answers that do not truly reflect her behavior of sometimes looking at nearby students’ papers during examinations, but instead match the person she aspires to be or the behaviors she believes the world values— that is, someone who does not cheat on exams. Self-report data may not always reflect people’s true attitudes and behavior. Some argue that we are not always fully aware of our feelings and therefore cannot always provide useful insight into our own thoughts and behavior with the use of self- report measures (Westen, 1998). Whereas interviews and questionnaires measure people’s self-reports of their attitudes, beliefs, and behaviors, observational measures examine people in action as they go about their daily lives.

Observational Measures

Are you a people watcher? Have you ever sat in a coffee shop or at the student center and observed people interact, rush from place to place, laugh with others, or scowl at their laptops? If so, you have used observational skills that are similar to those used by scientists who conduct research in everyday settings. Observational measures are methods that scientists use to collect and organize information based on watching and monitoring people’s behavior. Developmental scientists employ two types of observational measures: naturalistic observation and structured observation.

Scientists who use naturalistic observation observe and record behavior

Scientists who use naturalistic observation observe and record behavior in natural, real-world settings. For example Ginsburg, Pappas, and Seo (2001) analyzed videotapes of 4- and 5-year-old children’s everyday behavior during free play to determine the extent to which they used mathematical thinking in their play. Naturalistic observation is challenging because one must first decide on an operational definition of the behavior of interest. In this case, many operational definitions were required as Ginsburg and colleagues designed an elaborate coding system to categorize children’s behaviors in terms of their mathematical content, location, preferred play objects, peer interaction, and play activity.

naturalistic observation A research method in which a researcher views and records an individual’s behavior in natural, real-world settings.

Sometimes the presence of an observer causes the person to behave in unnatural ways or ways that are not typical for him or her. This is known as participant reactivity, and it poses a challenge to gathering by naturalistic observation. To minimize the effect that observation might have on the children’s behaviors, Ginsburg and colleagues made video recordings and permitted the children to get used to the video recorder by exposing them to it many times before using it to collect observations. The video recorded observations revealed that children spend a surprising amount of play time (almost 50%) spontaneously engaging in mathematical activities like ordering objects, counting, comparing sizes and quantities, and exploring positions, direction, distances, and patterns. These results suggest that children naturally engage in mathematics-related play and are more competent in mathematics than many adults realize (Ginsburg et al., 2001).

Researchers use video cameras to observe and record the facial expressions a newborn baby makes while it sleeps.

Thierry Berrod, Mona Lisa Production / Science Source

Naturalistic observation permits researchers to observe behaviors in real- world settings and to observe patterns, such as whether a particular event or behavior typically precedes another. Such observations can help researchers determine which behaviors are important to study in the first place. For example, a scientist who studies bullying by observing children’s play may notice that some victims act aggressively before a bullying encounter. The scientist may then decide to examine aggression in victims not only after a bullying incident, but beforehand. Naturalistic observation is a useful way of studying events and behaviors that are common. Some behaviors and events, however, are uncommon or are difficult to observe, such as physical aggression among adults, requiring a researcher to observe for very long periods of time to obtain data on the behavior of interest. For this reason, many researchers make structured observations.

Table 1.6 Data Collection Methods Table 1.6 Data Collection Methods

Advantage Disadvantage

Open-ended interview

Gathers a large amount of information quickly and inexpensively.

Nonstandardized questions. Characteristics of the interviewer may influence participant

responses.

Structured interview

Permits gathering a large amount of information quickly and inexpensively.

Characteristics of the interviewer may influence participant responses.

Questionnaire

Permits collecting data from a large sample more quickly and inexpensively than by interview methods.

Some participants may respond in socially desirable or inaccurate ways.

Naturalistic observation

Gathers data on everyday behavior in a natural environment as behaviors occur.

The observer’s presence may influence the participants’ behavior. No control over the observational environment.

Structured observation

Observation in a controlled setting.

May not reflect real-life reactions and behavior

Physiological measures

Assesses biological indicators and does not rely on participant report

May be difficult to interpret

Lifespan Brain Development

Methods of Studying the Brain Modern brain imaging techniques enable us to view the active brain as it thinks and solves problems.

What parts of the brain are active when we solve problems or feel emotions? How does the brain change with development? Until recently, the brain was a mystery. Over the last hundred years, researchers have devised several methods of studying brain activity that have increased our understanding of how the brain functions and how it develops.

The earliest instrument created to measure brain activity was the electroencephalogram, first used with humans in the 1920s (Collura, 1993). Electroencephalography (EEG) uses electrodes placed on the scalp to measure electrical activity patterns produced by the brain. Researchers study fluctuations in activity that occur when participants are presented with stimuli or when they sleep. EEG recordings measure electrical activity in the brain, but they do not provide information about the location of activity.

It was not until the invention of positron emission tomography (PET), in the early 1950s, that researchers obtained the first glimpse of the inner workings of the brain (Portnow, Vaillancourt, & Okun, 2013). A small dose of radioactive material is injected into the participant’s blood stream and detected by the PET scan. The radioactive material enables researchers to monitor the flow of blood. Blood flows more readily to active areas of the brain, and the resulting images can illustrate what parts of the brain are active as participants view stimuli and solve problems.

Developed in 1971, computerized tomography, known as the CT scan, produces X-ray images of brain structures (Cierniak, 2011). A movable X-ray unit rotates around a person’s head and records images of the brain (Herman, 2009). The images are then combined to make a 3-D picture of a person’s brain, providing images of bone, brain vasculature, and tissue. CT scans can provide researchers with information about the density of brain structures to illustrate, for example, how the thickness of the cortex changes with development.

Functional magnetic resonance imaging (fMRI) measures brain activity

by monitoring changes in blood flow in the brain (Bandettini, 2012). Developed in the 1990s, MRI machines house a powerful magnet that uses radio waves to measure blood oxygen level. Active areas of the brain require more oxygen-rich blood. Like PET scans, fMRI enables researchers to determine what parts of the brain are active as individuals complete cognitive tasks. However, fMRI images are much more detailed than PET scans. An important advantage of fMRI over a PET scan is that it does not rely on radioactive molecules, which can only be administered a few times before becoming unsafe.

Another imaging process, called diffusion tensor imaging (DTI), uses a MRI machine to track how water molecules move in and around the fibers connecting different parts of the brain (Soares, Marques, Alves, & Sousa, 2013). DTI gauges the thickness and density of the brain’s connections, permitting researchers to measure the brain’s white matter and determine changes that occur with development and with age- related illnesses, such as Alzheimer’s disease. Researchers have devised many ways of studying brain activity, an important physiological measure.

What Do You Think? 1. If you were going to study the brain, which measure would

you choose and why? What type of information would you obtain from your chosen measure?

2. Identify a research question that your measure might help you answer.

Structured observation entails observing and recording behaviors displayed in a controlled environment, which is a situation constructed by the experimenter. For example, children might be observed within a laboratory setting as they play with another child or complete a puzzle- solving task. The challenges of identifying and categorizing which behaviors to record are similar to those entailed by naturalistic observation. However, the laboratory environment permits researchers to exert more control on the situation than is possible in natural settings. In addition to cataloguing observable behaviors, some researchers use technology to measure biological functions such as heart rate, brain waves, and blood pressure. One challenge to conducting structured observations is that people do not always behave in laboratory settings as they do in real life.

structured observation An observational measure in which an individual’s behavior is viewed and recorded in a controlled environment; a situation created by the experimenter.

Physiological Measures

Physiological measures are increasingly used in developmental research because cognition, emotion, and behavior have physiological indicators. For example, when speaking in public, such as when you give a class presentation, do you feel your heart beat more rapidly or your palms grow sweaty? An increase in heart rate and perspiration are physiological measures of anxiety. Other researchers might measure cortisol, a hormone triggered by the experience of stress. An advantage of physiological measures is they do not rely on verbal reports and generally cannot be faked. They are also useful for studying infants. A researcher who employs physiological measures might use an infant’s heart rate as a measure of interest or may measure the infant’s eye movement or pupil dilation. A challenge to physiological measures is that, although physiological responses can be recorded, they may be difficult to interpret. For example, excitement and anger may both cause an increase in heart rate. Physiological measures of brain activity are a particularly promising source of data, as discussed in the Lifespan Brain Development feature. Data collection methods are summarized in Table 1.6.

Research Designs There are many steps in conducting research. In addition to determining the research question and deciding what information to collect, scientists must choose a research design—a technique for conducting the research study.

Case Study

A case study is an in-depth examination of a single person (or small group of individuals). It is conducted by gathering information from many sources, such as through observations, interviews, and conversations with family, friends, and others who know the individual. A case study may include samples or interpretations of a person’s writing, such as poetry or

journal entries, artwork, and other creations. A case study provides a rich description of a person’s life and the influences on his or her development. It is often employed to study individuals who have unique and unusual experiences, abilities, or disorders. Conclusions drawn from a case study may shed light on an individual’s development, but they may not be generalized or applied to others. Case studies can be a source of hypotheses to examine in large scale research.

Correlational Research

Are children with high self-esteem more likely to excel at school? Are older adults with more friends happier than those with few? Are college students who work part-time less likely to graduate? All of these questions can be studied with correlational research, which permits researchers to examine relations among measured characteristics, behaviors, and events. For example, in one study scientists examined the relationship between children’s after-school activities and their academic achievement and found that children who reported watching more television on school nights scored lower on achievement tests (Cooper, Valentine, Nye, & Lindsay, 1999). However, this correlation does not tell us why television viewing was associated with academic achievement. Correlational research cannot answer this question because it simply describes relationships that exist among variables; it does not enable us to make conclusions about the causes of those relationships. It is likely that other variables influence both a child’s television watching and achievement (e.g., motivation), but correlation does not enable us to determine the causes for behavior; for that, we need an experiment.

correlational research A research design that measures relationships among participants’ measured characteristics, behaviors, and development.

Experimental Research

Scientists who seek to test hypotheses about causal relationships, such as whether media exposure influences behavior or whether hearing particular types of music influences mood, employ experimental research. An

experiment is a procedure that uses control to determine causal relationships among factors, known as variables. Specifically, one or more variables thought to influence a behavior of interest are changed, or manipulated, while other variables are held constant. By doing so, researchers can examine how the changing variable influences the behavior under study. If the behavior changes as the variable changes, this suggests that the variable caused the change in the behavior.

experimental research A research design that permits inferences about cause and effect by exerting control, systematically manipulating a variable, and studying the effects on measured variables.

For example, suppose a scientist examined the influence of exposure to aggressive media on children’s aggressive behavior by choosing two cartoons: one containing many aggressive acts (e.g., hitting or punching) and another depicting few aggressive acts (e.g., including themes of sharing). Each child is asked to play with a set of toys containing cars, dolls, and stuffed animals. Researchers observe and record the number of aggressive acts the child engages in, such as hitting and throwing. Each child is tested in the same room, controlling other sounds, the temperature, and time of day of testing. If researchers’ ratings of children’s aggression change in response to varying the type of media—showing more or less aggressive behavior—then the results suggest a causal relationship: Media exposure changed behavior.

Let us take a closer look at the components of an experiment. Conducting an experiment requires choosing at least one dependent variable, the behavior under study (e.g., hitting and throwing), and one independent variable, the factor proposed to change the behavior under study (e.g., type of cartoon). The independent variable is manipulated or varied systematically by the researcher during the experiment (e.g., a child views many aggressive acts or few aggressive acts). The dependent variable is expected to change as a result of varying the independent variable, and how it changes is thought to depend on how the independent variable is manipulated.

dependent variable The behavior under study in an experiment; it is expected to be affected by changes in the independent variable.

independent variable The factor proposed to change the behavior under study in an experiment; it is systematically manipulated during an experiment.

In an experiment, the independent variable is administered to one or more experimental groups, or test groups whose experiences are manipulated by varying the independent variable. The control group is treated just like the experimental group except that it does not receive the independent variable in order to compare the effect of the manipulation. For example, in an experiment investigating whether particular types of music influence mood, the experimental group would experience a change in music (e.g., from “easy listening” to rock), whereas the control would hear only one type of music (e.g., “easy listening”). Random assignment, whereby each participant has an equal chance of being assigned to the experimental or control group, is essential for ensuring that the groups are as equal as possible in all preexisting characteristics (e.g., age, ethnicity, and gender). Random assignment makes it less likely that any observed differences in the outcomes of the experimental and control groups are not due to preexisting differences between the groups. After the independent variable is manipulated, if the experimental and control groups differ on the dependent variable, it is concluded that the independent variable caused the change in the dependent variable. That is, a cause and effect relationship has been demonstrated.

random assignment A method of assigning participants that ensures each participant has an equal chance of being assigned to the experimental group or control group.

By experimentally manipulating which infants receive massage therapy, researchers determined that massage can help preterm infants gain weight, an important correlate of health.

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AP Photo/AL GOLDIS

As another example, consider a study designed to examine whether massage therapy improves weight gain in preterm infants (infants who were born well before their due date; Dieter, Field, Hernandez-Reif, Emory, & Redzepi, 2003). Infants housed in a neonatal unit were randomly assigned either to a massage group (independent variable), who were touched and their arms and legs moved for three 15-minute periods per day, or to a control group, which received no massage. Other than the massage/no massage periods, the two groups of infants were cared for in the same way. After five days, the preterm infants who received massage therapy gained more weight (dependent variable) than those who did not receive massage therapy. The researchers concluded that massage therapy causes improved weight gain in preterm infants.

Developmental scientists conduct studies that use both correlational and experimental research. Studying development, however, requires that scientists pay close attention to age and how people change over time, which requires the use of specialized research designs, as described in the following sections.

Developmental Research Designs Does personality change over the lifespan? Do children outgrow shyness? Are infants’ bonds with their parents associated with their adult relationships? These challenging questions require that developmental scientists examine relationships among variables over time. The following sections discuss the designs that researchers use to learn about human development. As you learn about each design, consider how we might employ it to answer a question about development. For example, how does alcohol use among adolescents change from 6th grade through 12th grade?

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Cross-Sectional Research Design

A common way in which developmental scientists examine questions about how variables change with age is to conduct cross-sectional research, comparing groups of people of different ages at one time. For example, to examine how alcohol use changes from 6th through 12th grade, a scientist might visit a school system in 2020 and administer a survey about alcohol use to students in 6th, 8th, 10th, and 12th grades. By analyzing the survey results, the scientist can describe grade differences in alcohol use, such as how 6th graders differ from 12th graders. Cross- sectional research permits scientists to draw conclusions about age differences, for example, how the 6th graders differed in alcohol use from the 8th, 10th, and 12th graders. However, it is unknown whether the observed age differences in alcohol use reflect age-related or developmental change. In other words, it is unclear whether 6th graders will show the same pattern of change in alcohol use over the high school years as the 12th graders.

cross-sectional research A developmental research design that compares people of different ages at a single point in time to infer age differences.

Cross-sectional research gathers information from people of several ages at one time. It permits age comparisons, but because participants differ in terms of age and cohort, it does not permit conclusions about development. Recall that a cohort is a group of people of the same age who are exposed to similar historical events and cultural and societal influences. The 6th- grade students are a different age than the 12th-grade students, but they are also a different cohort in the school, so the two groups may differ in reported alcohol use because of development (age-related changes) or cohort (group-related changes). For example, perhaps the 6th-grade students received a new early prevention program in the school that was not available to the 12th-grade students back when they were in 6th grade. In this example, the difference in alcohol use between 6th graders and 12th graders may be related to the prevention program, not to age. Cross- sectional research is an important source of information about age differences, but it cannot provide information about developmental change.

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Longitudinal Research Design

Developmental scientists who study age-related change must examine individuals over time. In longitudinal research, one group of participants is studied at many points in time. To examine how alcohol use changes from 6th through 12th grade, a developmental scientist who used longitudinal research might administer a survey on alcohol use to 6th graders and then follow up 2 years later when they enter 8th grade, again when they enter 10th grade, and finally in 12th grade. If a researcher began this study in 2020, the last round of data collection would not occur until 2026. Longitudinal research provides information about age change because it follows people over time, enabling scientists to describe how the 6th graders’ alcohol use changed as they progressed through the school years. However, because longitudinal research studies only one cohort or one generation, it is prone to cohort effects. Do the findings indicate developmental change, or are they an artifact of the cohort under study? Was the group of 6th graders that the scientist chose to follow through 12th grade somehow different from the cohorts or groups of students who came before or after? Because only one cohort is assessed, it is not possible to determine whether the observed changes are age-related changes or changes that are unique to the cohorts examined.

longitudinal research A developmental study in which one group of participants is studied repeatedly to infer age changes.

Lives in Context Video 1.2

Children of Katrina: Longitudinal Research

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Sequential Research Designs

Both cross-sectional and longitudinal studies provide useful information but, as we have seen, each has limitations. A sequential research design combines the best features of cross-sectional and longitudinal research by assessing multiple cohorts over time, enabling scientists to make comparisons that disentangle the effects of cohort and age (see Table 1.7). Consider the alcohol use study once more. A sequential design would begin in 2020 by administering a survey to students in 6th, 8th, 10th, and 12th grades. Two years later, in 2022, the initial sample is surveyed again; the 6th graders are now 8th graders, 8th graders have become 10th graders, 10th graders have become 12th graders, and the 12th graders have graduated from the school and so are not assessed. Instead, a new group of 6th graders is surveyed. Two years later, in 2024, the participants are surveyed again, and so on.

sequential research design A developmental design in which multiple groups of participants of different ages are followed over time, combining cross-sectional and longitudinal research.

The sequential design provides information about age, cohort, and age- related change. The cross-sectional data (comparisons of 6th, 8th, 10th, and 12th graders from a given year) permit comparisons among age groups. The longitudinal data (annual follow-up of 6th graders through 12th grade) permit study of age-related change. The sequential component helps scientists separate cohort effects from age-related change. Because several cohorts are studied at once, the effect of the cohort can be studied. The sequential design is complex, but it permits human development researchers to disentangle the effects of age and cohort and answer questions about developmental change.

In summary, scientists use the scientific method to systematically ask and seek answers to questions about human development. Researchers’ decisions about measures, such as whether to use self-report or observational measures, influence the information that they collect and the conclusions that they make. Choice of research method also influences conclusions researchers make about development, including statements about age differences, age change, and information about cohort effects.

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Researchers have responsibilities to conduct sound research and also to adhere to standards of ethical conduct in research, as the next section describes. See Table 1.8 for a comparison of research designs.

Table 1.7 Sequential Research Design Table 1.7 Sequential Research Design

2020 2022 2024 2026 2028

6th grade A E F

8th grade B A E F

10th grade C B A E F

12th grade D C B A E A sequential design combines cross-sectional and longitudinal designs, permitting the researcher to study multiple cohorts over time. Source: Table 1 from Kim & Böckenholt, Psychological Methods, 5(3), Sep 2000, 380–400.

Table 1.8 Comparing Research Designs Table 1.8 Comparing Research Designs

Design Strengths Limitations

Research Designs

Case study Provides a rich description of an individual.

Conclusions may not be generalized to other individuals.

Correlational

Permits the analysis of relationships among variables as they exist in the real world.

Cannot determine cause and effect relations.

Experimental Permits a determination of

Data collected artificial environments may not represent behavior in

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real-world environments.

Developmental Research Designs

Longitudinal

Permits the determination of age-related changes in a sample of participants assessed for a period of time.

Requires a great deal of time, resources, and expense. Participant attrition may limit conclusions. Cohort- related changes may limit the generalizability of conclusions.

Cross- sectional

More efficient and less costly than the longitudinal design. Permits the determination of age differences.

Does not permit inferences regarding age change. Confounds age and cohort.

Sequential

More efficient and less costly than the longitudinal model. Allows for both longitudinal and cross- sectional comparisons which reveal age differences and age change, as well as cohort effects.

Time consuming, expensive, and complicated in data collection and analysis.

Thinking in Context 1.4

Dorothy is interested in understanding smoking in middle school students. Specifically, she believes that low self-esteem causes students to smoke.

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1. How might Dorothy gather information to address her hypothesis? 2. What kind of research design should Dorothy use? What are the

advantages and disadvantages of this design? 3. What are some of the challenges of measuring behaviors such as

smoking and internal characteristics such as self-esteem? 4. How can her study be improved to overcome the weaknesses you

have identified?

Ethical Issues in Research Suppose a researcher wanted to determine the effects of an illegal drug on pregnant women, or the effects of malnutrition on kindergarteners. Would it be possible to design a study in which certain pregnant women were assigned to ingest the illegal drug? Or one in which certain kindergarteners were deprived of food? If you answered “no,” you are correct, for United States and international laws regulate what kinds of research can be conducted and whether such research can expose participants to any harm, or risk of harm. These kinds of questions, laws, and regulations are in the realm of ethics—the determination of right and wrong.

Developmental scientists’ work is guided by five ethical principles: (1) beneficence and nonmaleficence; (2) responsibility; (3) integrity; (4) justice; and (5) respect for autonomy (American Psychological Association, 2010). Beneficence and nonmaleficence are the dual responsibilities to do good and not to do harm. Researchers must protect and help the individuals, families, and communities with which they work by maximizing the benefits and minimizing the potential harms of their work. For example, when interviewing survivors of a natural disaster, such as an earthquake or tornado, a scientist pays attention to their participants’ demeanor. If a participant shows distress in response to a particular set of questions, the scientist might direct, or even accompany, the participant to a therapist or mental health professional who can help him or her manage the distress.

Scientists act responsibly by adhering to professional standards of conduct, clarifying their obligations and roles to others, and avoiding conflicts of interest. For example, a psychologist who conducts research with children and parents must clarify her role as scientist and not therapist and help her participants understand that she is simply gathering information from them rather than conducting therapy. In this way, scientists recognize that they

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are responsible to people, communities, and society.

The principle of integrity requires that scientists be accurate, honest, and truthful in their work and make every effort to keep their promises to the people and communities with which they work.

Scientists have a special obligation to respect participants’ autonomy, the ability to make and implement decisions. Scientists show respect for the individuals and families they work with by giving them information about the research study, answering questions, helping them to make their own decisions about whether to participate in the study, and accepting their decisions. Respecting people’s autonomy also means protecting those who are not capable of making judgments and asserting themselves. For example, some adults, such as those who have suffered traumatic brain injuries, may have cognitive and social deficits that make them unable to make and carry out decisions about whether to participate in research. Scientists who work with patients who may be unable to make such judgments must carefully assess each patient’s capacity and devise ways of protecting those who are not competent, such as by approaching the individual who is responsible for making legal decisions on the part of the patient.

The decision to participate in research must be reasoned, with an understanding of what is involved and that participation is voluntary.

Robert Kneschke/Shutterstock.com

Finally, the principle of justice means that the benefits and risks of participation in research must be spread equitably across individuals and

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groups. Scientists must take care to ensure that all people have access to the contributions and benefits of research.

These ethical principles form the basis of professional codes of ethics of the Society for Research in Child Development (2007) and American Psychological Association (2010), which provide guidelines for researchers who work with human participants.

Responsibilities to Participants Researchers’ desire to answer questions, learn, and solve problems by conducting research may sometimes conflict with the need to protect participants. For example, suppose a physician is testing the effectiveness of a drug designed to lower blood pressure. Over the course of the study, the scientist discovers that a participant has a heart defect that might someday require treatment. If the scientist discloses this information to the participant and encourages him or her to seek treatment, the scientist will have to remove the participant from the study. How should the scientist balance the research needs with the needs of participants? Scientists work to balance the benefits of research against the possible harm that can occur to participants, which includes mental, emotional, and physical risks.

In the United States and most other developed countries, carrying out research is a regulated activity. Each college, university, hospital, and organization that conducts research has an institutional review board (IRB) that examines all plans for conducting a study before it can begin. The IRB examines the proposed study in light of professional ethical codes as well as those articulated by the U. S. Department of Health and Human Services (2009). Do the study’s benefits for advancing knowledge and improving conditions of life outweigh the potential costs in terms of time, money, and possible harm on the part of participants? IRBs act to protect participants by ensuring that the study has scientific merit and that risks of participating in research do not outweigh its potential benefits.

Ethical codes of conduct require that researchers obtain informed consent from each participant—their informed, rational, and voluntary agreement to participate. Consent must be informed, meaning it is made with knowledge of the scope of the research, the potential for harm (if any), and the possible benefits of participating. Consent must be rational, meaning it must be made by a person capable of making a reasoned decision. Parents provide parental permission for their minor children to participate because

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researchers (and lawmakers) assume that minors are not able to meet the rational criteria of informed consent. Finally, participation must be voluntary, meaning that the decision to participate must be made freely and without coercion—individuals must understand that they are free to decide not to participate in the research study and that they will not be penalized in any way if they refuse.

informed consent A participant’s informed (knowledge of the scope of the research and potential harm and benefits of participating), rational, and voluntary agreement to participate in a study.

Although children cannot provide informed consent, researchers respect their growing capacities for decision making in ways that are appropriate to their age by seeking assent, children’s agreement to participate. For a young child, obtaining assent may involve simply asking if he or she wants to play with the researcher and answer some questions. With increasing cognitive and social development, children are better able to understand the nature of science and engage meaningfully in decisions about research participation (Thompson, 1990). Researchers should tailor discussions about the nature of research participation to children’s capacities, provide more detailed information, and seek more comprehensive assent as children grow older (Kuther, 2003; Roth-Cline & Nelson, 2013). For example, a researcher about to administer early adolescents a questionnaire about their experiences with parental divorce might explain the kinds of questions the adolescents will encounter; explain that in some cases a question might feel personal and might bring up memories; remind the adolescents that they are free to stop or skip any questions they choose; and, finally, remind the adolescents that if they feel uncomfortable or would like to talk to someone about their feelings about the issues examined in the study, a counselor is available or the researcher can help them find someone who can help them. Moreover, seeking assent helps children learn how to make decisions and participate in decision-making as they are able. Assent provides minors with opportunities to gain decision- making experience within safe contexts.

The researcher’s ethical responsibilities do not end with obtaining informed consent. Most research studies are routine and uneventful

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because they are carried out according to plan. Sometimes, however, ethical issues arise during the course of a study. For example, suppose a researcher learns that a participant is in jeopardy, whether engaging in health-compromising behaviors (e.g., cigarette smoking, unsafe driving, or unhealthy behavior), contemplating suicide, or engaging in illegal or harmful activities (e.g., drug addiction, stealing, or violence). Is a researcher responsible for helping the participant? Although current ethical guidelines address questions of researchers’ responsibilities to help participants in such situations, they leave a certain amount of judgment to the researcher.

The Society for Research in Child Development (SRCD) code of ethics (2007) suggests that researchers must help children in jeopardy by discussing the information with parents and guardians or with experts who may offer insight. Moreover, researchers may be faced with a conflict if they believe that helping the participant and dropping him or her from the research study may compromise the scientific integrity of the research, which may be especially likely if many participants are dropped. One study investigated this very issue by asking adolescents for their opinions on what researchers should do if they discover that a minor participant has a problem (Fisher, Higgins-D’Alessandro, Rau, Kuther, 1996). Older adolescents (e.g., age 17) tended to prefer that researchers not tell others about the problems and provide minors with self-referral information, whereas young adolescents (e.g., age 13) tended to prefer that researchers report problems and potential threats to parents or trusted adults (Fisher et al., 1996). In addition, the adolescents’ judgments depended on how serious they believed each problem to be. Adolescents favored reporting serious problems like abuse and threats of suicide to a parent or adult who can help. However, they preferred that the researcher not tell anyone about the problem and provide the child with self-referral information in cases of problems they rated as less serious, like smoking and nonviolent delinquent acts. Many questions remain unresolved. For example, does the age of the child matter in determining when to provide help? These are difficult decisions. Fortunately, serious ethical issues do not arise in most studies, but scientists should remain vigilant so that problems can be addressed should they arise. Table 1.9 summarizes the rights of research participants.

Table 1.9 Rights of Research Participants Table 1.9 Rights of Research Participants

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Right Description

Protection from harm

Regardless of age, research participants have the right to be protected from physical and psychological harm. Investigators must use the least stressful research procedure in testing hypotheses and when in doubt, consult with others. When harm is possible, researchers must determine another way to study the problem or abandon the research.

Informed consent

Participants have the right to be informed about the purpose of the research, expected duration, procedures, risks and benefits of participation, and any other aspects of the research that may influence their willingness to participate. When children are participants, a parent or guardian must provide informed consent on behalf of the child. The child should be provided information about research participation in terms appropriate to his or her development and the investigator should seek assent from the child as a way of respecting the child’s autonomy.

Voluntariness

Participants, regardless of age, have the right to choose not to participate or to discontinue participation in research at any time and without penalty.

Confidentiality Participants have the right to conceal their identity on all information and reports obtained in the course of research.

Reporting results

Participants have the right to be informed of the results of research in language that is appropriate to their level of understanding.

Right to treatment

If an experimental treatment under investigation is believed to be beneficial, participants in control groups have the right to obtain the beneficial

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treatment. Source: APA (2010); SRCD (2007).

Responsibilities to Society Researchers are responsible not only to their participants but also to society at large. In reporting results, researchers should be mindful of the social and political implications of their work (SRCD, 2007). Researchers must consider how their findings will be portrayed in the media and attempt to foresee ways in which their results may be misinterpreted. This is a difficult task, but it is very important for researchers to be prepared to address questions raised as well as correct misinterpretations of research (National Academy of Sciences, 1995).

For example, one highly publicized study compiled the existing research literature examining college students who had become sexually involved with an adult prior to reaching the legal age of consent (Rind, Tromovitch, & Bauserman, 1998). After using statistics to summarize the findings of many research studies, the scientists determined that the college students’ coping and development varied depending on a number of other factors within the individual, situation, and broader context. Not all appeared to be harmed and many did well. However, some organizations, media outlets, and politicians misinterpreted the researchers’ findings as suggesting that sexual involvement with minors was acceptable or even beneficial (Garrison & Kobor, 2002). Instead, the findings suggested that there are a range of outcomes to adult–minor relationships, and that the outcomes varied with the age of the minor and other characteristics of the situation. For example, the participants who seemed to be unharmed were more likely to be older (e.g., age 17) when the relationship began. Researchers must consider the potential social and political implications of their work, attempt to foresee the inferences that people may draw about their findings, and prepare to correct misinterpretations.

Lifespan human development is a broad field of study that integrates theory and research from many disciplines in order to describe, predict, and explain how we grow and change throughout our lifetime. Developmental scientists apply their knowledge to identify, prevent, and solve problems, and improve opportunities for individuals, families, and communities. Throughout this book you will learn the fundamentals of lifespan human development, including physical, cognitive, and socioemotional change, as well the implications development science

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holds for social issues. We begin our journey by considering the role of genetics and environment in shaping who we become, as described in Chapter 2.

Thinking in Context 1.5

1. Suppose, as part of your research, you wanted to interview children at school. What ethical principles should you keep in mind? Why? What challenges do you anticipate?

2. Consider collecting observations and interviews of older adults in a nursing home. What ethical issues can you anticipate? What principles are most pertinent?

Apply Your Knowledge

1. Steven enters the school psychologist’s office with a frown, grumbling to himself. His teacher, Ms. Marta, has suggested that he visit the school psychologist for help understanding and treating his academic problems. Steven is a bright fifth grader, but he has great difficulties reading and his mathematics skills lag far behind his peers. Ms. Marta contacts Steven’s mother, reassuring her that the school has excellent resources for diagnosing children’s learning problems and special education professionals who can intervene and help children overcome learning difficulties.

The school psychologist interviews Steven’s mother in order to compile a history of Steven’s development. Through this interview he learns that Steven suffered a great deal of trauma early in life; as an infant he was physically abused by his biological mother, then taken away and placed in foster care. At age 3 he was adopted into a middle-class, suburban family with two older, non-adopted, children.

As we have seen, each developmental theory has a unique emphasis. How might each theory address Steven’s academic

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difficulties? a. What factors would psychoanalytic theories point to in order

to explain Steven’s functioning? b. How would cognitively oriented theories, such as Piaget’s

cognitive-developmental theory and information processing theory, account for and intervene with Steven’s difficulties?

c. Identify contextual factors that may play a role in Steven’s academic problems; from Bronfenbrenner’s bioecological theory, what factors may be addressed?

2. Suppose you wanted to conduct research on academic achievement during elementary and middle school.

a. Identify a research question appropriate for a correlational research study.

b. How would you address that question with a cross-sectional research study? Longitudinal? Sequential?

c. What are the advantages and disadvantages of each type of study?

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Chapter 1 in Review

1.1 Outline five principles of the lifespan developmental perspective.

Summary

Development is a lifelong process. It is multidimensional, multidirectional,

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http://edge.sagepub.com/kuthertopical

plastic, influenced by the multiple contexts in which we are embedded, and multidisciplinary.

Key Terms

lifespan human development physical development cognitive development socioemotional development plasticity resilience context culture cohort

Review Question

What are five principles developmental scientists use to explain lifespan development?

1.2 Discuss three theoretical controversies about human development.

Summary

Theories of human development can be compared with respect to their stance on the following questions. First, in what ways is developmental change continuous, characterized by slow and gradual change; or discontinuous, characterized by sudden and abrupt change? Second, to what extent do people play an active role in their own development, interacting with and influencing the world around them? Finally, is development caused by nature or nurture—genetic endowments and heredity or the physical and social environment? Most developmental scientists agree that some aspects of development appear continuous and others discontinuous, individuals are active in influencing their development, and development reflects the interactions of nature and

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nurture.

Key Terms

continuous (development) discontinuous (development) nature-nurture issue

Review Question

What position do most contemporary developmental scientists take on each of the three theoretical controversies about human development?

1.3 Summarize five theoretical perspectives on human development.

Summary

Freud’s psychosexual theory explains personality development as progressing through a series of psychosexual stages during childhood. Erikson’s psychosocial theory suggests that individuals move through eight stages of psychosocial development across the lifespan, with each stage presenting a unique psychosocial task, or crisis. Behaviorist theory emphasizes environmental influences on behavior, specifically classical conditioning and operant conditioning. In classical conditioning neutral stimuli become associated with stimuli that elicit reflex responses. Operant conditioning emphasizes the role of environmental stimuli in shaping behavior through reinforcement and punishment. Bandura’s social learning theory includes cognition, and Bandura suggested that individuals and the environment interact and influence each other through reciprocal determinism. Piaget’s cognitive-developmental theory explains that children actively interact with the world around them and their cognition develops through four stages. Information processing theorists study the steps entailed in cognition: perceiving and attending, representing, encoding, retrieving, and problem solving. Sociocultural systems theories look to the importance of context in shaping development. Vygotsky’s

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sociocultural theory emphasizes interactions with members of our culture in influencing development. Bronfenbrenner’s bioecological model explains development as a function of the ongoing reciprocal interaction among biological and psychological changes in the person and his or her changing context: the microsystem, mesosystem, exosystem, macrosystem, and chronosystem. Ethology and evolutionary developmental psychology integrate Darwinian principles of evolution and scientific knowledge about the interactive influence of genetic and environmental mechanisms.

Key Terms

theory hypotheses Psychoanalytic theories behaviorism classical conditioning operant conditioning reinforcement punishment social learning theory observational learning reciprocal determinism cognitive-developmental perspective cognitive schemas information processing theory sociocultural theory bioecological systems theory microsystem mesosystem exosystem macrosystem chronosystem ethology evolutionary developmental theory psychosocial development

Review Question

How do five major theoretical perspectives account for human development?

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1.4 Describe the methods used in studying human development, including types of data and designs.

Summary

A case study is an in-depth examination of an individual. Interviews and questionnaires are called self-report measures because they ask the persons under study questions about their own experiences, attitudes, opinions, beliefs, and behavior. Observational measures are methods that scientists use to collect and organize information based on watching and monitoring people’s behavior. Physiological measures gather the body’s physiological responses as data. Scientists use correlational research to describe relations among measured characteristics, behaviors, and events. To test hypotheses about causal relationships among variables, scientists employ experimental research. Developmental designs include cross-sectional research, which compares groups of people at different ages simultaneously, and longitudinal research, which studies one group of participants at many points in time. Sequential designs combine the best features of cross- sectional and longitudinal designs, by assessing assess multiple cohorts over time.

Key Terms

applying developmental science scientific method open-ended interview structured interview questionnaire naturalistic observation structured observation correlational research experimental research dependent variable independent variable random assignment cross-sectional research

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longitudinal research sequential research design

Review Questions

1. What are methods for collecting data and answering research questions?

2. What designs do researchers use to study development?

1.5 Discuss the responsibility of researchers to their participants and how they may protect them.

Summary

Researchers must maximize the benefits to research participants and minimize the harms, safeguarding participants’ welfare. They must be accurate and honest in their work and respect participants’ autonomy, including seeking informed consent and child assent. In addition, the benefits and risks of participation in research must be spread equitably across individuals and groups.

Key Term

informed consent

Review Question

What ethical responsibilities do researchers have to their participants?

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Part II Biological Development and Health

Chapter 2 Biological and Environmental Foundations and Prenatal Development 49 Chapter 3 Physical Development and Aging 91 Chapter 4 Brain, Perception, and Motor Development 129 Chapter 5 Health 163

Physical development is perhaps the most easily recognizable developmental change that we experience over our lives. It comprises growth and maturation, and changes in sensory, neurological, and motor abilities.

Physical development begins at conception with the formation of a zygote. Our traits are influenced by complex interactions of genes and contextual factors, such as environmental circumstances, stressors, and opportunities, that determine whether genetic potentials are realized.

Most of us are born with all of our senses—able to see, hear, smell, taste, and touch. Likewise, we are born with billions of brain cells called neurons. As we develop, the number of connections among neurons increases, and neural communication becomes quicker, contributing to more efficient cognition. Brain development continues throughout life. Some neural plasticity, the capacity to change in response to experience, is retained in adulthood.

Like other aspects of physical development, motor development unfolds in a predictable sequence in infancy and childhood and continues to change over the lifespan. In adulthood the rate and extent of change varies. Adults who remain physically active can compensate for age-related declines and may retain their strength, balance, and endurance as well as experience better overall health and well-being, with positive implications for cognitive and socioemotional functioning in the many contexts in which they live.

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2 Biological and Environmental Foundations and Prenatal Development

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Johann Van Tonder/Alamy

Learning Objectives 2.1 Describe the process of cell reproduction and patterns of genetic inheritance. 2.2 Define and provide examples of genetic disorders and chromosomal abnormalities. 2.3 Explain how the dynamic interactions of heredity and environment influence development. 2.4 Discuss the stages of prenatal development, stages of childbirth, and challenges for infants at risk. 2.5 Identify the principles of teratology, types of teratogens, and ways that teratogens can be used to predict prenatal outcomes.

Digital Resources

Sickle Cell Disease

Genomic Imprinting

Iceland’s Down Syndrome Dilemma

Amniocentesis

Twins Separated at Birth

Holocaust Survivors’ Trauma

Ultrasound

The Process of Childbirth

Fetal Alcohol Spectrum Disorders

Marijuana During Pregnancy

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Master these learning objectives with multimedia resources available at edge.sagepub.com/kuthertopical and Lives in Context video cases available in the interactive eBook.

“Roger and Ricky couldn’t be more different,” marveled their mother. “People are surprised to find out they are brothers.” Roger is tall and athletic, with blond hair and striking blue eyes. He spends most afternoons playing ball with his friends and often invites them home to play in the yard. Ricky, two years older than Roger, is much smaller, thin and wiry. He wears thick glasses over his brown eyes that are nearly as dark as his hair. Unlike his brother, Ricky prefers solitary games and spends most afternoons at home playing video games, building model cars, and reading comic books. How can Roger and Ricky have the same parents and live in the same home yet differ markedly in appearance, personality, and preferences? In this chapter, we discuss the process of genetic inheritance and principles that can help us to understand how members of a family can share a great many similarities—and many differences. We also examine the process by which a single cell containing genes from two biological parents develops over a short period of time into an infant.

Genetic Foundations of Development Although Roger is quite different from his older brother, Ricky, he shares so many of his father’s characteristics that most people comment on the strong physical resemblance. In other ways, however, Roger is more like his highly sociable mother. Ricky also shares similarities with each of his parents: In physical appearance, he resembles his mother and her brothers, but his quiet personality is similar to that of his father. Most of us learn early in life, and take it for granted, that children tend to resemble their parents. But to understand just how parents transmit their inborn characteristics and tendencies to their children, we must consider the human body at a cellular level.

Genetics The human body is composed of trillions of units called cells. Within each cell is a nucleus that contains 23 matching pairs of rod-shaped structures called chromosomes (Plomin, DeFries, Knopik, & Neiderhiser, 2013). Each chromosome holds the basic units of heredity, known as genes, composed of stretches of deoxyribonucleic acid (DNA), a complex

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molecule shaped like a twisted ladder or staircase. The 20,000 to 25,000 genes that reside within our chromosomes are the blueprint for creating all of the traits that organisms carry (Barlow-Stewart, 2012; Finegold, 2013). People around the world share 99.7% of their genes (Watson, 2008). Although all humans share the same basic genome, or set of genetic instructions, every person has a slightly different code, making him or her genetically distinct from other humans.

chromosome One of 46 rodlike molecules that contain 23 pairs of DNA found in every body cell and collectively contain all of the genes.

DNA Deoxyribonucleic acid; the chemical structure, shaped like a twisted ladder, that contains all of the genes.

Figure 2.1: Meiosis and Mitosis

Cell Reproduction

Most cells in the human body reproduce through a process known as mitosis, in which DNA replicates itself, permitting the duplication of chromosomes and, ultimately, the formation of new cells with identical genetic material (Sadler, 2015). Sex cells reproduce in a different way, called meiosis, which results in gametes (sperm in males and ova in

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females; see Figure 2.1). Gametes each contain 23 chromosomes (one-half of the 46 chromosomes, or 23 pairs, present in body cells). This permits the joining of sperm and ovum at fertilization to produce a fertilized egg, or zygote, with 46 chromosomes forming 23 pairs, half from the biological mother and half from the biological father. Each gamete has a unique genetic profile. It is estimated that individuals can produce millions of versions of their own chromosomes (National Library of Medicine, 2013).

mitosis The process of cell duplication in which DNA is replicated and the resulting cell is genetically identical to the original.

meiosis The process by which a gamete is formed, containing one- half of the cell’s chromosomes producing creating ova and sperm with 23 single, unpaired chromosomes.

zygote A fertilized ovum.

Figure 2.2: Chromosomes

U.S. National Library of Medicine

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As shown in Figure 2.2, 22 of the 23 pairs of chromosomes are matched; they contain similar genes in almost identical positions and sequence, reflecting the distinct genetic blueprint of the biological mother and father. The 23rd pair are sex chromosomes that specify the biological sex of the individual. In females, sex chromosomes consist of two large X-shaped chromosomes (XX). Males’ sex chromosomes consist of one large X- shaped chromosome and one much smaller Y-shaped chromosome (XY; Moore & Persaud, 2016; Plomin et al., 2013).

Because females have two X sex chromosomes, all ova contain one X sex chromosome. Males’ sex chromosome pair includes both X and Y chromosomes. Therefore, one half of the sperm males produce contains an X chromosome and one half contains a Y. Whether the fetus develops into a boy or girl is determined by which sperm fertilizes the ovum. If the ovum is fertilized by a Y sperm, a male fetus will develop, and if the ovum is fertilized by an X sperm, a female fetus will form, as shown in Figure 2.3.

Genes Shared by Twins

Twins are siblings who share the same womb. Twins occur in about 1 out of every 30 births in the United States (Martin, Hamilton, & Osterman, 2012). About two-thirds of naturally conceived twins are dizygotic (DZ) twins, or fraternal twins, conceived when a woman releases more than one ovum and each is fertilized by a different sperm. DZ twins share about one-half of their genes and, like other siblings, most fraternal twins differ in appearance, with different hair color, eye color, and height. In about half of fraternal twin pairs, one twin is a boy and the other a girl. DZ twins tend to run in families, suggesting a genetic component that controls the tendency for a woman to release more than one ovum each month. However, rates of DZ twins also increase with in vitro fertilization, maternal age, and with each subsequent birth (Fletcher, Zach, Pramanik, & Ford, 2012; Martin et al., 2012).

dizygotic (DZ) twin Also known as a fraternal twin; occurs when two ova are released and each is fertilized by a different sperm; the resulting offspring share 50% of the genetic material.

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Figure 2.3: Sex Determination

Monozygotic (MZ) twins, or identical twins, originate from the same zygote, sharing the same genotype with identical instructions for all physical and psychological characteristics. MZ twins occur when the zygote splits into two separate but identical zygotes that develop into two infants. It is estimated that MZ twins occur in 4 of every 1,000 U.S. births (Fletcher et al., 2012). The causes of MZ twinning are not well understood. Temperature fluctuations are associated with MZ births in animals, but it is unknown whether similar effects occur in humans (Aston, Peterson, & Carrell, 2008). In vitro fertilization and advanced maternal age (35 and older) may increase the occurrence of MZ twins (Aston et al., 2008; Knopman et al., 2014).

monozygotic (MZ) twin Also known as an identical twin; occurs when the zygote splits apart early in development. The resulting offspring share 100% of their genetic material.

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Monozygotic, or identical, twins share 100% of their DNA.

AP Photo/Charlie Neibergall

Patterns of Genetic Inheritance Although the differences among various members of a given family may appear haphazard, they are the result of a genetic blueprint unfolding. Researchers are just beginning to uncover the instructions contained in the human genome, but we have learned that traits and characteristics are inherited in predictable ways.

Dominant–Recessive Inheritance

Lynn has red hair while her brother, Jim, does not—and neither do their parents. How did Lynn end up with red hair? These outcomes can be explained by patterns of genetic inheritance, how the sets of genes from each parent interact. As we have discussed, each person has 23 pairs of chromosomes, one pair inherited from the mother and one from the father. The genes within each chromosome can be expressed in different forms, or alleles, that influence a variety of physical characteristics. When alleles of the pair of chromosomes are alike with regard to a specific characteristic, such as hair color, the person is said to be homozygous for the characteristic and will display the inherited trait. If they are different, the person is heterozygous, and the trait expressed will depend on the relations among the genes (Moore & Persaud, 2016; National Center for Biotechnology Information, 2004). Some genes are passed through dominant–recessive inheritance, in which some genes are dominant and are always expressed regardless of the gene they are paired with. Other genes are recessive and will be expressed only if paired with another

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recessive gene (see Table 2.1). Lynn and Jim’s parents are heterozygous for red hair; both have dark hair, but they each carry a recessive gene for red hair. When an individual is heterozygous for a particular trait, the dominant gene is expressed, and the person becomes a carrier of the recessive gene, as shown in Figure 2.4.

homozygous Refers to a chromosomal pair consisting of two identical alleles.

heterozygous Refers to a chromosomal pair consisting of two different alleles.

dominant–recessive inheritance A form of genetic inheritance in which the phenotype reflects only the dominant allele of a heterozygous pair.

Table 2.1 Dominant and Recessive Characteristics Table 2.1 Dominant and Recessive Characteristics

Dominant Trait Recessive Trait

Dark hair Blond hair

Curly hair Straight hair

Hair Baldness

Non-red hair Red hair

Facial dimples No dimples

Brown eyes Blue, green, hazel eyes

Second toe longer than big toe Big toe longer than second toe

Type A blood Type O blood

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Type B blood Type O blood

Rh-positive blood Rh-negative blood

Normal color vision Color blindness Source: McKusick (1998); McKusick-Nathans Institute of Genetic Medicine (2014).

Figure 2.4: Dominant–Recessive Inheritance

Incomplete Dominance

In most cases, dominant–recessive inheritance is an oversimplified explanation for patterns of genetic inheritance. Incomplete dominance is a genetic inheritance pattern in which both genes influence the characteristic (Plomin et al., 2013). For example, consider blood type. Neither the alleles for blood type A and B dominate each other. A heterozygous person with the alleles for blood type A and B will express both A and B alleles and have blood type AB.

incomplete dominance A genetic inheritance pattern in which both genes are expressed in the phenotype.

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A different type of inheritance pattern is seen when a person inherits heterozygous alleles in which one allele is stronger than the other yet does not completely dominate. In this situation, the stronger allele does not mask all of the effects of the weaker allele. Therefore some, but not all, characteristics of the recessive allele appear. For example, the trait for developing normal blood cells does not completely mask the allele for developing sickle-shaped blood cells. About 8% of African Americans (and relatively few Caucasians or Asian Americans) carry the recessive sickle cell trait (Ashley-Koch, Yang, & Olney, 2000; Ojodu, Hulihan, Pope, & Grant, 2014). Sickle cell alleles cause red blood cells to become crescent, or sickle, shaped. Cells that are sickle-shaped cannot distribute oxygen effectively throughout the circulatory system (Ware, de Montalembert, Tshilolo, & Abboud, 2017). However, sickle cell carriers do not develop full-blown sickle cell anemia. Carriers of the trait for sickle cell anemia may function normally but may show some symptoms such as reduced oxygen distribution throughout the body and exhaustion after exercise. Only individuals who are homozygous for the recessive sickle cell trait develop sickle cell anemia.

sickle cell trait A recessive trait, more often affecting African Americans than Caucasians or Asian Americans, that causes red blood cells to become crescent or sickle shaped, resulting in difficulty distributing oxygen throughout the circulatory system.

Recessive sickle cell alleles cause red blood cells to become crescent shaped and unable to distribute oxygen effectively throughout the circulatory system. Alleles for normal blood cells do not mask all of the characteristics of recessive sickle cell alleles, illustrating incomplete dominance.

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Wikimedia

Polygenic Inheritance

Hereditary influences act in complex ways, and researchers cannot trace most characteristics to only one or two genes. Most traits are a function of the interaction of many genes, known as polygenic inheritance. Examples of polygenic traits include height, intelligence, temperament, and susceptibility to certain forms of cancer (Bouchard, 2014; Plomin et al., 2013). As the number of genes that contribute to a trait increases, so does the range of possible traits. Genetic propensities interact with environmental influences to produce a wide range of individual differences in human traits.

polygenic inheritance Occurs when a trait is a function of the interaction of many genes, such as with height, intelligence, and temperament.

Genomic Imprinting

The principles of dominant–recessive and incomplete dominance inheritance can account for more than 1,000 human traits (McKusick, 2007). However, a few traits are determined by a process known as

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genomic imprinting. Genomic imprinting refers to the instance in which the expression of a gene is determined by whether it is inherited from the mother or the father (Kelly & Spencer, 2017; National Library of Medicine, 2013). For example, consider two conditions that illustrate genomic imprinting: Prader-Willi syndrome and Angelman syndrome. Both syndromes are caused by an abnormality in the 15th chromosome (Kalsner & Chamberlain, 2015). If the abnormality occurs on chromosome 15 acquired by the father, the individual—whether a daughter or son—will develop Prader-Willi syndrome, a set of specific physical and behavioral characteristics including obesity, insatiable hunger, short stature, motor slowness, and mild to moderate intellectual impairment. If the abnormal chromosome 15 arises from the mother, the individual—again, whether it is a daughter or a son—will develop Angelman syndrome, characterized by hyperactivity, thin body frame, seizures, disturbances in gait, and severe learning disabilities including severe problems with speech. Prader- Willi and Angelman syndromes each occur in about 1 in 15,000 persons (Everman & Cassidy, 2000). Patterns of genetic inheritance can be complex, yet they follow predictable principles. For a summary of patterns of genetic inheritance, refer to Table 2.2.

genomic imprinting The instance when the expression of a gene is determined by whether it is inherited from the mother or father.

Table 2.2 Summary: Patterns of Genetic Inheritance Table 2.2 Summary: Patterns of Genetic Inheritance

Inheritance Pattern

Description

Dominant– recessive inheritance

Genes that are dominant are always expressed, regardless of the gene they are paired with, and recessive genes are expressed only if paired with another recessive gene.

Incomplete dominance

Both genes influence the characteristic, and aspects of both genes appear.

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Polygenic inheritance

Polygenic traits are the result of interactions among many genes.

Genomic imprinting

The expression of a gene is determined by whether it is inherited from the mother or the father.

Thinking in Context 2.1

1. Why do twins occur? From an evolutionary developmental perspective, does twinning serve an adaptive purpose for our species? Why or why not?

2. Consider your own physical characteristics, such as hair and eye color. Are they indicative of recessive traits or dominant ones?

3. Do you think that you might be a carrier of recessive traits? Why or why not?

Chromosomal and Genetic Problems Many disorders are caused by inherited genes. Some disorders and abnormalities are the result of dominant–recessive inheritance to which one or both parents contribute. Others are the result of variations in chromosomes.

Genetic Disorders Disorders and abnormalities that are inherited through the parents’ genes include such well-known conditions as cystic fibrosis and sickle cell anemia, as well as others that are rare and, in some cases, never even noticed throughout the individual’s life.

Dominant–Recessive Disorders

Recall that in dominant–recessive inheritance, dominant genes are always expressed, regardless of the gene they are paired with, and recessive genes are expressed only if paired with another recessive gene. Table 2.3

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illustrates diseases that are inherited through dominant–recessive inheritance. Few severe disorders are inherited through dominant– recessive inheritance because individuals who inherit the allele often do not survive long enough to reproduce and pass it to the next generation. One exception is Huntington’s disease, a fatal disease in which the central nervous system deteriorates (National Library of Medicine, 2013; Sadler, 2015). Individuals with the Huntington’s allele develop normally in childhood, adolescence, and young adulthood. Symptoms of Huntington’s disease do not appear until age 35 or later. By then, many individuals have already had children, and one half of them, on average, will inherit the dominant Huntington’s gene.

Phenylketonuria (PKU) is a common recessive disorder that prevents the body from producing an enzyme that breaks down the amino acid phenylalanine from proteins (Blau, van Spronsen, & Levy, 2010; Romani et al., 2017). Without treatment, the phenylalanine builds up quickly to toxic levels that damage the central nervous system, contributing to intellectual developmental disability, once known as mental retardation. PKU illustrates how genes interact with the environment to produce developmental outcomes because intellectual disability results from the interaction of the genetic predisposition and exposure to phenylalanine from the environment (Blau, 2016a). The United States and Canada require all newborns to be screened for PKU (Blau, Shen, & Carducci, 2014). If the disease is discovered, the infant is placed on a diet low in phenylalanine. Children who maintain a strict diet usually attain average or near-average levels of intelligence (Blau, 2016; Widaman, 2009). Some cognitive and psychological problems may appear in childhood and persist into adulthood, particularly difficulty in attention and planning skills, emotional regulation, depression, and anxiety (Blau et al. 2010; Enns et al., 2010; Huijbregts, Gassió, & Campistol, 2013).

phenylketonuria (PKU) A recessive disorder that prevents the body from producing an enzyme that breaks down phenylalanine (an amino acid) from proteins, that, without treatment, leads to buildup that damages the central nervous system.

Table 2.3 Diseases Inherited Through Dominant–Recessive Inheritance Table 2.3 Diseases Inherited Through Dominant–Recessive Inheritance

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Table 2.3 Diseases Inherited Through Dominant–Recessive Inheritance

Disease Occurrence Mode of Inheritance

Description Treatment

Huntington’s disease

1 in 20,000 Dominant

Degenerative brain disorder that affects muscular coordination and cognition

No cure; death usually occurs 10 to 20 years after onset

Cystic fibrosis 1 in 2,000– 2,500

Recessive

An abnormally thick, sticky mucus clogs the lungs and digestive system, leading to respiratory infections and digestive difficulty

Bronchial drainage, diet, gene replacement therapy

Phenylketonuria (PKU)

1 in 8,000– 10,000 Recessive

Inability to digest phenylalanine that, if untreated, results in neurological damage and death

Diet

Sickle cell anemia

1 in 500 African Recessive

Sickling of red blood cells leads to inefficient distribution of oxygen

No cure; blood transfusions, treat infections,

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Sickle cell anemia

African Americans

Recessive throughout the body that leads to organ damage and respiratory infections

bone marrow transplant; death by middle age

Tay-Sachs disease

1 in 3,600 to 4,000 descendants of Central and Eastern European Jews

Recessive Degenerative brain disease

None; most die by 4 years of age

Source: McKusick-Nathans Institute of Genetic Medicine (2014).

This young man is diagnosed with fragile X syndrome, a recessive disorder carried on the X chromosome and the most common form of inherited intellectual impairment.

Chris Walker/MCT/Newscom

X-Linked Disorders

Some recessive genetic disorders are carried on the X chromosome, like the gene for hemophilia, a condition in which the blood does not clot normally (Barlow-Stewart, 2012). Males are more likely to be affected by X-linked genetic disorders because they have only one X chromosome, and therefore any genetic marks on their X chromosome are displayed. Females (XX) have two X chromosomes; a recessive gene located on one

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chromosome. Females are, therefore, less likely to display X-linked genetic disorders because both of their X-chromosomes must carry the recessive genetic disorder for it to be displayed. In contrast, fragile X syndrome is an example of a dominant–recessive disorder carried on the X chromosome (Hagerman, 2011). Because the gene is dominant, it need appear on only one X chromosome to be displayed. That means that fragile X syndrome occurs in both males and females. Table 2.4 illustrates diseases acquired through X-linked inheritance.

fragile X syndrome An example of a dominant–recessive disorder carried on the X chromosome.

Table 2.4 Diseases Acquired Through X-Linked Inheritance Table 2.4 Diseases Acquired Through X-Linked Inheritance

Syndrome/Disease Occurrence Description Treatment

Color blindness 1 in 12 males

Difficulty distinguishing red from green; less common is difficulty distinguishing blue from green

No cure

Duchenne muscular dystrophy

1 in 3,500 males

Weakness and wasting of limb and trunk muscles; progresses slowly but will affect all voluntary muscles

Physical therapy, exercise, body braces; survival rare beyond late 20s

Symptoms include cognitive impairment;

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Fragile X syndrome

1 in 2,000 males

impairment; attention problems; anxiety; unstable mood; long face; large ears; flat feet; and hyperextensible joints, especially fingers

No cure

Hemophilia 1 in 3,000– 7,000 males

Blood disorder in which the blood does not clot

Blood transfusions

Source: McKusick-Nathans Institute of Genetic Medicine (2016)

Chromosomal Abnormalities Chromosomal abnormalities are the result of errors during cell reproduction, meiosis, or mitosis or damage caused afterward. Occurring in 1 of about every 700 births, the most widely known chromosome disorder is trisomy 21, more commonly called Down syndrome (Parker et al., 2010). Down syndrome occurs when a third chromosome appears alongside the 21st pair of chromosomes. Although individuals with Down syndrome vary in the severity of their symptoms, Down syndrome is associated with marked physical, health, and cognitive attributes, including a short, stocky build and striking facial features, such as a round face, almond-shaped eyes, and a flattened nose (Davis & Escobar, 2013; Kruszka et al., 2017). Children with Down syndrome tend to show delays in physical and motor development relative to other children and health problems such as congenital heart defects, vision impairments, poor hearing, and immune system deficiencies (Ram & Chinen, 2011; Zampieri et al., 2014). Down syndrome is the most common genetic cause of intellectual developmental disability (Davis & Escobar, 2013), but children’s abilities vary. Children who participate in early intervention and receive sensitive caregiving and encouragement to explore their environment show positive outcomes, especially in the motor, social, and emotional areas of functioning (Hazlett, Hammer, Hooper, & Kamphaus, 2011).

Down syndrome Also known as trisomy 21; a condition in which

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a third, extra chromosome appears at the 21st site. Down syndrome is associated with distinctive physical characteristics accompanied by developmental disability.

Table 2.5 Sex Chromosome Abnormalities Table 2.5 Sex Chromosome Abnormalities

Female Genotype

Syndrome Description Prevalence

XO Turner

As adults, they are short in stature, often have small jaws with extra folds of skin around their necks (webbing), lack prominent female secondary sex characteristics, such as breasts, and show abnormal development of the ovaries. Elevated risk for thyroid disease, vision and hearing problems, heart defects, diabetes, and autoimmune disorders.

1 in 2,500 females

XXX Triple-X

Grow about an inch or so taller than average, with unusually long legs and slender torsos, and show normal development of sexual characteristics and fertility. Because many cases of triple-X syndrome often go unnoticed, little is known about the syndrome.

Unknown

Male Genotype

Syndrome Description Prevalence

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XXY Klinefelter

Symptoms range in severity from unnoticeable to severe symptoms such as a high-pitched voice, feminine body shape, breast enlargement, and infertility. Many boys and men with Klinefelter syndrome have short stature, a tendency to be overweight, and language and short-term memory impairments that can cause difficulties in learning.

1 in 500 to 1 in 1,000

XYY XYY, Jacob’s Syndrome

Accompanied by high levels of testosterone.

Prevalence of XYY syndrome is uncertain as most men with XYY syndrome are unaware that they have a chromosomal abnormality

Sources: Bardsley et al. (2013); Bird & Hurren (2016); Herlihy & McLachlan (2015); National Library of Medicine (2013); Otter, Schrander-Stumpel, & Curfs (2009); Pinsker (2012); Powell & Schulte (2011).

Down syndrome is the most common cause of intellectual disability. Children with Down syndrome show more positive developmental outcomes when adults are sensitive to their needs. Interventions that encourage children to interact with their environment can promote motor, social, and emotional development.

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Digital Light Source/Universal Images Group/Getty Images

Advances in medicine have addressed many of the physical health problems associated with Down syndrome so that today, many individuals with Down syndrome live well into middle age, with an average life expectancy of 60 (Glasson, Dye, & Bittles, 2014; Torr, Strydom, Patti, & Jokinen, 2010). As more adults age with Down syndrome, we have discovered a link between Down syndrome and Alzheimer’s disease, a brain degenerative disease that typically strikes in older adulthood (Hithersay, Hamburg, Knight, & Strydom, 2017; Wiseman et al., 2015). This is an example of how disorders and illnesses can be influenced by multiple genes and complex contextual interactions; in this case, Down syndrome and Alzheimer’s disease share genetic markers.

Some of the most common chromosomal abnormalities concern the 23rd pair of chromosomes: the sex chromosomes. Given their different genetic makeup, sex chromosome abnormalities yield different effects in males and females. They are summarized in Table 2.5.

Mutation Not all inborn characteristics are inherited. Some result from mutations, sudden changes and abnormalities in the structure of genes that occur spontaneously or may be induced by exposure to environmental toxins such as radiation and agricultural chemicals in food (Burns & Bottino, 1989; Lewis, 2006). A mutation may involve only one gene or many. It is estimated that as many as one-half of all conceptions include mutated chromosomes (Plomin et al., 2013). Most mutations are fatal—the

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developing organism dies very soon after conception, often before the woman knows she is pregnant (Lewis, 2006; Rimoin, Connor, & Pyeritz, 1997).

mutation A sudden permanent change in the structure of genes.

Sometimes mutations are beneficial. This is especially true if the mutation is induced by stressors in the environment and provides an adaptive advantage to the individual. For example, the sickle cell gene is a mutation that originated in areas where malaria is widespread, such as Africa. Children who inherited a single sickle cell allele were more resistant to malarial infection and more likely to survive and pass it along to their offspring (Allison, 2004; Gong, Parikh, Rosenthal, & Greenhouse, 2013). The sickle cell gene is not helpful in places of the world where malaria is not a risk. The frequency of the gene is decreasing in areas of the world where malaria is uncommon. For example, only 8% of African Americans are carriers, compared with as many as 30% of black Africans in some African countries (Maakaron & Taher, 2017). Therefore, the developmental implications of genotypes—and mutations—are context specific, posing benefits in some contexts and risks in others.

Predicting and Detecting Genetic Disorders The likelihood of genetic disorders often can be predicted before conception. Moreover, advances in technology permit abnormalities to be detected earlier than ever before.

Genetic Counseling

When considering having children, many couples seek genetic counseling to determine the risk of their children inheriting genetic defects and chromosomal abnormalities (Uhlmann, Schuette, & Yashar, 2009). The genetic counselor constructs a family history of heritable disorders for both prospective parents. If either member of the couple appears to carry a genetic disorder, genetic screening blood tests may be carried out on both parents to detect chromosomal abnormalities and the presence of dominant and recessive genes for various disorders.

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Candidates for genetic counseling include those whose relatives have a genetic condition, couples who have had difficulties bearing children, women over the age of 35, and couples from the same ethnic group. Once prospective parents learn about the risk of conceiving a child with a disorder, they can determine how to proceed—whether to conceive a child naturally or through the use of in vitro fertilization—after screening gametes for the disorders of concern. Given advances in our knowledge of genetic disorders and ability to screen for them, some argue that genetic counseling should be available to all prospective parents (Minkoff & Berkowitz, 2014).

Prenatal Diagnosis

Prenatal testing is recommended when genetic counseling has determined a risk for genetic abnormalities, when the woman is older than age 35, when both parents are members of an ethnicity at risk for particular genetic disorders, or when fetal development appears abnormal (Barlow-Stewart & Saleh, 2012). Technology has advanced rapidly, equipping professionals with an array of tools to assess the health of the fetus. Table 2.6 summarizes methods of prenatal diagnosis.

Expectant parents view ultrasound images of the developing fetus.

Monkey Business Images/Shutterstock.com

Table 2.6 Methods of Prenatal Diagnosis Table 2.6 Methods of Prenatal Diagnosis

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Method Explanation Advantages Disadvantages

Ultrasound

High-frequency sound waves directed at the mother’s abdomen provide clear images of the womb projected on to a video monitor.

Ultrasound enables physicians to observe the fetus, measure fetal growth, reveal the sex of the fetus, and to determine physical abnormalities in the fetus.

Many abnormalities and deformities cannot be easily observed.

Amniocentesis

A small sample of the amniotic fluid that surrounds the fetus is extracted from the mother’s uterus through a long, hollow needle inserted into the mother’s abdomen. The amniotic fluid contains fetal cells. The fetal cells are grown in a laboratory dish in order to create enough cells for genetic analysis.

It permits a thorough analysis of the fetus’s genotype. There is 100% diagnostic success rate.

Safe, but poses a greater risk to the fetus than ultrasound.

If conducted before the 15th week of pregnancy, it may increase the risk of miscarriage.

Chorionic villus sampling requires studying a small amount of tissue

It permits a thorough analysis of the

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Chorionic villus sampling (CVS)

from the chorion, part of the membrane surrounding the fetus, for the presence of chromosomal abnormalities. The tissue sample is obtained through a long needle inserted either abdominally or vaginally, depending on the location of the fetus.

fetus’s genotype.

CVS is relatively painless, and there is a 100% diagnostic success rate. Can be conducted earlier than amniocentesis, between 10 and 12 weeks.

It may pose a higher rate of spontaneous abortion and limb defects when conducted prior to 10 weeks’ gestation.

Noninvasive prenatal testing (NIPT)

Cell-free fetal DNA is examined by drawing blood from the mother.

There is no risk to the fetus. It can diagnose several chromosomal abnormalities.

It cannot yet detect the full range of abnormalities.

It may be less accurate than other methods. Researchers have identified the entire genome sequence using NIPT, suggesting that someday NIPT may be as effective as other, more invasive

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techniques. Sources: Akolekar, Beta, Picciarelli, Ogilvie, & D’Antonio (2015); Chan, Kwok, Choy, Leung, & Wang (2013); Fan et al. (2012); Gregg et al. (2013); Odibo (2015); Shahbazian, Barati, Arian, & Saadati (2012); Shim et al. (2014); Tabor & Alfirevic (2010); Theodora et al. (2016).

Prenatal Treatment of Genetic Disorders

What happens when a genetic or chromosomal abnormality is found? Advances in genetics and in medicine have led to therapies that can be administered prenatally to reduce the effects of many genetic abnormalities. For example, hormones and other drugs, as well as blood transfusions, can be given to the fetus by inserting a needle into the uterus (Fox & Saade, 2012; Lindenburg, van Kamp, & Oepkes, 2014). Most strikingly, fetal surgery can repair defects of the heart, lung, urinary tract, and other areas (Danzer & Johnson, 2014; Sala et al., 2014). Researchers believe that one day we may be able to treat many heritable disorders thorough genetic engineering, by synthesizing normal genes to replace defective ones. It may someday be possible to sample cells from an embryo, detect harmful genes and replace them with healthy ones, then return the healthy cells to the embryo, where they will reproduce and correct the genetic defect (Coutelle & Waddington, 2012). This approach has been used to correct certain heritable disorders in animals and holds promise for treating humans.

During amniocentesis, ultrasound is used to guide the insertion of a long, hollow needle into the mother’s abdomen in order to extract a sample of the amniotic fluid that surrounds the fetus. The amniotic fluid contains fetal cells, which are grown in a laboratory dish and tested for genetic and chromosomal anomalies and defects.

Saturn Stills / Science Source

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1. Discuss how PKU illustrates the following two themes in human development: (1) the role of nature and nurture in development and (2) interactions among domains of development.

2. Identify risk factors for genetic and chromosomal disorders. What can prospective parents do to minimize the risks? What specific advice do you give?

3. Suppose you are a 36-year-old woman pregnant with your first child. What would be the advantages and disadvantages of the four types of prenatal diagnostic testing described in Table 2.6? What information would your health care provider need in order to recommend testing appropriate for your particular case?

Heredity and Environment We have learned a great deal about genetic inheritance. Most human traits, however, are influenced by a combination of genes working in concert with environmental influences. Our genetic makeup, inherited from our biological parents, consists of a complex blend of hereditary characteristics known as genotype. Our genotype is a biological influence on all of our traits, from hair and eye color to personality, health, and behavior. However, our phenotype, the traits we ultimately show, such as our specific eye or hair color, is not determined by genotypes alone. Phenotypes are influenced by the interaction of genotypes and our experiences.

genotype An individual’s collection of genes that contain instructions for all physical and psychological characteristics, including hair, eye color, personality, health, and behavior.

phenotype The observable physical or behavioral characteristics of a person, eye, hair color, or height.

Behavioral Genetics

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Behavioral Genetics Behavioral genetics is the field of study that examines how genes and experience combine to influence the diversity of human traits, abilities, and behaviors (Maxson, 2013; Plomin et al., 2013). Genotypes alone do not determine people’s traits, characteristics, or personalities; instead, development is the process by which our genetic inheritance (genotype) is expressed in observable characteristics and behaviors (phenotype). Behavioral geneticists recognize that even traits that have a strong genetic component, such as height, are modified by environmental influences (Dubois et al., 2012; Plomin, DeFries, Knopik, & Neiderhiser, 2016). Moreover, most human traits, such as intelligence, are influenced by multiple genes, and there are often multiple variants of each gene (Bouchard, 2014; Chabris, Lee, Cesarini, Benjamin, & Laibson, 2015).

behavioral genetics The field of study that examines how genes and environment combine to influence the diversity of human traits, abilities, and behaviors.

Methods of Behavioral Genetics

Behavioral geneticists devise ways of estimating the heritability of specific traits and behaviors. Heritability refers to the extent to which variation among people on a given characteristic is due to genetic differences. The remaining variation not due to genetic differences is instead a result of the environment and experiences. Heritability research therefore examines the contributions of the genotype but also provides information on the role of experience in determining phenotypes (Plomin & Daniels, 2011). Behavioral geneticists assess the hereditary contributions to behavior by conducting selective breeding and family studies (Maxson, 2013).

heritability A measure of the extent to which variation of a certain trait can be traced to genes.

Using selective breeding studies, behavioral geneticists deliberately

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modify the genetic makeup of animals to examine the influence of heredity on attributes and behavior. For example, in a classic study, behavioral geneticists demonstrated that they can breed mice to be very physically active or sedentary. They selectively breed highly active mice only with each other and, similarly, breed mice with a very low level of activity with each other. Over subsequent generations, mice bred for high levels of activity become many times more active than those bred for low levels of activity (DeFries, Gervais, & Thomas, 1978). Selective breeding in rats, mice, and other animals such as chickens has revealed genetic contributions to many traits and characteristics, such as aggressiveness, emotionality, sex drive, and even maze learning (Plomin et al., 2016).

Behavioral geneticists conduct family studies to compare people who live together and share varying degrees of relatedness. Two kinds of family studies are common: twin studies and adoption studies (Koenen, Amstadter, & Nugent, 2012). Twin studies compare identical and fraternal twins to estimate how much of a trait or behavior is attributable to genes. If genes affect the attribute, identical twins should be more similar than fraternal twins because identical twins share 100% of their genes whereas fraternal twins share about only 50%. Adoption studies, on the other hand, compare the degree of similarity between adopted children and their biological parents whose genes they share (50%) and their adoptive parents with whom they share no genes. If the adopted children share similarities with their biological parents, even though they were not raised by them, it suggests that the similarities are genetic.

Adoption studies also shed light on the extent to which attributes and behaviors are influenced by the environment. For example, the degree to which two genetically unrelated adopted children reared together are similar speaks to the role of environment. Comparisons of identical twins reared in the same home with those reared in different environments can also illustrate environmental contributions to phenotypes. If identical twins reared together are more similar than those reared apart, an environmental influence can be inferred.

Genetic Influences on Personal Characteristics

Research examining the contribution of genotype and environment to intellectual abilities has found a moderate role for heredity. Twin studies have shown that identical twins consistently have more highly correlated scores than do fraternal twins. For example, a study of intelligence in over

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of comparisons of intelligence scores from individuals who share different genetic relationships with each other. Note that correlations for all levels of kin are higher when they are reared together, supporting the role of environment. Average correlations also rise with increases in shared genes.

Genes contribute to many other traits, such as sociability, anxiety, temperament, obesity, happiness, and susceptibility to various illnesses such as heart disease and cancer, poor mental health, and a propensity to be physically aggressive (H. Chen et al., 2013; Pemment, 2013; Veroude et al., 2016; Yoon-Mi, 2009). Yet even traits that are thought to be heavily influenced by genetics can be modified by physical and social interventions. For example, growth, body weight, and body height are largely predicted by genetics, yet environmental circumstances and opportunities influence whether genetic potentials are realized (Dubois et al., 2012). Even identical twins who share 100% of their genes are not 100% alike. Those differences are due to the influence of environmental factors, which interact with genes in a variety of ways.

Table 2.7 Average Correlation of Intelligence Scores From Family Studies for Related and Unrelated Kin Reared Together or Apart

Reared Together

Reared Apart

MZ twins (100% shared genes) .86 .72

DZ twins (50% shared genes) .60 .52

Siblings (50% shared genes) .47 .24

Biological parent/child (50% shared genes)

.42 .22

Half-siblings (25% shared genes) .31 —

Unrelated (adopted) siblings (0% shared genes)*

.34 —

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Unrelated (adopted) siblings (0% shared genes)*

.34 —

Nonbiological parent/child (0% shared genes)*

.19 —

Notes: * Estimated correlation for individuals sharing neither genes nor environment = .0; MZ = monozygotic; DZ = dizygotic. Source: Adapted from Bouchard & McGue (1981).

Gene–Environment Interactions “You two are so different. Edward and Evan, are you sure you’re twins?” kidded Aunt Joan. As fraternal twins, Edward and Evan share 50% of their genes and are reared in the same home. One might expect them to be quite similar, but their similar genes are not the whole story. Genes do not act alone in shaping our development. Instead, genes and the environment work together in complex way to determine our characteristics; behavior; physical, cognitive, and social development; and health (Chabris et al., 2015; Rutter, 2012). Gene–environment interactions refer to the dynamic interplay between our genes and our environment. Several principles illustrate these interactions.

gene–environment interactions Refer to the dynamic interplay between our genes and our environment in determining out characteristics, behavior, physical, cognitive, and social development as well as health.

Range of Reaction

Everyone has a different genetic makeup and therefore responds to the environment in a unique way. In addition, any one genotype can be expressed in a variety of phenotypes. There is a range of reaction (see Figure 2.5), a wide range of potential expressions of a genetic trait, depending on environmental opportunities and constraints (Gottlieb, 2000). For example, consider height. Height is largely a function of genetics, yet an individual may show a range of sizes depending on

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environment and behavior. Suppose that a child is born to two very tall parents. She may have the genes to be tall, but unless she has adequate nutrition, she will not fulfill her genetic potential for height. In societies in which nutrition has improved dramatically over a generation, it is common for children to tower over their parents. The enhanced environmental opportunities, in this case nutrition, enabled the children to fulfill their genetic potential for height. Therefore, a genotype sets boundaries on the range of possible phenotypes, but the phenotypes ultimately displayed vary in response to different environments (Manuck & McCaffery, 2014). In this way, genetics sets the range of development outcomes and the environment influences where, within the range, that person will fall.

range of reaction The concept that a genetic trait may be expressed in a wide range of phenotypes dependent on environmental opportunities and constraints.

Figure 2.5: Range of Reaction

Source: Gottlieb (2007).

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Canalization

Some traits illustrate a wide reaction range. Others are examples of canalization, in which heredity narrows the range of development to only one or a few outcomes. Canalized traits are biologically programmed, and only powerful environmental forces can change their developmental path (Flatt, 2005; Waddington, 1971). For example, infants follow an age- related sequence of motor development, from crawling, to walking, to running. Around the world, most infants walk at about 12 months of age. Generally, only extreme experiences or changes in the environment can prevent this developmental sequence from occurring. For example, children reared in impoverished Romanian and Ethiopian orphanages and exposed to extreme environmental deprivation demonstrated delayed motor development, with some children not walking by 2 years of age (Miller, Tseng, Tirella, Chan, & Feig, 2008; Wilson, 2003). The Lives in Context feature examines gene–environment interactions and responses to child maltreatment.

canalization The tendency for a trait that is biologically programmed to be restricted to only a few outcomes.

Motor development is not entirely canalized, however, because some minor changes in the environment can subtly alter its pace and timing. For example, practice facilitates stepping movements in young infants, prevents the disappearance of stepping movements in the early months of life, and leads to an earlier onset of walking (Ulrich, Lloyd, Tiernan, Looper, & Angulo-Barroso, 2008; Zelazo, Zelazo, Cohen, & Zelazo, 1993). These observations demonstrate that even highly canalized traits, such as motor development, which largely unfolds via maturation, can be subtly influenced by contextual factors.

Gene–Environment Correlations

Heredity and environment are each powerful influences on development. Not only do they interact, but heredity and environmental factors are often correlated with each other (Plomin & Asbury, 2001; Scarr & McCartney, 1983). Gene–environment correlation refers to the idea that many of our traits are supported by both our genes and environment (Plomin, DeFries,

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correlated with each other (Plomin & Asbury, 2001; Scarr & McCartney, 1983). Gene–environment correlation refers to the idea that many of our traits are supported by both our genes and environment (Plomin, DeFries, & Loehlin, 1977). Genes give rise to behaviors, which are associated with the environment (Knafo & Jaffee, 2013). There are three types of gene– environment correlations—passive, reactive, and active—as shown in Figure 2.6.

gene–environment correlation The idea that many of an individual’s traits are supported by his or her genes and environment; there are three types of correlations: passive, reactive, and active.

Parents create homes that reflect their own genotypes. Because parents are genetically similar to their children, the homes that they create are not only in line with their own interests and preferences but they also correspond with the child’s genotype—an example of a passive gene–environment correlation (Wilkinson, Trzaskowski, Haworth, & Eley, 2013). For example, parents might provide genes that predispose a child to develop music ability and also provide a home environment that supports the development of music ability, such as by playing music in the home and owning musical instruments. This type of gene–environment correlation is seen early in life because children are reared in environments that are created by their parents, who share their genotype.

Lives in Context

Gene–Environment Interactions and Responses to Child Maltreatment The MAOA gene influences adaptation to adversity, such as the trauma of child maltreatment

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Children who are maltreated or abused by their parents are at risk for developing many problems, including aggression and violent tendencies. Yet not all children who are maltreated become violent adolescents and adults. Why? A classic study examined this question.

Caspi and colleagues (2002) followed a sample of males from birth until adulthood and observed that not all maltreated boys developed problems with violence. Only boys who carried a certain type of gene were at risk for becoming violent after experiencing maltreatment. Specifically, there are two versions of a gene that controls monoamine oxidase A (MAOA), an enzyme that regulates specific chemicals in the brain; one produces high levels of the enzyme and the other produces low levels. Boys who experienced abuse and other traumatic experiences were about twice as likely to develop problems with aggression, violence, and to even be convicted of a violent crime—but only if they carried the low-MAOA gene. Maltreated boys who carried the high-MAOA gene were no more likely to become violent than non- maltreated boys. In addition, the presence of the low MAOA gene itself was not associated with violence. The low-MAOA gene predicted violence only for boys who experience abuse early in life. These findings have been replicated in another 30-year longitudinal study of boys (Fergusson, Boden, Horwood, Miller, & Kennedy, 2011) as well as a meta-analysis of 27 studies (Byrd & Manuck, 2014).

Similar findings of a MAOA gene x environment interaction in which low-MAOA, but not high-MAOA, predicts negative outcomes in response to childhood adversity has been extended to include other mental health outcomes such as antisocial personality disorder and

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depression (Beach et al., 2010; Cicchetti, Rogosch, & Sturge-Apple, 2007; Manuck & McCaffery, 2014; Nikulina, Widom, & Brzustowicz, 2012). Many of these studies have examined only males. Females show a more mixed pattern with some studies showing that girls display the MAOA gene x environment interaction but to a much lesser extent than boys whereas other studies suggest no relationship (Byrd & Manuck, 2014).

Although there is no single gene that will predict general developmental outcomes, these findings suggest that some genes may increase or decrease our risk for problems in the presence of particular contexts (Belsky & Hartman, 2014a; Conradt, 2017).

In addition, some genes might increase our sensitivity to, and the effectiveness of, environmental interventions (Bakermans-Kranenburg & van IJzendoorn, 2015). Just as we may adjust contextual factors to contribute to successful developmental outcomes and resilience, in the future we might learn how to “turn on” protective genes and “turn off” those that contribute to risk.

What Do You Think? 1. In your view, how important are genetic contributors to

development? 2. If some genes may be protective in particular contexts, should

scientists learn how to turn them on? Why or why not? What about genes that may be harmful in particular contexts?

People naturally evoke responses from others and the environment, just as the environment and the actions of others evoke responses from the individual. In an evocative gene–environment correlation, a child’s genetic traits (e.g., personality characteristics including openness to experience) influence the social and physical environment, which shape development in ways that support the genetic trait (Burt, 2009; Klahr, Thomas, Hopwood, Klump, & Burt, 2013). For example, active, happy infants tend to receive more adult attention than do passive or moody infants (Deater- Deckard & O’Connor, 2000), and even among infant twins reared in the same family, the more outgoing and happy twin receives more positive attention than does the more subdued twin (Deater-Deckard, 2001). Why? Babies who are cheerful and smile often influence their social world by evoking smiles from others, which in turn support the genetic tendency to be cheerful. In this way, genotypes influence the physical and social

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environment to respond in ways that support the genotype. Children who engage in disruptive play tend to later experience problems with peers (Boivin et al., 2013). To return to the music example, a child with a genetic trait for music talent will evoke pleasurable responses (e.g., parental approval) when she plays music; this environmental support, in turn, encourages further development of the child’s musical trait. In addition, some individuals may be more affected by environmental stimuli due to their genetic makeup (Belsky & Hartman, 2014).

Figure 2.6: Gene–Environment Correlation

The availability of instruments in the home corresponds to the child’s musical abilities and she begins to play guitar (passive gene– environment correlation). As she plays guitar, she evokes positive responses in others, increasing her interest in music (evocative gene– environment correlation). Over time she seeks opportunities to play, such as performing in front of an audience (niche-picking).

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Children also take a hands-on role in shaping their development. Recall from Chapter 1 that a major theme in understanding human development is the finding that individuals are active in their development; here we have an example of this pattern. As children grow older, they have increasing freedom in choosing their own activities and environments. An active gene–environment correlation occurs when the child actively creates experiences and environments that correspond to and influence his genetic predisposition. For example, the child with a genetic trait for interest and ability in music actively seeks experiences and environments that support that trait, such as friends with similar interests and after-school music classes. This tendency to actively seek out experiences and environments compatible and supportive of our genetic tendencies is called niche- picking (Scarr & McCartney, 1983).

niche-picking An active gene–environment correlation in which individuals seek out experiences and environments that complement their genetic tendencies.

Figure 2.7: Development Stage and Gene–Environment Correlations

The strength of passive, evocative, and active gene–environment correlations changes with development, as shown in Figure 2.7 (Scarr, 1992). Passive gene–environment correlations are common at birth as caregivers determine infants’ experiences. Correlations between their genotype and environment tend to occur because their environments are

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made by genetically similar parents. Evocative gene–environment correlations also occur from birth, as infants’ inborn traits and tendencies influence others, evoking responses that support their own genetic predispositions. In contrast, active gene–environment correlations take place as children grow older and more independent (Scarr & McCartney, 1983). As they become increasingly capable of controlling parts of their environment, they engage in niche-picking by choosing their own interests and activities, actively shaping their own development. Niche-picking contributes to the differences we see in siblings, including fraternal twins, as they grow older. But identical twins tend to become more similar over time, perhaps because they are increasingly able to select the environments that best fit their genetic propensities (Bouchard et al., 2004; Steves, Spector, & Jackson, 2012). As they age, identical twins—even those reared apart—become alike in attitudes, personality, cognitive ability, intelligence, and preferences; as well, they select similar spouses and best friends (Briley & Tucker-Drob, 2013; Plomin & Deary, 2015; Rushton & Bons, 2005).

Epigenetic Framework We have seen that every aspect of our development is the result of dynamic interactions of heredity and environment. Without a doubt, genes provide a biological foundation for our development. However, genes never act alone in determining human characteristics. Moreover, genes themselves may show stable changes not due to DNA (Holliday, 2006a; Lux, 2013). The dynamic interplay between heredity and environment is known as the epigenetic framework (Gottlieb, 2003, 2007; Lickliter & Honeycutt, 2013). From this perspective, development results from ongoing reciprocal interactions between genetics and environment.

epigenetic framework A perspective stating that development results from reciprocal interactions between genetics and the environment such that the expression of genetic inheritance is influenced by environmental forces.

Genes provide a blueprint for development, determining a range of reaction in which characteristics may develop, depending on environmental circumstances. Not all genes are expressed, however.

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Genetic expression is influenced by epigenetics (Crews, Gillette, Miller- Crews, & Gore, 2014; Holliday, 2006b; Lester, Conradt, & Marsit, 2016). The term epigenetics literally means “above the gene.” The epigenome is a molecule that stretches along the length of DNA and provides instructions to genes, determining how they are expressed and whether they are turned on or off. Epigenetic mechanisms determine how genetic instructions are carried out to determine the phenotype. At birth, each cell in our body turns on only a fraction of its genes. Genes continue to be turned on and off over the course of development and also in response to the environment (Gottlieb, 2000). In this way, even traits that are highly canalized can be influenced by the environment. Environmental factors such as toxins, injuries, crowding, diet, and responsive parenting can influence the expression of genetic traits.

Applying Developmental Science

Altering the Epigenome These two mice are genetically identical. Both carry the agouti gene but in the yellow mouse the agouti gene is turned on all the time. In the brown mouse it is turned off.

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One of the earliest examples of epigenetics is the case of agouti mice, which carry the agouti gene. Mice that carry the agouti gene have yellow fur, are extremely obese, shaped much like a pincushion, and prone to diabetes and cancer. When agouti mice breed, most of the offspring are identical to the parents—yellow, obese, and susceptible to life shortening disease. However, a groundbreaking study showed that

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yellow agouti mice can produce offspring that look very different (Waterland & Jirtle, 2003). The mice in the photo above both carry the agouti gene, yet they look very different; the brown mouse is slender, lean, and has a low risk of developing diabetes and cancer, living well into old age.

Why are these mice so different? Epigenetics. The epigenome carries the instructions that determine what each cell in your body will become —a heart cell, muscle cell, or brain cell, for example. Those instructions are carried out by turning genes on and off.

In the case of the yellow and brown mice, the phenotype of the brown mice has been altered, but the DNA remains the same. Both carry the agouti gene, but in the yellow mouse the agouti gene is turned on all the time. In the brown mouse, it is turned off. In 2003, Waterland and Jirtle discovered that the agouti female’s diet can determine her offspring’s phenotype. In this study, female mice were fed foods containing chemicals that attach to a gene and turn it off. These chemical clusters are found in many foods such as onions, garlic, beets, soy, and the nutrients in prenatal vitamins. Yellow agouti mothers fed extra nutrients passed along the agouti gene to their offspring, but it was turned off. The mice looked radically different from them (brown) and were healthier (lean, not susceptible to disease) even though they carried the same genes.

Another example supports the finding that the prenatal environment can alter the epigenome and influence the lifelong characteristics of offspring. Pregnant mice were exposed to a chemical (bisphenol-A or BPA, found in certain plastics). When female mice were fed BPA two weeks prior to conception, the number of offspring with the yellow obese coat color signaling an activated agouti gene increased (Dolinoy, 2008). When the pregnant mice were exposed to BPA plus nutritional supplementation (folic acid and an ingredient found in soy products), the offspring tended to be slender and have brown coats, signaling that the agouti gene was turned off. These findings suggest that the prenatal environment can influence the epigenome—and thereby influence how genes are expressed—and that nutrition has the potential to buffer harm.

The most surprising finding emerging from studies of epigenetics, however, is that the epigenome can be influenced by the environment before birth and can be passed by males and females from one generation to the next without changing the DNA itself (Soubry, Hoyo, Jirtle, & Murphy, 2014; Szyf, 2015). This means that what you eat and do today could affect the epigenome—the development, characteristics, and health—of your children, grandchildren, and great grandchildren

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(Bale, 2015; Vanhees, Vonhögen, van Schooten, & Godschalk, 2014).

What Do You Think? 1. Much of the research on epigenetics examines animals, but

there is a growing body of work studying humans. In what ways, if any, might you expect research findings based on people to differ from the findings of animal research, described previously? Explain.

2. What might you do to “care for” your epigenome? Identify activities and behaviors that you think might affect the health of your genome.

For example, consider brain development. Providing an infant with a healthy diet and opportunities to explore the world will support the development of brain cells, governed by genes that are switched on or off. Brain development influences motor development, further supporting the infant’s exploration of the physical and social world, thereby promoting cognitive and social development. Active engagement with the world encourages connections among brain cells. Exposure to toxins might suppress the activity of some genes, potentially influencing brain development and its cascading effects on motor, cognitive, and social development. In this way, brain development, like all other aspects of development, is influenced by dynamic interactions between biological and environmental factors.

Figure 2.8: Epigenetic Framework

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Source: Gottlieb (2007).

Evocative gene–environmental correlations and niche-picking illustrate the ways in which genetically expressed characteristics can influence the environment. Genes, and the epigenome, influence development and experience, yet gene expression is also influenced by development and experience, as illustrated in Figure 2.8 (Dodge & Rutter, 2011). These complex gene–environment interactions mean that humans are more than their genes. Interactions between heredity and environment change throughout development as does the role we play in constructing environments that support our genotypes, influence our epigenome, and determine who we become. For a striking example of epigenetics, see the Applying Developmental Science feature.

Thinking in Context 2.3

To answer the following questions, begin by thinking about how your own development reflects interactions among your genes and sociocultural context. Then, describe a skill, ability, or hobby in which you excel.

1. How might a passive gene–environment correlation account for this ability? For example, in what ways has the context in which you were raised shaped this ability?

2. In what ways might this ability be influenced by an evocative- genetic-environment correlation?

3. Provide an example of how this ability might reflect an active gene–environment correlation.

4. Which genetic-environment correlation do you think most accurately accounts for your skill, ability, or hobby?

5. How might you apply the epigenetic framework to account for your ability?

Prenatal Development

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Remarkably, a human infant progresses from fertilization to birth in just 166 days or 38 weeks. Conception, the union of ovum and sperm, marks the beginning of prenatal development, the transformative process in which the fertilized ovum, or zygote, progresses through several periods of development, finally emerging from the womb as a neonate. Prenatal development takes place over several stages representing shifts in developmental processes.

ovum The female reproductive cell or egg cell.

Germinal Period (First 2 Weeks After Conception) During the germinal period, also known as the period of the zygote, the newly created zygote begins cell division as it travels down the fallopian tube, where fertilization took place, toward the uterus. About 30 hours after conception, the zygote then splits down the middle, forming two identical cells (Moore & Persaud, 2016; Sadler, 2015). As shown in Figure 2.9, the two cells each split to form four cells, then eight, and so on. This process of cell division continues at a rapid pace. Any of these cells may become a person (or two, in the case of monozygotic or identical twins).

germinal period Also referred to as the period of the zygote, refers to the first two weeks after conception.

Figure 2.9: Germinal Period

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Cell differentiation begins roughly 72 hours after fertilization when the organism consists of about 16 to 32 cells. Differentiation means that the cells begin to specialize and are no longer identical. At 4 days, the organism consists of about 60 to 70 cells formed into a hollow ball called a blastocyst, a fluid-filled sphere with cells forming a protective circle around an inner cluster of cells from which the embryo will develop.

cell differentiation Begins roughly 72 hours after fertilization when the organism consists of about 16 to 32 cells.

blastocyst A thin-walled, fluid-filled sphere containing an inner mass of cells from which the embryo will develop; is implanted into the uterine wall during the germinal period.

embryo Prenatal organism between about 2 and 8 weeks after conception; a period of major structural development.

Implantation, in which the blastocyst burrows into the wall of the uterus, begins at about day 6 and is complete by about day 11 (Moore & Persaud, 2016; Sadler, 2015). By the end of the second week, when fully implanted into the uterine wall, the outer layer of the blastocyst begins to develop

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into part of the placenta, the principal organ of exchange between the mother and developing organism. The placenta will enable the exchange of nutrients, oxygen, and wastes via the umbilical cord. Also during this stage, the developing organism is encased in amniotic fluid, providing temperature regulation, cushioning, and protection from shocks.

implantation The process by which the blastocyst becomes attached to the uterine wall, completed by about 10 days after fertilization.

placenta The principal organ of exchange between the mother and the developing organism, enabling the exchange of nutrients, oxygen, and wastes via the umbilical cord.

Embryonic Period (3 to 8 Weeks After Conception) By the third week after conception, the developing organism—now called an embryo—begins a period of structural development during which the most rapid developments of the prenatal period take place. All of the organs and major body systems form during this embryonic period. The mass of cells composing the embryonic disk develops into two layers: The ectoderm, the upper layer, will become skin, nails, hair, teeth, sensory organs, and the nervous system; and the endoderm, the lower layer, will become the digestive system, liver, lungs, pancreas, salivary glands, and respiratory system. The middle layer, the mesoderm, forms later and will become muscles, skeleton, circulatory system, and internal organs.

embryonic period Occurs about 2 to 8 weeks after pregnancy, in which rapid structural development takes place.

Development proceeds very quickly during the embryonic period. Note the dramatic changes from the fifth week (left) to the seventh week (right) of prenatal development.

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During the third week, at about 22 days after conception, the endoderm folds to form the neural tube, which will develop into the central nervous system (brain and spinal cord; Moore & Persaud, 2016; Stiles & Jernigan, 2010). Now the head can be distinguished. A blood vessel that will become the heart begins to pulse and blood begins to circulate throughout the body (Dye, 2000; Larsen, 2001). During days 26 and 27 arm buds appear, followed by leg buds on days 28 through 30 (Moore & Persaud, 2016; Sadler, 2015). The brain develops rapidly and the head grows faster than the other parts of the body during the fifth week of development. The eyes, ears, nose, and mouth begin to form during the sixth week. Upper arms, forearms, palms, legs, and feet appear. The embryo shows reflex responses to touch.

neural tube Forms during the third week after conception and will develop into the central nervous system (brain and spinal cord).

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During the seventh week, webbed fingers and toes are apparent; they separate completely by the end of the eighth week. A ridge called the indifferent gonad appears; it will develop into the male or female genitals, depending on the fetus’s sex chromosomes (Moore & Persaud, 2016). The Y chromosome of the male embryo instructs it to secrete testosterone, causing the indifferent gonad to create testes. In female embryos, no testosterone is released, and the indifferent gonad produces ovaries. The sex organs take several weeks to develop. The external genital organs are not apparent until about 12 weeks.

indifferent gonad A gonad in an embryo that has not yet differentiated into testes or ovaries.

At the end of the embryonic period, 8 weeks after conception, the embryo weighs about one-seventh of an ounce and is one inch long. All of the basic organs and body parts have formed in a very rudimentary way. The embryo displays spontaneous reflexive movements, but it is still too small for the movements to be felt by the mother (Hepper, 2015). Serious defects that emerge during the embryonic period often cause a miscarriage, or spontaneous abortion (loss of the fetus); indeed, most miscarriages are the result of chromosomal abnormalities (Bainbridge, 2003; Suzumori & Sugiura-Ogasawara, 2010). The most severely defective organisms do not survive beyond the first trimester, or third month of pregnancy. It is estimated that up to 45% of all conceptions abort spontaneously, and most occur before the pregnancy is detected (Larsen, 2001; Moore & Persaud, 2016).

Lives in Context Video 2.1

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Ultrasound

Fetal Period (9 Weeks to Birth) The fetal period is marked by the appearance of bone—at about the end of the eighth week. From 9 weeks until birth, the fetus grows rapidly, and its organs become more complex and begin to function. The end of the third month marks the close of the first trimester, at which time all parts of the fetus’s body can move spontaneously, the legs kick, and the fetus can suck its thumb (an involuntary reflex). By the end of the 12th week, the upper limbs have almost reached their final relative lengths, but the lower limbs are slightly shorter than their final relative lengths (Sadler, 2015).

Second Trimester (14 to 26 Weeks)

By the 14th week, at the start of the second trimester, limb movements are coordinated, but they will be too slight to be felt by the mother until about 17 to 20 weeks. The heartbeat gets stronger. Eyelids, eyebrows, fingernails, toenails, and tooth buds form. The first hair to appear is lanugo, a fine down-like hair that covers the fetus’s body; it is gradually replaced by human hair (Dye, 2000). The skin is covered with a greasy material called the vernix caseosa, which protects the fetal skin from abrasions, chapping, and hardening that can occur with exposure to amniotic fluid (Moore & Persaud, 2016). At 21 weeks, rapid eye movements begin, signifying an important time of growth and development for the fetal brain. The brain begins to become more responsive. For example, startle responses have been reported at 22 to 23 weeks in response to sudden vibrations and noises (Hepper, 2015; Sadler, 2015). During weeks 21 to 25, the fetus gains substantial weight, and its body proportions become more like those of a newborn infant. Growth of the fetal body begins to catch up to the head, yet the head remains disproportionately larger than the body at birth.

lanugo A fine, down-like hair that covers the fetus’s body.

vernix caseosa Greasy material that protects the fetal skin from abrasions, chapping, and hardening that can occur from exposure to amniotic fluid.

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Third Trimester (27 to 40 Weeks)

During the last 3 months of pregnancy, the fetal body grows substantially in weight and length; specifically, it typically gains over 5 pounds and grows 7 inches. At about 28 weeks after conception brain development grows in leaps and bounds. The cerebral cortex develops convolutions and furrows, taking on the brain’s characteristic wrinkly appearance (Dye, 2000). The fetal brain wave pattern shifts to include occasional bursts of activity, similar to the sleep-wake cycles of newborns. By 30 weeks, the pupils of the eyes dilate in response to light. At 35 weeks, the fetus has a firm hand grasp and spontaneously orients itself toward light.

During the third trimester, pregnant women and their caregivers are mindful that the baby may be born prematurely. Although the expected date of delivery is 166 days or 38 weeks from conception (40 weeks from the mother’s last menstrual period), about one in every eight American births is premature (Centers for Disease Control, 2014a). The age of viability—the age at which advanced medical care permits a preterm newborn to survive outside the womb—begins at about 22 weeks after conception (Sadler, 2015). Infants born before 22 weeks rarely survive more than a few days because their brain and lungs have not begun to function. Although a 22- to 25-week fetus born prematurely may survive in intensive care, it is still at risk because its immature respiratory system may lead to death in early infancy. At about 26 weeks, the lungs become capable of breathing air and the premature infant stands a better chance of surviving if given intensive care. About 80% of infants born at 26 weeks survive and 87% of those born at 27 weeks (Stoll, Hansen, Bell, & Shankaran, 2010; Tucker & McGuire, 2004). Ninety-eight percent of 32- week premature infants survive.

At about the 166th day after conception, the placenta releases a hormone that triggers the onset of labor (Bainbridge, 2003). Hormones cause the mother’s uterus to contract and relax at regular intervals, aiding delivery.

Lives in Context Video 2.2

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The Process of Childbirth

Childbirth Childbirth, also known as labor, progresses in three stages, as shown in Figure 2.10.

Sometimes a vaginal birth is not possible because of concerns for the health or safety reasons of the mother or fetus. A cesarean section, or C- section, is a surgical procedure that removes the fetus from the uterus through the abdomen. About 33% of all singleton births are cesarean deliveries (Hamilton, Martin, Osterman, Curtin, & Mathews, 2015). Cesarean sections are performed when labor progresses too slowly, the fetus is in breech position (feet first) or transverse position (crosswise in the uterus), the head is too large to pass through the pelvis, or the fetus or mother is in danger (Jha, Baliga, Kumar, Rangnekar, & Baliga, 2015; Visscher & Narendran, 2014). Babies delivered by cesarean are exposed to more maternal medication and secrete lower levels of the stress hormones that occur with vaginal birth that are needed to facilitate respiration, enhance circulation of blood to the brain, and help the infant adapt to the world outside of the womb. Interactions between mothers and infants, however, are similar for infants delivered vaginally and by cesarean section (Durik, Hyde, & Clark, 2000). The Cultural Influences on Development feature examines some cultural differences in childbirth.

cesarean section Also known as a C-section; a surgical procedure that removes the fetus from the uterus through the abdomen.

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Figure 2.10: Stages of Labor

The average newborn is about 20 inches long and weighs about 7½ pounds. Boys tend to be slightly longer and heavier than girls. Newborns have distinctive features, including a large head (about ¼ of body length) that is often long and misshapen from passing through the birth canal. The newborn’s skull bones are not yet fused—and will not be until about 18 months of age—permitting the bones to move and the head to mold to the birth canal, easing its passage. A healthy newborn is red-skinned and wrinkly at birth; skin that is bluish in color indicates that the newborn has experienced oxygen deprivation. Some babies emerge covered with lanugo, the fuzzy hair that protects the skin in the womb; other babies lose the lanugo prior to birth. The newborn’s body is covered with vernix caseosa, a waxy substance that protects against infection; this dries up within the first few days. Although many hospital staff wash the vernix caseosa away, research suggests that it is a naturally occurring barrier to infection and should be retained at birth (Jha et al., 2015).

Cultural Influences on Development

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Cultural Differences in Childbirth An Uzbekistan midwife prepares to deliver a baby by first listening to its heartbeat.

Peter Turnley/Corbis Historical/Getty Images

Societies vary in their customs and perceptions of childbirth, including the privacy afforded to giving birth and how newborns are integrated into the community. In the United States, birth is a private event that usually occurs in a hospital, attended by medical personnel and one or two family members. In most cases, the first-time mother has never witnessed a birth but is well educated and may have well-informed expectations. After birth, the mother and infant are often visited by family during designated hospital visiting hours; the newborn usually rooms with the mother all or part of the day.

In a small village in southern Italy, birth is a community event. It usually takes place in a hospital, attended by a midwife (Fogel, 2007; Schreiber, 1977). Just after birth, the midwife brings the mother’s entire family (immediate and extended) to the mother’s room and they take turns congratulating the mother and baby, kissing them. The family provides a party including pastry and liqueurs. During labor and afterward the mother is supported and visited by many of her friends and relatives, to recognize the contribution that the mother has made to the community. The mother-in-law is an example of the social support system in place because from a few days before until about 1 month after the birth, she brings and feeds the mother ritual foods of broth, marsala, and fresh cheeses (Fogel, 2007; Schreiber, 1977).

In other cultures, birth is an even more public process. The Jahara of South America give birth under a shelter in full view of everyone in the village (Fogel, 2007). On the Indonesian island of Bali it is assumed that the husband, children, and other family will want to be present. The birth occurs in the home with the aid of a midwife and female relatives. As a result, Balinese women know what to expect in giving birth to their first child because they have been present at many births (Diener,

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2000). The baby is immediately integrated into the family and community as he or she is considered a reincarnated soul of an ancestor. Many kin are present to support the mother and baby because the child is considered to be related to many more people than its parents.

Childbirth is tied to social status in the Brong-Ahafo region in Ghana: After a delivery, women achieve a higher social position and can then give advice to other women (Jansen, 2006). Home deliveries are highly valued. The more difficult the delivery and the less skilled assistance she receives, the more respect a woman attains, the higher her position will be, and the more influence she has on the childbirth decisions of other women, such as whether to give birth at home or in a medical setting and how to combine traditional and modern practices (Bazzano, Kirkwood, Tawiah-Agyemang, Owusu-Agyei, & Adongo, 2008).

Many cultures conduct rites that they believe protect newborns from evil spirits. Among the Maya of the Yucatan region of Mexico, there are few changes in the expectant mother’s surroundings; the Mayan woman lies in the same hammock in which she sleeps each night. The father-to-be is expected to be present during labor and birth to take an active role but also to witness the suffering that accompanies labor. If the father is not present and the child is stillborn, it is blamed on the father’s absence. The pregnant woman’s mother is present, often in the company of other females including sisters, sisters-in-law, mothers-in- law, godmothers, and sometimes neighbors and close friends. The mother and child must remain inside the house for one week before returning to normal activity after birth because it is believed that the mother and newborn are susceptible to the influence of evil spirits from the bush (Gardiner & Kosmitzki, 2018).

A neighboring ethnic group, the Zinacanteco, place their newborns naked before a fire. The midwife who assisted the mother says prayers asking the gods to look kindly upon the infant. The infant is dressed in a long skirt made of heavy fabric extending beyond the feet; this garment is to be worn throughout the first year. The newborn is then wrapped in several layers of blankets, even covering the face, to protect against losing parts of the soul. These traditional practices are believed to protect the infant from illnesses as well as evil spirits (Brazelton, 1977; Fogel, 2007).

What Do You Think? 1. Which of these birthing customs most appeals to you? Why? 2. If you, a family member, or friend have given birth, describe

the process. Where did the birth occur? Who witnessed it?

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What happened afterward? When did family and friends meet the baby?

After birth, newborns are routinely screened with the Apgar scale, which provides a quick and easy overall assessment of the baby’s immediate health. As shown in Table 2.8, the Apgar scale is composed of five subtests: appearance (color), pulse (heart rate), grimace (reflex irritability), activity (muscle tone), and respiration (breathing). The newborn is rated 0, 1, or 2 on each subscale for a maximum total score of 10. A score of 4 or lower means that the newborn is in serious condition and requires immediate medical attention. The rating is conducted twice, 1 minute after delivery and again 5 minutes after birth; this timing ensures that hospital staff will monitor the newborn over several minutes. More than 98% of all newborns in the United States achieve a 5-minute score of 7 to 10, indicating good health (Martin, Hamilton, Osterman, Curtin, & Mathews, 2013).

Apgar scale A quick overall assessment of a baby’s immediate health at birth, including appearance, pulse, grimace, activity, and respiration.

Table 2.8 Apgar Scale Table 2.8 Apgar Scale

Rating (Absence-Presence)

Indicator 0 1 2

Appearance (Color) Blue Pink body, blue extremities

Pink

Pulse (Heart rate) Absent Slow (below 100) Rapid (over 100)

Grimace (Reflex irritability)

No response

Grimace Coughing, crying

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Activity (Muscle tone) Limp Weak and inactive

Active and strong

Respiration (Breathing)

Absent Irregular and slow Crying, good

Source: Apgar (1953).

Infants at Risk: Low Birth Weight and Small-for- Date Babies One of the leading causes of infant mortality is low birth weight, accounting for 35% of mortality cases in infancy (Mathews & MacDorman, 2013). There are two types of low birth weight infants: those who are preterm, or premature (born before their due date) and those who are small for date, who are full term but have experienced slow growth and are smaller than expected for their gestational age. Infants are classified as low birth weight when they weigh less than 2,500 grams (5 ½ pounds) at birth; “very low” birth weight refers to a weight less than 1,500 grams (3 ½ pounds), and “extremely low” birth weight refers to a weight less than 750 grams (1 lb. 10 oz.; Alexander & Slay, 2002). Infants who are extremely low birth weight are most at risk for developmental challenges, handicaps, and difficulty surviving (under 1,000 grams; Fogel, 2007).

preterm A birth that occurs 35 or fewer weeks after conception.

small for date Describes an infant who is full term but who has significantly lower weight than expected for the gestational age.

low birthweight Classifies infants who weigh less than 2,500 grams (5.5 pounds) at birth.

Low birth weight infants are at a disadvantage when it comes to adapting to the world outside the womb. At birth, they often experience difficulty breathing and are likely to suffer from respiratory distress syndrome, in which the newborn breathes irregularly and, at times, may stop breathing. Their survival depends on care in neonatal hospital units, where they are

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body temperature, aiding their breathing with the use of respirators, and protecting them from infection. Many low birth weight infants cannot yet suck from a bottle, so they are fed intravenously.

The deficits that low birth weight infants endure range from mild to severe and correspond closely to the infant’s birth weight, with extremely low birth weight infants suffering the greatest deficits (Hutchinson, De Luca, Doyle, Roberts, & Anderson, 2013). Low birth weight infants are at higher risk for poor growth, cerebral palsy, seizure disorders, neurological difficulties, respiratory problems, and illness (Adams-Chapman et al., 2013; Agustines et al., 2000; Aylward, 2005; McGowan, Alderdice, Holmes, & Johnston, 2011; J. E. Miller et al., 2016). Higher rates of sensory, motor, and cognitive problems mean that low birth weight children are more likely to require special education and display poor academic achievement in childhood, adolescence, and even adulthood (Aarnoudse-Moens, Weisglas-Kuperus, van Goudoever, & Oosterlaan, 2009; Eichenwald & Stark, 2009; Hutchinson et al., 2013; MacKay, Smith, Dobbie, & Pell, 2010). Low birth weight children often experience difficulty in self-regulation, poor social competence, and poor peer relationships, including peer rejection and victimization in adolescence (Georgsdottir, Haraldsson, & Dagbjartsson, 2013; Ritchie, Bora, & Woodward, 2015; Yau et al., 2013). As adults, low birth weight individuals tend to be less socially engaged, show poor communication skills, and may score high on measures of anxiety (Eryigit Madzwamuse, Baumann, Jaekel, Bartmann, & Wolke, 2015).

Low birthweight infants require extensive care. They are at risk for poor developmental outcomes and even death.

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Parenting a low birth weight infant is stressful even in the best of circumstances (Howe, Sheu, Wang, & Hsu, 2014). Such infants tend to be easily overwhelmed by stimulation and difficult to soothe; they smile less and fuss more than their normal-weight counterparts, making caregivers feel unrewarded for their efforts. Often these infants are slow to initiate social interactions and do not attend to caregivers, looking away or otherwise resisting attempts to attract their attention (Eckerman, Hsu, Molitor, Leung, & Goldstein, 1999). Because low birth weight infants often do not respond to attempts to solicit interaction, they can be frustrating to interact with, can be difficult to soothe, and are at risk for less secure attachment to their parents (Jean & Stack, 2012; Mangelsdorf et al., 1996; Wolke, Eryigit Madzwamuse, & Gutbrod, 2014). Research also indicates that they may experience higher rates of child abuse (Bugental & Happaney, 2004; Klein & Stern, 1971).

Parental responses to having a low birth weight infant influence the child’s long-term health outcomes, independently of perinatal risk, suggesting that the parenting context is an important influence on infant health (Pierrehumbert, Nicole, Muller-Nix, Forcada-Guex, & Ansermet, 2003). When mothers have knowledge about child development and how to foster healthy development, are involved with their children, and create a stimulating home environment, low birth weight infants tend to have good long-term outcomes (Benasich & Brooks-Gunn, 1996; Jones, Rowe, &

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Becker, 2009). For example, one study of low birth weight children showed that those who experienced sensitive parenting showed faster improvements in executive function and were indistinguishable from their normal-weight peers by age 5; however, those who experienced below- average levels of sensitive parenting showed lasting deficits (Camerota, Willoughby, Cox, Greenberg, & Investigators, 2015). Likewise, exposure to sensitive, positive, parenting predicted low birth weight children’s catching up to their normal birth weight peers at age 8 in academic achievement, but exposure to insensitive parenting predicted much poorer functioning (Jaekel, Pluess, Belsky, & Wolke, 2015). Longitudinal research has found that low birth weight children raised in unstable, economically disadvantaged families tend to remain smaller in stature, experience more emotional problems, and show more long-term deficits in intelligence and academic performance than do those raised in more advantaged homes (Taylor, Klein, Minich, & Hack, 2001).

Interventions to promote the development of low birth weight children often emphasize helping parents learn coping strategies for interacting with their infants and managing stress (Chang et al., 2015; Lau & Morse, 2003). Interventions focused on teaching parents how to massage and touch their infants in therapeutic ways as well as increase skin-to-skin contact with their infants are associated with better cognitive and neurodevelopmental outcomes at age 2 (Procianoy, Mendes, & Silveira, 2010). One intervention common in developing countries where mothers may not have access to hospitals is kangaroo care, in which the infant is placed vertically against the parent’s chest, under the shirt, providing skin- to-skin contact (Charpak et al., 2005). As the parent goes about daily activities, the infant remains warm and close, hears the voice and heartbeat, smells the body, and feels constant skin-to-skin contact. Kangaroo care is so effective that the majority of hospitals in the U.S. offer kangaroo care to preterm infants. Babies who receive early and consistent kangaroo care grow more quickly, sleep better, score higher on measures of health, and show more cognitive gains throughout the first year of life (Boundy et al., 2015; Jefferies, 2012).

kangaroo care An intervention for low-birthweight babies in which the infant is placed vertically against the parent’s chest, under the shirt, providing skin-to-skin contact.

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Thinking in Context 2.4

1. Petra noticed that her abdomen has not grown much since she became pregnant 3 months ago. She concluded that the fetus must not undergo significant development early in pregnancy. How would you respond to Petra?

2. Parents’ decisions about childbirth reflect their knowledge about birth options as well as cultural values. Referring to Bronfenbrenner’s bioecological model (see Chapter 1), identify factors at each bioecological level that may influence childbirth. For example, how might neighborhood factors influence birth options? Culture?

3. Thinking of how society and medical science have changed in recent decades, in what ways might recent cohorts of parents differ from prior cohorts? What implications might these differences hold for prenatal development and childbirth?

Environmental Influences on Prenatal Development The vast majority of infants are born healthy, but some are exposed before birth to environmental obstacles that hinder their development. A teratogen is an agent that causes damage to prenatal development, such as a disease, drug, or other environmental factor, producing a birth defect. The field of teratology attempts to find the causes of birth defects so that they may be avoided. Health care providers help pregnant women and those who intend to become pregnant to be aware of teratogens and avoid them, as much as possible, to maximize the likelihood of having a healthy baby.

teratogen An environmental factor that causes damage to prenatal development.

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Principles of Teratology There are many ways in which teratogens may affect prenatal development, but it is not always easy to predict the harm caused by teratogens. Generally, the effects of exposure to teratogens on prenatal development vary depending on the following principles (Collins, 2006; Moore & Persaud, 2016; Sadler, 2015).

Critical Periods. There are critical periods during prenatal development in which an embryo is more susceptible to damage from exposure to teratogens. The extent to which exposure to a teratogen disrupts prenatal development depends on the stage of prenatal development when exposure occurs. Generally, sensitivity to teratogens begins at about 3 weeks after conception (Sadler, 2015). Structural defects occur when the embryo is exposed to teratogen while that part of the body is developing. As shown in Figure 2.11, each organ of the body has a sensitive period in development during which it is most susceptible to damage from teratogens. Once a body part is fully formed, it is less likely to be harmed by exposure to teratogens; however, some body parts, like the brain, remain vulnerable throughout pregnancy. Dose. The amount of exposure (i.e., dosage) to a teratogen influences its effects. Generally, the greater the dose, the more damage to development; however, teratogens also differ in their strength. Some teratogens, like alcohol, display a powerful dose–response relationship so that larger doses—heavier and more frequent drinking —result in greater damage. Individual differences. Individuals vary in their susceptibility to particular teratogens based on the genetic makeup of both the organism and mother, as well as the quality of the prenatal environment. Teratogens show complicated effects on development. Different teratogens can cause the same birth defect, and a variety of birth defects can result from the same teratogen. Also, some teratogens have subtle effects that result in developmental delays that are not obvious at birth. For example, infants exposed prenatally to as little as an ounce of alcohol a day usually display no obvious physical deformities, but later, as children, they may demonstrate cognitive delays (Jacobson & Jacobson, 1996). Other teratogens display sleeper effects—effects that are not visible until many years later. For example, infants born to women who consumed diethylstilbestrol

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(DES), a hormone that was widely prescribed between 1945 and 1970 to prevent miscarriages, were born healthy, but as adults they were more likely to experience problems with their reproductive systems. Daughters born to mothers who took DES were more likely to develop a rare form of cervical cancer, have miscarriages, and give birth to infants who were premature or low birth weight (Barnes et al., 1980; Schrager & Potter, 2004).

Figure 2.11: Sensitive Periods in Prenatal Development

Source: Levine and Munsch (2010, p. 113).

Types of Teratogens Prenatal development can be influenced by many contextual factors, including maternal consumption of over-the-counter (OTC), prescription, and recreational drugs; illness; environmental factors; and more, as shown in Table 2.9. Although the developing organism is vulnerable to many teratogens, the mother’s body is designed to protect the growing fetus.

Some teratogens can be avoided by choice; for example, a woman can choose not to drink alcohol or smoke cigarettes during pregnancy. Others, however, may be involuntary, as in the case of maternal illness. Sometimes a pregnant woman and her doctor may have to make a difficult choice between forgoing a needed prescription drug and putting the fetus at risk. And, in any case, a woman may not know she is pregnant until after the

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first few weeks of the embryonic stage are already past. Thus, in the real world, almost no pregnancy can be entirely free of exposure to teratogens. However, each year about 97% of infants are born without defects (Centers for Disease Control, 2014).

Prescription and Nonprescription Drugs

More than 90% of pregnant women take prescription or over-the-counter (OTC) medications (Servey & Chang, 2014). Prescription drugs that can act as teratogens include antibiotics, certain hormones, anticoagulants, anticonvulsants, and some acne drugs (Collins, 2006; Moore & Persaud, 2016; Sadler, 2015). In several cases physicians have unwittingly prescribed drugs to ease pregnant women’s discomfort that caused harm to the fetus. For example, in the late 1950s and early 1960s many pregnant women were prescribed thalidomide to prevent morning sickness. However, it was found that taking thalidomide 4 to 6 weeks after conception (in some cases, even just one dose) caused deformities of the child’s arms and legs, and, less frequently, damage to the ears, heart, kidneys, and genitals (Laughton, Cornell, Boivin, & Van Rie, 2012; Vargesson, 2009). Nonprescription drugs, such as diet pills and cold medicine, can also cause harm, but research on OTC drugs lags far behind research on prescription drugs, and we know little about the teratogenic effect of many OTC drugs (Cabbage & Neal, 2011).

Table 2.9 Hazards to Prenatal Development Table 2.9 Hazards to Prenatal Development

Drugs

Alcohol Fetal alcohol syndrome, mental retardation; retarded fetal growth; joint abnormalities; ocular abnormalities

Amphetamines Premature delivery; stillbirth; irritability and poor feeding among newborns

Antibiotics (Tetracycline,

Streptomycin, Premature delivery; restricted skeletal growth; cataracts

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Terramycin)

Barbiturates Lethargy in the fetus; large doses cause anoxia (oxygen starvation), restricts fetal growth

Cocaine Retarded fetal growth; prematurity, microcephaly; neurobehavioral disturbances; genital abnormalities

Heroin Retarded fetal growth; premature labor; newborns suffer withdrawal

Lithium Heart and blood vessel abnormalities

Marijuana Retarded fetal growth

Tobacco Retarded fetal growth; miscarriage, still birth; infant mortality

Maternal Illness

HIV/AIDS Retarded fetal growth; microcephaly; mental retardation; mother-to-child transmission

Rubella During embryonic period, causes blindness and deafness; in first and second trimesters, brain damage

Environmental Pollutants

Lead and mercury

Spontaneous miscarriage; preterm labor; brain damage

Radiation Retarded fetal growth; microcephaly; mental retardation; skeletal anomalies; cataracts

Sources: Moore & Persaud (2016); Sadler (2015); Weinhold (2009).

Fetal alcohol syndrome is associated with distinct facial

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characteristics, growth deficiencies, and deficits in intellectual development, language, motor coordination, and the combined abilities to plan, focus attention, problem solve, and use goal directed behavior that persist throughout childhood and into adulthood.

Betty Udesen/KRT/Newscom

Alcohol

An estimated 14% to nearly 30% of pregnant women report consuming alcohol during their pregnancies (Arria et al., 2006; Meschke, Holl, & Messelt, 2013; Zhao et al., 2012). Indeed, alcohol abuse during pregnancy has been identified as the leading cause of developmental disabilities (O’Leary et al., 2013; Warren, Hewitt, & Thomas, 2011). Fetal alcohol spectrum disorders refer to the continuum of effects of exposure to alcohol, which vary with the timing and amount of exposure (Riley, Infante, & Warren, 2011). At the extreme end of the spectrum is fetal alcohol syndrome (FAS), a cluster of defects appearing after heavy prenatal exposure to alcohol that is detected in 2 to 7 infants per 1,000 births (May et al., 2014; Thomas, Warren, & Hewitt, 2010). FAS is associated with a distinct pattern of facial characteristics (such as small head circumference, short nose, small eye opening, and small midface), pre- and postnatal growth deficiencies, and deficits in motor coordination,

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language, and cognitive development, including the combined abilities to plan, focus attention, problem solve, and use goal-directed behavior (Jirikowic, Gelo, & Astley, 2010; Mattson, Crocker, & Nguyen, 2011; Thomas et al., 2010). The effects of exposure to alcohol within the womb persist throughout childhood and have been found to be associated with deficits in learning and memory in early adulthood (Coles et al., 2011; McLachlan, Roesch, Viljoen, & Douglas, 2014; Wheeler, Kenney, & Temple, 2013).

fetal alcohol syndrome (FAS) The most severe form of fetal alcohol spectrum disorder accompanying heavy prenatal exposure to alcohol, including a distinct pattern of facial characteristics, growth deficiencies, and deficits in intellectual development.

fetal alcohol spectrum disorders The continuum of physical, mental, and behavioral outcomes caused by prenatal exposure to alcohol.

Even moderate drinking is harmful as children may be born displaying some, but not all, of the problems of FAS, or fetal alcohol effects (Thomas et al., 2010). Consuming 7 to 14 drinks per week during pregnancy is associated with lower birth size; growth deficits through adolescence; and deficits in attention, memory, and cognitive development (Alati et al., 2013; J.-H. Chen, 2012; Lundsberg, Illuzzi, Belanger, Triche, & Bracken, 2015; O’Leary & Bower, 2012). Even less than one drink per day has been associated with negative effects on fetal growth (Day et al., 2002; Day & Richardson, 2004; Mariscal et al., 2006) and with deficits in cognition at 1 year of age (Lu, 2005; Testa, Quigley, & Das Eiden, 2003) and behavior problems through 5 years of age (Flak et al., 2014). Scientists have yet to determine whether there is a safe level of drinking, but the only way to be certain of preventing alcohol-related risks is to avoid alcohol during pregnancy altogether.

Cigarette Smoking

Every package of cigarettes sold in the United States includes a warning about the dangers of smoking while pregnant. Fetal deaths, premature births, and low birth weight are up to twice as frequent in mothers who are

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smokers than in those who do not smoke (Juárez & Merlo, 2013). Infants exposed to smoke while in the womb are prone to congenital heart defects, respiratory problems, and sudden infant death syndrome and, as children, show more behavior problems and attention difficulties and score lower on intelligence and achievement tests (Kiechl-Kohlendorfer et al., 2010; Lee & Lupo, 2013). Moreover, maternal smoking during pregnancy shows epigenetic effects on offspring, influencing how genetic processes and pathways of growth and development unfold in childhood into late adolescence and likely beyond (Han et al., 2015; Knopik, Maccani, Francazio, & McGeary, 2012; Richmond et al., 2015). There is no safe level of smoking during pregnancy.

Marijuana

The effects of marijuana on prenatal development are not well understood. Marijuana use during early pregnancy negatively affects fetal length and birth weight (A. C. Huizink, 2013; Hurd et al., 2005; Moore & Persaud, 2016). Although some studies suggest few consistent findings from infancy through adolescence (Huizink, 2013), others link prenatal exposure to marijuana to impairments in attention, memory and cognitive skills, as well as impulsivity at ages 4 and 10 and poor achievement in adolescence (Goldschmidt, Richardson, Willford, Severtson, & Day, 2012; Gray, Day, Leech, & Richardson, 2005; A. Huizink & Mulder, 2006; Wu, Jew, & Lu, 2011). Some researchers have found that once the effects of exposure to other teratogens is controlled, marijuana does not show a teratogenic effect (Nordstrom-Klee, Delaney-Black, Covington, Ager, & Sokol, 2002; van Gelder et al., 2010). Regardless, the safest course is for pregnant women to avoid marijuana.

Cocaine and Heroin

Infants exposed to cocaine and heroin face special challenges, such as signs of addiction and withdrawal symptoms including tremors, irritability, abnormal crying, disturbed sleep, and impaired motor control. Prenatal exposure to cocaine and heroin is associated with reduced birthweight, shorter length, smaller head circumference, and impaired motor performance at birth (Frank, Augustyn, Knight, Pell, & Zuckerman, 2001). Exposure to these drugs during prenatal development influences brain development, particularly the regions associated with attention, arousal, and regulation (Behnke & Smith, 2013; Coyle, 2013; Lebel et al., 2013;

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Roussotte et al., 2011). At one month after birth, babies who were exposed to cocaine had difficulty regulating their arousal states and showed poor movement skills, poor reflexes, and greater excitability (Fallone et al., 2014).

Though it was once believed that cocaine- and heroin-exposed infants would suffer life-long cognitive deficits, research suggests more mixed and subtle effects (Bandstra, Morrow, Mansoor, & Accornero, 2010; Behnke & Smith, 2013; Lambert & Bauer, 2012). Prenatal cocaine exposure has a small but lasting effect on attention and behavioral control and language skills through late childhood (Lewis et al., 2011, 2013; Singer, Minnes, Min, Lewis, & Short, 2015), but it is not linked with impairments in overall development, IQ, or school readiness in toddlers, elementary school–aged children, or middle school–aged children (Accornero et al., 2011; Behnke & Smith, 2013; Goldschmidt et al., 2012; Min, Minnes, Yoon, Short, & Singer, 2014). Moreover, quality care can lessen the long-term impact of prenatal exposure to substances (Behnke & Smith, 2013; Lewis et al., 2011).

The challenge of determining the effects of prenatal exposure to drugs is that most infants exposed to illicit drugs, such as cocaine and heroin, are also exposed to other substances, including tobacco, alcohol, and marijuana (Jones, 2006; Passey, Sanson-Fisher, D’Este, & Stirling, 2014), making it difficult to isolate the effect of each drug on prenatal development. We must be cautious in interpreting findings about illicit drug use and the effects on prenatal development because there are many other contextual factors that often co-occur with substance use and also pose risks for development—including poverty, malnutrition, social isolation, stress, and diminished parental responsiveness (Bandstra et al., 2010; Bendersky & Lewis, 1999; Frank et al., 2001). For example, parents who abuse drugs tend to provide poorer quality care, a home environment less conducive to cognitive development, and parent–child interaction that is less sensitive and positive than the environments provided by other parents (Hans, 2002). Children raised by substance-abusing parents are at risk for being subjected to overly harsh discipline and lack of supervision (Burlew et al., 2012) as well as disruptions in care due to factors such as parental incarceration, inability to care for a child, and even death (e.g., from a drug overdose or drug gang violence). Disentangling the long-term effects of prenatal exposure to substances, subsequent parenting, and contextual factors is challenging. Researchers and health care providers who construct interventions must address the contextual and parenting-

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related risk factors to improve the developmental outlook for children exposed to drugs prenatally (Butz et al., 2001; Calhoun, Conner, Miller, & Messina, 2015; Kilbride, Castor, Hoffman, & Fuger, 2000).

Maternal Illness

Depending on the type and when it occurs, an illness experienced by the mother during pregnancy can have devastating consequences for the developing fetus. For example, rubella (German measles) prior to the 11th week of pregnancy can cause a variety of defects including blindness, deafness, heart defects, and brain damage, but after the first trimester, adverse consequences become less likely (Santis, Cavaliere, Straface, & Caruso, 2006). Some sexually transmitted diseases, such as syphilis, can be transmitted to the fetus during pregnancy (Gomez et al., 2013; Sánchez & Wendel, 1997). Others, such as gonorrhea, genital herpes, and HIV, can be transmitted as the child passes through the birth canal during birth or though bodily fluids after birth (see the Lives in Context feature). Because some diseases, such as rubella, can be prevented with vaccinations, it is important for women who are considering becoming pregnant to discuss their immunization status with their health care provider.

Some illnesses with teratogenic effects, such as the Zika virus, are not well understood. Children born to women infected with the Zika virus are at greater risk of microcephaly (reduced head size). They may also show a pattern of defects now known as congenital Zika syndrome, which includes severe microcephaly characterized by partial skull collapse, damage to the back of the eye, and body deformities including joints and muscles with restricted range of motion (Centers for Disease Control and Prevention, 2017a).

Environmental Hazards

Prenatal exposure to chemicals, radiation, air pollution, and extremes of heat and humidity can impair development. Infants prenatally exposed to heavy metals, such as lead and mercury, whether through ingestion or inhalation, score lower on tests of cognitive ability and intelligence and have higher rates of childhood illness (Sadler, 2015; Vigeh, Yokoyama, Matsukawa, Shinohara, & Ohtani, 2014; Xie et al., 2013). Exposure to radiation can cause genetic mutations. Infants born to mothers pregnant during the atomic bomb explosions in Hiroshima and Nagasaki and after

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the nuclear power accident at Chernobyl displayed many physical deformities, mutations, and intellectual deficits. Prenatal exposure to radiation is associated with Down syndrome, reduced head circumference, intellectual disability, reduced intelligence scores and school performance, and heightened risk of cancer (Chang, Lasley, Das, Mendonca, & Dynlacht, 2014). About 85% of the world’s birth defects occur in developing countries, supporting the role of context in influencing prenatal development directly via environmental hazards and also indirectly through the lack of opportunities and resources for education, health, and financial support (Weinhold, 2009).

Maternal Characteristics and Behaviors Teratogens—and the avoidance of them—are, of course, not the only determinants of how healthy a baby will be. A pregnant woman’s characteristics, such as her age, and her behaviors during pregnancy, including nutrition and emotional well-being, also influence prenatal outcomes.

Maternal Age

U.S. women are becoming pregnant later in life than ever before. Between 1990 and 2010, the pregnancy rate for women aged 35 to 39 increased from 119 per 1,000 women to 137 per 1,000 women. During the same 20- year period, the rate for women aged 40 to 44 increased from 11 to 19 per 1,000 (Curtin, Abma, & Kost, 2015). Women who give birth past the age of 35, and especially past 40, are at greater risk for pregnancy and birth complications, including miscarriage and stillbirth, than are younger women. They are more vulnerable to pregnancy-related illnesses such as hypertension and diabetes, and their pregnancies involve increased risks to the newborn, including low birth weight, preterm birth, respiratory problems, and related conditions requiring intensive neonatal care (Grotegut et al., 2014; Kenny et al., 2013; Khalil, Syngelaki, Maiz, Zinevich, & Nicolaides, 2013). The risk of having a child with Down syndrome also increases sharply with maternal age, especially after age 40 (Hazlett et al., 2011; see Figure 2.12).

Lives in Context

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HIV Infection in Newborns

HIV can be transmitted from mother to infant through breastfeeding.

David Turnley/Corbis Historical/Getty Images

The rate of mother-to-child transmission of HIV has dropped in recent years as scientists have learned more about HIV. The use of cesarean delivery as well as prescribing anti-HIV drugs to the mother during the second and third trimesters of pregnancy, and to the infant for the first six weeks of life, has reduced mother-to-child HIV transmission from more than 20% to less than 2% in the United States and Europe (Rudin, 2004; Torpey, Kabaso, et al., 2010; Torpey, Kasonde, et al., 2010). Aggressive treatment may further reduce the transmission of HIV to newborns, and research suggests that it may even induce remission (Rainwater-Lovett, Luzuriaga, & Persaud, 2015; Pollack & McNeil, 2013; National Institute of Allergy and Infectious Diseases, 2014). However, in developing countries such interventions are widely unavailable. Worldwide, mother-to-child HIV transmission remains a serious issue. For example, in Zambia, 40,000 infants acquire HIV each

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year (Torpey, Kasonde, et al., 2010). Treating newborns is critical, though not always possible. Worldwide, 20% to 30% of neonates with HIV develop AIDS during the first year of life and most die in infancy (United Nations Children’s Fund, 2013).

Globally, breastfeeding accounts for 30% to 50% of HIV transmission in newborns (Sullivan, 2003; World Health Organization, 2011). The World Health Organization (2010) recommends providing women who test positive for HIV with information about how HIV may be transmitted to their infants and counseling them not to breast feed. Yet cultural, economic, and hygienic reasons often prevent mothers in developing nations from seeking alternatives to breastfeeding. For example, the widespread lack of clean water in some countries makes the use of powdered formulas dangerous. Also, in some cultures, women who do not breast feed may be ostracized from the community (Sullivan, 2003). Balancing cultural values with medical needs is a challenge.

Children with HIV are at high risk for a range of illnesses and health conditions, including chronic bacterial infections; disorders of the central nervous system, heart, gastrointestinal tract, lungs, kidneys, and skin; growth stunting; neurodevelopmental delays, including brain atrophy, which contribute to cognitive and motor impairment; and delays in reaching developmental milestones (Blanchette, Smith, Fernandes-Penney, King, & Read, 2001; Laughton, Cornell, Boivin, & Van Rie, 2013; Sherr, Mueller, & Varrall, 2009; Palmer, 2003; Venkatesh et al., 2010).

What Do You Think? Imagine that you work as an HIV educator with women in an underdeveloped country. What challenges might you face in encouraging women to take steps to reduce the potential for HIV transmission to their infants? How might you help them?

Figure 2.12: Maternal Age and Risk of Down Syndrome

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Although the risk for Down Syndrome increases dramatically with maternal age, most infants are born healthy, regardless of maternal age.

Sources: Data from Cuckle, Wald, and Thompson (1987); figure from Newberger (2000).

Although risks for complications rise linearly with each year (Salem Yaniv et al., 2011), it is important to realize that the majority of women older than 35 give birth to healthy infants. Differences in context and behavior may compensate for some of the risks of advanced maternal age. For example, longer use of oral contraceptives is associated with a lower risk of giving birth to a child with Down syndrome (Nagy, Győrffy, Nagy, & Rigó, 2013). Older mothers tend to be healthier and show lower rates of alcohol consumption and cigarette smoking than do younger mothers (Salihu, Shumpert, Slay, Kirby, & Alexander, 2003).

Nutrition

The quality of the father’s and mother’s diets influences the health of the sperm and egg (Sinclair & Watkins, 2013). Most women need to consume 2,200 to 2,900 calories per day to sustain a pregnancy (Kaiser, Allen, &

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American Dietetic Association, 2008; Simkin, Whalley, & Keppler, 2001), but over 1 billion people in the world are chronically hungry (Food and Agriculture Organization of the United Nations, 2009) and even more are food insecure. Dietary supplements can reduce many of the problems caused by maternal malnourishment, but adequate caloric intake is crucial for healthy prenatal development (Ortolano, Mahmud, Iqbal Kabir, & Levinson, 2003).

Mothers who consume nutritious diets tend to have fewer complications during pregnancy and give birth to healthier babies

Some deficits resulting from an inadequate diet cannot be remedied. For example, inadequate consumption of folic acid (a B vitamin) very early in pregnancy can result in the formation of neural tube defects stemming from the failure of the neural tube to close. Spina bifida occurs when the lower part of the neural tube fails to close and spinal nerves begin to grow outside of the vertebrae, often resulting in paralysis. Surgery must be performed before or shortly after birth, but lost capacities cannot be restored (Scott Adzick, 2013). Another neural tube defect, anencephaly, occurs when the top part of the neural tube fails to close and all or part of the brain fails to develop, resulting in death shortly after birth. As

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researchers have learned and disseminated the knowledge that folic acid helps prevent these defects, the frequency of neural tube defects has declined to about 1 in 1,000 births (Cordero et al., 2010; Williams et al., 2015). However, in a national study of U.S. mothers, only 24% consumed the recommended dose of folic acid during pregnancy (Tinker, Cogswell, Devine, & Berry, 2010).

spina bifida A neural tube that results in spinal nerves growing outside of the vertebrae, often resulting in paralysis and developmental disability.

anencephaly A neural tube defect that results in the failure of all or part of the brain to develop, resulting in death prior to or shortly after birth.

Emotional Well-Being

Although stress is inherently part of almost everyone’s life, exposure to chronic and severe stress during pregnancy poses risks including low birth weight, premature birth, and a longer postpartum hospital stay (Dunkel, Schetter, & Tanner, 2012; Field, 2011). Maternal stress influences prenatal development because stress hormones cross the placenta, raising the fetus’s heart rate and activity level. Long-term exposure to stress hormones in utero is associated with higher levels of stress hormones in newborns (Kapoor, Lubach, Ziegler, & Coe, 2016). As a result, the newborn may be more irritable and active than a low-stress infant and may have difficulties in sleep, digestion, and self-regulation (Davis, Glynn, Waffarn, & Sandman, 2011; Kingston, Tough, & Whitfield, 2012). Later in childhood, he or she may have symptoms of anxiety, attention- deficit/hyperactivity disorder, and aggression (Glover, 2011). Stress in the home may make it difficult for parents to respond with warmth and sensitivity to an irritable infant (Brockington, 1996; Sameroff & Chandler, 1975). Social support can mitigate the effects of stress on pregnancy and infant care (Feldman, Dunkel-Schetter, Sandman, & Wadhwa, 2000; Ghosh, Wilhelm, Dunkel-Schetter, Lombardi, & Ritz, 2010).

Lifespan Brain Development

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Pregnancy and the Maternal Brain Pregnancy is associated with neurological changes especially in the areas of the brain responsible for social cognition.

How does pregnancy influence mothers? The developing embryo and fetus receive a great deal of research attention, but what does pregnancy mean for mothers’ development? Women’s bodies undergo a radical transformation during pregnancy. For example, the hormone progesterone increases up to 15-fold and is accompanied by a flood of estrogen that is greater than the lifelong exposure prior to pregnancy. Research has shown that hormonal shifts are associated with brain changes during puberty as well as later in life. Do the hormonal changes with pregnancy influence women’s brain structure? Animal research suggests that pregnancy is accompanied by neurological changes, including changes in neural receptors, neuron generation, and gene expression, that are long-lasting (Kinsley & Amory-Meyer, 2011). It is likely that pregnancy is also associated with neural changes in humans, but there is little research to date (Hillerer, Jacobs, Fischer, & Aigner, 2014).

In a recent groundbreaking study, Elseine Hoekzema and colleagues (2017) conducted brain scans of women who were attempting to become pregnant for the first time, as well as their partners. Women who became pregnant were scanned again after giving birth and again at least 2 years later. The fathers and women who had not become

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pregnant were also assessed. The new mothers experienced reductions in the brain’s gray matter, signifying increased neural efficiency in regions of the brain involved in social cognition—specifically, theory of mind, which enables us to sense another person’s emotions and perspective (Schurz, Radua, Aichhorn, Richlan, & Perner, 2014). Theory of mind underlies a mother’s ability to interpret her infant’s mental states and is important for secure parent–infant attachment and for the development of the child’s own social cognitive functions (Meins, Fernyhough, Fradley, & Tuckey, 2001). The changes in gray matter volume predicted mothers’ attachment to their infants in the postpartum period, as indicated by mothers’ increased neural activity in response to viewing photos of their infant as compared with other infants. Other research suggests that pregnancy is associated with the enhanced ability to recognize faces, especially those displaying emotions (Pearson, Lightman, & Evans, 2009). Gestational alterations in the brain structures that are implicated in social processes may offer an adaptive advantage to a mother by facilitating her ability to recognize the needs of her child and to promote mother–infant bonding. Moreover, similar to findings with animals (Kinsley & Amory-Meyer, 2011), the neural changes that accompanied pregnancy were long- lasting and persistent 2 years after giving birth.

The pregnancy-related neurological changes were so marked and predictable that all of the women could be classified as having undergone pregnancy or not on the basis of the volume changes in gray matter. Notably, fathers did not show a change in gray matter volume, suggesting that the neural effects of pregnancy are biological in nature, rather than associated with the contextual changes that occur with the transition to parenthood.

What Do You Think? What adaptive purpose might pregnancy-related neurological changes serve?

Prenatal Care

Prenatal care, a set of services provided to improve pregnancy outcomes and engage the expectant mother, family members, and friends in health care decisions, is critical for the health of both mother and infant. About 26% of pregnant women in the U.S. do not seek prenatal care until after the first trimester; 6% seek prenatal care at the end of pregnancy or not at

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all (U.S. Department of Health and Human Services, 2014). Inadequate prenatal care is a risk factor for low birth weight and preterm births as well as infant mortality during the first year (Partridge, Balayla, Holcroft, & Abenhaim, 2012). In addition, use of prenatal care predicts pediatric care throughout childhood, which serves as a foundation for health and development throughout the lifespan (Handler et al., 2003).

Why do women delay or avoid seeking prenatal care? A common reason is the lack of health insurance (Maupin et al., 2004). Although government- sponsored health care is available for the poorest mothers, many low- income mothers do not qualify for care, or lack information on how to take advantage of care that may be available. Other barriers to seeking prenatal care include difficulty in finding a doctor, lack of transportation, demands of caring for young children, ambivalence about the pregnancy, depression, lack of education about the importance of prenatal care, lack of social support, poor prior experiences in the health care system, and family crises (Daniels, Noe, & Mayberry, 2006; Heaman et al., 2015; Mazul, Salm Ward, & Ngui, 2016).

Moreover, there are significant ethnic and socioeconomic disparities in prenatal care. Inadequate prenatal care is most likely among Native American women (23%), followed by African American (19%), Latino (17%), Asian American (14%), and white American women (13%; U.S. Department of Health and Human Services, 2013a). African American women, in particular, are far more likely than all other groups to give birth to low birth weight or preterm infants (U.S. Department of Health and Human Services, 2014). Ethnic differences are thought to be largely influenced by socioeconomic factors, as the ethnic groups least likely to seek early prenatal care are also the most economically disadvantaged members of society.

Although prenatal care predicts better birth outcomes, cultural factors also appear to protect some women and infants from the negative consequences of inadequate prenatal care. In a phenomenon termed the Latino paradox, Latino mothers, despite low rates of prenatal care, tend to experience low birth weight and mortality rates below national averages. These favorable birth outcomes are striking because of the strong and consistent association between socioeconomic status and birth outcomes, and because Latinos as a group are among the most socioeconomically disadvantaged ethnic populations in the United States (McGlade, Saha, & Dahlstrom, 2004; Ruiz, Hamann, Mehl, & O’Connor, 2016).

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Several factors are thought to account for the Latino paradox, including strong cultural support for maternity, healthy traditional dietary practices, and the norm of selfless devotion to the maternal role (marianismo; Fracasso & Busch-Rossnagel, 1992; McGlade et al., 2004). These protective cultural factors interact with strong social support networks and informal systems of health care among Latino women, in which women tend to take responsibility for the health needs of those beyond their nuclear households. Mothers benefit from the support of other family members such as sisters, aunts, and other extended family. In this way, knowledge about health is passed down from generation to generation. There is a strong tradition of women helping other women in the community and warm interpersonal relationships, known as personalismo, are highly valued (Fracasso & Busch-Rossnagel, 1992; McGlade et al., 2004).

Although these cultural factors are thought to underlie the positive birth outcomes seen in Latino women, they appear to erode as Latino women acculturate to American society: The birth advantage has been found to decline in subsequent U.S.-born generations. Recent findings have called the existence of the Latino paradox into question, as some samples have illustrated that socioeconomic disadvantage cannot be easily ameliorated by cultural supports (Hoggatt, Flores, Solorio, Wilhelm, & Ritz, 2012; Sanchez-Vaznaugh et al., 2016).

Thinking in Context 2.5

1. Referring to Bronfenbrenner’s bioecological model (see Chapter 1), identify factors at each bioecological level that may influence development in the womb.

2. Imagine that you are a health care provider conferring with a woman who is contemplating becoming pregnant. Give some examples of specific advice you would offer to help her promote a healthy pregnancy and baby.

Apply Your Knowledge

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Dr. Preemie is conducting a research study of the prevalence and correlates of drug use in college students. Because of the sensitive nature of the research topic, Dr. Preemie promises her participants confidentiality. Each college student who participates completes a set of surveys and an interview about his or her lifestyle and drug use habits. One participant, Carrie, reveals that she engages in moderate to heavy drug use (i.e., drinks two to four alcoholic beverages each day, and smokes marijuana several times per week). During the interview, Carrie mentions that she’s feeling nauseous. Concerned, Dr. Preemie asks, “Do you want to stop the interview and go to the campus medical center?” “No,” Carrie replies, “It’s just morning sickness. I’m pregnant.” “Oh,” says Dr. Preemie, who nods, and continues with the interview.

Afterward, in her office, Dr. Preemie is torn and wonders to herself, “I’m worried about Carrie. Drugs and alcohol disrupt prenatal development, but I promised confidentiality. I can’t tell anyone about this! Should I say something to Carrie? I’m supposed to be nonjudgmental! Intervening might keep other students from participating in my research, for fear that I’d break my promises. I don’t know what to do.”

1. What are the effects of teratogens, like drugs and alcohol, on prenatal development?

2. Describe the course of prenatal development. How do the effects of exposure to teratogens change during prenatal development?

3. Consider Dr. Preemie’s dueling obligations. As a researcher, is she is responsible to Carrie as a participant in her study? Is Dr. Preemie responsible to the developing fetus? Her institution? Do Dr. Preemie’s actions have any ramifications for the other participants in her study? How might these responsibilities conflict?

4. What should Dr. Preemie do? 5. How might your response change if Carrie were smoking

cigarettes rather than using alcohol and drugs? What are the effects of smoking on prenatal development?

Give your students the SAGE edge!

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Chapter 2 in Review

2.1 Describe the process of cell reproduction and patterns of genetic inheritance.

Summary

Most cells in the human body reproduce through mitosis, but sex cells reproduce by meiosis, creating gametes with 23 single, unpaired chromosomes. Some genes are passed through dominant–recessive inheritance, in which some genes are dominant and will always be expressed regardless of the gene it is paired with. Other genes are recessive and will only be expressed if paired with another recessive gene. When a person is heterozygous for a particular trait, the dominant gene is expressed and the person remains a carrier of the recessive gene. Incomplete dominance is a genetic inheritance pattern in which both genes influence the characteristic. Polygenic traits are the result of interactions among many genes. Some traits are determined by genomic imprinting, determined by whether it is inherited by the mother or the father.

Key Terms

chromosomes deoxyribonucleic acid (DNA) mitosis meiosis zygote dizygotic (DZ) twins monozygotic (MZ) twins

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http://edge.sagepub.com/kuthertopical

homozygous heterozygous dominant–recessive inheritance incomplete dominance sickle cell trait polygenic inheritance genomic imprinting

Review Questions

1. How do cells reproduce? 2. What are four patterns of genetic inheritance?

2.2 Define and provide examples of genetic disorders and chromosomal abnormalities.

Summary

PKU is a recessive disorder that occurs when both parents carry the allele. Disorders carried by dominant alleles, such as Huntington’s disease, are expressed when the individual has a single allele. Some recessive genetic disorders, like the gene for hemophilia, are carried on the X chromosome. Males are more likely to be affected by X-linked genetic disorders, such as hemophilia. Fragile X syndrome is an example of a dominant recessive disorder carried on the X chromosome. Because the gene is dominant, it must appear on only one X chromosome to be displayed. Klinefelter syndrome occurs in males born with an extra X chromosome (XXY) and Jacob’s syndrome occurs when males have an extra Y chromosome (XYY). Females are diagnosed with triple X syndrome when they are three X chromosomes and Turner syndrome when they are born with only one X chromosome. The most common chromosome disorder is trisomy 21, known as Down syndrome.

Key Terms

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phenylketonuria (PKU) fragile X syndrome Down syndrome mutations

Review Questions

Give an example of:

a dominant-recessive disorder an X-linked disorder a chromosomal abnormality

2.3 Explain how the dynamic interactions of heredity and environment influence development.

Summary

Behavioral genetics is the field of study that examines how genes and experience combine to influence the diversity of human traits, abilities, and behaviors. Heritability research examines the contributions of the genotype in determining phenotypes but also provides information on the role of experience through three types of studies: selective breeding studies, family studies, and adoption studies. Genetics contributes to many traits, such as intellectual ability, sociability, anxiety, agreeableness, activity level, obesity, and susceptibility to various illnesses.

Passive, evocative, and active gene–environment correlations illustrate how traits often are supported by both our genes and environment. Gene- environment interactions illustrate the ways that heredity and environment influence each other. Reaction range refers to the idea that there is a wide range of potential expressions of a genetic trait, depending on environmental opportunities and constraints. Some traits illustrate canalization and require extreme changes in the environment to alter their course. The epigenetic framework is a model for understanding the dynamic ongoing interactions between heredity and environment whereby

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the epigenome’s instructions to turn genes on and off throughout development are influenced by the environment.

Key Terms

genotype phenotype behavioral genetics heritability gene–environment interactions range of reaction canalization gene–environment correlation niche-picking epigenetic framework

Review Questions

1. What is behavioral genetics? 2. What are three types of gene–environment correlations? 3. What is the range of reaction? 4. What is the epigenetic framework?

2.4 Discuss the stages of prenatal development, stages of childbirth, and challenges for infants at risk.

Summary

The germinal period is a time of rapid cell division. The embryonic period, from weeks 2 to 8, is a period of rapid cell differentiation. From 9 weeks until birth, the fetus grows rapidly, and the organs become more complex and begin to function. At about the 166th day after conception, the placenta releases a hormone that triggers the onset of labor. The first stage of labor begins when the mother experiences regular uterine contractions

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that cause the cervix to dilate so that the fetus’s head can pass through. Delivery occurs during the second stage, and the placenta is expelled during the third stage. At birth, low birth weight infants often experience difficulty breathing and are at high risk for mortality. Low birth weight infants experience higher rates of sensory, motor, and language problems, learning disabilities, behavior problems and deficits in social skills into adolescence. The long-term outcomes of low birth weight vary considerably and depend on the environment in which the children are raised.

Key Terms

ovum germinal period cell differentiation blastocyst embryo Implantation placenta embryonic period neural tube indifferent gonad lanugo vernix caseosa cesarean section Apgar scale preterm small for date low birth weight kangaroo care

Review Questions

1. What are the three periods of prenatal development? 2. What are the stages of childbirth? 3. What challenges do at-risk infants face and what outcomes can be

expected?

2.5 Identify the principles of teratology, types of

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teratogens, and ways that teratogens can be used to predict prenatal outcomes.

Summary

Teratogens include diseases, drugs, and other agents that influence the prenatal environment to disrupt development. Generally, the effects of exposure to teratogens on prenatal development vary depending on the stage of prenatal development and dose. There are individual differences in effects, different teratogens can cause the same birth defect, a variety of birth defects can result from the same teratogen, and some teratogens have subtle effects that result in developmental delays that are not obvious at birth or not visible until many years later. Prescription and nonprescription drugs, maternal substance use, material illness, and environmental factors can potentially harm the developing fetus.

Key Terms

teratogen fetal alcohol spectrum disorders fetal alcohol syndrome (FAS) spina bifida anencephaly

Review Questions

1. Define and provide examples of teratogens. 2. What are four principles that determine the effects of exposure to

teratogens during prenatal development?

Test your understanding of the content. Review the flashcards and quizzes at edge.sagepub.com/kuthertopical

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