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1The Study of Lifespan Development

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Learning Objectives

After completing this chapter, you should be able to:

• Define the lifespan perspective and summarize its primary characteristics.

• Distinguish between developmental domains and provide examples of overlapping characteristics.

• Describe nine stages of human development.

• Analyze key issues in the study of lifespan development.

• Identify the different contextual factors in lifespan development.

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Prologue

Chapter Outline

Prologue

1.1 The Lifespan Perspective Characteristics of the Lifespan Perspective

1.2 Topical Areas in Lifespan Development Physical Development Cognitive Development Psychosocial Development

1.3 Stages of Development

1.4 Key Issues in the Study of Lifespan Development Continuous Versus Discontinuous Development Nature and Nurture

1.5 Contextual Factors in Lifespan Development Sex and Gender Peer Groups Race, Ethnicity, and Culture Socioeconomic Status

Summary & Resources

Prologue Satchel Paige, a famous American baseball player, never admitted to the day or year of his birth. When reporters inquired about his age, Paige would often turn the question around: “How old would you be if you didn’t know how old you was?” And because Paige displayed atypical abilities for someone of the various chronological ages that he did report, his actual age was a frequent source of debate.

So how old would you be if you didn’t know the year of your birth? How would you determine if a person is an adult, entering middle age, or simply “old”? Other than chronological mark- ers, there are no definitive indicators of age. There are some 50-year-olds who seem “young” and some who seem “old.” There are some 80-year-olds who are active, spry, and enjoying life and others who are incapacitated, depressed, or show characteristics of the stereotypical curmudgeon. There are some 25-year-olds who have a career and family and others who have barely decided on a future course for their lives. Such differences lead to a number of ques- tions about human development:

• How old is somebody who is “old”? • At what age should children begin formal school? • When does puberty begin? Adolescence? • Why are some people more independent than others, and how does that characteris-

tic affect social, economic, and educational opportunities? • Does having a family or a job demonstrate emotional maturity?

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Section 1.1 The Lifespan Perspective

• Is retirement a distinct stage of life? • If you could choose, how long would you want to live? Why?

This list identifies just a few of the questions that we might ask when studying the course of human development. If you think about it carefully, the answer to each of these questions is, “It depends.” For example, school readiness among children varies tremendously, both physi- cally and psychologically; similarly, some people in their 20s act more like carefree teenagers and others act the part of responsible adults.

There are many different ways to look at growth and development. Satchel Paige had it right when he implied that it is not enough to describe aging as a simple series of chronological numbers. Instead, aging is best viewed as a multifaceted process. The goal of this text is to examine the various processes and how we think they occur.

1.1 The Lifespan Perspective Lifespan development, or what the American Psychological Association (APA) refers to as developmental psychology, is the study of human growth, stability, and change. This field of study is often divided into subcategories like “child development,” “early adulthood,” and “aging.” The traditional view of development emphasized the patterns of growth during childhood and adolescence, stability during early adulthood, and decline in the later years. However, contemporary developmentalists have largely rejected this notion. Instead, devel- opmentalists embrace the idea that development should be studied as a function of growth, stability, and change, not simply a matter of growth and decline. This lifespan perspective acknowledges that although development is often systematic and predictable, there are dif- ferent kinds of gains and losses for each individual at any particular time. For instance, a person who is not introduced to specialized physical skills during childhood, like dribbling a soccer ball or playing a musical instrument, is unlikely as an adult to ever have elite skills in those areas, even if the person was born with exceptional potential. Rather than explor- ing a “decline” in an ability that never existed, developmentalists focus on how variations in perception, experiences, and thoughts influence behavior. Likewise, lifespan researchers also explore factors that empower us to reach goals and to avoid dysfunctional outcomes as we age (Baltes, Lindenberger, & Staudinger, 1998).

Characteristics of the Lifespan Perspective The study of development attempts to find explanations for both the similarities and the dif- ferences in feelings, thoughts, and behaviors that occur between birth and the end of life, “from the womb to the tomb.” Dramatic changes occur as infants shift from being completely dependent on others to being self-reliant adults. But adults may then become less autono- mous in old age as they revert to some form of dependence. The study of the lifespan also includes genetics and the prenatal (before birth) period, as these factors have a strong influ- ence on later development.

We will begin by laying some groundwork for how we view lifespan development. There are several theoretical propositions that form a basis for the lifespan perspective, summarized in Table 1.1 at the end of this section (Baltes, 1987). The course of individual development is directed by these guiding principles.

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Section 1.1 The Lifespan Perspective

Development Is a Lifelong Process It is unfitting to adopt the idea that individuals reach some “peak” kind of performance—say, during early adulthood—and then simply decline. People never stop developing, no mat- ter how old they are. Whether we look at how babies bond to their primary caregivers, teenagers join cliques, young adults find intimate partners, or retirees consciously filter out less desirable social activities, develop- ment is viewed as a dynamic, lifelong process.

Development Is Multidirectional The same aspect of development can change in more than one way. For example, one type of intelligence, such as how fast an individual can complete a puzzle that has multiple visual elements, begins to decline sometime after the age of 30 (as described in Chapter 9). But another type of intelligence that relies on rote learning and experience, such as completing a crossword puzzle, increases after the age of 30. In this comparison, overall intelligence is multidirectional; there are both advances and declines associated with aging.

Development Is a Balance Between Gains and Losses Psychologists have expanded the lifespan model to include the idea that developmental change involves more than just progress and gains; in addition, they determine that aging does not mean declining. Instead, development is a balance between gains and losses—changes involve both benefits and costs. For example, a young couple may have a child (gain) but lose some of their independence (loss). (Conversely, a couple may gain financially by choosing to remain childless but potentially lose some social opportunities.) Or grandparents, compared to their abilities during early adulthood, may not be able to play as actively with their grand- children (loss), but they may have comparatively more time to be with grandchildren (gain).

Development Is Plastic Abilities are not wholly predetermined at birth. While development is guided in part by biol- ogy and genetics, the concept of plasticity reminds us that possible outcomes are wide-ranging and events do not shape every person the same way. Musical talents, the regulation of emo- tions, writing, socialization skills, athleticism, and other abilities can be fostered and lead to a wide range of outcomes, depending upon individual opportunity, support, and motivation. For example, we do not hear stories of “natural” athletes who never played on an official court or field, who never practice, yet still know how to play at a professional level. But there are many stories of professional athletes who gain success by working harder than their peers.

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The study of lifespan development covers topics from the prenatal period to death.

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Section 1.1 The Lifespan Perspective

Development Is Historically Embedded People cannot be separated from their historical and cultural contexts; this is a concept referred to as historical embeddedness. Age-related development is influenced by the kind of sociocultural conditions that exist in a given historical period and how these conditions evolve over time. Because the cultural climate has changed substantially, today’s young chil- dren, recent high school graduates, middle-age mothers, minorities, disabled, and others have different developmental pathways than generations ago, even though comparison groups might be the same age.

Development Is Contextual Development occurs within certain settings, or contexts. Three contextual systems work together to influence development: normative age-graded, normative history-graded, and nonnormative influences. Normative age-graded influences include contextual changes that are based on biological, psychological, social, or cultural forces that are shared by most people of the same age. For instance, age and cultural expectations influence expectations of kindergarten, the meaning of high school graduation, the social excitement of turning 21, the experience of menopause, and what it means to retire.

Sometimes there are distinct cultural influences that affect the psychological development of entire groups of individuals, or cohorts. These normative history-graded influences may provide an identity to an entire generation, like Baby Boomers (those born between 1945 and the early 1960s), Generation X (those born after the Baby Boomers in the early 1960s and until the later 1970s), or the Millennial Generation (also called Generation Y, born between the late 1970s and 2000). Individuals raised during the Arab Spring, a famine in Africa, or under repressive governments also share particular cultural and historical experiences. Some cohorts are more or less likely than others to have access to technology, or experience the effects of malnutrition, war, disease, or economic downturn.

Every individual also has unique, unpredictable experiences that affect personal develop- ment. These are called nonnormative influences because they do not fit any kind of standard cohort or standard of development. Examples might include moving in with grandparents after a family home is destroyed, unexpectedly becoming a teenage parent, having a spouse die at an early age, or winning the lottery. These unique events have the potential to influence the trajectory of development.

Development Is Multidisciplinary There are no universal models that can accurately forecast how a person will grow. Academic contributions come from disciplines other than psychology and development, including health care, public policy, community outreach, sociology, anthropology, social work, educa- tion, neuroscience, and economics, to name a few. In this way, the study of the lifespan is multidisciplinary.

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Section 1.1 The Lifespan Perspective

Table 1.1: Guiding principles in the study of lifespan development

Concepts Principles

Development is lifelong process Every age period is important in understanding the nature of development. During all stages of the life- span, both cumulative and novel events (biological and experiential) contribute to developmental change.

Development is multidirectional No single direction of change dominates. At any point in time, some systems show increases and others show decreases. Both growth and decline are dynamic and continuous among multiple dimensions and vary by categories of behavior.

Development is a balance between gain and loss Throughout the lifespan, there is continuous interplay between gain and loss. Development is accompanied by both growth and decline in any particular stage.

Development is plastic There is considerable individual capacity for change. Depending on a person’s life conditions and experi- ences, development is modified in response to environ- mental conditions.

Development is historically embedded Lifespan development can vary substantially depend- ing on historical and cultural conditions. The path of development is markedly influenced by sociocultural conditions that exist in a given historical period and how they evolve over time.

Development is contextual Development can be understood as the outcome of the interactions between biological systems and individual and historical events. People are exposed to both group and individual events in a dynamic world. Some influ- ences are shared with others of the same age; some influences are specific to a generation; other influences are uniquely individual.

Development is multidisciplinary Multiple disciplines inform the study of development, including psychology, sociology, biology, anthropology, neuroscience, economics, political science, and others.

Source: Adapted from Baltes, P. B. (1987). Theoretical propositions of life-span developmental psychology: On the dynamics between growth and decline. Developmental Psychology, 23(5), 611–626. doi:10.1037/0012-1649.23.5.611 . 1987 by the American Psychological Association. Adapted with permission.

Activity To demonstrate the multidisciplinary study of lifespan development, go through the college catalog and identify subject areas outside of psychology that are important to the study of lifespan development. Then, identify one lifespan topic within that discipline.

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Section 1.2 Topical Areas in Lifespan Development

1.2 Topical Areas in Lifespan Development To make sense of the multidisciplinary nature of lifespan development, it is important to organize the different kinds of change into broad categories, or domains. In this section, we explore the areas of physical, cognitive, and psychosocial development, which make up the three overlapping domains of development. Development is also commonly organized by age-related classifications called periods (or stages) of development, which we will discuss in section 1.3. Though development rarely occurs in perfectly isolated categories, classifying development into domains and periods makes the study of the lifespan more convenient and orderly for researchers, teachers, and students.

Physical Development Physical development is the most noticeable kind of change. It includes the biologically driven transitions in height, weight, muscles, sexual devel- opment, and perceptual abilities, such as vision, hearing, and motor skills. There is also physical development that is less visible, like changes in brain mass that are associated with faster (and then slower) speed in pro- cessing information. Bone growth and deterioration, the strengthening and weakening of heart tissues and other organs, susceptibility to disease, and hormonal changes are all part of the physical domain of development. Even if such changes are not visible, they can be behaviorally remarkable. For instance, hormones are involved in basic reproduction, first leading to fer- tility and then later preventing it; age-related diseases of the brain can cause rapid declines in physical and intellectual abilities. We understand physical development by studying such topics as differences exhibited by preterm infants and active versus sedentary adults.

More than the other domains, physical development depends on maturation, or the biologi- cal unfolding of growth over time. Each individual has a schedule built into his or her genes that controls both the timing and degree of physical growth and decline. Under ordinary con- ditions, a person cannot be prevented from experiencing a range of predetermined physical changes. Although maturation plays an essential role, environmental forces and individual choices, like nutrition and exercise, also mediate physical development.

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Physical traits like height are easy to notice, but also changing as a body develops are the brain, bone mass, and organ tissues.

Section Review Provide examples that demonstrate each of the guiding principles of lifespan development.

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Section 1.2 Topical Areas in Lifespan Development

Cognitive Development A second domain of development consists of mental activities—what we call cognition. The study of cognition includes how people think, make decisions, use language, solve problems, and pay attention to the stimuli they encounter within the environment. Cognitive develop- ment is therefore a broad domain that refers to overall development of the mind. Cognitive processes are intimately connected to the use of language and to gains and losses of intelli- gence and memory. For example, compared to teenagers, older adults have a greater store of information and therefore generally make better judgments about people, the community, and the world. However, on average, older adults take longer to learn novel information, such as how to use a new technology, and are more likely to forget newly learned names (Glisky, 2007; Whiting, Chenery, & Copland, 2011). As age-related diseases affect the brain, a deterio- rating memory may even compromise self-care functions, like grooming and toileting activities.

Like the way in which age affects memory, it is apparent that the cognitive and physical domains often overlap. Not only do physical changes lead to cognitive consequences (e.g., reexam- ining capabilities as the body is declining), but the reverse is true as well. For example, what depressed individuals think about themselves and their condition often influences the

degree of malaise. Or consider variability in attention-deficit/hyperactivity disorder (ADHD), which is partially explained by expectations in cognitive tasks and how an observer defines appropriate behavior. Relatedly, physical exertion is associated with prevention of depression, and physical play is often a successful part of treatment for the cognitive problems associated with ADHD (Abdollahian, Mokhber, Balaghi, & Moharrari, 2013; Blumenthal, Smith, & Hoff- man, 2012). Moreover, research tells us that more (physical) movement in general improves long-term cognitive function throughout the lifespan (Kirk-Sanchez & McGough, 2014; Mam- men & Faulkner, 2013; Timmons et al., 2012).

Like physical development, there is evidence that maturation plays a significant role in cogni- tion. For instance, all infants babble (the precursor to using recognizable words) at about 3 or 4 months of age, no matter what language or culture children are exposed to. Even deaf babies babble, so it appears that babbling is programmed into us as a necessary physical and cognitive preparation for speech. Psychosocial development, which we will discuss next, is influenced by maturation as well.

Psychosocial Development Beginning with a newborn baby’s temperament, or the early observable parts of personality, we know that at least part of personality and emotional development is inborn. (Tempera- ment is a concept that will be discussed more in Chapter 11.) Temperament includes how infants and toddlers respond to new people (getting excited versus withdrawing) and the amount of patience exhibited before getting frustrated. Like later personality, temperament characteristics are somewhat consistent during childhood, and appear to be at least partly inherited (Caspi, Roberts, & Shiner, 2005). Temperament and later personality are also linked

Critical Thinking

How might culture affect a person’s cognitive development?

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Section 1.3 Stages of Development

1.3 Stages of Development Typically, professionals in the field of development limit their specializations to the study of growth, stability, and change that occur in one of the three domains. There is often further specialization within a limited age range or stage (see Figure 1.1). For instance, a psychologist might study the cognitive changes that occur during adolescence or the changes in personality evident during late adulthood. But it is difficult to point to any one aspect of a person’s physi- cal, cognitive, or psychosocial development and say that we know exactly why it unfolded in a particular way. Development is best viewed as a fluid process, not one of absolutes. Even the transitions between different stages are sometimes blurry. For instance, we know what (physical) puberty and (psychosocial) adolescence look like, but it is difficult to identify the exact time either one begins or ends. Other periods in life are even more difficult to identify. Is middle age defined best by a number (i.e., chronological age), by types of relationships, or by financial security?

to the acquisition of social skills and attitudes, as these factors are a reflection of how people act. For example, being “kind” (a personality trait) is usually a better social strategy than being “mean.” The degrees to which young children are content, display negative emotions (like anger and fear), and focus their attention are all parts of personality that persist into adolescence and adulthood (Congdon et al., 2012; Garstein, Slobodskaya, & Kinsht, 2003). A natural leader may become impatient when others do not plan well; a natural introvert is likely to become frustrated or anxious when there are inescapable social demands. Therefore, differences in an individual’s traits and exposure to external demands will lead to changes in personality development that will affect outcomes, including career paths, choices for roman- tic partners, and living arrangements in old age.

Together, these kinds of personality, emotional, and social factors make up the domain of psychosocial development. This concentration includes the way society and culture shape people and, in turn, the way people shape society and culture. It is difficult to separate the parts of personality and self-image that are strictly individual “choice” from those that are the result of social or cultural expectations. As people develop, their individual experiences and thoughts incrementally modify their psychosocial characteristics. As people change, society changes as well.

Section Review Provide examples of processes that are representative of the three domains of development.

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10 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 25 30 35 40 45 50 55 60 65 70 70+

Years

Periods in Child Development

Infancy

Early childhood

Middle childhood

Adolescence

Prenatal

Early adulthood

Late adulthood

Middle adulthood

Emerging adulthood

Section 1.3 Stages of Development

We therefore cannot always neatly define a group of individuals by physical, mental, or psy- chosocial characteristics. Additionally, any one period of development is usually dependent on culture and society. For example, in the agrarian society of the United States that predated the Industrial Revolution, life often fell into three stages: infancy, childhood, and adulthood. Children played; adults worked and raised families. Today, many young adults who are attend- ing school or settling into their careers delay the move to become independent. This cultural change has prompted some to embrace the idea of a new stage called emerging adulthood that is sandwiched between adolescence and early adulthood (Arnett, 2000).

Therefore, stages of development should not be thought of as having absolute beginnings and endings; they should be thought of as dynamic ideas rather than limited constructs. Table 1.2 presents the most commonly recognized divisions of development among academicians. Notice that other than the prenatal period, the stages overlap, following the lifespan view that these are not universally defined ages, but more generally accepted group patterns. Recall also that there are intersecting physical, cognitive, and psychosocial processes. The stages are organized around chronological age, which, as noted in the prologue, is only one way to view development and sometimes lacks meaning. Other forms of classification correspond to physical maturation, cognitive change, and psychosocial experience.

Figure 1.1: Stages of development

Periods of development should not be thought of as having absolute beginnings and endings. With the exception of the prenatal period, the periods should be conceptualized as approximate age ranges.

10 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 25 30 35 40 45 50 55 60 65 70 70+

Years

Periods in Child Development

Infancy

Early childhood

Middle childhood

Adolescence

Prenatal

Early adulthood

Late adulthood

Middle adulthood

Emerging adulthood

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Section 1.3 Stages of Development

Table 1.2: Stages of lifespan development and their associated characteristics

Stage of life and age range Characteristics

The prenatal period

Conception to birth

The only period with definitive physical beginning and ending points; the other age ranges originate from social constructs and have become useful groupings. The prenatal period lasts from the time of conception until birth, whether the infant is born at full term or not.

Infancy Birth to age 2 The second year of infancy is often referred to as toddlerhood. During infancy, there is tremendous growth in all developmental domains. Physically, children begin to move on their own (“toddle”). Cognitively, children begin to talk, and there is tremendous growth in language comprehension. Psychosocially, children begin to engage in independent activities and self-soothing behaviors, and they begin to form meaningful relationships.

Early childhood

About age 2 to 5 or 6

Commonly referred to as the “preschool” years in mainstream literature and conversation. Body proportions change and children use more coordinated movements, partly because of rapid changes in neuron (brain) growth. Cognitively, children show great progress in the use of words and phrases to form sentences. They also become a bit more discerning of friendships as they spend generous amounts of time playing if given opportunities to do so. Understanding what different playmates can offer leads to advances in psychosocial development.

Middle childhood

About age 6 to 11

Generally encompasses the elementary school years. Physical and cognitive differences among children become more noticeable. Children are often acutely aware of the exceptional handball players, mathematicians, and readers. Formal education allows children to master basic language and computational skills. From a psychosocial perspective, social comparisons begin to affect how we feel about ourselves. Games and play become more rule oriented as morality becomes more sophisticated.

Adolescence About age 11 to 18

Coincides with the dramatic physical changes that mark puberty and is thought of as a transition to adulthood. Depending on how the changes are measured, on average puberty begins at about age 10 for girls and at about age 12 for boys. It marks the change into an adult body and includes sexual maturation. Significant changes in cogni- tion, due at least partly to physical maturation of the brain, begin to surface. Thought processes become more abstract as teenagers think about the future in a way that younger children cannot. From a psychosocial standpoint, adolescence lasts until around the end of high school. Self-identity becomes prominent as adolescents look toward the future and establish goals. Adolescents look to friends for emotional support rather than strictly shared activities; they also begin romantic relationships. Personal and cultural context often affects much of the transition to adulthood. For instance, when adults say that a child has “grown up fast” because of circumstances such as war or the death of a parent, the comment usually alludes to the psychosocial domain.

(continued)

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Section 1.3 Stages of Development

Stage of life and age range Characteristics

Emerging adulthood

About age 19 to mid-20s

Because the transition time between adolescence and adulthood has lengthened in recent years, this classification is a newer addition to conceptualizations of lifespan stages. The characteristic time of exploration is most common in Westernized young adults, especially those in the United States who have options due to economic oppor- tunity. It is a time of feeling “in-between” adolescence and adulthood, as emerging adults explore future goals related to school, career, and family without committing to one path. After graduating from college, emerging adults may take a “gap year” without specific goals, travel before entering graduate school or the workforce, or remain dependent on parents for an extended period of time.

Early adulthood

Early 20s to mid-40s

Physical capabilities peak during this time, but those abilities are not always particularly noticeable. Metabolism slows at the same time that opportunities for activity typically decline in Western countries, resulting in weight gain. Individuals leave home to get a job, get mar- ried, go to college, or join the military as career development, work, and identity become interconnected. Intimate, long-term relation- ships are established. Showing new kinds of thinking and learning, individuals in this stage have not yet reached their peak cognitive capabilities.

Middle adulthood

Mid-40s to mid-60s

Physical changes that began in the late 20s/early 30s become notice- able. Disease becomes more prevalent; reaction time slows; eyesight diminishes. Later, height begins to slowly decline and menopause occurs among women. Couples remain sexually active; frequency of intercourse sometimes increases when menopause signals that childbearing years have ended. Abilities in knowledge acquisition and problem solving peak and most other cognitive abilities continue to improve. There are some delays in memory retrieval, but slower declines are associated with increased physical fitness. Children leaving home leads to expanded opportunities; there is high relative marital satisfaction. Earning power is often at its peak. Retirement planning becomes paramount. There is a focus on appraisal of worth and legacy for next generation.

Late adulthood Mid-60s and beyond

When classifying differences among certain cohorts, this period is sometimes sub-divided into the young old, old-old, and the very old. Senses and height continue their gradual decline, which become more noticeable. Bone diseases, cancer, and cardiovascular diseases become prevalent. There is considerable variation in cognitive development. Some people have little degradation, while others suffer from severe dementia, including Alzheimer’s disease. Short- term memory is not as efficient; long-term memory remains largely intact. For most, learning remains a vital part of development. Social networks are more selective. There is movement into activities with more competence and away from those where skills are diminishing (like playing golf instead of basketball). Retirement often affects self- worth and identity. “Life review” is a distinguishing feature, which can lead to despair or a great sense of fulfillment. Role reversal often occurs, as adults become dependent on their children.

Table 1.2: Stages of lifespan development and their associated characteristics (continued)

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Section 1.3 Stages of Development

Regardless of the generalizations identified in Table 1.2, individual and cultural variations are the norm. The typical age and course of marriage, work, and retirement (if they even exist!) varies considerably throughout the world, even among Western cultures. Because of these individual and group differences, we use caution in generalizing development to describe pat- terns or traits that occur in “all older people” or “all young adults.” Because there is so much variation among how individuals display developmental changes, there are also areas of study that are met with frequent debate. We touch upon these issues in the next section.

Section Review Describe characteristics that are associated with each stage of lifespan development.

Psychology in Action: Defining and Studying Biomarkers

New research highlights the difficulty in studying the lifespan using only chronology to orga- nize changes. In addition to individual behavior, health status, including biological aging, can vary widely at any particular age. While educators often turn to online longevity calculators to demonstrate how biological and environmental factors influence life expectancy, none has been clinically standardized. To fill the gap, a team of researchers recently followed 954 men and women from age 26 to age 38, looking for systematic biological changes that are indicative of aging (Belsky et al., 2015). In order to quantify biological aging, they developed a scientific measure for longevity that identified 18 risk factors. The factors were validated as “biomark- ers” for longevity and included measures such as waist-to-hip ratio, cholesterol levels, and immune system and organ functions.

After 12 years of studying how the biomarkers changed over time, the researchers were able to determine who aged faster or slower than normal, what they termed the “pace” of aging. Most people aged one year for each chronological year, but some aged as many as three bio- logical years and others made no increase in biological years at all. They determined that indi- viduals indeed age at a different pace, beginning at least as early as 26. In addition, lifestyle variables that are typically associated with behavioral changes are also associated with the biomarkers. In other words, even before they reached middle adulthood, those in the study who were assigned “older” ages due to the study’s biomarkers were also found to be less phys- ically active, had relatively greater cognitive decline, reported worse health, and were judged to “look” older by an unrelated experimental group.

Similarly, investigators were also able to detect the pace at which the sample was aging. Rela- tively young adults who were physically weak, showed cognitive decline, worse health, and looked older, were also aging more rapidly, according to the biomarkers. The authors conclude that when we study how to extend the lifespan, we are too focused on the elderly. They sug- gest that much can be accomplished by also studying those who have not yet experienced age- related diseases. We continue to expand the field of lifespan psychology by studying develop- ment from multiple perspectives.

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Infancy

Adulthood

Infancy

a) Continuous Development b) Discontinuous Development

Adulthood

Section 1.4 Key Issues in the Study of Lifespan Development

1.4 Key Issues in the Study of Lifespan Development The field of lifespan development includes issues that also help to guide and organize research. These issues direct theories and are encountered repeatedly throughout the text. They include discussions about how specific kinds of growth occur (continuous and discon- tinuous development), the relative importance of biology and genetics versus environmental influences (the issue of nature and nurture), and the value of studying development as a uni- versal idea versus one that is culturally specific.

Continuous Versus Discontinuous Development Debates among developmentalists generally focus on how change occurs. For example, some postulate that growth occurs in relatively distinct stages, as when a child suddenly begins to walk; others support a view that development is due to gradual changes. Instead of an abrupt event, walking is viewed as a result of small, incremental changes: learning to walk includes standing, cruising (walking while holding on to tables or other objects), muscle maturation, and brain development, among other processes. Children do not suddenly walk; they gradu- ally build up to it.

Regardless of where growth originates, when it is viewed as an incremental, gradual process, it is called continuous development. Development is viewed as a continuous process that evolves from simple thoughts, emotions, and behaviors to ones that are more complex (Figure 1.2a). Changes are small and cumulative, like those that occur in numeracy and many kinds of athletic pursuits. Instead of abrupt change, the mind and body gradually incorporate new information and add to the old store.

Figure 1.2: Continuous and discontinuous development

Discontinuous development produces an abrupt, qualitative change, whereas continuous development produces a smooth, gradual, quantitative change.

Infancy

Adulthood

Infancy

a) Continuous Development b) Discontinuous Development

Adulthood

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Section 1.4 Key Issues in the Study of Lifespan Development

Some kinds of development will not occur until the time is right: walking, certain kinds of thinking processes, the start of puberty, and the end of childbearing (menopause), for exam- ple. We have specific psychosocial markers as well: beginning formalized school, high school or college graduation, marriage, having children, beginning a career, and retirement. Each of these events can imprint on development and change. Furthermore, the distinct qualitative events are processes that are described as discontinuous development, because they lack a smooth progression (Figure 1.2b). Discontinuous change implies that there is a connec- tion between biology and an organism’s consequent behaviors and skills. Changes occur only when the body or mind has matured in some specific way. That is, genetic programming dic- tates when humans are ready to babble, walk, think abstractly, understand geometry, show empathy, or form intimate relationships.

Consider video gaming as a possible metaphor for development. Some video games require a specific amount of time and experience at one level in order to advance to a more com- plex level (discontinuous), but other video games gradually speed up as players become more proficient (continuous). Psychologists today generally agree that human development includes both continuous and discontinuous changes. Sometimes the same type of develop- ment may even include both. For example, children start reading only when they have begun to understand sound–symbol relationships, which is a discontinuous development. But once that happens, there is a constant upward movement in reading and comprehension skills— a continuous trend. We can also compare the discussion on continuous and discontinuous development to the growth of a tree. At first glance, it looks as if a tree has continuous growth. But on further inspection, it is apparent that there is a seedling phase, a fruit or seed phase, and perhaps a dormancy phase. Importantly, conceptualizing how development occurs often differentiates a researcher’s field of study. For instance, while some researchers might study the continuous patterns of mental health among long-term couples, others might study the potential abrupt, discontinuous changes that might occur after the death of a spouse.

Nature and Nurture The interacting forces of biology (including heredity) and the environment is the subject in lifespan development that probably receives the most deliberate and intense examination. Instead of viewing these processes as opposing forces, there is now a more concerted effort to understand how nature and nurture interact. Certainly there are distinctions in thought and kinds of relationships that can occur only through maturation and the passage of time. And environmental forces are essential to growth in this area. But a person must be exposed to certain social structures and coached in some kinds of relationships in order to achieve potential. Small bits of change are dependent on people’s interactions with their surround- ings, including even the unique and changing prenatal environment.

Behavioral genetics is a relatively new field that studies the role of genetics in species- specific behavior. It has gained more widespread attention with the completed mapping of the human genome in 2003. The anticipation of its completion led to a great deal of excite- ment about the possibility of discovering individual genes that control behavior. Instead, breakthroughs in gene mapping have determined that separating genetic and environmental influences may not be the right approach. Finding an individual gene that affects a specific behavior (like the ability to pay attention) has remained elusive. Though single genes have been identified in some conditions, like Huntington’s disease, it appears that other disorders, like schizophrenia, have a more complex, polygenetic (“many genes”) inheritance (Crow,

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Section 1.4 Key Issues in the Study of Lifespan Development

2007; Réthelyi, Benkovits, & Bitter, 2013; Walker, 2007). The influence of environmental fac- tors on gene expression, along with the complex analysis of these relationships, is something scientists are working to understand.

The Interactionist Perspective Therefore, rather than drawing conclusions based on nature or nurture, investigating the roots of the interaction between genes and the environment is more consistent with contem- porary perspectives. Scientists no longer believe that either experiences or biology are singu- larly responsible for a person’s destiny. For instance, biological aging is the strongest variable involved in the prediction of Alzheimer’s disease and other forms of dementia, but there is also evidence that diet, physical and cognitive exercises, and other environmental factors are influential. Physical activity plays an especially important protective role against dementia (Grande et al., 2014; Kirk-Sanchez & McGough, 2014).

One of the clearest examples of how nature and nurture interact comes from a study in which researchers bred strains of rats to show specific traits. One group was bred with a high level of aggression and the other with a low level of aggres- sion. In separate colonies, they behaved according to their biological predis- positions. But when they were raised together, all the rats showed similar lev- els of aggression (Hood, 2005). Studies like this suggest that environment has the potential to override genetic predisposi- tion. Alternatively, nature often trumps nurture, as in the case of people born with physical limitations. Regardless, the inter- actionist perspective has slowly replaced the theory that we can trace observable traits and behaviors to specific genes.

The Epigenetic View In line with the interactionist perspective, there has been a renewed emphasis on epigenetics, the study of the bidirectional influences of genes and environmental forces. Rather than depending strictly on maturational schedules, gene expression may be the result of non- genetic circumstances, like the fetal environment, where people grow up (e.g., temperature, availability of clean water and nutrition), or how encounters with different people are resolved. Importantly, epigenetic influences are bidirectional. That is, environmental events affect gene expression, and certain environmental experiences will lead to developmental changes only if the right combination of genes exists. For instance, a number of genes appear to have a cumulative effect on the expression of anti-social or delinquent behavior. One par- ticular set of genes appears to moderate the negative effects of childhood maltreatment; they decrease the chances of an abused child later becoming a delinquent. However, the genes appear to have a protective effect only in the presence of maltreatment. Among children who

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Contemporary perspectives favor studying how genes and the environment interact with each other to express certain traits.

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Section 1.5 Contextual Factors in Lifespan Development

1.5 Contextual Factors in Lifespan Development Related to the debate over how nature and nurture interact is the growing discussion about whether development should be viewed as mostly universal or more dependent on individual circumstances (Shweder et al., 2006). In the modern view, developmental sequences vary as a consequence of individual and environmental contexts, especially unique cultural and gen- erational experiences. For instance, acting more “man-like” or “woman-like” is viewed differ- ently depending on whether a person is male or female. Worldwide there is broad contextual diversity. Small differences in infant care and parenting have been found to prescribe widely different developmental pathways (Keller, 2013). The Arab Spring and other social changes may have opened physical, psychosocial, or learning opportunities that did not exist in pre- vious years. The expression of one’s sexuality has become less stressful in many U.S. cities, Europe, and elsewhere, but remains difficult in other contexts.

Because of its size and unique diversity, the United States provides dynamic examples of the importance of contextual factors. There are cultural and generational differences in how chil- dren should behave and be disciplined, attitudes about education, the importance of mar- riage and children, the meaning of work, and caring for elderly family members. Contextual issues are often noticed during adolescence, when psychosocial development may be affected by choices in music and friendships, which in turn may affect academics, cognitive develop- ment, and risk-taking behaviors. The way in which these seemingly small issues are viewed both individually and culturally may in fact lead teenagers to entirely different adult lives. Peer groups, ethnicity and culture, and financial and educational status also affect a person’s developmental trajectory. Rather than approaching development as a universal theme, the extent to which behavior is viewed in contexts is an important area of study.

Sex and Gender In psychology, sex and gender are separate concepts. Sex refers to a person’s biology: whether someone is born male or female. It is rare (but still possible) that someone cannot be defini- tively identified as either male or female at birth; this occurs in about 1 out of 5,500 births

are not maltreated, the set of genes do not have a behavioral expression (Caspi et al., 2002). Similar epigenetic processes are thought to occur in the onset of diabetes. Because of genetic inheritance, it appears that some people are at higher risk for the expression of “diabetes” genes; certain behaviors (e.g., overeating and obesity) may turn disease genes either on or off, but genes alone do not appear to cause either obesity or diabetes. In the absence of the envi- ronmental catalyst, the disease does not occur (Gottlieb, 2007; Stankov, Benc, & Draskovic, 2013).

Section Review Explain how the key issues in development affect how those in the field view growth, stability, and change.

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Section 1.5 Contextual Factors in Lifespan Development

(Sax, 2002). On the other hand, gender is more of a social construct or a custom that pertains to a specific group. It refers to how a person behaves or identifies him- or herself, partly in comparison to societal norms. Some people act more “male-like” while others act more “female-like.” In contrast to sex, which is usually either one or the other, there is a broad con- tinuum of gender-typed behavior.

Sex It should not be surprising that simply being male or female has a profound effect on devel- opment. For instance, there are differences in the symptoms and course of osteoarthritis, an inflammation of the joints that affects nearly everyone by age 70 or so. Although it affects men and women equally before age 55, it is more common in women after age 55. The effect on mobility affects physical and social opportunities, which may in turn affect cognitive develop- ment (van Dijk, Veenhof, Lankhorst, van den Ende, & Dekker, 2011).

Biological sex has an effect on a variety of other diseases too. Certain cancer rates and heart disease are affected by estrogen, a hormone that is found in much larger concentrations in women than in men (Fuhrman et al., 2012). Although behavioral differences may be a con- tributing factor, being male is a higher risk factor for lung and colorectal cancer (CDC, 2014d, 2014f ). Furthermore, compared to women, men are more likely to drive recklessly and com- mit suicide; women are more likely to be overweight (but equally likely to be obese) and more likely to attempt suicide (CDC, 2014d; Flegal, Carroll, Kit, & Ogden, 2012; Taubman & Findler, 2003). However, determining which of these differences are due to nature and which to nurture is analogous to asking whether each were the result of sex or gender. For example, is more reckless driving associated with the greater activity level inherent in males, or is it a learned behavior associated with “masculinity”?

Gender Because gender is a function of social and cultural factors, it is related to the extent to which people embrace roles. Even young infants look to adults to provide signals about how to behave in ambiguous situations. In addition to using explicit language, adults use smiles, frowns, and other nonverbal gestures to provide powerful feedback on how to behave (Stenberg, 2009). As young children discover the meaning of sex differences, they begin to process the expectations and requirements related to their gender. These expectations include how to dress, what toys to play with, which games and activities to engage in, and methods of interacting with others.

Throughout later childhood and adulthood, societal expectations are learned and integrated into personality along with moral and ethical codes, sexual behavior, and sexual identity. Notably, gender contributes to choices in education, family responsibilities, and employment. For example, perceived gender roles account for the fact that there are more male dentists in the United States than there are female, and more female dental assistants than there are male (BLS, 2014a). But in the United States, the trends in education, employment, and family responsi- bilities have changed considerably over the last several decades, demonstrating the cultural component of gender.

Critical Thinking

Imagine a woman in a lesbian relation- ship who transitions to a man and is now known as Chaz. Chaz wants to remain with the woman in his previous relation- ship. How would you now identify Chaz’s sexual orientation (is he gay or straight?), sex, and gender?

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Section 1.5 Contextual Factors in Lifespan Development

The media play a strong role in the construction of gender roles. Both children’s television programming and shows that are geared toward adults provide constant models of scien- tists, investigators, and especially mothers and fathers. Television and other media exert their influence by reinforcing traditional roles and by providing role models for alternative behav- iors. But media portrayals have also changed considerably over the last 50 years since the Father Knows Best mentality of the 1950s and 60s. In the appropriately titled sitcom Modern Family, there are some characters who fit the mold of a traditional family, with a husband, wife, and three children. However, fathers are shown taking on parenting roles that were once the exclusive domain of women. There is also a blended family and a married gay couple who have adopted a child together.

Peer Groups Social groups not only teach individu- als about expected gender roles and appropriate behavior, they also pro- vide a sense of belongingness, which helps build a sense of identity. In one example, older adolescents who were identified as nonconforming with indistinct social roles were later found to have higher rates of depression and lower ratings of life satisfaction (Toomey, Ryan, Diaz, Card, & Russell, 2010). On the other hand, learning social competence in peer groups leads to a strong sense of identity and has a positive effect on well-being (Larson, Whitton, Hauser, & Allen, 2007; Zhou & Fang, 2015).

Peers and social status during child- hood can predict a number of behav- iors in adulthood. The influence of peers on antisocial behavior during young adulthood can be traced back as early as fourth grade (Nelson & Dishion, 2004). Gender roles and peers strongly influence drinking behavior among college students (e.g., Barnett et al., 2014; Bot, Engels, & Knibbe, 2005). Of course, peer groups influence initial sexual attitudes, but they can also reverse mindsets, even when they are entrenched (Kaponda et al., 2011). One way or another, peer groups influence the way that people see themselves, from childhood onward.

Race, Ethnicity, and Culture Traditionally, differences between race and ethnicity have been considered analogous to sex and gender, and nature and nurture. Race usually refers to observable characteristics that societies have traditionally used to distinguish one group from another, like skin color and hair texture. However, it is easily argued that the concept of race is not a natural scientific division. That is, there are no distinct group differences in genetic makeup among humans because we all belong to the same taxonomic subspecies (homo sapiens sapiens). Accordingly,

iStock/Thinkstock

Peer groups can have a profound impact on individuals’ senses of belonging and how they see themselves.

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Section 1.5 Contextual Factors in Lifespan Development

absolute definitions of race vary widely in scientific literature (Ferguson, Kerr, & Rynn, 2011; Lieberman et al., 2004).

It is perhaps more useful to look at race as a part of ethnicity. A person’s ethnicity includes characteristics that are immersed in culture, including differences in nationality, language, religion, values, and beliefs. As a function of historical and personal circumstances, including observable characteristics like skin color, ethnicity contributes to individual and group identity.

Ethnicity and culture can have a profound effect on development. Culture contributes to sta- tus, both individually and collectively, which in turn affects health, as well as educational and social opportunities. These differences may be inadvertently institutionalized or the result of historical legacy, as in the United States. Other times there are direct efforts to create differ- ences, as in countries that impose legal restrictions on literacy and other opportunities for women. Culture shapes a person’s view of the world, impacts goals in adulthood, and pre- scribes how people are regarded in old age. Simply identifying with one group or another can have a powerful psychological influence on development.

Culture and ethnicity are at times used to explain group differences in development, but there are often confounding variables. For example, evidence indicates there is a higher prevalence of dementia among blacks than whites, including regional (subcultural) differences, as if dementia is caused by something specifically found in the local community (Gillum & Obis- esan, 2011). On further investigation, it appears that the variance in dementia between racial groups is more likely due to the timing of diagnoses, quality of patient care, and prior medical history (Husaini et al., 2003; Sengupta, Decker, Harris-Kojetin, & Jones, 2012). That is, differ- ences identified in dementia by race may be due to the way blacks and whites are diagnosed and treated rather than biology. It is difficult to know the precise mechanisms that lead to disparities in health outcomes for different cultural and economic groups.

Socioeconomic Status Dementia is one example of how factors related to economics and acquired knowledge can affect development. Together, income, education, occupation, and the social and financial opportunities that they represent contribute to socioeconomic status (SES). In research, families are usually categorized into high-, middle-, and low-SES groups. Consider the poten- tial implications of nature, nurture, and context on issues like education and health care. It is well known that individuals from low-SES families have poorer health and do poorer in school when compared to children from high-SES families. This relationship contributes to a lifelong disadvantage in career opportunity. But, of course, not all low-SES children fare poorly later, which presents at least two important questions: (1) What factors contribute to the poor outcomes among low-SES children, and (2) What factors contribute to the success that so many low-SES children do experience?

Among social variables, SES often has a stronger predictive value than race or ethnicity. For instance, poorly educated, impoverished (low-SES) groups wait longer than others before seeking medical treatment, regardless of race. People with comparatively more education and income are more likely to have both the means and the knowledge to seek early treat- ment. SES affects choices in grade schools and colleges, access to professional connections, and knowledge about healthy personal habits. The rate of smoking, for instance, decreases consistently as a function of educational level (see Table 1.3).

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Section 1.5 Contextual Factors in Lifespan Development

Table 1.3: Cigarette smoking by level of education Percentage of current cigarette smokers aged ≥25 years by education level.

Education level* 2013

Men (% of 15,440) Women (% of 19,117) Total (% of 34,557)

0–12 years (no diploma) 30.6 18.0 24.2

High school diploma 26.7 17.6 22.0

Some college, no diploma 22.4 19.5 20.9

Associate degree 17.8 17.7 17.8

Undergraduate degree 10.4 7.9 9.1

Graduate degree 5.7 5.5 5.6

* Among persons aged ≥25 years.

Source: Adapted from Auld, a. F., Agolory, S. G., Shiraishi, R. W., Wabwire-Mangen, F., Kwesigabo, G., . . . Ellerbrock, T. V. (2014). Current cigarette smoking among adults—United States, 2005–2013. Morbidity and Mortality Weekly Report, 63(47), 1108– 1112.

The SES of a person or family often dictates what opportunities are available, as the social environment often places barriers—or offers advantages—to optimal development. SES is related to whether a person has a more or less physically taxing job. Some families need to depend on a public computer and public transportation while others have more convenient and less time-consuming access to resources. Lower income neighborhoods usually have fewer grocery stores that carry fresh produce; wealthier neighborhoods usually have safer recreational facilities. An environment that has richer material and educational assets usually results in children who are advantaged physically (e.g., better nutrition, more varied recre- ation, better access to quality healthcare), cognitively (e.g., better technology and educational opportunities) and psychosocially (e.g., a safer environment and access to friends), leading to better outcomes throughout the lifespan. Understanding these issues can lead to public policy changes and contribute to intervention strategies.

Research consistently shows that blacks, Hispanics, and those in lower economic classes have more chronic diseases, poorer health, and a lower life expectancy than those who are in mid- dle and upper income brackets. However, if blacks and Hispanics are divided by their income brackets, the racial differences mostly disappear. Although it appears that simply being minority can be a form of social disadvantage, income level has remained the most important factor associated with optimal development, not race (Barr, 2014; Guralnik, Land, Blazer, Fil- lenbaum, & Branch 1993). Stated another way, within-group differences among races and ethnicities in the United States are much larger than between-group differences. Wealthy people have similar health advantages and outcomes regardless of race or ethnicity.

Section Review Find specific examples of contextual factors that have had an influence on your own development.

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Summary & Resources

Chapter Summary Contemporary psychologists rely on seven guiding principles, as described by Paul Baltes. Development is organized into overlapping domains and broadly defined stages, and there are key issues that often determine a person’s research focus. The issues of nature and nur- ture, for example, provide an especially rich source of discussion in the field.

There are several contextual factors that will remain a common theme throughout this text. Factors like gender and socioeconomic status can often be used to predict developmental trajectories. Developmentalists work to understand how these variables affect development so that we can devise intervention strategies that will improve developmental outcomes. Moving forward, organizing development in these ways allows us to differentiate psycholog- ical theories of development and provides the foundation for scientific endeavor, two topics which will be the focus of the next chapter.

Summary of Key Concepts The Lifespan Perspective

• Lifespan development, or developmental psychology, is the scientific study of changes in behavior, thoughts, and emotions from birth through the end of life— from “the womb to the tomb.”

• Contemporary psychologists rely on seven guiding principles as described by Paul Baltes: development is lifelong, multidirectional, a balance between gain and loss, plastic, historically embedded, contextual, and multidisciplinary.

Topical Areas of Lifespan Development

• Though there is considerable overlap, the study of development is usually organized into physical, cognitive, and psychosocial domains.

• Physical development refers to body changes and is the most noticeable develop- mental domain. It includes genetically prescribed changes in height, weight, muscles, and sexual development. We also study changes in brain size and mass; perceptual abilities, such as vision and hearing; and motor skills. Physical development depends largely on maturation: the biological unfolding of growth.

• Cognitive development is a broad domain that refers to development of the mind, including the gains and losses of intelligence and memory. We want to understand how people think, make decisions, use language, solve problems, and pay attention to the stimuli they encounter within the environment.

• Psychosocial development consists of personality, emotional, and social factors. This domain includes a focus on the way society and culture shape people and the reverse.

Stages of Development

• Chronological age ranges should be thought of as a guide to development, not abso- lute markers.

• The nine periods of the lifespan referred to in this text are standardized for convenience. The most commonly recognized stages are the prenatal period, infancy (including toddlerhood), early childhood (preschool), middle childhood,

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Summary & Resources

adolescence, emerging adulthood, early adulthood, middle adulthood, and later adulthood.

• Only the prenatal period, which is determined by biology, is fixed. Other develop- mental periods are often socially defined and overlap.

• Emerging adulthood is not universally recognized and is a newer concept that applies mostly to wealthier individuals in industrialized countries.

• Later adulthood is sometimes divided into the young old, old-old, and very old.

Key Issues in the Study of Lifespan Development

• Most psychologists today believe that human development includes both continu- ous and discontinuous changes. Continuous development is defined as cumulative, incremental growth; discontinuous development is more stage-like.

• The study of nature and nurture generally focuses on their complementary, relative influences. Scientists understand that maturational and environmental influences are both involved in development and cannot be easily studied in isolation.

• Epigenetics focuses on how gene expression changes as a function of environment circumstances.

Contextual Factors in Lifespan Development

• Development is seen as a fluid, individual process that varies according to context, especially unique cultural and generational experiences. These factors include sex, gender, peer groups, race, ethnicity, culture, and socioeconomic status.

• Sex refers to a person’s biological makeup, whereas gender refers to behaviors that correspond with social expectations. Though there is often considerable overlap, the two factors have a strong individual influence on development.

• Peer groups can have a strong influence on a person’s developmental trajectory. They teach us about expected gender roles and behavior, provide a sense of belong- ingness, and help build a sense of identity.

• A person’s ethnicity includes characteristics that are immersed in culture, including differences in nationality, language, religion, values, and beliefs. Race and ethnicity are embedded in historical and personal circumstances, and as such contribute to individual and group identity.

• Socioeconomic status and the social and financial opportunities they represent have a stronger predictive role than race or ethnicity on health and development.

Critical Thinking and Discussion Questions

1. Baby boomers and other groups are identified in this chapter as normative history- graded influences. Recently, observations and research have led social psychologist Jean Twenge to characterize much of the millennial generation as “Generation Me” and “The Entitlement Generation.” Based on what you have learned and can discover through research, how do Twenge’s conceptualizations compare to other history- graded influences mentioned in the text?

2. Table 1.3 in this chapter shows that the prevalence of smoking is associated with level of education. Among adults with a GED, however, the prevalence of smokers is 41% (CDC, 2014e). As a preview to the research methods presented in Chapter 2, discuss some reasons why this figure seems out of place.

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Summary & Resources

3. Identify areas of development where the three domains strongly overlap. Identify one area in each domain where there appears to be minimal overlap.

4. Which of the guiding propositions of lifespan development do you think best explains your personal developmental experience? In what ways does this same approach also fail to explain your experience?

5. Provide one physical, one cognitive, and one psychosocial example of how both nature and nurture have contributed to your own development.

6. Explain how contextual factors have impacted your development.

Additional Resources Web Resources

• American Psychological Association (APA) http://www.apa.org/

• APA Division 7, Developmental Psychology http://www.apadivisions.org/division-7/index.aspx

• Dan Buettner’s Blue Zone, longevity research https://www.bluezones.com/about-blue-zones/

• Time magazine’s “Generation Me and the Millennials” by Joel Stein http://time.com/247/millennials-the-me-me-me-generation/

Further Research

• Arnett, J. J. (2000). Emerging adulthood: A theory of development from the late teens through the twenties. American Psychologist, 55(5), 469–480. Retrieved from http:// jeffreyarnett.com

• Belsky, D. W., Caspi, A., Jouts, R., Cohen, H. J., Corcoran, D. L., Danese, A., . . . Moffitt, T. E. (2015). Quantification of biological aging in young adults. Proceedings of the National Academy of Sciences of the United States of America. Advance online publica- tion. doi: 10.1073/pnas.1506264112 Retrieved from http://www.pnas.org/content /112/30/E4104.full

Key Terms

behavioral genetics The field of study that examines the role of genetics in species- specific behavior.

cognition Mental actions or processes, including thought, memory, and language.

cognitive development The domain of development that includes the study of changes in thinking, language, and intelligence.

continuous development The perspective that views development as a smooth, incre- mental process.

discontinuous development Distinct, stage-like developmental events that lack a smooth progression.

domains of development Three over- lapping categories of developmental changes, including physical, cognitive, and psychosocial.

epigenetics The study of gene expres- sion that arises due to contact with the environment.

ethnicity A person’s characteristics that are immersed in culture, nationality, language, religion, values, and beliefs.

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http://www.apa.org/

http://www.apadivisions.org/division-7/index.aspx

https://www.bluezones.com/about-blue-zones/

http://time.com/247/millennials-the-me-me-me-generation/

http://jeffreyarnett.com

http://www.pnas.org/content/112/30/E4104.full

Summary & Resources

gender Refers to how a person behaves according to norms for maleness/masculin- ity and femaleness/femininity.

historical embeddedness Proposition that says that age-related development is influ- enced by sociocultural conditions existing in a given historical period and how these conditions evolve over time.

lifespan development The study of human growth, stability, and change from concep- tion until death.

maturation The biological unfolding of growth over time.

multidisciplinary Tying together ideas from psychology, biology, sociology, anthro- pology, and other sciences.

nature and nurture The study of the rela- tive strength of both biological and environ- mental influences on development.

nonnormative influences Sources of developmental change that are unique to an individual.

normative age-graded influences Sources of developmental change based on biologi- cal, psychological, social, or cultural forces that are shared by most people of the same age.

normative history-graded influences Sources of developmental change that are associated with an entire group.

physical development The biologically driven changes evident with changes in height, weight, muscles, sexual development, brain mass, perceptual abilities (such as vision and hearing), and motor skills.

psychosocial development Changes that occur in identity development, personality, emotions, and socialization. Includes the way society and culture shape people and the way people shape society and culture.

race Usually refers to observable charac- teristics that have traditionally been used to distinguish one group from another, like skin color and hair texture.

sex Refers to a person being born with specific chromosomes, genitalia, and other physical characteristics that are categorized as male or female.

socioeconomic status (SES) The status and opportunities that are associated with income, education, and occupation.

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