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P A R T T W O

Biological Properties of Motivation

Does the makeup of the human body and mind determine what is motivating? In 1748, the Frenchman La Mettrie published his book Man a Machine, which introduced the idea that the human body is a machine. This machine, however, is different because it has self- awareness/consciousness. Chapter 3 (Evolutionary Antecedents of Motivation) examines how the machine progressed to its current form. The human body evolved because it be- came the best solution for problems of survival. As a result of evolution, humans possess motives and values that are geared toward survival. Motives and values include what we prefer for the beginning and the maintenance of interpersonal relationships, for what we fear, the foods we prefer, even the music we enjoy. These preferences emerge in conscious- ness as likes and dislikes, which motivate behaviors.

Hedonism motivates beneficial behavior, but can it also explain behavior that is detri- mental to a person? Chapter 4 (Addictions and Addictive Behaviors) assumes that pleasure is the reward provided by the natural environment for behaviors that benefit survival. How- ever, we have learned to enhance these pleasures by artificial means with psychoactive drugs like nicotine and alcohol and activities like gambling. Addictive behaviors are exam- ples of natural motivation gone awry. Pleasures designed to reward behaviors necessary for survival are now enjoyed for their own sake to the point of being detrimental to our health.

If the body is a machine, then what motivates a person to keep it in good condition? Chapter 5 (Homeostasis: Temperature, Thirst, Hunger, and Eating) states that sources inside and outside a person provide the motivation for the maintenance of the body. Internally, unpleasant feelings of hot or cold, thirst or hunger motivate behaviors to reduce those feel- ings. Externally, incentives like food, especially sweets and fats, and clothes for tempera- ture control also prompt motivation. The incentive value of food can be so strong, however, that people eat to obesity while others shun it to the point of emaciation (anorexia).

Is behavior always performed as efficiently as possible? Or does efficiency depend on the level of body arousal? Chapter 6 (Behavior, Arousal, and Affective Valence) exam- ines how the body’s degree of arousal determines the efficiency of behavior. Physiological arousal that is too low or too high is associated with poor performance; intermediate arousal is best. Arousal is also associated with the pleasantness of affect. Arousal is most pleasant

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at middle intensities; too little arousal is akin to boredom and too much arousal is distress- ing. Arousal comes from stimulus novelty, incongruity, and complexity as found in humor, music, and suspenseful films.

Finally, can the body as machine have too many demands placed on it? Chapter 7 (Stress, Coping, and Health) shows that if the demands for motivation are too many or too intense, then the machine does not fare well. It breaks down both physically by getting sick and psychologically by worry, anxiety, tension, and unhappiness. Appraisal, social support, and personality traits, however, can intervene between a demand and its potential negative impact. Also, a person can deal directly with the stressor through problem-focused coping or with the stress through emotion-focused coping.

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C H A P T E R

Evolutionary Antecedents of Motivation

Human nature is the same all over the world, but its operations are so varied by education and habit that one must see it in all its dresses in order to be entirely acquainted with it.

—Lord Chesterfield, 1747

Human action can be modified to some extent, but human nature cannot be changed.

—Abraham Lincoln, 1809–1865

■ In reading this chapter, keep the following questions in mind. They concern universal dispositions, which are characteristic of all people and which play a role in motivating certain behaviors.

1. What is human nature, and how does it relate to motivation and emotion?

2. Are there dispositions or universal motives that apply to all humans?

3. What are the evolutionary and social characteristics for mate preferences, reproductive behavior, and jealousy?

4. What is the contribution of evolution to fear?

5. How did food preferences evolve?

6. Why do people the world over enjoy music?

Evolution of Universal Motives Where in a person’s past is the motivational origin of his or her behavior? By way of anal- ogy, what caused the fall of the last domino pictured in Figure 3.1? Notice that some event must have toppled the first domino, which eventually led to the fall of the last one. Is the cause the domino prior to the last one or the one prior to it and so on back to the initial event? In the case of a person’s current behavior, is the motivation in the recent past like the fall of an immediately preceding domino or in the remote past like the very first domino? Now imagine a man and woman of average height dancing together. First, the man most likely is taller than the woman. This height difference reflects our evolutionary history, which is analogous to the fall of the early dominos. In addition, our imaginary couple is taller today than they would have been a century ago. This increased height is part of our personal history during which more nutritious food became available (Floud et al., 1990)

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FIGURE 3.1 A Metaphor for Evolutionary and Personal History. The toppling of the initial dominoes represents evolutionary history, which topple later dominoes that represent personal his- tory. The 10th or last domino represents motivated behavior in the present.

and is analogous to the fall of later dominos. In other words, the current height of men and women resulted from the interaction between our evolutionary and personal past. Al- though determined in the past, men and women’s current height has an effect on their current behaviors. For example, during conversation women might gaze slightly upward while men gaze downward, women pass more easily through small doorways while men must stoop, and women may need a stool to reach the top shelf that men can reach flat footed. In addition, compared to a century ago, today’s beds are longer, clothes are bigger, and doorways are higher all because of our increased height. Just as these differences in height affect certain behaviors, so too other unspecified characteristics affect behavior. For example, if the couple were ballroom dancing, then the man would lead and the woman would follow.

The purpose of this section is to describe how our evolutionary history and our per- sonal history interact to affect motivation and emotion. There will be an emphasis on the uniformity of certain motives despite the variety of environmental and cultural situations in which people live.

Evolutionary History and Personal History Just as human evolutionary history has shaped the difference in height between men and women, it has also shaped psychological characteristics that determine what does and does not motivate people.

Evolutionary history as a source of motivation focuses on what behaviors humans have in common in spite of vast social and cultural differences. For instance, all humans have brains and faces, but each brain and face is different. All humans are motivated by incentives, but the same incentive does not motivate everyone. All humans laugh and cry, but what triggers these behaviors may differ among humans. Human nature refers to the behavioral, motivational, and emotional similarity among people that results from their common evolutionary history. It is their disposition to behave in a particular fashion,

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Environment

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FIGURE 3.2 Relative Contributions of Heredity and Environment. Length and width both contribute to the area of a rectangle, since Area = Length × Width. The relative contribution of length decreases, and width increases from a to d, yet both length and width still contribute to the total area of each rectangle. Similarly, heredity and environment both contribute to the motivation of behavior. The relative contribution of heredity decreases and that of environment increases from a to d, yet both heredity and environment still contribute to the motivation of behavior.

depending on the situation. Human nature is most striking when similarities occur in spite of environmental and cultural differences. It is shaped by natural selection and is geneti- cally transmitted from one generation to the next. It is universal, which means it is the same in societies all over the world. Finally, the behavioral expression of human nature tends to be innate—that is, it is influenced little by experience. The term universal motives will be reserved for the commonality of motives among humans that has evolved over their evolu- tionary history. For example, this term refers to the commonality in what motivates sexual behavior, fear, food preferences, and music enjoyment.

Evolutionary and Personal History Interact. Evolutionary history created human nature, which in turn interacts with our personal history much like the fall of later domi- noes depend on the fall of earlier ones (Figure 3.1). The interaction between evolution- ary history and personal history is another way of stating that the interaction between heredity (nature) and environment (nurture) motivates behavior. The nature of this inter- action was recognized more than 125 years ago by Sir Francis Galton (1883). He claimed that it was difficult to distinguish between that part of human character that results from education and circumstances and that which results from the human constitution. Today, it is accepted that both heredity and environment interact to determine behavior (Plomin et al., 2001).

The relative contribution of heredity and environment is different for various be- haviors. Some behaviors are genetically disposed to occur and thus require little envi- ronmental experience. Other behaviors are genetically neutral and require much environmental experience to occur. For instance, learning to eat is almost automatic, whereas it takes a lot of practice to master long division. The interaction between hered- ity and environment in motivating behavior is illustrated in Figure 3.2 by a series of rectangles (Plomin et al., 2001). A rectangle’s length and width both contribute to its area, since Area = Length × Width, although the relative contribution of each may vary. Simi- larly, heredity and environment both contribute to behavior, but their relative contributions may also vary. Changes in the contribution of heredity and environment are illustrated by

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rectangles a through d in Figure 3.2: the contribution of length (heredity) decreases, and the contribution of width (environment) increases. Although the change from rectangle a to rectangle d represents a decrease in heredity and an increase in environment, both heredity and environment contribute to behavior. Behaviors that are strongly influenced by heredity (rectangle a) are known as innate, which means not taught or not benefitting from experience.

It is important to remember, however, that heredity can influence behavior in more than one way. First, inherited physical features affect a person’s behavior, such as the rela- tionship between the thumb and fingers. How difficult would it be to write, tie a ribbon, or grasp a ball without the use of either a thumb or fingers? Or consider how size and strength differences between men and women contribute to a general division of labor. Men, on average, are bigger and physically stronger and so tend to do heavy work, such as farming, mining, and construction. Women, on average, are smaller and have less muscle mass and so tend to do lighter work, such as cooking and clerical tasks. Second, the hereditary nature, or innateness, of certain feelings or motives disposes humans to react in one way rather than another to various stimuli. The influence of these seemingly innate feelings becomes ap- parent in the prevalence of sexual behavior, certain fears, a baby’s taste preferences, and the universal pleasure of music.

Experience and Motives. As the rectangles in Figure 3.2 illustrate, even behaviors that appear to be totally innate may actually require at least some minimal environmental ex- perience in order to occur (rectangle a). Other behaviors require the benefit of additional experiences (rectangles b through d). To illustrate, we might think of walking as being in- nate, but some prior experience in sitting upright and crawling appears necessary for walking to occur in a timely manner (Dennis, 1960). Other examples of behaviors that occur with little experience are an infant’s crying to indicate hunger or distress. This behavior is fairly complete immediately following birth. As new parents quickly learn, their baby requires little if any practice at this activity. Facial reactions to taste stimuli also seem to be in place in the first few hours of an infant’s life. Little practice, if any, is needed to indicate whether something is tasty or awful (Menella & Beauchamp, 1998; Steiner, 1977).

Finally, an individual’s innate disposition and personal experience usually operate in tandem, which happens for example in the development of gender roles. Thus, infants iden- tified as girls and boys are nurtured along feminine and masculine roles, respectively.

Evolutionary Psychology Human minds are not blank slates at birth upon which experience begins to write. Neither are minds passive recipients of experience. Instead, human minds have been shaped by evolution to adapt to their environment. Our evolutionary past interacts with people’s experiences to determine current motivation. This interaction is the view of evolutionary psychology, which analyzes universal motives in the context of evolution. According to evolutionary psychol- ogy, psychological mechanisms have evolved through natural selection to solve specific problems of adaptation to the environment (Buss, 1995, 1999, 2005). Several of these psy- chological mechanisms are represented by universal motives. Fear of snakes, for instance, evolved to motivate behavior to escape or avoid such dangerous creatures. Food preferences

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TABLE 3.1 Categories of Universal Motives

Universal Motive/Incentive Characteristics

Aesthetics: art, hygiene, music, standards of beauty

Control environment: fire, mood altering substances, shelter, tools

Emotions: anger, contempt, disgust, fear, happy, sad, surprise

Facial expressions: for emotions, for communication, and are modifiable

Fears: loud noises, snakes, strangers in childhood

Goal setting: predict and plan for the future

Self-concept: self as subject, object, and different from other person

Sexual interactions: attraction, sexual jealousy, and regulation

Social milieu: live in social units, rights, obligations of membership, and status

Source: Based on Human Universals by D. E. Brown, 1991, Chapter 6.

for sugar and fat evolved to ensure a person liked food that provided sufficient calories. Women evolved a preference for mates who had the economic resources to provide for them and their children. Male attraction to beauty and desire for sexual variety evolved to ensure the selection of fertile mates and to motivate the seeking of more sexual partners. The func- tion of male sexual jealousy developed to increase a man’s confidence regarding the pater- nity of his children. Each human motive can be considered an instance of a psychological mechanism that evolved because it aided humans in adapting to their environment.

➣ To learn more about evolutionary psychology go to http://www.psych.ucsb.edu/research/cep/

Universal Motives. For a motive to be considered universal it must occur in all countries and cultures of the world even though it might be expressed differently. Different geographical regions, climates, societies, cultures, and customs exist around the world. These differences produce differences in the foods people eat, in social customs, and in educational practices. In spite of these geographical, climatic, and societal differences, uni- versal motivation and behavior are presumably the same for food, custom, and learning. The existence of universal needs or motives was noted by the anthropologist Bronislaw Malinowski (1941), who derived a list of basic needs that he believed existed in societies all around the world. The existence of these needs pushed cultures into ways of satisfying them, although the manner by which this was accomplished varied from culture to culture. Thus, the need for food was satisfied by hunting, gathering, and today a sophisticated system of farm- ing, ranching, and the commerce of bringing food to market. Other bodily needs such as sex, physical comfort, and safety resulted in marriage, shelter, health practices, and systems of laws and justice.

Brown (1991) uses the term universals to describe traits that are found in almost all cultures and societies the world over. Some items in his list can be categorized together for their relevance to universal motives and universally valued incentives (see Table 3.1). Emotional behaviors seem to predominate the list as reflected by the presence of fears, emo- tions, and their accompanying facial expressions. The social nature of human motives is

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exhibited in categories of sexual interactions and the social milieu. Universals with external characteristics express themselves in terms of controlling the environment and setting goals, which contribute to the prevention and alleviation of stress. Universals that seem more removed from human biology are beliefs about aesthetics and concepts about the self. The universal motive categories in Table 3.1 are taken for granted. We forget that entire institu- tions and customs have developed in order to satisfy these motives or attain these valued incentives in today’s societies.

Inherited Structures for Behavior, Motives, and Emotions. How can universal motives, such as fear or food preferences, evolve and pass on to succeeding generations? They do so by way of natural selection (see Chapter 2), which operates at the level of the individual. In turn, an individual’s genes transmit universal motives to the next generation (Mayr, 2001). Genes are those parts of a person’s DNA content that provide the informa- tion necessary for the construction of proteins, which form the building blocks of the var- ious neurophysiological structures that make up the brain and nervous system. Humans receive one-half of their genes from each parent at conception. At this time the sperm con- taining the male’s genetic information unites with the ovum (egg), which contains the female’s genetic information. The resulting combination contains information from each parent, which in turn came from their parents, and so on. Our genes or our genetic past do not influence motivation or behavior directly. Genes provide the information for the build- ing of proteins that are used to create “the skeletal system, muscles, the endocrine system, the immune system, the digestive system, and most important for behavior, the nervous system” (Plomin et al., 2001, p. 47). To say that genes or heredity influence behavior is re- ally a shorthand way of stating that genes are the recipes for various proteins, which in turn produce neurophysiological systems that determine the particular reaction to environmen- tal stimulation (Plomin et al., 2001). Thus, the seeming genetic inheritance of motives or psychological mechanisms simply means that the brain or body appears sensitive to the stimuli evoking or satisfying those motives. For example, different neurons in the tongue and brain react to sweet and bitter stimuli such that infants prefer sweet taste. Genes carry the information for how the tongue’s neurons and the brain’s structure are constructed. At a more global level, however, it appears that variation and selection occur at the level of behavior. After all, behavioral and environmental events are visible, while genes are not; only their end results are visible.

Section Recap The motivation for current behavior has its roots in our evolutionary and personal history. Evolutionary history refers to a person’s genetic makeup or nature, and personal history is the person’s experiences or nurture. Both nature and nurture contribute to what motivates behavior just as length and width both contribute to the area of a rectangle. Usually ten- dencies that are part of human nature operate in tandem with personal experiences as in the development of gender roles. Evolutionary history created human nature, which encom- passes all the behavioral, motivational, and emotional characteristics that all people have in common despite different environmental and cultural differences. Evolutionary psy- chology supposes that part of human nature consists of psychological mechanisms, which have evolved to solve problems of adaptation to the environment. Universal motives are psychological mechanisms that refer to similarities in what motivates people, such as a set

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of basic needs, valued incentives, and social interactions. Societies developed in order to satisfy universals, which are traits found the world over such as fears, emotions, facial ex- pressions, environmental control, goal setting, and beliefs about aesthetics and the self.

Genes are DNA segments that provide information from each parent on how to build the child’s neurophysiological structures. These structures, in turn, are the physical basis for psychological mechanisms or universal motives that, according to evolutionary psychology, evolved to meet environmental problems that humans faced in their evolutionary past.

Universal Motives of Sex, Fear, Food, and Music Much like early dominoes caused the fall of the final domino, natural selection operating in the evolutionary past caused the development of psychological mechanisms and univer- sal motives. These universal motives in turn are satisfied in the current environment. This section examines four major categories of evolved universal motives. One is the motive for sexual behavior in the context of short- and long-term relationships. A second is the mo- tive to prefer certain basic foods and reject others. A third motive concerns the survival value of fear and the stimuli that humans avoid as a consequence. Finally, there is the puz- zle of music. Why do people the world over enjoy music? These motives from our evolu- tionary past push individuals to seek satisfaction, which is achieved in their environment.

Selecting a Mate “They stroke, kiss, nip, nuzzle, pat, tap, lick, tug, or playfully chase this chosen one. Some sing. Some whinny. Some squeak, croak, or bark. Some dance. Some strut. Some preen. Some chase. Most play” (Fisher, 2004, p. 27). In her book Why We Love, Fisher gives many behavioral examples of various animals engaging in behaviors that we can anthropomor- phize as romantic love. In addition to this love play, animals, like humans, exhibit a choosi- ness and do not mate indiscriminately with members of the other sex. A further similarity is that animals, like humans, appear possessive and guard their mates closely as if they are motivated by jealousy. This section examines what factors determine mate choice in humans and how jealousy affects human relationships.

The point of natural selection is to ensure survival and longevity. However, living a long time because of natural selection may benefit an individual but may not benefit the species. For a species to receive the benefits of natural selection, adaptive traits must be passed on to succeeding generations. This requires short- and long-term cooperation between men and women. Short-term cooperation is required for sexual intercourse that leads to conception, and long-term cooperation is necessary for care of any infants. Conse- quently, a major area of interest in evolutionary psychology concerns the establishment and maintenance of human relationships. In terms of pull motivation, what characteristics do men and women look for or select in the other sex to establish a relationship and what do they look for or select to maintain that relationship?

Darwin (1859/1936) used the term sexual selection to refer to the “struggle between males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring” (p. 88). The male could be very aggressive and fight off all other males, thereby having a harem of females all to himself. However, if he could not be the most aggressive then maybe he could be the most charming and attract the most females in that manner. In such cases, the female acts as the selecting agent because it is what she likes

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TABLE 3.2 Mate Value Inventory

Describe yourself as accurately as possible on the traits listed below. Use the following scale:

extremely low on this trait = �3 �2 �1 0 �1 �2 �3 � extremely high on this trait

Ambitious ______ Faithful to partner ______ Kind & understanding ______

Attractive face ______ Financially secure ______ Loyal ______

Attractive body ______ Good sense of humor ______ Responsible ______

Desire for children ______ Generous ______ Shares my values ______

Emotionally stable ______ Healthy ______ Shares my interests ______

Enthusiastic about sex ______ Independent ______ Sociable ______

Note: To compute your mate value, sum your scores on all of the items. The total score reflects the amount of a person’s mate value.

Source: Adapted from “Self, Friends, and Lovers: Structural Relations among Beck Depression Inventory Scores and Perceived Mate Values” by B. R. Kirsner et al., 2003, Journal of Affective Disorders, 75, pp. 135, 147.

about the male that determines whether she allows him to mate with her. For example, the number of copulations performed by a peacock correlates positively with the number of eyespots he has on his train of tail feathers. The greater the number of eyespots, the more likely a peahen is to consent to copulation (Petrie et al., 1991).

➣ Pictures of a peacock’s tail feather display to a peahen are at http://www.pbase.com/ lesliej/peafowl

Mate Value. The possession of characteristics that are desired by the other sex defines a person’s mate value. The higher your mate value, the greater your appeal. The Mate Value Inventory in Table 3.2 is one way to measure one’s self-perceived physical attractiveness and psychological characteristics that may be valued by the other sex (Kirsner et al., 2003). No- tice that a person’s mate value consists of physical features, psychological characteristics, and a value system. Physical features are immediately noticeable in a person but fade with time and are ones to which the other person habituates. Psychological characteristics, how- ever, take time to discover and are less likely to fade. Finally, when interests and values are shared, it increases people’s attraction to each other.

Facial attractiveness is one physical indicator of mate value in Table 3.2 that is of great interest to evolutionary psychologists (Rhodes, 2006). What makes a face attractive to the other sex? One feature is that a more attractive face is more symmetrical, which means the right and left half of a face match up. Another feature is that an attractive face also represents the average of many facial configurations that occur in the population. It is a face that has average lip, eye, and nose size, for example. A final feature that contributes to facial attractiveness is sexual dimorphism, which refers to differences in the form or structure between men and women. More attractive male faces show greater masculinity and more attractive female faces show greater femininity (Rhodes, 2006).

If facial and physical attractiveness are determinants of mate value, then one obvious question is whether increases in attractiveness do indeed increase one’s chances of attracting a mate. Rhodes and coresearchers (2005) investigated this question in an Australian sample of men and women. As a measure of success in attracting a mate, the researchers asked the

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individuals to report their number of sexual partners, age of first intercourse, and the length of each relationship. The photos of the participants were rated for attractiveness, sexual di- morphism, averageness, and symmetry by a separate group of people. Do these indicators of physical attractiveness correlate with sexual experience? The results showed that they did. Individuals with higher physical mate values had more relationship experiences. Men with attractive faces and attractive and masculine bodies had more sexual partners and also became sexually active at an earlier age. Women with attractive faces became sexually active at an earlier age and had more relationships that exceeded 12 months. The results provide some evidence that as one’s mate value increases, the likelihood of attracting others also increases.

➣ Research on attractiveness can be found at http://www.beautycheck.de/english

Good Genes Hypothesis. It is probably safe to state that both women and men prefer at- tractive partners. But what is the reason for this preference? One answer is that attractive- ness is a universally valued incentive that arose during our evolutionary past as a result of sexual selection. The member of the other sex selects an attractive individual based on the assumption that attractiveness signals genes for health, fertility, and intelligence according to the good genes hypothesis. A person with an attractive face presumably has genes for high intelligence, health, a good immune system, and for potentially good parenting skills (Rhodes, 2006). Consequently, if a person selects an attractive long-term mate, then they will produce more offspring, who are more intelligent, healthy, and have the benefit of good parents. Their children would have an increased chance of survival. However, evidence that attractiveness signals health, for example, has been difficult to establish partly because modern medicine and grooming practices obscure a person’s attractiveness and hence any relationship with health (Weeden & Sabini, 2005).

An inverse to the good genes hypothesis is that individuals reject those people whose physical appearance suggests the possibility of bad genes—that is, genes that signal poten- tial disease and low intelligence (Zebrowitz & Rhodes, 2004). The emphasis is on rejecting people, not attracting them. Zebrowitz and Rhodes (2004) tested this hypothesis with lon- gitudinal data from individuals for whom facial photos, intelligence test scores, and health indicators were available at ages 10, 11–15, 17, and 30–40 years. The photos were rated for facial quality, such as attractiveness, symmetry, averageness, and sexual dimorphism. The individuals were also judged for intelligence and health on the basis of their photos. In order to examine whether people with unattractive faces are rejected, the researchers divided the photos at the median based on attractiveness. Individuals categorized below the median were judged as less attractive at all ages, had less facial symmetry, and male faces showed less masculinity. The researchers reasoned that if facial attractiveness correlates with health and intelligence, it is likely to be exhibited in faces below the median. In other words, to be selected as a mate one must possess a face with a minimal level of attractiveness, which would indicate some minimal level of health and intelligence. The results showed a positive correlation between facial attractiveness, intelligence, and health, but only for individuals whose faces were below the median. For these faces, as rated attractiveness decreased, judg- ments of the individuals’ health and intelligence decreased correspondingly. This relation- ship was also true when actual indicators of health and intelligence were used: faces with lower attractiveness were associated with poorer health and lower intelligence. Thus,

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according to the bad genes hypothesis, people avoid mating with individuals who have extremely poor physical appearance or low facial attractiveness. In regard to sexual selection, it is not that people are pulled toward a face with high mate value but instead are repelled by one with poor mate value—that is, one that signals poor health and low intelligence.

Universality of Beauty and Health. Facial attractiveness evolved through sexual selec- tion. Consequently, the basis of attractiveness and its relationship to health is assumed to be universal and not culturally specific. This claim is based on research that has resulted in sev- eral convincing conclusions (Langlois et al., 2000). First, people agree on who is beautiful and who is not within their culture. Second, people agree on the standards of beauty for faces in cultures other than their own. Third, people agree on the degree of attractiveness among chil- dren. Presumably, then, the association between an evolved set of features and physical health or intelligence should be similar everywhere. For example, a runny nose and watery eyes that are linked to a cold would be assumed to be unattractive compared to the same face when a person does not have a cold. However, there may be instances of cultural standards of beauty that are not linked to health. For example, thinness in women is associated with beauty and health, although extreme thinness is associated with poor health (Weeden & Sabini, 2005).

Sex Differences in Long-Term Mate Selection. Once mates are selected and relation- ships are formed, then the birth of offspring and parenthood is frequently the next step. Thus, other aspects of mate value besides physical beauty are important for relationships. These aspects are important because evolutionary success is based on leaving the most number of surviving offspring. Furthermore, the biological differences between men and women determine what mate values are important. What are these differences?

First, men and women differ in the time investment they make in their offspring (D. M. Buss, 1989). After sexual intercourse, a woman invests an additional 38 weeks as the baby develops so that at birth the woman already has invested much more time in the child than the man. In addition, since she can produce many fewer children than a man, it is more important that a woman help each child that is born to survive; by doing so, she increases her reproductive success. Since a man is capable of having innumerable children, he may not in- vest as heavily in each individual child as a woman would. He increases his reproductive suc- cess by having intercourse with as many women as possible, thereby conceiving many children. Thus, the strategies a woman employs to ensure the survival of her children and hence the perpetuation of her genes is different than the strategies a man employs for the per- petuation of his genes. Consequently, we would expect a woman to look for characteristics in a man that indicate greater commitment and help in raising children. Men should prefer characteristics related to reproductive value, such as a woman’s physical health and youth. In mating with a fertile woman a man can maximize his reproductive success by having many children with her (D. M. Buss, 1989).

This difference in what men and women value in long-term mates is assumed to have universal appeal and has led evolutionary psychologists to concentrate on three mate-value characteristics: good financial prospect, ambition and industriousness, and good looks (D. M. Buss, 1989). If differences in sexual preferences among men and women are uni- versal, then ratings of these characteristics should differ in societies all over the world. This is exactly what D. M. Buss (1989) attempted to show by surveying men and women in 37 different countries. Figure 3.3 shows the results of six different countries: Japan, India,

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Importance or Desirability

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Ambition and industriousness

Good looks

Women's ratings

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FIGURE 3.3 Preferences for Mate Characteristics. Top: The importance of good financial prospects in a long-term mate was rated more important by women than by men. Middle: The im- portance of ambition and industriousness in a long-term mate was rated more important by women than by men. Bottom: The importance of good looks in a long-term mate was rated more impor- tant by men than by women. There is no significant difference regarding the importance of good looks between men and women sampled in India.

Source: Adapted from “Sex Differences in Human Mate Preferences” by D. M. Buss, 1989, Behavioral and Brain Sciences, 12, table 2, p. 6 (top); table 3, p. 7 (middle); table 5, p. 10 (bottom).

Nigeria, Germany, Brazil, and the United States. These countries were selected for display because they seem culturally diverse.

Figure 3.3 (top) shows that in all countries women rate “good financial prospect” as more important in a mate than men rate it. Figure 3.3 (middle) shows that women rate “ambition and industriousness” more important than men rate them. These characteristics are good ones for a woman to look for if she expects her mate to be mature enough to com- mit to the relationship and to be a good provider of material things necessary for family life. Figure 3.3 (bottom) shows that men rate “good looks” to be more important than women consider them when searching for a long-term mate. If young age and good looks are con- sidered signs of health and fertility, then men consider these important because they imply that the woman is capable of producing many children.

Maintaining Relationships Once a relationship is established, then what motivates processes that promote conception and maintenance of the relationship? This section examines the function of sexual pleasure and jealousy in these matters.

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Function of Sexual Pleasure. What motivates sexual intercourse, which is necessary for conception? It is as a result of intercourse that the male sperm unites with the female egg, which may eventually lead to conception and eventually the birth of a baby. However, animals or people might well consider sexual intercourse as requiring too much effort or time or as being too dangerous if there were not some kind of immediate reward. Orgasm is that reward; it is the incentive and reinforcer for sexual intercourse (Gould, 1987). For males, the pleasure of orgasm is usually always associated with ejaculation, at which time semen and sperm are expelled from the penis. Even though men may achieve orgasm close to 100% of the time during sexual intercourse, women experience orgasm much less frequently. In a summary of 32 published reports, Lloyd (2005, p. 36) concludes that as a result of sexual intercourse 25% of women always have orgasm, 55% have it more than half the time, 23% sometimes do, 33% rarely or never do, and 5–10% never do. Thus, although men are reinforced consistently for sexual intercourse, the reward for women is inconsistent, which may be the reason why the value of orgasm for women has been pondered more extensively (Lloyd, 2005; Symons, 1979). Several interpretations have been proposed to account for female orgasm.

One interpretation is based on a functional view of evolution, which holds that all body parts must be accounted for in terms of their survival value. This view encounters difficulty in explaining, for example, why men have nipples, which have no function. Another view, how- ever, is that not all body parts have survival value and are merely by-products of the evolution of some other part. In this view, male nipples might be considered the by-products of the evo- lution of female nipples, which are necessary for nursing children (Gould, 1987). Following this way of thinking, natural selection resulted in the development of the penis as the organ for sexual intercourse and orgasm. Although orgasm is highly pleasurable for women, the clitoris is not the result of natural selection but is instead an evolutionary by-product of the develop- ment of the penis (Gould, 1987). In other words, while the penis has an adaptive function, the clitoris does not. According to Gould (1987), the clitoris and penis developed out of the same homologous anatomical structure. At the tenth week of fetal development, for example, the cli- toris and penis look very much alike (Van De Graaff, 1988). Eventually, the penis becomes larger and capable of consistently producing orgasm as a reward for ejaculation, while the clitoris remains a nonadaptive by-product of the development of the penis.

Not everyone accepts this view, of course, and several interpretations have been pro- posed to account for the clitoris and female orgasm. One such interpretation is that female orgasm is very important because it helps promote pregnancy. Since orgasm is pleasurable, it encourages a woman to seek sexual intercourse, especially with a man who can help her achieve it, thereby increasing the chances of pregnancy (Alcock, 1987; Fisher, 1992; Levin, 1992). A woman’s orgasm signals her satisfaction to a man, thereby assuring him that she is less likely to seek sexual intercourse with another man (Fisher, 1992; Rancour-Laferriere, 1983). This information increases his confidence that he is the father of any children. Much like a big meal, orgasm also has a satiating effect in that a woman remains calm and in a prone position, which may also increase her chances of conception (Fisher, 1992). Finally, the mechanical action of orgasm itself may increase the likelihood of pregnancy by pro- moting the transfer of sperm from the vagina into the uterus. The timing of orgasm is also important, as discovered by Baker and Bellis (1993). They found that a woman retained the most sperm when she climaxed any time between one minute before the man ejaculated and up to 45 minutes afterward. The lack of orgasm or one that occurred more than one minute before the man ejaculated resulted in a much lower level of sperm retention.

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Even though women might not attain orgasm during sexual intercourse, they still en- joy it because it provides excitement and feelings of intimacy and closeness with their male partners (Lloyd, 2005). Thus, another interpretation for the pleasure of sex is that it is asso- ciated with the development of a relatively strong lasting relationship or pair bond (Symons, 1979). This relationship is important, because by remaining together the couple can jointly raise any children that result and thus increase the chances of the children’s survival. A cou- ple that parts soon after sexual intercourse will greatly decrease the likelihood of any child from that union surviving. Feelings of sexual arousal and orgasm contribute to pair bond- ing and the accompanying emotion of romantic love. This emotion is characterized by intense attraction to another person, often involving strong sexual desires. Jankowiak and Fischer (1992) consulted ethnographic files of 166 societies from around the world. In 88.5% of these societies they were able to document the occurrence of romantic love, implying that this emotion is universal among humans.

Romantic love and sexual desire are strongly associated in the minds of women and men (Regan & Berscheid, 1999). The presence of one feeling corresponds to the presence of the other. For example, Regan and coresearchers (1998) had men and women univer- sity students list those features that they felt defined romantic love. The second-highest- ranked feature of romantic love was sexual desire, which was listed by almost 66% of the respondents. To expand on this connection, Regan (2000) asked 25 heterosexual dating couples to rate the amount of sexual desire and passionate love they felt for their partners. Partners were also asked how frequently in the past week they thought of ending their re- lationships, starting new ones, or had actually cheated (infidelity). Analyses of the rat- ings indicated that those individuals who felt the greatest amount of sexual desire for their partners also disclosed the most passionate love. In addition, these individuals were also less likely to have thoughts of ending their relationships, starting new ones, or having cheated. In conclusion, orgasm has been naturally selected as the reinforcer for sexual in- tercourse, at least in men, and increases the chances of pregnancy in women. It also pro- motes the development of pair bonds and, along with sexual desire, enhances the development of romantic love.

Guarding Relationships. However, a relationship can end as a result of external factors. It can end through death but also from desertion, especially when someone has stolen one’s part- ner. Mate poaching refers to the attempt to attract someone who is already in a romantic rela- tionship in order to form either a short-term or long-term relationship with the poached individual (Schmitt et al., 2004). Mate poaching occurs worldwide based on a survey of nearly 17,000 mostly college students from North and South America; Western, Eastern, and South- ern Europe; the Middle East; Africa; Oceania; and South, Southeast, and East Asia. In the survey, nearly 60% of men and 40% of women have reported attempts at poaching. In addition, men are more likely than women to succumb to the temptations of short-term poaching. Thus, individuals who are currently in a romantic relationship need to be on guard for potential poach- ers. Perhaps the necessity for a guard against poachers was the evolutionary reason for jealousy.

Jealousy. Known as the “green eyed monster” (Shakespeare’s Othello), jealousy is a negative emotion triggered by an actual or suspected loss of a mate’s sexual services or a mate’s affection. These two losses produce different degrees of jealousy in men and women because of the biological fact that a woman is always certain of her maternity but a man is less certain of his paternity. According to evolutionary psychology, the reproductive

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strategies for men require knowing that they fathered the children they are helping to raise. Hence, a man is worried about any sexual infidelity on the part of his mate. If she was sex- ually unfaithful, then he is in doubt about his paternity of the children; they may not be car- rying his genes. Since a woman obviously knows that her baby is carrying her genes, her major reproductive concern lies in successfully raising it. Hence, a woman is worried about any emotional infidelity on the part of her mate. To illustrate the differences between jeal- ousy in men and women, imagine being asked some questions regarding the person with whom you are in love or with whom you are in a committed romantic relationship. One day you discover that your partner has become interested in another person. Which of the fol- lowing statements from each pair would upset you more—that is, evoke the most jealousy?

Emotional infidelity: “Imagining your partner forming a deep emotional attachment to that person.”

Sexual infidelity: “Imagining your partner enjoying passionate sexual intercourse with that other person.”

Sexual infidelity: “Imagining your partner trying different sexual positions with that other person.”

Emotional infidelity: “Imagining your partner falling in love with that other person.” (Buss et al., 1992, p. 252; Buunk et al., 1996, p. 360)

Both pairs of statements contrast sexual infidelity with emotional infidelity. The pre- diction, based on evolutionary psychology, is that men should be more distressed regarding sexual infidelity. In these situations a man would be more uncertain of being the father and thus may be supporting children that are not carrying his genes. Women, however, should consider the emotional infidelity scenario to be more distressing. It represents the possibil- ity of losing her mate’s parental investment, protection, and commitment. When these ques- tions were asked of male and female students, the results showed that men consider imagining sexual infidelity to be more distressing, whereas women consider imagining emotional infidelity to be more distressing (Buss et al., 1992).

To demonstrate the universality of these findings, Buunk and associates (1996) pre- sented these choices between sexual and emotional infidelity in three different countries: the United States, Germany, and the Netherlands. The results, presented in Figure 3.4a, clearly show that in all three countries men are more distressed when they suspect their part- ners of sexual infidelity rather than emotional infidelity. Women, in contrast, are much more distressed by emotional infidelity (Buunk et al., 1996). These findings regarding sex differences in jealousy have been replicated in three other countries. Researchers asked uni- versity students in Korea and Japan (Buss et al., 1999) and in Sweden (Wiederman & Kendall, 1999) whether emotional or sexual infidelity was more distressing. The results in Figure 3.4b again show that for men, in all three countries, sexual infidelity was more distressing than emotional infidelity while for women, in all three countries, the reverse was true.

Biosocial Theory Remember that behavior depends on both nature (heredity) and nurture (environment) like the area of a rectangle depends on length and width. The discussion of sexual relationships

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FIGURE 3.4a Sexual versus Emotional Infidelity. Percentage of subjects reporting that they would be more distressed by imagining their partner enjoying passionate sexual intercourse with another person than by imagining their partner forming a deep emotional attachment to that per- son. Results are shown separately for men and women from the United States, Germany, and the Netherlands.

Source: From “Sex Differences in Jealousy in Evolutionary and Cultural Perspective: Tests from the Netherlands, Germany, and the United States” by B. P. Buunk et al., 1996, Psychological Science, 7, figure 1, p. 361. Copyright 1996 by Blackwell Publishers. Reprinted by permission.

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FIGURE 3.4b Sexual versus Emotional Infidelity. The percentage of students who reported more distress from imagining their partner enjoying passionate sexual intercourse with another per- son than by imagining their partner forming a deep emotional attachment to that person. Results are shown separately for men and women from Sweden, Korea, and Japan.

Source: Adapted from “Evolution, Sex, and Jealousy: Investigation with a Sample from Sweden” by M. W. Wiederman & E. Kendall, 1999, Evolution and Human Behavior, 20, p. 127. And from “Jealousy and the Nature of Beliefs About Infidelity: Tests of Competing Hypotheses About Sex Differences in the United States, Korea, and Japan” by D. M. Buss et al., 1999, Personal Relationships, 6, pp. 139, 141.

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has emphasized the nature part—that is, how our human evolutionary past determines current sexual relationships. However some psychologists maintain that we are emphasizing our evolutionary past too much. Instead, more emphasis should be given to a person’s cur- rent environment in the formation of sexual relationships (Eagly & Wood, 1999; Wood & Eagly, 2002). Biosocial theory stresses the interaction between social experiences and the evolved sex differences of strength and reproductive capacity. This interaction helps explain gender differences in long-term mate preferences and jealousy. What is important in bioso- cial theory is that men are physically bigger and stronger and that women can bear and nurse children. What is not relevant in this theory are the evolved psychological mechanisms that are postulated by evolutionary psychology. According to Wood and Eagly (2002; Eagly & Wood, 1999), the biological sex differences in strength and in reproductive capacity inter- act with societal expectations that men should have greater power and status while women should accommodate to a lesser role. One consequence is that in adjusting to these expec- tations, men become providers and heads of households, while women become homemak- ers, cooks, and primary child-rearers. Thus, the biological differences between men and women contribute to the increase in psychological differences, because each sex tries to adjust to their expected social roles. According to biosocial theory, this adjustment is based on the cost-benefit analysis that typical sex roles provide greater satisfaction with lesser ef- fort than would nontypical sex roles. Thus, it is less costly and more beneficial for men to enter male-dominated occupations like construction worker, farmer, and warrior and for women to enter female-dominated occupations like office manager, nurse, and child-care worker. However, the bulk of professions in our society may be staffed equally well by both sexes. Furthermore, although male and female genetic dispositions remain constant, soci- ety’s views are changing. As a consequence, men and women may begin to enter profes- sions that have been dominated by the other sex.

The evolutionary psychology explanation of why women prefer industrious men has also been challenged on the basis of biosocial theory and how society affects the earning power of men and women (D. M. Buss, 1989; Caporael, 1989; Tattersall, 1998; Wiederman & Allgeier, 1992). According to the structural powerless hypothesis, both men and women want the same financial resources. However, since women are relatively powerless to achieve these in the working world, they do so in one of the ways available—that is, by marrying men who have these resources. If this is the case, reasoned Wiederman and Allgeier (1992), then as women earn more money, the prospect of a man’s financial prospects should become less important to them. However, based on a sample of working women, the researchers found no relationship between how much money women personally earned and the importance to them of good financial prospects in a prospective mate. In other words, all women regardless of their income wanted a long-term mate who had good financial prospects. Eagly and Wood (1999) have challenged these results by reexamining some of the data from D. M. Buss’s (1989) original survey of 37 countries. Do men’s preferences for good housekeepers and cooks and women’s preferences regarding earning potential depend on the degree of inequality in power and earnings between the sexes? Using various indi- cators, Eagly and Wood found that as gender equality increases, differences in preference decrease. For example, in countries with greater equality, men’s preference for mates with good housekeeping and cooking skills decreases and women’s emphasis on a spouse’s income potential decreases.

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Fear as a Universal Motive Fear is an excellent example of a universal motive that evolved to push individuals to avoid and escape dangerous stimuli. Fear springs from the interaction between evolutionary his- tory and personal history with dangerous stimuli. Evidence for the evolution of fear comes from the observation that it is a universal emotion experienced by people in every country (Hupka et al., 1999; Scherer, 1997). In addition, fear can occur spontaneously to a seem- ingly dangerous event with prior experience (Marks, 1987). Fear is also conditionable, which means it can result from experience but only for some stimuli.

Occurrence of Fears. “What do you fear most?” (Muris et al., 1997, p. 929). In response to the question, 9- to 13-year-old Dutch children responded with a number of fears, the top 10 of which are listed in Figure 3.5. These fears ranged from being burglarized to encoun- tering spiders. When 11- to 14-year-old Australian children listed their three greatest fears they duplicated five of the ones from Figure 3.5: parents dying, being hit by a car or truck, snakes, the dark, and spiders (Lane & Gullone, 1999). When American adults were asked to pick their fears from a list presented to them, snakes and spiders were selected (Roper Report, 1984). Several fears included in these three surveys are attributable to our evolu- tionary past: spiders, the dark, snakes, heights, death of a loved one, thunder and lightning. One interesting feature that came out in the survey with the Dutch children was that many

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FIGURE 3.5 What Do You Fear? The percentage of children who responded with one of the 10 shown fears to the question “What do you fear most?” Notice that 23% of the children responded with either a fear of snakes or spiders.

Source: Adapted from “Common Childhood Fears and Their Origins” by P. Muris et al., 1997, Behaviour Research and Therapy, 35, table 2, p. 932.

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of them did not know how their fears began (Muris et al., 1997). For example, 33% did not know how their fears originated when asked, “How did your fear of ... begin?” (p. 931). In addition, 46% did not know how their fear of spiders began. Either the children did not remember what conditioning experiences produced these fears or the fears were innate and resulted from natural selection.

Survival Value. Fear has an evolutionary history that helped animals adapt to survival problems that occurred in their environment (Öhman & Mineka, 2001; Plutchik, 1980). First, fear induces the preparation for escape or avoidance responses. Depending on the species, escape may consist of scrambling, freezing, flying, or running away. Second, ani- mals have evolved to fear specific stimuli. The prevalence of a fear of reptiles, for example, may be an archaic remnant of when mammals tried to avoid being eaten by dinosaurs (Öhman, 1986). Öhman (1993) speculates that “feature detectors” in the brain are naturally selected because of their sensitivity to stimulus characteristics of reptile predators. These feature detectors may be located in the amygdala, a part of the brain that is sensitive to stim- uli that are ambiguous or that predict probable threat (Whalen, 1998; see also Chapter 14). Sensitivity to fear-relevant stimuli was demonstrated in an experiment in which human par- ticipants were asked either to identify snakes or spiders in a background array composed of flowers or mushrooms or to identify flowers or mushrooms in a background array of snakes and spiders (Öhman, Flykt, & Esteves, 2001). Participants identified the fear-relevant snakes and spiders more rapidly than they identified flowers and mushrooms. Furthermore, indi- viduals who feared snakes identified them more rapidly than an individual who did not. A similar result was obtained for individuals who feared spiders.

Preparedness. One characteristic of universal motives is that some can occur without prior experience, as illustrated in case studies of fear. Marks (1987), in his book Fears, Phobias, and Rituals, reports on his 2 1⁄2-year-old son’s reaction to seaweed on the beach. The seaweed skeins looked like tiny snakes. As soon as his son saw them “he screamed in terror and clutched me tightly, trying to stop me from sitting on the sand. When I touched the seaweed he shrieked and refused to do the same. His panic increased when gentle waves rolled the seaweed nearby or when I held him over the water to show him the moving fronds” (p. 40).

Do all fears occur the first time a threatening or dangerous stimulus appears, or is some minimal experience required? After conditioning his daughter to fear a caterpillar after only a single association with a loud whistle, Valentine (1930) concluded that fear is an “an instinct lurking ready to appear when the occasion arises” (p. 404; italics in orig- inal). In this case, the instinct was a fear of woolly caterpillars that could be awakened when paired with a loud sound from a whistle. This awakening idea is similar to Selig- man’s (1971) concept of prepared learning, or preparedness, to describe the ease with which a behavior is learned. Behaviors for which humans are prepared are ones that oc- cur easily as a result of experience, as if they are disposed toward learning them. Contraprepared behaviors are ones that occur with difficulty and only after much experi- ence. Thus, to assume that certain fears are the result of evolution means that there are things of which humans are prepared to become afraid. If humans are prepared to become afraid of snakes, then it will take little experience to learn to fear them. Humans are prob- ably contraprepared to become afraid of flowers. Seligman (1971) points out that humans

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are more likely to fear insects, heights, and the dark rather than their pajamas, grass, electrical outlets, and hammers.

Preparedness and Observational Fear Conditioning. The concept of preparedness also connotes the possibility that fear of naturally dangerous stimuli can occur indirectly; that is, by observational conditioning. This possibility received support from experiments in which monkeys were conditioned by observation to fear snakes and crocodiles but not flowers or other neutral objects (Cook & Mineka, 1990; Mineka, 1992; Mineka & Cook, 1993). The experiment involved two main groups of monkeys: models and observers. The model monkeys were videotaped acting calmly or acting fearfully. Spliced underneath the videotaped scene of the model monkey were different stimuli, such as a toy or real snake or silk flowers. This resulted in different videotaped scenes of the model monkey acting calmly or fearfully in the presence of one of these stimuli (see Figure 3.6). An ob- server monkey watched one of the videotapes. Would the observer monkey become afraid of both stimuli to which the model monkey acted fearfully, or would the observer become afraid of only one stimulus, such as the snake? Following the viewing of a video, an observer monkey was placed in an apparatus in which it could obtain a food treat. To reach this treat, however, the observer monkey had to reach over an open box containing a snake or a flower. The indication of fear was how long (latency) it took the observer

Model monkey acts calmly to

Flower or Snake

Model monkey acts fearfully to

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FIGURE 3.6 Preparedness and Fear. The design of the experiment involved four video versions of a model monkey acting calmly or fearfully in reaction to a flower or a snake. The observer monkey watched one of these four versions.

Source: Adapted from “Selected Associations in the Observational Conditioning of Fear in Rhesus Monkeys” by M. Cook and S. Mineka, 1990, Journal of Experimental Psychology, 16.

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monkey to reach for the food. Other indicators of fear included disturbance behaviors, such as withdrawing, clutching the bars, shaking the cage, staring at the stimulus, or making a grimace or threat.

Observer monkeys learned to fear snakes but not flowers from watching the behavior of model monkeys. The observer monkeys’ reactions to the snake or flower were affected by the model monkeys’ fear behavior in the presence of a snake but not by that behavior in the presence of a flower. For instance, it took the observer monkeys longer to reach over the open box containing a toy snake when the model monkey had acted fearfully toward the snake. The observer monkeys’ reachings were not affected by the flower or by how the model monkeys had acted toward the flower. The observer monkeys also acted more dis- turbed in the presence of a snake compared to a flower, again provided that the model mon- keys acted fearfully toward the snake. The observer monkeys were not disturbed in the presence of a flower even when the model monkeys had acted disturbed. Thus, monkeys ap- pear to be prepared to fear snakes but not harmless stimuli like flowers. The fear of snakes may have been a universal motive that evolved to aid survival.

Preparedness of Classical Fear Conditioning in Humans. A series of experiments per- formed by E. Cook and associates (1986) show that humans are also prepared to fear some stimuli more readily than others. The researchers compared fear conditioning to pictures of phobic stimuli like snakes and spiders versus neutral stimuli like flowers and mushrooms. During the conditioning procedure, one phobic stimulus was paired with an uncomfortable shock to the forearm, whereas the other phobic stimulus was presented alone, without a shock. For example, the picture of a snake was paired with the application of a shock, while the picture of a spider was presented without a shock. Conditioning with neutral stimuli involved pairing a flower with a shock and a mushroom with no shock. Heart rate was used as an indicator of fear. Increased heart rate prepares a person to fight or flee from a danger stimulus, such as an approaching snake or spider. The results of a series of experiments showed that humans were more reactive to phobic stimuli compared to neutral stimuli. Accelerated heart rate only occurred when phobic stimuli (snakes, spiders) were paired with a shock. Neutral stimuli (flowers, mushrooms) did not produce an accelerated heart rate even when paired with a shock. Thus, like monkeys, humans are prepared to fear snakes and spiders, which may have been an important survival reaction during our evolutionary past.

Sensitivity and preparedness to phobic stimuli are so great that humans even react when those stimuli are presented below awareness (Öhman & Mineka, 2001). During the conditioning phase of one experiment, Katkin and coresearchers (2001) presented a slide of a snake or spider very briefly, which was then followed by another slide so as to obliterate any visual memory of the first one. Using this procedure, the presentation of a snake slide (con- ditioned stimulus) was paired with a moderately painful electric shock (unconditioned stim- ulus) to the nondominant forearm, while a spider slide was paired with the absence of a shock. For another group, this procedure was reversed: spider slides were paired with shock and snake slides, with the absence of shock. Fear (conditioned response) evoked by a conditioned stimulus was measured by the magnitude of the skin conductance responses, which is an in- dicator of autonomic nervous system arousal. Also, after a slide was presented, participants rated the likelihood that a shock would actually follow. As a result of conditioning, partici- pants made stronger fear responses to the conditioned stimulus that was paired with shock than to the conditioned stimulus not paired with shock. The ability to predict the onset of

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shock, following a slide, depended on the participant’s sensitivity to her visceral activity (heart rate). More sensitive individuals were better able to predict that shock would follow a conditioned stimulus slide. Thus, when phobic stimuli are presented below the level of con- scious awareness, individuals are still sensitive to them at another level. They associate them with shock and can predict their occurrence based on sensitivity to their own heart rate.

In summary, fear has been used to illustrate a universal motive that is shaped by evolution. It is a prepared tendency or psychological mechanism in mammals that is ready to occur in response to certain stimuli, such as reptiles or the dark. The evolutionary value of fear is that it increases an animal’s chance of survival. Fear motivates the analysis of unusual stimuli and motivates escape and avoidance behaviors like fleeing, hiding, or freezing.

➣ More information about fears and phobias is available at http://www.helpguide.org/ mental/phobia_symptoms_types_treatment.htm

Liking and Preferences for Foods Another universal motive that humans possess is exhibited in their food preferences. The char- acteristics of this motive are uncovered from examining young children’s innate dispositions toward and away from edible substances. The reason for studying children is that their prefer- ences are not yet unduly influenced by the food environment that parents provide. The effects of this environment are immediate, since in making the transition from milk, infants are dis- posed toward learning to accept the foods associated with their country and culture (Birch, 1992). Food acceptance is possible because humans are omnivorous, which means that they are able to eat a variety of foods. In fact, nutritionists recommend that people should do this to obtain all the nutrients that they need. Being omnivorous allowed humans to make use of whatever food sources a geographical area had to offer, in spite of any innate taste preferences.

Food Neophobia. As an introduction, there are several generalizations regarding innate food preferences. First, as many parents have discovered, in the transition from milk to solid foods, children often show food neophobia, which is the tendency to avoid novel foods and prefer familiar foods. Second, children innately prefer sweet and later salty foods. They avoid sour and bitter foods. Third, children are prepared to avoid food associated with neg- ative digestive consequences and prefer those with positive consequences (Birch, 1999). Fourth, humans have a preference for fatty foods (Birch, 1992).

Would you like to eat some hummus, halvah, or funistrada? A “no” answer may be indicative of the universal motive of food neophobia. People vary in their degree of this neophobia and hence their willingness to try new foods. Pliner and Hobden (1992) con- structed the Food Neophobia Scale to measure the extent individuals avoided or were reluctant to eat novel foods. Individuals who scored in the upper 15% of the Food Neopho- bia Scale were labeled neophobics, and those who scored in the lower 15% were labeled neophilics (individuals willing to try new foods). Raudenbush and Frank (1999) asked neo- phobics and neophilics about their potential reactions to familiar foods (yogurt, icing, apple- sauce, and peanut butter) and unfamiliar foods (hummus, a chickpea paste; halvah, crushed sesame seeds in honey; and funistrada, a fictitious food). Their reactions to these foods were measured on a 12-point scale on several dimensions: willingness to try, expected liking, ac- tual liking, and willingness to try the foods again. Analyses of the ratings indicated that both

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neophobics and neophilics were less favorably disposed toward novel foods than toward familiar foods. The unfavorable ratings for novel foods were very apparent for neophobics. Compared to neophilics, neophobics were less willing to try novel foods, expected and actu- ally liked novel foods less, and were less willing to try them again. Also, both groups ate less unfamiliar than familiar food, and neophobics ate significantly less than neophilics.

An explanation for neophobia is based on its survival value. Neophobia protects a person from eating a toxic substance that can cause illness and even death (Birch, 1999). By avoiding novel foods, an individual is less likely to be poisoned or to become very ill. However, neophobia also has some negative consequences. It can be a problem for individ- uals required to make dietary changes in support of good nutrition. Individuals may be reluctant to switch from familiar foods to new foods that provide diet and health benefits. Nevertheless, the extent of food neophobia diminishes with the amount of experience a person has with other foods (Birch, 1999).

Innate Preference and Aversion for Substances. The innate human preference for sweet and aversion for sour and bitter becomes apparent during the first few hours and days of life. Evidence for this comes from observing facial expressions made by newborn infants to various taste stimuli. To illustrate, Figure 3.7 shows the distinctive facial reactions of a 3-day-old infant to sweet-, sour-, and bitter-tasting stimuli but its indifference to salt (Mennella & Beauchamp, 1998). Although the infant in Figure 3.7 is indifferent to salt, by 4 months of age a salt preference has developed (Birch, 1999). Additional evidence for in- nate taste preferences comes from research by Steiner (1977), who showed that infants were sensitive to the taste of sweet, sour, and bitter prior to their first feeding. He placed a drop of flavored liquid on the tongues of infants, who clearly showed whether they liked it or not. Compared to a resting face or the reaction to distilled water, the sweet stimulus produced a

FIGURE 3.7 Innate Preference and Aversion of Tastes. Sequence of facial expressions elicited from 3-day- old infant in response to tasting different substances.

Source: From “Early Flavor Experiences” by J. A. Mennella and G. K. Beauchamp, 1998, Nutrition Reviews, 56, p. 207. Baby pictures were reprinted with permission from Pediatric Basics, 82, Winter 1998, Gerber Products Company.

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retraction of mouth corners resembling a smile, a sucking response, and a licking of the upper lips. The reaction to the sour stimulus, however, produced a pursing of the lips, wrin- kling of the nose, blinking of the eyes, and increased salivation. The reaction to the bitter stimulus produced protrusion of a flat tongue, salivation, spitting, and an expression re- sembling dislike and anger. The instinctive or innate nature of these expressions is also demonstrated by the finding that infants do not rely on higher cortical brain processes. Steiner (1977) tested four infants born without a cortex and with only a brain stem and mid- brain. They reacted to taste stimuli in a fashion similar to that of normal infants: a prefer- ence for sweet and an aversion for sour and bitter.

Evolutionary Value of Tastes and Facial Expressions. In addition to showing positive reactions to sweets, infants will also eat more of a sweet-tasting substance. Desor and associates (1973) offered 1- to 3-day-old infants plain water or sugar solutions of varying degrees of sweetness. Infants drank more of a sugar water solution than a plain water solu- tion; the sweeter the solution, the more they drank. In fact, one way parents make adult food acceptable to infants is to add sugar (Jerome, 1977). However, infants will eat less of a sub- stance the more bitter or sour it tastes. Desor and associates (1975) found that putting suf- ficient citric acid in a sugar solution to give it a sour taste led to a reduction in the amount infants drank. However, adding urea for a bitter taste or sodium chloride for a salty taste did not seem to suppress the amount of drinking. Perhaps bitterness is a more complex taste, although the infant in Figure 3.7 (Mennella & Beauchamp, 1998) and Steiner’s (1977) re- search clearly show that infants make an aversive response to bitter tastes.

Liking sugars and disliking sour or bitter foods are assumed to result from our ge- netic past for several reasons. First, the facial expressions reflecting infants’ likes or dis- likes are likely innate, or inborn, to use Steiner’s (1977) term. It does not seem possible that these expressions are learned by infants during their first few hours of life or while in the womb. However, this possibility does exist. For instance, Mennella and Beauchamp (1998) summarized the results of research showing that infants can detect and prefer the odor of their own amniotic fluids during their first few days of life. (Amniotic fluid surrounds the unborn fetus in the mother’s uterus.) Second, even infants lacking a cortex for learning more complex material are able to make these facial expressions. Third, there is an evolutionary advantage to liking sweets. In our evolutionary past sugar was only available in fruit, berries, or honey. It did not come neatly packaged in cakes, pies, ice cream, and soft drinks. A sweet taste is associated with ripe fruits, berries, some vegetables that are ripe, and moth- ers’ milk (Mennella & Beauchamp, 1998). The sweet taste comes from complex carbohy- drates, which are an essential nutrient for the body’s growth, repair, and maintenance. Thus, by eating more sweet-tasting substances, early humans obtained essential nutrients, which aided in their survival. Sour and bitter tastes are associated with bark, dirt, and unripe fruits, berries, and vegetables that are not ready to eat. If eaten, these things are likely to make a person ill. In addition, a bitter-tasting substance is probably associated with toxins or poi- sons that can kill an individual. Thus, a bitter taste serves as a warning to avoid bad food.

In addition to innate taste preferences, the accompanying facial expressions also have survival value. A newborn infant is totally dependent on its mother for nutrients and can only communicate its likes and dislikes using facial expressions. These expressions are readable (see Figure 3.7) and clearly resemble the reactions made by adults if they were to

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taste identical stimuli. Steiner (1977) demonstrated this by having a panel of observers in- terpret what emotion the infant was showing when tasting various stimuli. The panel viewed either a videotape or still photograph of the infant’s facial expression. The expression elicited by the sweet stimulus was interpreted as appreciation, enjoyment, or liking. The ex- pression elicited by the bitter stimulus was interpreted as disgust, aversion, or dislike. Thus, it appears that an infant “knows” what is good based on the idea that what an infant likes is nutritious and what an infant does not like is not nutritious.

The various facial responses that accompany different tastes also serve other func- tions (Rosenstein & Oster, 1988). Sucking responses in reaction to sweet stimuli are a means of ingesting what is presumably a nutritive substance. The increased salivation to a sour stimulus may be an attempt to dilute its concentration, thereby making it less aver- sive. In an experiment with 2-hour-old infants, Rosenstein and Oster (1988) observed in- fants’ attempts to block swallowing a bitter liquid by allowing it to drain from their mouths. These responses presumably are an adaptive way to get rid of bitter substances. These investigators also tested infants using a salty substance and found no distinctive facial responses. The lack of distinctive responding may have occurred because infants can- not consume enough salt to be dangerous or because they have not yet developed a taste for salt.

Early Experience Interacts with Innate Preference. Innate taste preferences are pre- sumably a function of our evolutionary past. However, taste may be affected by very early flavor experiences, which could affect food preferences later. Some flavors from foods that pregnant mothers eat may come to reside in the amniotic fluid that surrounds their babies. Consequently, when unborn babies swallow amniotic fluid they experience these flavors. What is the evidence that this early flavor experience affects an infant’s later food preferences? In order to answer this question, Mennella and coresearchers (2001) had pregnant women drink either water or carrot juice during their last three months of pregnancy or during the first month of breastfeeding their babies. Other mothers drank water both during their pregnancy and during breastfeeding. The question was: When ready to eat cereal, would infants prefer carrot-flavored over plain-flavored cereal? The infants’ preference was measured in three ways. One made use of infants’ negative facial expressions while eating, such as nose wrin- kling or head turning. Presumably fewer negative expressions implied greater acceptance of a cereal. A second measure involved the mothers’ ratings of their infants’ enjoyment of the ce- real on a scale from 1 (not at all) to 9 (very much). Third was the amount of cereal the infants ate. The results in Figure 3.8 indicate that the mothers’ intake of carrot juice while pregnant or nursing increased their infants’ acceptance of carrot-flavored cereal. Infants made fewer negative facial responses, showed more enjoyment, and ate more of the carrot-flavored cereal than the plain-flavored cereal. However, the amount eaten did not differ significantly among the three groups. An important implication of this finding is that this initial exposure to a flavor, even prior to birth, disposes an infant to accept the solid foods of its culture and may smooth the transition from nursing to eating solid foods (Mennella et al., 2001).

Fat Preference. Texture, taste, and smell contribute to our preferences for a food (Schiffman et al., 1998); for example, the higher the butter fat content of vanilla ice cream, the more it is preferred (Pick et al., 1990). To illustrate the power of human fat preferences, in 1991 the McDonald’s Corporation introduced the McLean hamburger to provide a more nutritious choice on its menu. This new hamburger contained half the fat and had 100 fewer

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calories than their quarter-pounder hamburger. The McLean hamburger fell in the accept- able range of daily fat consumption, with 30% of its calories derived from fat (Burros, 1991). In spite of its nutritional value, however, the consuming public did not want it, and eventually it was taken off the market (Gibson, 1996). Part of the reason may have been taste, since the McLean did not taste quite the same as other hamburgers. Fat provides fla- vor, and substitute flavors put into the McLean hamburger may not have provided the same taste. The decline of the McLean hamburger illustrates that people do not necessarily eat what is good for them but instead eat what tastes good.

Universal Appeal of Music The position of evolutionary psychology is that the function of psychological mechanisms is to solve problems of survival. Psychological mechanisms evolved through natural selec- tion or sexual selection because they increased the survival chances of individuals and their offspring. However, there are also some evolutionary puzzles—mechanisms that evolved as by-products but do not seem beneficial for survival on their own. For example, what is the survival value of male nipples? Music may be in this category of mechanisms for which the evolutionary benefits are not obvious.

Possible Evolution of Music. As Darwin (1871/1981) noted, music arouses emotions that are usually positive (like love) and not negative (like fear or rage). Yet, what is the func- tion of these positive feelings? Perhaps one function is that music can be used as a means of mood regulation: alleviate negative moods and boost positive moods (North et al., 2004; Thayer, 2001). A second possibility is that those feelings promote group or social bonding that can occur while listening to or creating music. Examples would include listening to

Carrot-Water

Water-Carrot

Water-Water

B e

h a v

io ra

l U

n it

0 Negative Faces Enjoyment Amount Eaten

FIGURE 3.8 Effects of Early Taste Experience. When mothers drank carrot juice while preg- nant (carrot-water) or during nursing (water-carrot) their infants preferred carrot-flavored cereal over plain cereal. When mothers drank water while pregnant or during nursing (water-water), their infants preferred carrot-flavored cereal less. Amount eaten is reported in decagrams.

Source: Adapted from “Prenatal and Postnatal Flavor Learning by Human Infants” [Electronic version] by J. A. Mennella et al., 2001, Pediatrics, 107, e88, table 2, p. 3.

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patriotic music during Fourth of July celebrations or singing the happy birthday song. How- ever, music may have evolved as a by-product in the evolution of other pleasures or motives (Peretz, 2006). In this case, music is an artificial stimulus that people discovered could evoke pleasurable feelings. Another interpretation, however, is that music is the result of sexual selection rather than natural selection. In the words of Darwin (1871/1981), the pur- pose of music was to charm the other sex. Thus, individuals who could make music were more likely to be sexually selected based on their ability to charm or instill positive feelings in the listener.

Music as Part of Human Nature. What is music? According to one definition, music refers to an organized movement of sound that is both regular and periodic. This organized movement allows an individual to keep time, which is what distinguishes music from other patterns of sound, such as speech (Cross, 2001). In addition, music seems to be part of human nature. Peretz (2006) describes several reasons why this is so. First, music is not a recent invention but has been part of human culture for at least 30,000 years. Second, music, although in different forms, is present in all cultures the world over. Third, the hu- man response to music seems innate—that is, learning how to respond is not necessary. For example, infants respond to music and early on they can discriminate between mu- sic and other sounds while most animals cannot. Fourth, music is functional in that it is a source of pleasure for most members of a culture, which is especially the case for popular music.

Infants Enjoy Music. The claim that the appreciation of music is innate comes from ob- serving infants. First, this appreciation appears early in the life of infants. Second, infants are calmer and pay greater attention to their mothers when the latter are singing rather than speaking to their infants (Nakata & Trehub, 2004). Third, infants prefer consonant (har- mony) over dissonant (non-harmony) music. Zenter and Kagan (1998) tested this last claim by presenting 4-month-old infants with either a consonant (harmonious) melody or a dis- sonant melody. (Undergraduates who listened to the dissonant version described it as “hurt- ing their ears.”) Preference for a melody was based on how much time infants fixated on the speaker-source of the melody. Dislike for a melody was based on the infants’ motor ac- tivity, such as flexion or movement of arms or legs. Infants seemed to like consonant music and dislike dissonant music. They spent more time visually fixating on the speaker when it transmitted consonant rather than dissonant melodies. Infants also made more motor move- ments and fretted more in the presence of dissonant melodies. Furthermore, the greater preference for consonant over dissonant music occurs for infants as early as two months of age (Trainor et al., 2002).

How should these results be interpreted? One interpretation favors the idea that hu- mans have an innate bias in favor of consonance over dissonance in musical notes. Perhaps humans evolved a motive to like musical instead of nonmusical sound. How this preference developed is not clear. Another possibility is that infants are neutral at birth in their prefer- ence regarding possible patterns of sound. They learn to like whatever they are exposed to immediately after being born, which happens to be consonant rather than dissonant music.

Section Recap Relationships between members of each sex, the arousal of jealousy, the emotion of fear, and food preferences are all categories of universal motives that resulted from natural

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selection or sexual selection. Music enjoyment may be a by-product of the evolution of other processes. According to Darwin’s concept of sexual selection, relationships are formed by members of one sex choosing individuals of the other sex based on the latter’s characteristics. Mate value includes those characteristics of a person that are desired by the other sex, such as attractiveness, intelligence, common interests, and parental possibilities. According to the good genes hypothesis, beauty, as a universal trait, signals that the person has genes for good health and intelligence. Individuals select others either because their attractiveness signals good genes or reject individuals whose unattractiveness signals bad genes for these traits. In the case of sexual selection for long-term relationships, women universally prefer ambitious and industrious men because they will provide the material means to support a family. Men usually prefer young and beautiful women because these features signal fertility.

There are several systems in place to maintain relationships. Orgasm evolved through natural selection and is one of the rewards for sexual behavior and for the development of romantic love as a help in forming pair bonds. It increases the chances of pregnancy. Mate poaching occurs when an outsider attempts to attract someone who is already in a roman- tic relationship. Thus, poaching is a threat to the maintenance of a relationship and jealousy may have evolved to provide the motivation to protect against it.

Jealousy is an emotion that has been sexually selected. According to evolutionary psychology, women become more jealous about the suspected or actual loss of affection, since it implies that they may lose their partners’ resources. Men are more jealous about their partners’ sexual infidelity, since men are uncertain about being the father of their part- ners’ children. According to biosocial theory, gender differences are the result of biologi- cal differences between men and women in physical strength and reproductive capacity. These biological differences interact with societal expectations for men and women to take on sex-relevant social roles. The consequence of adapting to these roles is to increase the psychological difference between men and women. These increased psychological differ- ences account for gender differences in preferred mate characteristics and in jealousy. Ac- cording to the structural powerless hypothesis, women are ineffectual in obtaining the same level of financial resources in the working world as men. Therefore, women can gain access to resources by marrying men who can provide these.

Survey research indicates that some fears are more prevalent than others, especially ones that have survival value, such as the fear of snakes and spiders. Not all fears occur the first time in a dangerous situation but can arise quickly, with little previous experience, de- pending on the preparedness of the behavior. Preparedness refers to the ease with which be- havior is conditioned. In cases of conditioning, some stimuli are easy to condition (prepared), such as fear stimuli, whereas other stimuli are difficult to condition (contrapre- pared). The preparedness to fear a particular stimulus is shown with classical conditioning, which is the procedure by which a neutral stimulus (e.g., a tone) signals a biologically sig- nificant unconditioned stimulus (e.g., an electric shock to forearm). Following several tri- als, the tone (conditioned stimulus) will evoke a response (conditioned response) that mimics the original unconditioned response to the shock. Monkeys and humans are pre- pared to become conditioned to fear snakes and spiders. Fear can also develop from ob- serving a fear reaction in other individuals. Humans are extremely sensitive to fear-relevant stimuli, even when these are presented below the level of awareness.

Another set of universal motives revolves around our interaction with food. Humans exhibit food neophobia, which is the tendency to avoid novel foods and select familiar

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foods. Another related universal motive is the human preference for sugar and fat, which indicate high caloric value. Work with infants just a few hours old shows that they prefer sweet substances over sour and bitter substances. Early taste preferences may also result from flavors that babies experienced from their mothers’ amniotic fluid or breast milk. Fortunately, humans are omnivorous, which means they can eat a variety of foods to obtain the necessary ingredients for growth and maintenance.

The universal appeal of music is also part of human nature. Music is patterned sound that people can keep time with. It is capable of eliciting emotions and is enjoyed all over the world in its many forms. Music may have evolved as a by-product of the evolution of other psychological mechanisms or may have evolved through sexual selection. Infants prefer their mothers’ singing to speaking and as early as two months of age, they prefer consonant melodies over dissonant melodies.

A C T I V I T I E S

1. Ask friends and acquaintances what things they fear. Then ask them how their particular fear de- veloped. Is there any commonality in the fears people report (e.g., tornadoes in the Midwest, earthquakes in California, or hurricanes in the Southeast)? Did the fear develop in the absence of any experience with the feared object? Did fear of the object develop as a result of its asso- ciation with a traumatic experience? Did the fear develop from watching someone else show a fear reaction to that stimulus?

2. What foods do you like and dislike? What is the source of these likes and dislikes? Is there anything that liked foods have in common or that disliked foods have in common?

3. Can you determine from watching a friend’s fa- cial expressions if she likes what is being eaten?

4. Ask some friends of each sex how important the following characteristics are for choosing a husband, wife, or long-term mate. Use this rat- ing scale:

Good financial prospect: 0 = Irrelevant or unimportant, to 3 = Indispensable

Ambition and industriousness: 0 = Irrelevant or unimportant, to 3 = Indispensable Good looks: 0 = Irrelevant or unimportant, to 3 = Indispensable

How do your findings compare to the results presented in Figure 3.3? Imagine the type of person with whom you would like to form a long-term relationship or with whom you al- ready have a relationship. Is your choice the result of a biological destiny, society’s expecta- tions, or the interaction between biology and society? In other words, do you think the evolu- tionary psychologists are correct, or are social psychological explanations more accurate, e.g., structural powerless hypothesis?

5. List situations that would make you jeal- ous. Compare your list with a member of the other sex. Are there any differences between the two lists? Which was the greater cause of jealousy: sexual infidelity or emotional infidelity? Did your results support evolu- tionary psychology?

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