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Psychology: Six Perspectives

Evolutionary Psychology

By: Dodge Fernald

Book Title: Psychology: Six Perspectives

Chapter Title: "Evolutionary Psychology"

Pub. Date: 2008

Access Date: November 3, 2022

Publishing Company: SAGE Publications, Inc.

City: Thousand Oaks

Print ISBN: 9781412938679

Online ISBN: 9781452224862

DOI: https://dx.doi.org/10.4135/9781452224862.n8

Print pages: 261-301

© 2008 SAGE Publications, Inc. All Rights Reserved.

This PDF has been generated from SAGE Knowledge. Please note that the pagination of the online

version will vary from the pagination of the print book.

Evolutionary Psychology

Evolutionary psychology

• Roots of Evolutionary Psychology ◦ The Darwinian Influence ◦ Genetic Transmission ◦ Mechanisms and Instincts ◦ Specificity in Adaptation

• Evolution of Sexual Behavior ◦ Preferences in Mate Selection ◦ Common Mating Patterns

• Adaptations in Parenting ◦ Pregnancy Sickness ◦ Infant-Directed Speech

• Dispositions in Group Living ◦ Acquisition of Language ◦ Shared Emotional Expressions ◦ Making Social Contracts ◦ Inclination Toward Aggression

• Promoting Behavioral Change ◦ Assessing Therapy Effectiveness ◦ A Catalogue of Hypotheses

• Commentary and Critique

Evolutionary psychology states that the newborn human mind is not a clean slate awaiting its contents. It is an adapted mind, containing specific fears, preferences, and behavioral tendencies inherited from our ancestors, especially those eons earlier.

The human mind of course is not completely shaped at birth; life experiences contribute enormously. But evolutionary psychology examines the presumably evolved mechanisms present in all of us at the outset of our lives, arising from our common genetic background as Homo sapiens.

Following an introduction on the roots of evolutionary psychology, this chapter describes these evolved mechanisms in a developmental sequence, beginning with human sexual behavior. Then it turns to adaptations in parenting, including pregnancy and child care, and finally to dispositions in group living, ranging from language acquisition to our inclination toward aggression. With no therapy available for our evolved makeup, the chapter ends with a general discussion on promoting behavioral change, followed by the customary commentary and critique.

According to evolutionary theory, these mental mechanisms evolved gradually in the course of human history, as our ancestors struggled for survival. Among our ancestors, those most adapted to the environment survived and typically reproduced, passing on their genetic makeup to their offspring. In this way, the characteristics most associated with mastery of these two tasks—individual survival and sexual reproduction—tended to be transmitted and augmented in successive generations. Reproductive men tended to be attracted to certain features in women, and reproductive women in turn tended to favor certain qualities in men.

In the sexual realm, Bertha was an exception. She showed no overt attraction to anyone and, in fact, no interest in closeness or intimacy. Even when working with others, she lived a lonely, loveless life. Her sexual behavior instead provides an important reminder that inherited predispositions of all sorts are always subject to modification by environmental factors. Both components are always present and influential in complex ways.

Then one day Bertha embarked on a mission that included human sexuality and a tour of forbidden

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places—but no sexual behavior on her part. In her fifties, she planned further combat, this time against the “world's oldest profession.” She would battle the corrupt businessmen and civic leaders who profited from the international traffic in women (Kimball, 2000). She would also meet the prostitutes at their places of work. Her itinerary would include houses of prostitution in Budapest, Jerusalem, Moscow, Warsaw, and several other cities.

Bertha possessed a background for this challenge. Working daily with former prostitutes, she understood their deprivations, especially their need for education. And these personal contacts gave her a strong sense of purpose. She viewed herself as the enemy of an underworld empire, threatening its financial gains.

Roots of Evolutionary Psychology

Selling, bartering, and otherwise contracting for sexuality have occurred throughout human history. In fact, the challenge of negotiating for sexual activity exists for all sexually reproducing species, and our ancestors evolved various solutions to it. As a new perspective, emerging prominently in the late 1990s, evolutionary psychology aims to understand our evolved solutions to these and other adaptive tasks.

Specifically, evolutionary psychology studies the design of the human mind, focusing on the psychological mechanisms evolved by human beings in solving the two adaptive tasks most fundamental to our species: individual survival and sexual reproduction. It seeks to identify the ways in which human beings, in solving these problems, have acquired certain longstanding fears, preferences, and other behavioral tendencies (Buss, 1995a).

Evolutionary theory has a long past. The idea that human beings are descended from animal ancestors dates back to early Greek philosophers. They suggested that one species could change into another, that human beings descended from fish, and that differences among species could either decrease or increase. By the 19th century, Jean-Baptiste Lamarck proposed a detailed theory of evolution, illustrating the ancestry of human and animal descendants, but he stressed the inheritance of acquired characteristics. Giraffes acquired their long necks by constantly reaching for leaves high in the trees. The results of this stretching somehow were passed from one generation to the next. But with no plausible conjecture about how an organism's repetitive behaviors might be transmitted to another generation, the Lamarckian view lost much of its credibility.

The Darwinian Influence

Also in the 19th century, Erasmus Darwin anticipated the modern concept of evolution. But scientists, philosophers, and the general public credit instead his grandson, Charles Darwin (1809–1882). The younger Darwin's massive contributions were both empirical and rational. He collected an extensive array of facts, and then he developed a far more complete, more carefully constructed theory of evolution. In this theory, incidentally, human beings are not viewed as descended from apes. Rather, the two species have common ancestors.

As a youth, Darwin collected specimens, and one day he discovered not one but two rare beetles, catching one in each hand. Then he spied still another, awaiting capture if he acted quickly. Fearful that it might escape, Darwin thrust one of the pair into his mouth. That creature emitted a bitter fluid that burned Darwin's tongue, causing him to spit out his prisoner and, alas, to lose the opportunity to capture even two members of the trio (Darwin, 1876).

That episode illustrates that Darwin pursued his own goals in tenacious fashion, but not those of his father, who insisted he attend Edinburgh University in preparation for a medical career. But Charles experienced an aversion to medicine, especially to witnessing surgery performed without anesthesia. Transferring to Cambridge University for training in the ministry, he showed little interest there too, finally completing an undistinguished academic program. But he greatly enjoyed informal contact with faculty members in the sciences, especially botany. After his graduation, one of them recommended him for unpaid work aboard H.M.S. Beagle, a vessel assigned to sail around the world to survey South American coastlines, Pacific

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islands, and other places. As an unpaid naturalist, Darwin's job was to study rock formations, plants, and animals. For five years and 40,000 miles, he gathered facts and collected specimens.

On his return, he decided that the information he had so meticulously gathered might “throw some light” on that mystery of mysteries—the origin of species. For several years, he catalogued his specimens, and then he continued to contemplate the significance of this work, writing occasional articles on related subjects and standing for hours in his garden puzzled by some plant, insect, or experience aboard the Beagle. He also ruminated on the possible repercussions of his conclusions for social, religious, and even political thought. Altogether, he pondered his findings for 23 years before publishing them—almost too late to earn credit for their originality.

When finally published, his work was favorably received by some, vigorously protested by others. The critics resisted any suggestion that human beings possessed an animal ancestry, pointing instead to divine origins. Ill and tired, Darwin suffered in silence. As a scholar and man of great integrity, he simply could not ignore the conclusion forced on him by the facts of his voyage.

Two events prompted him to publish the book: his failing health and the arrival of a rival manuscript. When Alfred Wallace expressed ideas remarkably similar to his own, Darwin, in three more years, published his epochal work, The Origin of Species (1859). It appeared just 20 years before the founding of scientific psychology.

Among Darwin's evidence, studies of emotion carried considerable weight. Observing animals, human infants, and adults in different cultures, he noted the continuity in emotional expression. People bare their teeth in rage, though this reaction serves no physical purpose in most adult combat. In animals, it prepares an organism's most powerful weapon. Also, it may frighten the adversary. Thus, he viewed human emotional expressions as carryovers from our animal ancestry.

For Darwin, the mind, like the body, evolved through natural selection. In this process of natural selection, poorly adapted organisms perish; unable to escape predators and outdo others of their own species, they produce fewer offspring and therefore pass on fewer or no genes. The better adapted survive and reproduce, transmitting their more favorable heredity to their descendants, resulting in the “survival of the fittest,” a phrase not suggested by Darwin. “Reproduction of the fittest” would be more to the point. In any case, selection of the fittest results in the adaptation of each species to its surroundings. According to this principle, any slight variation in a species, if useful for survival, is preserved by natural selection.

Variation within the species plays a vital role. Without random variations, there would be no evolution. Random variation provides the differences essential for natural selection, bringing about inheritable changes that may prove adaptive in later generations (Figure 8.1).

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Figure 8.1 Evolutionary Changes in Species' Characteristics. The large normal curve shows the usual distribution of a human trait. The smaller curves show the trait in successive generations. In species A, a slight variation appeared in era X, useful in the preservation of this species. Subsequent generations showed successive shifts toward this variation. In species B, a favorable variation appeared at Y, eventually producing species C, a related but different species (Futuyma, 1983)

In his book, Darwin described nature as a continuous series of struggles among all living creatures for their niches in the environment. The lion, with its teeth and claws, is equipped with knives and, with its thick mane, a shield as well. The parasite is equipped with legs and claws by which it clings to the hair on the lion's body. Lions do battle with one another and with other species, just as parasites struggle for their place in nature.

A battleground serves as the metaphor for evolutionary psychology. All individuals become warriors on three fronts: competing against the forces of nature, their predators, and others of their own species. In these battles, Darwin suggested, we can console ourselves knowing that those who adapt best to a specific environmental niche will survive and multiply, passing their inherited characteristics to the next generation (Darwin, 1859). In fact, in making his observations and developing his theory, Darwin knew nothing about the transmission process. He had no idea how living creatures pass on their inherited characteristics. He simply observed that they did so. The physical mechanism for this process had not yet been discovered.

Genetic Transmission

Today we understand that all our biological inheritance passes from generation to generation through many thousands of submicroscopic structures called genes, which guide the expression of most physical and certain behavioral characteristics. The word guide appears appropriate, rather than control or direct, for today the expression of genes seems less rigid and automatic than once thought. All genes exist in an environmental context, and that context can augment or diminish any genetic predisposition.

Incidentally, the erroneous notion that genes inevitably and unavoidably control behavior is known as genetic determinism. Instead, genes always operate within an environment, and that environmental input influences the behavioral outcome. Legions of experimental studies with selectively bred animals and quasi- experimental studies with human beings underscore this point. Genes never act alone, which is the fallacy of genetic determinism. Human behavior occurs through a particular genetic background and environmental influences that mediate those inborn dispositions.

Evolutionary psychology must be understood in this same way. It is not a form of genetic determinism. It studies interactions. It examines behavioral outcomes of our genetic adaptations as triggered by specific stimuli in the modern environment.

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Within this environment, all human genes operate in pairs, and sometimes one member is dominant. The characteristic carried by the dominant gene becomes manifest whenever it is present, though its expression may vary, depending on diverse factors. A recessive gene becomes influential only when paired with another recessive gene.

A few human characteristics, such as eye color and certain diseases, become expressed through a single pair of genes. But most characteristics are more complexly determined. In these outcomes a polygenic trait emerges, influenced by multiple pairs of genes acting with various degrees of expression but without dominance, making the outcomes less predictable. The full genetic makeup of an individual, called the genome and estimated to include thousands of genes, can only be inferred.

In any species, some genes increase the chances of survival and reproduction; others diminish these prospects or play no significant role. Insofar as these differences in genes are transmitted from one generation to another, they give rise to evolution through their interplay with the environment, which is constantly changing. From the Ice Age to the Electronic Age, the environment has been altered by forces of nature and changes induced by human and other beings. Without these environmental changes, all living creatures theoretically would evolve to a maximum adaptation in their particular niches.

Genetic differences occur on two bases. First, at conception each individual receives a random assortment of countless genes from the two parents. Thus, all individuals except identical twins differ in their genetic backgrounds. These differences emerge from a tiny but vital portion of the genes passed on to us by our particular parents, each with his or her own genetic background, providing us with our own unique genetic makeup. Second, a sudden alteration, called mutation, sometimes occurs within a gene, producing the potential for a characteristic in the offspring not found in the parents. These intermittent deviations in gene replication are usually disruptive or inconsequential, but some are useful. With the massive number of genes possessed by each parent and the potential combinations in the union of the mother and father, together with the capacity of genes to mutate, the possibilities for diversity among human beings are almost unfathomable.

In more fundamental ways, however, human beings also have a common genetic background. With an overwhelming preponderance of common genes, we all share the numerous physical and behavioral characteristics that make us human beings, just as members of other species possess common characteristics.

Evolutionary theory states that the genes underlying these common characteristics have been selected by features of the environment over millions and millions of years. After countless generations exposed to natural selection, the most adaptive traits in a particular environment become prominent; the less-adaptive traits tend to die out and disappear. According to evolutionary biology, the human thumb, lumbar curve, and other physical structures emerged through this selective process.

For Darwin, the human mind also underwent adaptation, producing evolved tendencies in human behavior. He closed his book with this prediction: Psychology some day would be based on the idea that human mental capacities have been acquired by gradual adaptation (Darwin, 1859).

Mechanisms and Instincts

The fundamental premise of evolutionary psychology is that human mental characteristics also have been shaped by the process of natural selection over the eons of hunter-gatherer existence. Recorded human history is the product of a few thousand years. In contrast, our Pleistocene ancestors lived as hunter- gatherers for two million years, and their ancestors spent several hundred million years in a forager existence of one sort or another (Cosmides, Tooby, & Barkow, 1992). Compared with those indefinitely lengthy periods in human prehistory, our agrarian ancestors lived just yesterday, and the Industrial Age happened but an instant ago. Speculation about the nature of these long-evolved traits, together with empirical research to test these hypotheses, are the province of evolutionary psychology.

Especially since the 1990s, the evolutionary approach has gained increasing prominence in psychology, much of it through the energetic efforts of Leda Cosmides, John Tooby, and others, especially David Buss.

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With grades too low for college, Buss gained admission by a lottery and promptly developed interests in evolution and psychology, earning national recognition for his promise as a young scientist (Distinguished Scientific Awards, 1989). These and other modern pioneers have established a perspective that Darwin envisioned but did not pursue. Articulating the theory of evolution became enough for his lifetime.

As emphasized throughout this chapter, evolutionary psychology does not investigate the theory of evolution, which is impossible to confirm. Instead, starting with the idea of evolution, it develops specific hypotheses about human beings and then tests them for empirical support.

Often these studies begin with some common behavioral characteristic, such as the tendency of pregnant women to experience sickness or the tendency of people everywhere to speak a language. Then evolutionary psychologists speculate on the ways in which this behavior solved a problem of survival or reproduction in much earlier human history. Afterward, through widely diverse methods, especially the survey, they investigate this tendency in different cultures. The aim is to discover whether this behavior occurs throughout these societies. If so, it probably is not a culturally acquired trait but rather a product of human inheritance, and it is interpreted from the standpoint of evolutionary theory (Buss, 1999).

Many behaviors occur only in some cultures. Alcoholism, arranged marriages, and alimony are not universal. They stimulate little research among evolutionary psychologists. Traffic in women flourished in Alexandria, Buenos Aires, and Constantinople—places of interest to Bertha—but moral and legal conditions prohibited it elsewhere. On this basis, evolutionary psychologists would not study enforced prostitution as an adaptive phenomenon. However, in one form or another prostitution occurs in every carefully studied society around the world, and men become virtually the sole consumers of this practice. It emerges as an outcome of two related factors: the male desire for short-term sex, which has a long evolutionary history, and the female need or choice to provide sexual services for economic gain (Buss, 1999). Thus, the male desire for short-term sex has become a topic of research in evolutionary psychology.

Also called adaptationists, evolutionary psychologists aim to understand the adapted human mind—how the contemporary human mind has been designed by natural selection to solve the highly specific problems of survival and reproduction confronted by our hunter-gatherer ancestors. This effort to determine what the mind was shaped to do then, and how it operates today, is the basis of the evolutionary approach.

Evolutionary psychologists therefore take a controversial position. They resist the tabula rasa view that the contents of the contemporary human mind arise solely from the world outside the individual, through experiences in the environment, guided by just one or a few basic tendencies such as intelligence and learning. As in cognitive psychology, they do not regard the mind as a general-purpose computer that uses global intelligence to solve a wide array of problems. Instead, they view the human mind as designed through natural selection to respond in particular ways to specific circumstances. In this view, the human mind is a complex network of functionally specific computer programs (Cosmides & Tooby, 1992).

Each of these highly specialized programs is regarded as an evolved mechanism. In general terms, an evolved psychological mechanism is an inherited set of processes within the individual that responds to specific information about a recurrent problem of survival or reproduction and initiates a response to that problem. It becomes activated whenever the individual is confronted with events similar to those that signaled the problem in prehistoric life. In other words, an evolved psychological mechanism emerged gradually in human ancestors as a solution to some specific problem of individual survival or reproduction. It responds only to a narrow stimulus or piece of information informing the organism about that adaptive problem. Through decision rules, that input is transformed into an output that may be behavioral, physiological, or merely cognitive, directed toward a solution to that problem (Buss, 1999).

Now consider a simpler definition. As the central concept in evolutionary psychology, an evolved psychological mechanism often takes the form of a fear, preference, or behavioral tendency. It does not inevitably solve an adaptive problem in the current environment, but it tended to do so in the environment in which it evolved (Buss, 1999).

At this point, the reader may wonder how an evolved psychological mechanism differs from an instinct, a

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concept with a long and checkered history in psychology. Eventually instinct became defined as a relatively complex, unlearned behavior pattern occurring in all members or same-gender members of a species. On this basis, most modern psychologists regard human behavior as too flexible and too variable across cultures to be considered instinctive, although debate continues on several points, especially language. In any case, the concept of instinct does not explain much. It simply states that a certain behavior is somehow automatic.

The concept survives in everyday speech, nevertheless. People speak of someone as possessing an instinct for public speaking. Sports announcers describe certain athletes as having “good instincts.” But if performance in sports and public speaking were instinctive, all of us could perform at a high level without any training or practice. Clearly, learning is required, as well as good reflexes in cases of physical abilities.

One major difference between an evolved psychological mechanism and an instinct lies with the variability in response. The fears, preferences, and behavioral tendencies in evolved psychological mechanisms are less predictable and more open to diversity than instinctive behavior. Their genetic background is more “tentatively wired,” and the resulting behavior is only relatively fixed. An instinct is more fully fixed, its genetic background “firmly wired.”

A man's interest in a potential mate is triggered partly by a woman's appearance, including her waist-to-hips ratio. According to extensive cross-cultural surveys, men of different ages and diverse backgrounds almost universally find a waist-to-hip ratio of 0.70 most attractive. Larger and smaller ratios are less appealing (Singh & Young, 1995). This triggered preference is the essence of this evolved psychological mechanism, for the man's subsequent behavior is not highly predictable. It may range from a fleeting thought about the woman's posture to a prompt bid for a close encounter.

Among fish, the male, three-spined stickleback also responds to the shape of the female's body. If she exhibits a swollen abdomen, showing that she is about to lay eggs, the male immediately constructs a nest and commences an elaborate mating dance, swimming rapidly in circles, then back and forth, all in highly specific patterns, by which he induces her to enter the nest and lay her eggs (Tinbergen, 1953). All normal male sticklebacks emit this same intricate mating dance in response to the shape of the female's body.

In other words, male sticklebacks possess an instinct, an inborn, firmly fixed reaction to the female's swollen belly. The concept of instinct implies inevitability and complexity. Adult human males are not so universally and explicitly responsive, even to the most compelling female abdomen. They possess an evolved psychological mechanism—a behavioral tendency, far less predictable as a pattern of reactions. The concept implies only a broad tendency or predisposition. There may be no overt reaction at all.

Women are different from men in this respect. They show a mild preference for a 0.90 ratio in men, with the waist and hips almost the same size. Compared to men, this preference is even more variable and the woman's overt response even less predictable (Singh, 1995).

Specificity in Adaptation

From the perspective of evolutionary psychology, modern human beings are living, inexact fossils. They carry with them ancient tendencies for all sorts of reactions shaped by natural selection over the millennia. Still present today as part of “human nature,” these reactions are evoked by cues for the earlier adaptive problems—a wayward mate, poisonous food, loss of status, invasions of territory, and many others. As remnants from life long ago, they can be maladaptive today. They give us, in some respects, a cave dweller's brain in a modern skull. But of course all current brain processes are not necessarily an outcome of evolution.

In addition, each broad adaptive problem—survival and reproduction—includes specific subproblems, resulting in numerous evolved psychological mechanisms. The subproblems in the survival realm include obtaining food, managing in harsh climates, avoiding parasites, cooperating with others, acquiring a language, and becoming a competent worker, among others. In the reproductive realm, the chief subproblems include attracting a mate, preventing the mate from another alliance, achieving conception, avoiding poisonous foods during pregnancy, escaping from dangerous situations, and recognizing emotional expressions in infants and children and responding appropriately to them. But all subproblems involve a host

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of even more specific tasks. Attracting a mate, for instance, typically entails the following actions: acquiring the resources or characteristics anticipated by a potential mate, negotiating social institutions, competing with members of one's own sex for potential mates, forming a successful alliance, appeasing—or at least not alienating—the potential mate's family and friends, successfully courting the mate, and engaging in other forms of alliance (Buss, 1991).

Many widespread human fears, preferences, and behavioral tendencies are viewed as responses to these specific problems, that is, as evolved psychological mechanisms. In the survival realm, human beings show more fear of snakes, insects, and high places than of automobiles and electrical appliances, which in contemporary civilization are far more dangerous. They show a strong taste preference for foods high in fats and sugar, a mechanism perhaps designed to increase caloric intake in the active life of hunter- gatherer societies but causing health problems in today's more sedentary world. Human beings show a greater ability to solve social-contract problems than other problems of equal difficulty, a possible adaptation to avoid exploitation in social exchange. And they show the universal acquisition of language, an evolved psychological mechanism that has greatly furthered human evolution, providing a means of cooperation within and across generations.

In the reproductive realm, modern men show greater preference for youth and beauty in their mates than do women, perhaps an adaptation to the younger female's reproductive promise. In turn, women traditionally have shown greater preference for experience and economic resources in the mate, a possible adaptation for the provision of offspring (Buss, 1995b).

These preferences, like all other evolved psychological mechanisms, do not require an intent to pass on one's genes. An individual of course may have this aim on occasion. But people sometimes misunderstand evolutionary psychology in this way. If people possessed only the goal of passing on their genes—to maximize their genetic reproduction—they would behave differently. Men would not visit houses of prostitution, and they would refrain from masturbation, lining up instead to make donations at sperm banks. And women might make their times of heightened fertility known more publicly (Buss, 1995a).

For the continuation of our species, people do not need to be motivated to replicate their genes. Instead, through natural selection, modern men and women have become especially responsive to cues most likely to result in reproduction anyway, just as they have become responsive to environmental cues triggering a wide variety of other behavioral dispositions, such as fears of snakes and darkness, taste preferences for fat and sugar, and the tendency to acquire language. The growing list of these adaptations extends from recognizing objects and judging distance to evading predators and avoiding disease. It includes, among many others, developing friendships, deterring aggression, and bargaining successfully (Cosmides & Tooby, 1992).

Moreover, common sense and mathematical calculations do not support the traditional view of the human mind as an all-purpose, general-capacity system. Rather, they indicate that a potentially infinite number of conclusions could be drawn from the facts of most circumstances in everyday life, and an infinitely accommodating “blank slate” simply could not function effectively. The human mind-brain mechanism must be designed to reach only a limited number of conclusions about a particular constellation of facts. Biological psychology points to specific adaptations throughout the animal kingdom. Different species show sharp, innate differences in drives, habits, and abilities, ranging from food preparation to celestial navigation. Cognitive psychology suggests that human beings are specifically prepared for the comprehension of language, recognition of faces, perception of color, analysis of physical space, and other ways to interpret the world (Hirschfeld & Gelman, 1994; Pinker, 2002). According to evolutionary psychology, many specific fears, preferences, and behavioral tendencies in modern life have been shaped by the demands of individual survival and reproduction in ancestral cultures.

In this view, the human mind is a series of modular mechanisms. The concept of modularity here, broadly consistent with the doctrine in biological psychology, emphasizes restrictions in information processing. The content or information available to one module does not necessarily become available to other modules in that same system. Cognitive neuroscientists are just beginning to understand how biological modularity mediates and constrains specific cognitive activities (Flombaum, Santos, & Hauser, 2002).

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This view that the human mind is divided into modular domains has aroused extensive debate within and outside evolutionary psychology. After all, we generally experience a unified self. How could this confederation of independent entities be possible?

Answers to that question await further research in psychology and related sciences. At this point, evolutionary psychologists simply assume that the modern human mind gradually evolved over the millennia of human history. It emerged through steady inheritance from countless ancestors who solved specific problems of survival and reproduction. The outcomes of their success appear today as evolved fears, preferences, and behavioral tendencies.

Afraid of snakes, fond of Viennese pastries, and fluent in four languages, Bertha showed some of these fears, preferences, and behavioral tendencies. Like the rest of us, she also showed some exceptions, notably with regard to sexuality. In all such instances, evolutionary psychology recognizes the reciprocal roles of heredity and environment in producing individual differences. For everyone, including Bertha, the result is an interplay between these influences.

In the sexual realm, Bertha apparently became an exception through environmental influences. Her success in mating had been seriously impeded by her early illness, which prevented socialization and sexual development at a crucial stage. Later, her domineering, self-centered personality disrupted prospects for reciprocal alliances, successful courting, and so forth. Her deepest involvement with human sexuality occurred in her expedition to the brothels.

Arriving in Budapest, she met with a tall Hungarian in clerical clothes. She explained her mission and he replied, “I am not interested in this matter.” Reminded that he served as chairman for the Society for the Protection of Children, he responded: “Yes, but only children up to 12 or 13 years. Older ones are not my business.” So ended Bertha's effort in Hungary, her first attempt to overthrow forced prostitution in Eastern Europe.

At a consulate in Greece, she raised the problem again and received a hasty disclaimer. “What do you want? The poor sell their children like chickens!”

On a Saturday night, she entered a house of prostitution in Salonika. There she met the women at their work. Later that night, she wrote about Jolanthe, one of these women. “The most beautiful one I saw here, maybe the most beautiful Jewish woman I ever saw, perhaps the most beautiful alive, I found today in a brothel.” Bertha pondered her discovery. “I can understand that a man will risk all for such a woman,” she mused (Pappenheim, 1924).

Evolution of Sexual Behavior

Human sexuality marks the starting point for a discussion of various evolved psychological mechanisms because reproduction marks the beginning of the life cycle. Without reproduction we would not exist. Without a fear of snakes, tendency toward language, or preference for sweets, we still might exist, though in modified form.

But there is a drawback to this focus on human sexuality. The chief criticisms of evolutionary psychology relate to the findings and interpretations of mate preferences and mating patterns. They have been viewed as counterproductive to the pursuit of gender equality. At this point, the reader is encouraged to follow the data and theories of evolutionary psychology, the focus of this chapter. As usual, the chapter closes with commentary and criticism of this approach to psychology.

Preferences in Mate Selection

From the standpoint of evolutionary psychology, Bertha was quite correct. Men would be attracted to Jolanthe's beauty. Other things being equal, they prefer beautiful women.

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Why does that happen? How does this preference arise?

Consider a society without mating preferences. Through random pairing, males who mated with infertile females would not become anyone's ancestors. Those who mated with females high in fertility would produce progeny, passing on their genes, including their preference for female characteristics associated with fertility. As this selective process continued for millions of years, even with very slight genetic variations among individual members, males would acquire a tendency for mating with fertile, rather than infertile, females. Without any intent or motivation in men, this tendency would be passed on as an evolutionary adaptation—an evolved psychological mechanism.

Through these reproductive adaptations, men and women have developed mate preferences. The concept of mate preferences refers to the characteristics desired in a partner, and these preferences are based largely on the gender roles in the reproductive process, which are quite different for men and women. With millions of sperm readily available, a reproductive man must find and engage a woman who is fertile—a characteristic difficult to assess. As a rule, the younger the mature woman, the greater is her potential for reproduction. But just as fertility is uncertain, age is not readily determined either. There are, however, reliable cues for age. A woman with smooth skin, glossy hair, shiny teeth, and a light, sprightly style is probably young and therefore likely to be fertile. Similarly, a woman with physical symmetry shows a sign of health and therefore likely fertility. Over the eons of evolution, men attracted to these fertility cues produced more offspring than men attracted to women without such cues. They thereby passed on this preference for these physical characteristics in a mate (Buss, 1999).

In Hungary, Greece, and elsewhere, Bertha found these characteristics among the prostitutes. The male preferences in mate selection were reflected in the brothels.

The woman's investment in reproduction is indeed different from that of a man. With a limited number of eggs, available only at certain times, and the extensive demands of gestation, birth, nurturance, and especially child rearing, women must find a mate with an ability and willingness to furnish the necessary resources for successful parenting. These include, among others, food, shelter, time, territory, and protection. Mates with such resources provide a selective advantage for the woman and her progeny. On this basis, status and possessions, power and territory, and so forth should emerge as female preferences in a mate. However, human beings often mate at relatively early ages, before a man's resources are fully acquired. For this reason, females too should use predictive cues, such as intelligence and industry (Buss, 1999). A man who is bright and hardworking is likely to acquire resources. Hence, these qualities have emerged as female preferences in mate selection.

These evolved preferences do not guide the selection process completely. They make a contribution as an inborn tendency or disposition. As evident in social psychology, other factors, conscious and otherwise, contribute to this complex process. Especially important are the extent to which potential partners are alike in fundamental ways, such as intelligence, interests, values, and in many societies, the extent to which they know one another (Botwin, Buss, & Shackelford, 1997; Homans, 1961). These two factors, similarity and familiarity, can distinctly moderate the tendency among men and women to seek mates high in attractiveness and resources, respectively.

Variations in these tendencies, produced by individual genetic differences and environmental factors, are of no special interest in evolutionary psychology. But they are not inconsequential. Without variations among individuals, there would be no grist for the mill producing the survival of the fittest.

Environmental factors may even produce group differences. For example, social-role theory suggests that as women in developed societies gain increased economic advantages, their preferences in mates may be shifting away from supportive males and toward attractive men as desirable partners (Eagly & Wood, 1999).

Whatever their preferences, members of the same sex vie with one another for mating opportunities. Men compete with men in intelligence, industry, and so forth, just as women compete with women in various ways. For the losers in these battles within the sexes, the result is not death of the individual but rather few or no offspring (Darwin, 1859).

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These mating preferences do not necessarily operate at a conscious level. There are, of course, “gold- digging” women, consciously aiming to tap a man's resources. Presumably, they are also impelled by their evolutionary history, directing their preferences toward male traits consistently associated with the resources, willingness, and ability to engage in the labor-intensive activity of successful parenting (Ellis, 1992). Similarly, men divorce older wives and marry younger women, sometimes called “trophy wives.” The label suggests that the men have been winners in some sort of contest, and their high-value mates are the prize. Again, men may consciously engage in this behavior, seeking a young and beautiful wife as a status symbol. But this conscious effort does not rule out for them, or for males throughout the world, a universal interest in such women as a function of a lengthy, selective evolutionary history.

Common Mating Patterns

In addition to mate preferences, this same evolutionary history has shaped the mating patterns of men and women, meaning their overall approach to sexual encounters during their lifetime. And different patterns have emerged. The ancestral man who experienced high reproductive success mated not only with one fertile woman but with many fertile women. Compared to monogamous men, he was far more likely to produce dependents. In this process, continued over millions and millions of years, males evolved a predisposition for sexual variety; they developed a tendency, or pattern, for mating with several partners (Symonds, 1979).

A woman who achieved reproductive success found a man capable of investing in the high costs of rearing offspring and willing to make that investment. Gaining continuous access to these resources became a primary benefit for the woman. On these bases, women evolved a reproductive pattern of sustained mating with a single partner.

Under these conditions, evolution has shaped men to a more polygamous disposition, oriented to sexual encounters with multiple partners. And it has shaped women to more monogamous relationships, the practice of mating with the same partner. These different outcomes evolved from the fundamental asymmetry between the sexes at minimum levels of parental investment. Such levels are much lower for men and much higher for women, leaving men less restrained by the consequences of the reproductive act. In other words, men have more interest in casual sex, as popular knowledge attests. Evolutionary psychology aims to understand the origins of this difference in evolutionary history, rather than in current social roles, which certainly are influential.

Impregnation by an ancestral man would require nine months of gestation on the woman's part but no further investment by him. During this same interval he might engage in numerous copulations with other women, resulting in several pregnancies. She in turn would experience only one birth. Thus, for men, compared with women, short-term mating resulted in a far greater number of offspring. Carried on through millions of generations, this inclination toward polygamy and short-term mating would become an evolved psychological mechanism in men.

Substantial support for this view comes from the presence of prostitution and extramarital affairs in modern life. Both provide evidence that men, more than women, seek short-term mating patterns. The consumers of prostitution are essentially all men. Participation by women remains negligible. The famous Kinsey Reports brought forth the first substantial scientific data, showing that 70% of men went to a prostitute at one time or another. The frequencies for women who did so were too miniscule for further consideration (Kinsey, Pomeroy, & Gebhard, 1953; Kinsey, Pomeroy, & Martin, 1948).

The Kinsey Reports also showed wide gender differences among those who participated in extramarital affairs, with men engaged at nearly twice the rate of women. Once again, these findings have been supported by subsequent surveys. But social-role theory enters here too. With fewer behavioral restrictions for women today, the gender difference in extramarital affairs has decreased, though it still remains substantial (Janus & Janus, 1993).

The difference between these two forms of short-term mating accounts at least in part for the stability of prostitution and changes in extramarital affairs. The former is only a sexual encounter; the latter includes some element of love or romance, as well.

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Moreover, casual sex involves far greater costs for women than for men. These costs include a higher risk of sexually transmitted disease, unwanted pregnancy, and loss of value as a long-term mate. Prostitution carries all these risks, including contact with other unstable activities.

This polygamous tendency in men worldwide of course promotes prostitution. After her meetings in Hungary and Greece, Bertha realized the extent of prostitution, appearing literally around the globe. The women most susceptible to recruitment were young, impoverished, and ignorant about sex. Their pregnancies became burdensome for all. Unwed mothers could not care for themselves, much less for their unplanned babies.

Adaptations in Parenting

Pregnancy, too, has been shaped by natural selection, according to evolutionary psychology. In particular, the early weeks reflect an adaptation over the millions of years in hunter-gatherer societies.

Pregnancy Sickness

Modern women in the 2nd to 10th week of pregnancy experience nausea, vomiting, and food aversions, incorrectly called morning sickness. This condition varies among different women but appears in virtually all societies. It is not limited to the morning and strictly speaking is not a sickness. Early in the pregnancy, avoiding certain foods and vomiting others are healthy responses, nevertheless known as pregnancy sickness. These aversive reactions, created by hormonal changes in pregnant women, shield the unborn baby from teratogens, poisonous and other substances that produce birth defects (Profet, 1992).

From the viewpoint of evolutionary psychology, food aversions evolved as an adaptation of our hunter- gatherer ancestors, who foraged for anything edible. Through a broad diet of nutritious and harmful foods over millions of years, aversions to poisonous foods became an evolved psychological mechanism, protecting the pregnant woman from malnutrition that would harm her unborn baby. Several studies have demonstrated that the absence of nausea and vomiting is associated with higher neonatal abnormality and mortality (Brandes, 1967; Tierson, Olsen, & Hook, 1986). In other words, pregnant women who vomit tend to experience fewer miscarriages, stillbirths, and related problems (Klebanoff, Koslowe, Kaslow, & Rhoads, 1985).

The timing of this sickness matches the development of the embryo, the prenatal period from the second week through the second month, during which the baby's neural organs, in particular, begin sustained growth. The embryonic period is thereby the most important of the entire pregnancy for the healthy, prenatal development of human organs. Expressed differently, it is the stage of maximum susceptibility to teratogens.

Plants are consumed by numerous predators, including insects, animals, and other plants. To defend themselves, they have evolved diverse chemical substances as weapons against attack. These toxins, or poisons, appear even in apples, bananas, cherries, and other common elements of human diets. However, coffee, tea, cocoa, and vegetables contain unusually high concentrations of toxins for human beings, and they are the foods women find most aversive early in the pregnancy.

Then too, the sense of smell becomes more acute during the first weeks of pregnancy. At this stage, pregnant women are repulsed by odors previously found satisfying. In particular, pungent and bitter odors arouse an aversive reaction, causing rejection of all highly spiced foods and many vegetables. This change in olfactory sensitivity favors bland foods, which contain lower concentrations of toxins, thereby diminishing the potential for toxicity during the embryonic period. In fact, many pregnant women experience food cravings as well. The aversions may be due to changes in the sense of smell, the cravings to an impaired capacity for taste. Both responses appear to play a protective role for the embryo (Dickens & Trethowan, 1971).

In addition to their role in pregnancy, most innate food aversions have emerged as protections against toxicity throughout the life of the individual. Pregnancy sickness is an extra, early, short-term defense against embryonic birth defects. During the period of the fetus, beginning at the third month and lasting through the remainder of the pregnancy, this nausea disappears; then prenatal neural developments require a substantial increase in maternal nutrition (Profet, 1992).

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Infant-Directed Speech

After the birth, the mother begins responding to the neonate, and once again evolution appears to shape the process. The new mother speaks to the baby long before the infant develops even the rudiments of language. Moreover, she speaks in a very distinct manner. Through highly specific, almost musical patterns of pitch, range, and intonation, known as infant-directed speech, the caretaker communicates her feelings and controls the infant. The baby cannot understand language but has the maturity for feelings. It becomes aroused, approved, prohibited, and comforted by the mother's speech, which uses modifications informally called motherese (Fernald, 1992).

Adults usually speak to one another in a quick, choppy fashion. Caretakers speak to their infants more slowly and with more emphases.

To arouse the infant and catch its attention, the mother uses a wide range of pitch. Then she ends these vocalizations with a sharp rise in the last syllable: “Can you get it?” To express approval, she again employs a wide range of pitch, but she ends with a falling tone: “That's a good bo-oy.” The mother is communicating her positive feelings and, at the same time, rewarding the baby.

For prohibition, infant-directed speech takes on a very different character. The caretaker employs a low pitch with little variation. The smooth, musical quality for catching attention and showing approval does not appear. Instead, the sounds are shorter, more intense, more abrupt: “No. No!” Staccato sounds serve as unconditioned stimuli; no learning is required. The infant responds to the noise completely apart from its linguistic features.

As with prohibition, infant-directed speech communicates comfort in a low pitch with little variation. However, the sounds are longer and softer, less intense: “Mmmmm. Oh, Honey.” Like prohibition speech, the sounds that induce comfort appear to be unconditioned stimuli. The infant's response is automatic. Low-frequency, continuous white-noise sounds also function effectively for soothing a distressed infant. In white noise, the intensity is constant, as in the common quieting sound, “Shhhh.”

In simple terms, infant-directed speech employs exaggerated intonation. Used consistently in cultures throughout Africa, America, Asia, Europe, and other parts of the world, it appears as an evolved adaptation of mothers' attempts to communicate with their prelinguistic infants. The baby's limited perceptual abilities require this responsiveness by the mother. These patterned modifications serve to regulate the infants' attention, communicate feelings, and increase the potential for speech perception and comprehension. They form an early basis for infants' experiences about themselves and those who care for them (Fernald, 1992).

One cross-cultural study of both parents compared infant-directed speech with adult-directed speech in English, French, German, Italian, and Japanese. Similar modifications from adult speech appeared in all languages, supporting the evolutionary predictions. They even occurred with men, although at a lower level, perhaps owing partly to infants' lesser interest in men's voices. The American mothers, speaking English, showed the most pronounced modifications, thereby illustrating cultural differences as well (Fernald, Taeschner, Dunn, Papousek, de Boyson-Bardies, & Fukui, 1989).

Virtually universal in women, infant-directed speech improves with experience. The caretaker makes adjustments according to the baby's response, eventually speaking “advanced motherese.” Without babies in her own home, Bertha missed the intensive child care that fosters this further development. An element of learning is involved in infant-directed speech.

Throughout her adult life, Bertha also missed a sustained relationship with an adult partner. And the two conditions appear related, both perhaps with roots in her Vienna days. Her work with residents and staff of The Home thereby played a major role in her personal life. But despite these associations, she remained without friends and even without regular companions (Edinger, 1968).

Alone on the ship sailing to Egypt, she sought social support. When her cabin neighbor discovered she was not married, he pointed out that it was still not too late. If she colored her hair, she might look 30. Bertha

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ignored the entreaty. Her birth certificate showed she was 52.

After that man left the ship, Bertha wrote, “There's nothing to report except that it's the worst day of my trip. It pours!”

In Alexandria, a police officer escorted her to several brothels. In one, she and her guide sat at a large table with three girls, all of whom were wearing colorful shawls and similar necklaces, made up of strings of tiny beads and coins. Two of the girls were 16 and 17 years old. They spoke freely, but the third prostitute remained silent. Later, she pointed at Bertha and remarked, “She shall be blessed, and her family also, for no such woman has ever thus spoken to us.”

In a visit to Lodz, then part of Russia, Bertha described her mission to a German woman who was highly respected in feminist and other circles. She readily understood Bertha's concern. Then she heard Bertha's goal: to diminish or destroy the slave trade.

She stared with raised eyebrows. “A swallow wants to drain the sea?” she asked incredulously.

Arriving in Warsaw, still alone, Bertha began again to doubt her mission and herself: “I am not necessary. For nothing and to no one.” She sorely missed conversation, companionship, even the most minimal social life.

Dispositions in Group Living

Human beings are fundamentally social creatures. Responsiveness to others is perhaps the most obvious aspect of human existence. Evolutionary psychologists speculate that the human tendency toward social behavior evolved through the advantages it offered in the struggle for survival. By working together for millions of years, people gained increased success in building shelters, finding food, caring for the young, and defending against attack.

In other words, to behave adaptively our remote ancestors needed to acquire a capacity for responding not only to their physical world but also to their social environment. As members of social groups, those most suited to survival were those who developed mental mechanisms for social exchange, a broad term referring to all sorts of behaviors for solving problems in a social context—dealing with other people, their relationships, emotions, motivations, interactions, and other conditions of social life. This capacity for social exchange is also known as cooperation, reciprocation, and reciprocal altruism (Cosmides & Tooby, 1992).

For several reasons, skill in social exchange appears to be a long-term adaptation. If it were a recent social invention, there would be evidence of some point of origin, and there is none. In addition, there is no substantial evidence that it has been spread by contact among different peoples. Social exchange is not sparse or absent in some cultures and complex in others. It appears in highly elaborated patterns in all cultures. Moreover, social exchange is not unique to human society. Social exchange occurs among chimpanzees, our nearest relatives, and among baboons, suggesting that it appeared at least as early as our common ancestors, several million years ago (Cosmides & Tooby, 1992). Major social tasks include using language, transmitting and interpreting facial expressions, and detecting cheating in a social contract.

Acquisition of Language

With the acquisition of language, the ultimate mechanism in social exchange, humanoids could assist one another in the nuances of these tasks. And language plays a central role in the most intimate social behavior—finding and maintaining a mate. There are, of course, competing explanations about how human beings acquired language.

From an evolutionary perspective, human language began with grunts and gestures, gradually increasing in complexity until, over the millennia, it reached its current intricate stage. A result of natural selection, learning language today is not like learning to play the piano or to balance a checkbook. Through natural selection, human beings have become genetically predisposed to learn language; it unfolds almost automatically, as

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another evolved psychological mechanism. Vocabulary, specific rules, and stylistic devices of course must be learned, but people are born with the basic structure in mind, a so-called universal grammar. Common to every normal person, this universal grammar is an innate understanding of how language works—an inborn comprehension of the fundamental components of language and their relationships (Chomsky, 1957, 1972).

Signs of this universal grammar appear in speech. All the world's many hundreds of languages are alike in important but non-essential ways. For example, they employ just a few of the many sounds human beings might use in speaking. Infants can make many sounds found among animals, including birds, but they do not use them as adults. There is no logical necessity for this narrow range of sounds in existing languages, and cultural differences would work against it. This uniformity appears to be a function of an inborn tendency, a common biological inheritance around the world.

In addition, no primitive language exists today. And there is no significant evidence that cultures are learning or developing their languages in basic ways. In complexity of structure, the languages of aborigines are comparable to those of the modern industrialized world. This condition might reflect the absence of written reports from much earlier times, but even the available records, some from 5,000 years ago, do not indicate any increase in complexity. The earliest reconstructible stage for families of languages includes all the complexities and capacities of Bertha's modern German, French, Italian, and English.

The speed, sequence, and universality of language learning add impressive evidence to the concept of a universal grammar. Children sometimes acquire 5 to 10 new words per day, and they learn in the same sequence, as noted earlier, moving in a few years from cooing and babbling to complex constructions, along the way making similar, predictable errors in grammar and syntax (Miller & Gildea, 1987).

In forming questions, and without being told, the child learns that the wh words—when, what, why, where—come first in the sentence. And the child already knows that nouns precede verbs. Hence, in some languages, children ask: “Where the ball is?” Later, they reverse the sequence with wh words. As the quintessential human skill, mastery occurs in a stable, reliable pattern (Brown, 1973).

Severely retarded persons, unable to acquire many basic skills, typically acquire language ability, although at a slower rate. In fact, children can understand language before they can comprehend many other social codes in their community—manners, customs, bartering, and reciprocity. These forms of social exchange are the fabric of society. They bind citizens together. Like the capacity for language, mastery is essential for survival in one's group. On all these and other bases, human beings appear predisposed to learning language, an evolved psychological mechanism.

Shared Emotional Expressions

The ability to express and recognize emotional states emerged as another mechanism of social exchange. Predecessors with this capacity possessed an adaptive advantage. They were more likely than others to identify desirable mates, anticipate attack, appeal successfully for assistance, and the like.

Darwin described the emergence of emotional expression through natural selection. Prior to fighting, certain animals thrust the head forward, assume a firm stance, bare the teeth, and gaze intently at the opponent. These postures and gestures, the first stages of attack, provide an advantage for the aggressor; they prepare fighting weapons. Moreover, if these preparatory behaviors suffice to subdue the opponent, the victory is accomplished without bloodshed. For the opponent, anticipation of the attack becomes crucial to defense and counterattack, and submissive behaviors sometimes prevent the physical encounter. Natural selection favors the expression and recognition of emotional signals (Darwin, 1859).

On the same bases, human beings have evolved the capacity to send and receive nonverbal signals about their emotions. These facial expressions in emotion are consistent patterns of movements and positions of the face associated with certain feelings: happiness, sadness, anger, fear, surprise, and disgust. Concentrated around the eyes and mouth, these movements and positions also appear in the forehead, nose, and even the chin. As still another evolved psychological mechanism, human beings reliably depict their feelings, wearing them not on their sleeves but on their faces.

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Contemporary research has examined these six emotional states—happiness, sadness, anger, fear, surprise, and disgust—in human beings. Obtaining many pictures of various people in these circumstances, investigators measured the position of each part of the face and its degree of displacement from the normal or relaxed state. Using these findings, they produced composite or “typical” photos for each state. Also, they asked actors to assume the various positions and again took photographs. Then they presented these photos to people in Argentina, Japan, Chile, Brazil, and the United States.

Asked to assign one of the six feelings to each photo, observers in all cultures attributed the same feelings to the same facial expressions, matching the original situations. Additional studies with eight different cultures provided the same result. Even preliterate people in the remote highlands of New Guinea responded the same way as people from other cultures—with one exception. They made no distinction between the expressions for surprise and fear (Ekman, 1992; Ekman & Friesen, 1975). These results suggest a universality in sending and interpreting these emotional expressions.

Other expressions vary from culture to culture. Scratching the cheeks may show indecision in the United States; in some Asian societies it is a sign of happiness. Clapping the hands, evidence of joy here, indicates worry or disappointment in certain Asian groups. Europeans show displeasure by whistling, a sign of approbation in this country (Fernald, 1997). All these expressions are learned, transmitted by elders in the culture. They are not universal, not evolved psychological mechanisms.

Human facial expressions are also accompanied by gestures and postures that vary markedly from one person and moment to another. Angry people may clench their fists, turn their head aside, or assume a stiff posture, and yet these same behaviors may accompany fear, sadness, or some other emotional state. In other words, their behavior shows the way they are coping with an emotion. Within the limits of the six basic emotional states, their facial expressions reveal what they are feeling, recognized universally, even by “foreigners.”

Making Social Contracts

Another form of social exchange, useful in almost any group, is skill in making social contracts—dealing with others on a cost-benefit basis. In a social contract, one individual, at some personal cost, becomes entitled to a benefit from another individual or group. The concern lies with the cost-benefit outcome. A well-formed social contract becomes mutually advantageous; each party gains a benefit that outweighs the cost.

In the evolutionary metaphor, people negotiating social contracts wage wily, subtle battles. Rather than attacking one another physically or fighting over limited supplies, the warriors compete in an exchange of property or services. Throughout history, human beings have made endless exchanges of all sorts, ranging from food and shelter to child care and combat assistance. Those who possessed special skill in making such bargains maintained an adaptive advantage. They obtained more food and mates and produced more descendants. Predecessors who lacked this skill negotiated unsuccessfully. They became less likely to survive and reproduce.

On this basis, the reasoning of modern human beings about social contracts should be superior to their reasoning about problems without a social contract. Indeed, people today do solve problems about violations of social contracts more readily and successfully than they solve comparable problems on other topics. Moreover, the possibility of a payoff, by itself, is not the critical factor. The superior reasoning occurs even when there is just the potential for a violation (Cosmides & Tooby, 1992). The critical issue seems to be a rule about potential costs, benefits, and wrongdoing, apart from the specific contents of the problem.

This capacity to detect violations, sometimes called a cheater-detection mechanism, does not imply that people are invariably successful in detecting cheating—far from it. It indicates that, other things being equal, most people are more successful in detecting cheating in a social contract than in solving other problems with the same structure but without a social contract, such as conventional nonsocial situations, abstract problems, or nonsense conditions. Human beings are not notably adept at solving logical problems, but they do better than usual when cheater detection becomes involved (Figure 8.2).

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Figure 8.2 Detecting Violation of a Social Contract. Which cards must be turned over to detect a rule violation? Most people respond successfully to the drinking problem, turning the first and third cards, and unsuccessfully to the vowel problem, again turning the first and third cards. Card 15, not 6, may violate the vowel rule. That rule does not state that a card with an even number must have a vowel. Similarly, the drinking rule does not state that anyone over age 21 must drink alcohol

A number of investigations support this viewpoint, demonstrating that the outcome is independent of one's familiarity with the topic. But the evidence is not yet complete or distinctly convergent (Evans & Chang, 1998). The hypothesis about cheater detection in social contracts awaits further support.

Human beings enter social contracts regularly. They satisfy many of them automatically by shaking hands, making a purchase, or obeying a rule. It is impossible to imagine human society without such contracts. They exist in fundamental ways within and across cultures.

Shortly after her arrival in yet another culture, Bertha shook hands and entered into an unwritten social contract with Countess Barbara, her hostess in Moscow. In return for a tour of the poor sections of the city, she would inform the Countess about social activism in Germany.

This social contract, or sharing of information, appeared beneficial to both. The cost to each, explaining one's culture, was relatively low and the benefit high because a first-hand description of that foreign land was otherwise a scarce commodity. When resources are scarce, sharing is one method of redistribution, thereby diminishing deprivation. Lack of food, even for a few days, makes individual survival impossible. Sharing in times of feast lessens the potential for times of famine. According to evolutionary psychology, the tendency to engage in social contracts evolved because it usually results in mutual benefits, though of course there are exceptions.

Mutual benefits occurred for Bertha and Barbara, and apparently neither cheated. But their contract bore more costs than either expected. They promptly found themselves ideologically opposed.

Both women were headstrong, and they possessed very different ideas about prostitution. The Countess repeatedly declared she had “no sympathy” for prostitutes. Bertha expressed deep compassion. They argued vehemently and finally dropped the subject—a tacit agreement that made the rest of their time together tolerable.

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The Countess supervised a government institution for the homeless. For their nighttime expedition, her part of the contract, she invited Bertha to come with strong nerves and a short skirt. Bertha accepted, wearing a skirt above the ankles. It would not drag on the floor and thereby collect vermin.

“I need not tell you what I saw,” Bertha reported to her subscribers. Then she gave some details anyway. “I almost suffocated when I saw drunken men and women, heard their yells and laughter … saw the basement where the bodies of those killed in all-night fights were dumped.” The amateurs, not the professional prostitutes, posed the most serious threats to themselves and others.

Finally, at 11:00 p.m., Bertha thanked the Countess for a most illuminating experience. The Countess replied that she was pleased to be useful.

“My thanks were sincere,” Bertha later declared, “though I knew that, conventionally and politely, I shook hands with an enemy.”

Returning to Frankfurt following 15 months of travel, Bertha organized national and international committees to combat slavery-induced prostitution. Later, she decided that she had failed in this compelling mission, noting that she had brought few people into the cause. This outcome became one of the few substantial disappointments in her working life. But she gained one small habit. During board meetings later, she occupied herself by stringing together tiny beads and coins, making necklaces like those she had admired on the three young prostitutes in Alexandria (Freeman, 1972).

Inclination toward Aggression

The different inherited dispositions of men and women toward sexual behavior and parental investment appear to be natural outcomes of their different biological structures. These biological differences also have profound implications for gender differences in aggression. They result in different tendencies toward within- gender rivalry and the type of aggression, physical or verbal.

Throughout the world men, more than women, resort to physical aggression, which includes any form of bodily assault, from simply pushing and shoving to homicide (Archer, 1994; Wrangham & Peterson, 1996). Women, more than men, engage in verbal aggression, which is any form of attack on another person by using language, ranging from insults to hostile gossip and slander. The latter behaviors can be potent indeed, sometimes causing more damage than a physical attack. In both cases, these forms of aggression are more likely to occur within than between genders (Buss, 1999).

Early research focused on the environmental factors stimulating physical aggression: the presence of weapons, observations of aggressive people, and frustrating circumstances. For example, observing television violence contributes to aggression in children (Eron, 1982; Hoberman, 1990). But the presence of physical aggression down through history and across societies suggests some inherited predisposition, and here evolutionary psychologists have collected data and proposed explanations.

In urban life, men have committed over 80% of the homicides, and their victims have been at least 80% males. In a large number of societies, male-male homicides exceed female-female homicides by a ratio of 30:1 (Daly & Wilson, 1988). Observed with such little variation throughout the world, this pattern has prompted questions about the reasons for this gender difference, and the chief hypotheses once again turn to the difference in reproductive roles. Men today respond aggressively in instances of direct sexual competition because throughout evolutionary history those who reacted in this way were more likely to reproduce and thus to contribute to the genetic inheritance of men. All men are exposed to paternity uncertainty, meaning the possibility that they are not the father of their partner's child. For this reason, some jealously guard their mate and fight with potential rivals. Women may not know who fathered their baby, but they do know that they are the mother.

On these bases it is not surprising to find gender differences in response to a partner's infidelity. A man exposed to infidelity risks the expenditure of energy and resources for another man's genes. A woman risks losing those resources, perhaps diverted to another woman. Thus, evolutionary psychologists predicted that

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male mating jealousy should be directed to cues of sexual infidelity, and female jealousy should arise from cues of emotional infidelity.

Several investigations have examined these hypotheses by measuring psychological and physiological responses, and replications have appeared in other cultures. In one instance, 256 college students in the United States imagined a scenario in which their partner had engaged in passionate sexual intercourse with someone else or had become deeply attached emotionally to that person. Then they indicated which type of involvement they would find more distressing. The results clearly supported the predictions and earlier findings. Follow-up studies investigated which types of infidelity they would be more likely to forgive and which would more likely prompt them to break up with their partner. Again, the results confirmed the prediction (Shackelford, Buss, & Bennett, 2002). These findings become vital in the context of male sexual jealousy, the most prominent cause of spouse battering around the world (Daly & Wilson, 1988).

In addition to sexual rivalries, other conditions fostered aggression in the long sweep of history. Aggressive people gained and stockpiled resources, defended against attack, negotiated for higher status in the social hierarchy, and also deterred their mates from infidelity. These specific contexts suggest that aggression today is not a blind instinct or totally unpredictable human tendency. It appears instead as an evolved psychological mechanism, closely tied to specific situations that are similar to those encountered by progenitors who responded aggressively and thereby gained adaptive advantages (Buss, 1999).

Aggression in women, typically verbal, usually occurs toward other women, labeling them as promiscuous or unattractive. Here too, sexual rivalry apparently plays a fundamental role in human aggression. Both remarks depict the slandered person as sexually undesirable (Campbell, 1993). Women also engage in physical aggression, but compared to men they are less prone to this behavior and less violent.

Again, environmental factors can sharply modify inherited tendencies. Studies of 20th-century college students show a decrease in verbal and physical aggression over a 10-year period. Questionnaire data were collected from 603 students in 1986, 414 students in 1992, and 571 students in 1996; all of these students were between 18 and 24 years old, and all were engaged in a dating relationship. For both men and women, self-report scores showed that physical and verbal aggression had diminished for each successive time period. Perhaps more significant, the reports also showed a decrease in the partner's aggressive reactions over the decades. Expressed differently, in recent years fewer men and women indicated that they were in a mutually violent relationship. And finally, an increased percentage of women described themselves as perpetrators of violence, rather than victims, a finding consistent with other research on dating couples (Billingham, Bland, & Leary, 1999).

Whether these results will be confirmed by future studies and whether they partly reflect changing social roles have yet to be determined. From a sociocultural context, it may be useful to recognize more fully that women also become aggressive and that a more egalitarian approach may be helpful to both genders.

Throughout her life, Bertha tended to resort to verbal aggression. Even 12 years after her battle of the brothels, she expressed anger over her almost complete failure. But she channeled her feelings in a productive fashion, writing a book entitled Sisyphus Work, describing her efforts as like those of the Greek mythical character compelled eternally to pushing a boulder toward the top of a hill, always losing his grasp, and watching it roll down again. In fact, the analogy is imperfect. Bertha never approached the top of the hill, and she discontinued her efforts after that one sustained attempt.

Promoting Behavioral Change

In dealing with her anger and disappointment, Bertha would find no assistance in evolutionary therapy. There is none. Evolutionary psychology offers no therapy for depression, frustration, or any other human reaction. Human beings can make changes in their lifestyles and environments, but they cannot change their evolutionary history.

Evolutionary psychology also does not study the ways one person is different from another. It has little interest in individual differences. It focuses exclusively on shared characteristics, aiming to understand humanity, not

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particular human beings. For this reason, too, there is no therapy in evolutionary psychology.

The absence of an evolutionary therapy leaves a space here to consider a vital issue for all psychological therapy. What are the outcomes? To what extent is therapy helpful? These questions present a challenge for scientists and practitioners, and several have undertaken the difficult task of finding answers.

Assessing Therapy Effectiveness

Modern therapies in psychology offer a range of choices. In choosing a therapy, one chooses a particular technique or focus. Biomedical therapy alters the nervous system; psychoanalysis explores unconscious motivation; the goal in behavior therapy is to modify overt behaviors; humanistic psychology aims to generate self-understanding and perhaps release the actualizing tendency; and cognitive therapy corrects irrational, depressive, self-deprecating thinking.

At the outset, it should be noted that all therapies certainly are not effective with everyone—far from it. In fact, much research in psychology has been devoted to discovering which therapies are most useful for which people experiencing what kinds of problems. No medicine, diet, exercise, or work situation is beneficial to all, and therapy for adjustment problems is no exception. The old expression applies: “Different strokes for different folks” (Lipsey & Wilson, 1993; Luborsky, Singer, & Luborsky, 1975).

Assessing the effectiveness of a therapy becomes a difficult task. First, it must be demonstrated that the therapy is superior to no therapy at all, for symptoms sometimes disappear without any formal treatment, an outcome called spontaneous remission. To demonstrate that a particular therapy is more effective than spontaneous remission, at least two groups of subjects are necessary, one receiving the therapy, the other without it.

Then another problem arises. The no-treatment group cannot be randomly selected from the general population. People seeking therapy are motivated to change, and motivation plays a vital role in therapy outcomes. The treatment and no-treatment groups must be similar in motivation. For this reason, studies of therapy effectiveness often assign to the no-treatment group people on waiting lists, seeking to enter therapy. They too are motivated to change.

And a further problem emerges. The no-treatment groups needs some sort of treatment in order to assess the placebo effect. A placebo is any event without therapeutic properties that the recipient nevertheless views as a treatment; it might be a conversation, group meeting, pill, shock, or séance, presumably offering therapeutic value. Thus, the placebo effect includes any improvement in therapy arising solely from a person's expectations about the value of the placebo treatment, which is assumed to be the real therapy. Especially with a new treatment, when hopes are high, the placebo effect may be as important as the therapy itself.

Thus, at least three groups are needed: a no-treatment group, called the control group; a no-therapeutic treatment group, called the placebo group; and the treatment group, known as the experimental group. If the placebo and control groups perform similarly, there is no placebo effect. If the placebo and experimental groups perform similarly, there is no therapy effect. The therapy serves no better than a placebo.

But here again, the answer is not simple. Including a placebo group enables the investigator to determine the influence of expectancy alone, apart from any treatment. But in the case of insight therapies, or talking cures, social interaction is part of the therapy. If the placebo involves social interaction, then it rules out the effect of social interaction in the therapy group. And yet, the personal-social dimension is widely acknowledged as a major ingredient in talking therapies (Elkin, Shea, Watkins, Imber, Sotsky, Collins, et al., 1989; Wilkins, 1986).

Finally, all sorts of other factors can influence therapy outcomes: characteristics of the person in therapy, the type of personal problem, type of therapy, qualities of the therapist, length of therapy, occurrence of other factors in the person's life, the criteria for reaching a decision, when they are applied, and so forth in seemingly endless numbers. Nevertheless, after 60 years of research, producing hundreds of studies involving thousands of people, the overall answer is that therapy does help. People who complete therapy show more gains in adjustment than comparable persons who do not enter therapy (Bentler, 1991; Lipsey &

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Wilson, 1993).

The findings of course vary from one investigation to another, depending on the many factors just enumerated. But the overall results show that 70 to 75% of the people in therapy achieve a more favorable outcome than those who sought or needed therapy but did not receive it (Grissom, 1996; Smith & Glass, 1977). Another early review revealed that approximately 80% of all investigations of therapy yielded basically positive results (Luborsky, Singer, & Luborsky, 1975).

Ultimately, successful outcomes in therapy depend on an interaction among three factors: the therapist, method, and person in therapy. As a rule, therapy is most promising when the person offering therapy is experienced; the person seeking help is relatively young and intelligent; and both parties truly believe in the specific therapeutic method. Overall, the essential ingredient for a positive outcome is a therapeutic alliance, meaning a relationship in which both parties make a deep commitment to the goals of therapy and to one another (Grotstein, 1990; Smith & Thompson, 1993).

But evolutionary psychology has no therapy; human beings cannot modify their genetic history. They can, however, find assistance in the management of some personal and social problems. These possibilities arise because evolution does not impose a genetic determinism, wherein behavior is completely controlled by the genes. Rather, evolution produces a disposition or tendency that sometimes can be modified by social and cultural factors.

A Catalogue of Hypotheses

Without a therapy, evolutionary psychology can still assist people with inherited fears, preferences, and behavioral tendencies. Appropriate information should enable them to increase their understanding of themselves and to adopt healthier, more productive views on life. In this regard, a systematic catalogue of evolutionary hypotheses, especially those with empirical support, could become a useful instructional device (Gray, 1996). It could describe each hypothesis, its rationale, evidence for and against it, and recommendations for further reading. The successful consumer would seek further information directly from peer-reviewed journals or indirectly through materials based on these sources. These materials would provide readers with second-hand reports about original research, broadening their outlook on their own and others' lives.

Most women in their first pregnancy, for example, remain cautious and a bit uncertain, seeking information on the birth process. When confronted with daily nausea, the expectant mother should find comfort and consolation from a reliable catalogue of information explaining that the greater her sickness, the greater are her child's chances of freedom from birth defects.

This catalogue could promote other benefits derived from understanding pregnancy sickness. Pregnant women experiencing only mild sickness may decide to avoid high levels of dietary toxins anyway, as a cautionary measure. Those who experience severe sickness may consider its advantages and disadvantages before consuming medications to alleviate this condition. And women who have smoked or suffered other impairment of the sense of smell might take extra precautions in their diet (Profet, 1992).

Information about child-directed speech should be helpful for new parents. When managing the highly sensitive infant, voice modulations can communicate approval, prohibition, and comfort, as well as call for the baby's attention. By the same token, a harsh or loud tone, directed anywhere within the baby's earshot, can be disruptive. Despite its lack of language, the baby is listening.

The somewhat older child may protest against going to bed alone, especially in darkness. Parents are sometimes surprised at this reaction in their child, particularly if they have taken precautions against any frightening circumstance. From an evolutionary view, the child's fear is quite normal. In hunter-gatherer life, predators were a constant threat, particularly when they could not be seen. With few animal predators in modern life, the child's problem may be alleviated by telling her that such fears were reasonable when wild animals roamed freely. Now dangerous animals are far away or in cages. Special lighting, music, and the proximity of adults may prevent the child from feeling abandoned in the dark (Gray, 1996).

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For parents, information on male-female differences in sex roles and relationships can be helpful with a significant social problem: men's physical violence, especially against the women in their lives. In all parts of the globe, husbands beat their wives, despite cultural and individual differences. This violence often emerges from sexual jealousy. Wives less frequently beat their spouses. From an evolutionary viewpoint, male jealousy and violence evolved as an adaptive response. A cuckolded man could spend his precious resources raising his rival's children. His jealous behavior played an important reproductive role. It ensured his paternity of the children born to his wife, whom he then supported (Wilson & Daly, 1993). Understood in this context, male violence certainly is not condoned or irremediable. But this evolutionary perspective may help citizens deal more effectively with this problem.

Violence toward children also has been viewed from an evolutionary perspective. A serious social problem, the incidence of child abuse varies with the genetic backgrounds of the parents. Child abuse is almost 40 times higher in families with stepchildren than in families in which the children are the biological offspring of the parents. Again, the interpretation centers around the evolved predisposition for expenditures of resources in behalf of one's own progeny (Buss, 1995a).

These irrational fears and forms of violence point again to the three fronts in Darwin's battleground metaphor. Human beings have made substantial progress against the forces of nature, developing weather forecasts about impending severe storms and constructing special shelters, clothing, and instruments for living in the coldest climates, highest altitudes, and deepest parts of the ocean. Also, human beings have conquered most of their predators, confining them largely to areas beyond human civilization. But we have not made comparable progress in living with one another. In the long run, our struggles among ourselves, especially over possession of nature's resources, may represent the most monumental challenge to our survival.

A catalogue of findings from evolutionary psychology could help us become more responsive to the dangers we create for ourselves, including the destruction we impose on our polluted and deteriorating environment. These reports could become a valuable part of public education and would be especially informative because many modern environments are so entirely different from those of the incomparably longer Pleistocene era.

Commentary and Critique

A partial list of these inferred psychological mechanisms shows their diversity: patterns of specific fears in infants, including stranger anxiety and darkness discomfort; adult phobias about harmless spiders, snakes, and other non-dangerous creatures; specific food preferences among children and adults, especially for fats and sugars; patterns of language acquisition in children, including its remarkable rate, invariant sequence, and predictable errors across cultures; the potential abuse of children, many times higher for preschoolers with adoptive as opposed to biological parents; morning sickness in pregnancy, occurring in embryonic development and in reference to fairly specific food categories; and adults' landscape preferences, favoring relatively open spaces as opposed to mountains or heavily wooded regions (Buss, 1999).

But these examples overlook a fundamental issue: gender differences. Human beings are men and women. To understand humanity, we need to know what women are like, as women, and men, as men.

In accepting this challenge, evolutionary psychology enters an arena fraught with controversy. The study of gender differences raises a special concern, as does the study of gender similarities. In almost any form, investigations of gender evoke criticism.

Research in evolutionary psychology has identified numerous gender differences as evolved psychological mechanisms: differences in risk-taking behavior, far greater for young males than females; differences in memory, with women superior in spatial-location and men in spatial-rotation capacity; differences in mate preferences, with men responding to reproduction potential and women to cues to a man's potential investment of resources; differences in mating patterns, with men more polygamous and women more monogamous; differences in sexual jealousy, greater for men than women; differences in interest in babies, with women far more involved than men; differences in sexual fantasy, with men engaging in it more frequently and more explicitly; and a host of other differences (Buss, 1995b, 1999).

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In the investigation of gender differences, one major issue concerns gender equality, an expression used in social, political, and economic spheres denoting equal rights and opportunities. This goal is laudable, and yet the term “gender equality” may contribute to misunderstanding and confusion. Men generally possess greater size and strength than women. In turn, women possess the capacity to give birth and breast-feed babies. The first difference is quantitative and variable, the second qualitative and fixed. On this basis, equality becomes impossible. The concept of gender parity might serve better, denoting functional equivalence in value without implying the impossible structural equality. Commonly used in expressing status or amount in different markets, parity acknowledges the obvious inequalities in physical capacities and thereby assists all of us in advancing toward the overriding goal—greater respect for the similarities and differences between the genders.

In any case, a useful behavioral science should enable people of both genders to gain increased understanding of themselves and their cultures. The usual obstacles in pursuing this goal are not only the accuracy of the scientific findings but also the way they may be interpreted and exploited in the media and elsewhere. Amid these difficulties, the politics of gender on one hand and the science of gender on the other create ideological issues, matters of controversy or debate between parties with different ideas and concerns about human life and cultural influences. Beginning with different assumptions, the science and politics of gender each demonstrate a way of thinking about human behavior, each with its own interests, assumptions, and goals.

A second major issue concerns the interpretation of the findings. In contrast to the evolutionary viewpoint, social-role theory states that men and women become psychologically different because their roles in society demand different adjustments. Gender differences are not necessarily the result of inherited differences but rather of unequal opportunities in society. They arise from the gender-typical ways men and women are expected to act—women more than men emitting communal behaviors, men more than women emitting agentic behaviors (Eagly & Wood, 1999). These behaviors emerge from the women's typical homemaker role, at least with infants, and the men's typical role as resource provider, at least in the family's early years.

Prominent gender differences appear in response to partner infidelity, as noted already. But there is no reason to believe that male sexual jealousy and female emotional jealousy arise solely on the basis of biological factors. Cross-cultural investigations with German and Dutch participants have demonstrated the same jealousy patterns identified in the United States. However, the differences were smaller in both European cultures, and these cultures approach sexuality and extramarital relationships with more openness and acceptance than generally occurs in the United States. Thus, the appearance of the predicted gender differences supports the evolutionary view. The fact that these differences were smaller than anticipated shows the impact of environmental factors (Buunk, Angleitener, Oubaid, & Buss, 1996).

Grandparents' differential investments in their grandchildren also illustrate the potential for different contributions by gender. Substantial research has demonstrated that when choosing among all four grandparents, the grandchildren typically identify the maternal grandmother as making the greatest contribution to their welfare, evident in the warmth of relationships, provision of resources, time spent together, and the like. Almost invariably, the paternal grandfather receives the lowest ranking, and the maternal grandfather and paternal grandmother stand in intermediate positions (Euler & Weitzel, 1996). The low position of the father's father involves two instances of paternity uncertainty; the high rank of the mother's mother involves no uncertainty. Each of the two remaining grandparents experiences one instance of uncertainty. All these outcomes were predictable according to paternity uncertainty. As genetic relatedness becomes doubtful, investment in relatives diminishes—a primary tenet of evolutionary psychology.

And, again, social-role theory can point to environmental factors. Women are typically trained in child care, and many find it gratifying. This inclination should not suddenly disappear on becoming a grandparent. Around the world, grandmothers contribute greatly to the raising of their grandchildren. Here too, evolutionary theory and social-role theory are not necessarily incompatible.

Many social-role theorists accept the concept of an evolved organism. And evolutionary psychologists have long discarded the false nature-nurture issue, which stated the problem in an oversimplified fashion, investigating inborn versus acquired factors. All living organisms have a heredity, and all exist in some

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environment. For years, later investigators focused on identifying the special contributions of each. But today we speak of the heredity-environment interaction, referring to their combined, catalytic influences, recognizing that each is directly influential and also indirectly influential through its capacity to modify the other (Figure 8.3).

Figure 8.3 The Heredity-Environment Research Question. Early in the 20th century, research focused on heredity versus environment, often emphasizing hereditary factors in human development. By mid-century, the debate changed to heredity and environment, shifting greater attention to environmental influences. Before the end of the century, the concern lay with the heredity- environment interaction, the ways in which each component influences the other, a major interest today (Wahlsten, 2000)

In other words, evolutionary psychology and social-role theory recognize both sets of influences. But they do so from different starting points. Evolutionary psychology begins with our lengthy primeval history, which produced genetically different psychological mechanisms in men and women. Social-role theory begins with our current social environment, which poses different opportunities and creates different restrictions for men and women. A bat, cat, rat, and human beings all have different natures, and all require specific types of environmental stimulation to develop and function properly (Buss, 1995a). Evolved psychological mechanisms are mediated by specific features of the environment, co-producing evolution through genetic and social processes (Buss, 1995b; Eagly & Wood, 1999).

But within the social-role viewpoint, differences have arisen over the extent of gender differences revealed in research—prompted partly by divergent views within the feminist movement. Taking a minimalist position, some observers favor or seek findings of no or small differences, weakening evidence for gender stereotypes (Eagly, 1995). Others, from a maximalist position, favor large gender differences, especially in language, conversational style, and nonverbal behavior. The latter are inevitably magnified in the mass media, which are always in search of differences, debate, and drama (Hyde & Plant, 1995). In fact, survey research has demonstrated that the perceived gender differences, whatever their true size, do not do women a disservice. As demonstrated by well-respected female investigators, the stereotypes attributed to women in the United States overall are more positive than those attributed to men (Eagly, 1995; Eagly, Mladinic, & Otto, 1991).

Evolutionary psychologists would respond that the psychological mechanisms in men, evolved over the millennia since life in the Stone Age, impel them toward physical battles and sexual promiscuity, traits not well tolerated in our different civilization. Evolved psychological mechanisms in women concern monogamy, pregnancy, communication with children, and their nurturance. These characteristics are far more respected in contemporary society.

Both these gender-related behaviors are associated with biochemical underpinnings. Prevalent in women, especially in the stages of childbirth, oxytocin also has implications for bonding. Regularly prevalent in men, testosterone is recognized as influential in aggression. These substances appear in both genders—but in very different amounts.

Turning to nonideological objections, critics state that evolutionary psychology engages in post hoc reasoning, the error of assuming that an event following another event was caused by that prior event. They point out the inability of evolutionary psychology to demonstrate that evolution caused any particular evolved mechanism,

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regarding post hoc reasoning as “storytelling.” A causal relationship may be present, but it is not verified merely by the sequence of events.

The elephant's trunk, a duck's mode of swimming with webbed feet, and human facial expressions in emotion could not have been predicted as evolutionary outcomes, for there are countless ways to solve any adaptive problem (Buss, 1996a, 1996b). Without interests in child care and investment in children, men might have evolved as less brave than women, accomplishing the task of survival by fleeing from dangers rather than risking their lives in fighting (Cornell, 1997). On such bases, it can only be speculated that evolution has been the responsible agent.

Evolutionary psychologists reply that they only assume evolution was the causal factor. This assumption stimulates hypotheses about human and animal behaviors as adaptive responses, serving as a springboard for investigations. The studies of gender differences in response to partner infidelity, for example, arose on this basis. But evolutionary theory exerted no influence on the research design or the merit of the research results.

Critics also state that evolutionary psychology encounters the falsification issue. Evolutionary theory cannot be shown to be wrong. It cannot return to earlier eons to examine directly the pressures and outcomes of natural selection. It is no more falsifiable than other views of our origins. But, again, supporters state that evolutionary psychology has no direct need to test the theory, and it makes no attempt to do so.

They also reply that evolution, even as a theory today, is widely accepted within and outside academic circles. Among scientists, nearly universal support often substitutes for falsifiability. Moreover, the falsifiability criterion does not apply to high-level assumptions in science, especially those with overwhelming acceptance. It applies instead to low-level empirical predictions. Nevertheless, the debate continues over the extent to which evolutionary psychology is a justifiable science.

Critics object on still another point—the idea of human mental life as composed of an inherited set of specific mental mechanisms. And they resist the idea that the multiplicity of these mechanisms accounts for the seeming versatility of human thought. Instead, the public regards the human mind as a general problem solver, capable of adapting to an almost endless variety of challenges. They explain human behavior with numerous broad concepts, such as learning, reasoning, remembering, problem solving, and the like, operating in unconfined fashion across a sweeping range of tasks.

Finally, some psychologists resist on more particular bases. They ask for more precise definitions of evolved psychological mechanisms. And what is the speculation on their number? If our mental apparatus has become modularized into separate components, how do we experience an integrated mind? And how are these mental mechanisms mapped onto the modular brain? Answers to such questions of course await further research.

Summary

Roots of Evolutionary Psychology

Evolutionary psychology proposes that natural selection has shaped human psychological structures, resulting in certain adaptive fears, preferences, and behavioral tendencies called evolved psychological mechanisms. In this context, a battleground becomes the metaphor for evolutionary psychology. Each individual battles against predators, the natural elements, and members of its own species. The most successful survive and transmit their genetic backgrounds to offspring.

Key Terms: evolutionary psychology, natural selection, genes, genetic determinism, evolved psychological mechanism, instinct

Evolution of Sexual Behavior

Through random pairings over the millennia, males have evolved a preference for fertile mates, females

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1.

2.

a preference for mates who can provide resources for raising offspring. Through their unequal levels of investment in children, the mating patterns of men have emerged as more polygamous and those of women as more monogamous.

Key Terms: mate preferences, mating patterns, polygamous, monogamous

Adaptations in Parenting

Pregnancy sickness appears to be an evolved psychological mechanism that protects the embryo against birth defects. Nausea and food aversions cause the pregnant woman to reject substances likely to be toxic for the developing embryo. Another evolved mechanism, infant-directed speech, enables the new mother to communicate with her linguistically undeveloped child. She uses exaggerated rhythms and tones to catch attention, express approval, indicate prohibition, and communicate comfort.

Key Terms: pregnancy sickness, teratogens, embryo, fetus, infant-directed speech

Dispositions in Group Living

The human capacity for language is viewed as an evolved psychological mechanism for reasons relating to the speed of learning, universality of language, and predictable errors in grammar and syntax. The capacity to recognize and transmit emotional expressions also appears to be an evolved psychological mechanism, offering advantages in obtaining a mate, anticipating attack, and so forth. Similarly, skill in making social contracts appears to be an evolved mechanism, providing an adaptive advantage in gaining property and detecting cheaters.

Key Terms: social exchange, universal grammar, facial expressions in emotion, social contract, physical aggression, verbal aggression, paternity uncertainty

Promoting Behavioral Change

Evaluating the effectiveness of any therapy often requires at least three groups of subjects: a control group, a placebo group, and a treatment group. Successful therapy outcomes usually depend on an interaction among the therapist, method, and person in therapy. Evolutionary psychology offers no therapy, but it can make its hypotheses and findings available to the public. These results are not confined to problems of adjustment; they also provide information on how to make everyday life more effective and fulfilling.

Key Terms: spontaneous remission, placebo effect

Commentary and Critique

Evolutionary psychology stimulates debate about ideological issues. Social-role theory states that the different adjustments of men and women are influenced by the expectations of the society in which they live. Other critics point out that evolutionary theory is not falsifiable and that the mind is a general-purpose problem solver. Evolutionary psychologists reply that the theory has stimulated many useful, testable hypotheses.

Key Terms: ideological issues, social-role theory, nature-nurture issue, heredity-environment interaction, post hoc reasoning

Critical Thinking

Assume that natural variation in earlier eons produced a genetic predisposition toward a highly mobile, swan-like neck in one or a few human beings. Describe the conditions under which that neck might have become prominent in people today. Describe the conditions under which it might have disappeared. As a member of a consulting team, how would Charles Darwin feel in partnership with a behaviorist? Describe the intellectual reasons for congeniality or discord.

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3. Consider the instinct for nest-building in rabbits and the evolved psychological mechanisms for mate preferences in human beings. Using these examples, explain how the concepts of instincts and evolved psychological mechanisms are similar and different.

• evolutionary psychology • mechanisms • gender differences • natural selection • genes • language • fear • child care • psychology • evolution

http://dx.doi.org/10.4135/9781452224862.n8

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