We are walking archives of ancestral wisdom.
—HELENA CRONIN, The Ant and the Peacock
HUMAN MATING DELIGHTS and amuses us and galvanizes our gossip. In all cultures, few domains of human activity generate as much discussion, as many laws, or such elaborate rituals. Yet the elements of human mating seem to defy understanding. Women and men sometimes find themselves choosing mates who make them unhappy. Some abuse them psychologically and physically. Some live mating lives of quiet desperation. Efforts to attract new mates often backfire. Conflicts erupt within couples, producing downward spirals of blame and despair. Despite their best intentions and vows of lifelong love, nearly half of all married couples end up divorcing.
Pain, betrayal, and loss contrast sharply with the usual romantic notions of love. We grow up believing in true love, in finding our “one and only.” We assume that once we do, we will marry in bliss and live happily ever after. But reality rarely coincides with our beliefs. Even a cursory look at the divorce rate, the 30 to 50 percent incidence of extramarital affairs, and the jealous rages that rack so many relationships shatters these illusions.
Discord and dissolution in mating relationships are typically seen as signs of failure. Regarded as distortions or perversions of the natural state of mating life, they are thought to signal personal inadequacy, immaturity, neurosis, failure of will, or simply poor judgment in the choice of a mate. This view is radically wrong. Conflict in mating is the norm and not the exception. It ranges from a man’s anger at a woman who declines his advances to a wife’s frustration with a husband who fails to listen or help in the home. These pervasive patterns defy easy explanation. Something deeper and more telling about human nature is involved—something we do not fully understand.
The problem is complicated by the centrality of love in human life. Feelings of love mesmerize us when we experience them and occupy our fantasies when we do not. The euphoria and anguish of love dominates poetry, music, literature, soap operas, and romance novels more than any other theme. Contrary to common belief in the social sciences, love is not a recent invention of the Western leisure classes. People in all cultures experience love and have coined specific words for it.1 Its pervasiveness convinces us that love, with its key components of commitment, idealized perceptions of loved ones, deep empathy, and overwhelming passion, is an inevitable part of the human experience, within the grasp of everyone.2
Our failure to understand the real and paradoxical nature of human mating is costly, both scientifically and socially. Scientifically, lack of knowledge leaves unanswered some of life’s most puzzling questions, such as why people sacrifice years of their lives to the quest for love and the struggle for fulfilling relationships. Socially, our ignorance leaves us frustrated, helpless, and often hurt when mating goes wrong, whether in the jungle of online dating sites, in hookups on college campuses, in the workplace, or in our home.
We need to reconcile the profound love that humans seek with the conflict that permeates our most cherished relationships. We need to square our dreams with reality. To understand these baffling contradictions, we must gaze back into our evolutionary past—a past that has grooved and scored our minds as much as our bodies, a past in which our strategies for mating have been as critical as our strategies for survival.
Evolutionary Roots
More than a century ago, Charles Darwin offered a revolutionary explanation, sexual selection theory, for the mysteries of mating.3 He had become intrigued by the puzzling fact that some animals have characteristics that hinder their survival. The elaborate plumage, large antlers, and other conspicuous features displayed by many species seem costly in the currency of survival. Peacocks look like a predator’s dream. Not only are peacocks packages of nutritious meat, but they come attached to a long train of brilliant feathers. This train can only encumber a peacock fleeing from predators, and it also serves as a neon sign pointing those predators straight to an easy meal. Darwin’s answer was that the peacocks’ displays evolved because they led to their bearer’s reproductive success by providing an advantage in the competition for desirable peahens. The evolution of characteristics because of their mating benefits, rather than survival benefits, is known as sexual selection.
Sexual selection, according to Darwin, takes two forms. In one form, same-sex competition, members of the same sex compete with each other, and the outcome of their contest gives the winner greater sexual access to members of the opposite sex. Two stags locking horns in combat is the prototypical image of this intrasexual competition. The characteristics that lead to success in these contests, such as greater strength, intelligence, or attractiveness to allies, evolve because the victors are able to mate more often and hence pass on genes for the qualities that have led to their success.
In the other type of sexual selection, members of one sex choose a mate based on their preferences for particular qualities in that mate. The desired characteristics evolve—that is, increase in frequency over time—because animals possessing them are chosen more often as mates and genes that cause them to be desirable get passed on with greater frequency. Animals lacking the desired characteristics are excluded from mating, and genes for undesirable qualities perish. Since peahens prefer peacocks with plumage that flashes and glitters, dull-feathered males get left in the evolutionary dust. Peacocks today possess brilliant plumage because over evolutionary history peahens have preferred to mate with dazzling and colorful males.
Darwin’s theory of sexual selection began to explain mating behavior by identifying two key processes by which evolutionary change can occur: preferences for a mate and competition for a mate. But the theory was vigorously resisted by male scientists for over a century, in part because the active choosing of mates seemed to grant too much power to females, who were thought to remain passive in the mating process. The theory of sexual selection was also resisted by mainstream social scientists because its account of human nature seemed to depend on instinctive behavior and thus to minimize humans’ uniqueness and flexibility. Culture, consciousness, and free will were presumed to have liberated us from evolutionary forces. The breakthrough in applying sexual selection to humans came in the late 1970s and 1980s, in the form of theoretical advances initiated by my colleagues and myself in the fields of psychology and anthropology.4 We tried to identify underlying psychological mechanisms that were the products of evolution—adaptations that would help to explain both the extraordinary flexibility of human behavior and the active mating strategies women and men pursue. This new discipline is called evolutionary psychology.
When I began work in the field, however, little was known about actual human mating behavior. There was a frustrating lack of scientific evidence on mating in the broad array of human populations and practically no documented support for grand evolutionary theorizing. No one knew whether some mating desires are universal, whether certain gender differences are characteristic of all people in all cultures, or whether culture exerts a powerful enough influence to override the evolved preferences that might exist. So I departed from the traditional path of mainstream psychology to explore which characteristics of human mating might follow from evolutionary principles. In the beginning, I simply wanted to verify a few of the most obvious evolutionary predictions about gender differences in mating preferences—for example, whether men desire youth and physical attractiveness in a mate and whether women desire status and economic security. Toward that end, I interviewed and administered questionnaires to 186 married adults and 100 unmarried college students within the United States.
The next step was to verify whether the psychological phenomena uncovered by this study are characteristic of our species. If mating desires and other features of human psychology are products of our evolutionary history, they should be found universally, not just in the United States. So I initiated an international study to explore how mates are selected in other cultures, starting with a few European countries, including Germany and the Netherlands. I soon realized, however, that since European cultures share many features, they do not provide the most rigorous test for the principles of evolutionary psychology. Over a period of five years, I expanded the study to include fifty collaborators from thirty-seven cultures located on six continents and five islands, from Australia to Zambia. Local residents administered the instruments assaying mating desires in their native language. We sampled large cities, such as Rio de Janeiro and Sao Paulo in Brazil, Shanghai in China, Bangalore and Ahmedabad in India, Jerusalem and Tel Aviv in Israel, and Tehran in Iran. We also studied rural peoples, including Indians in the state of Gujarat and Zulus in South Africa. We covered the well-educated and the poorly educated. We included respondents of every age from fourteen through seventy, as well as places in the entire range of economic systems from capitalist to communist and socialist. All major racial groups, religious groups, and ethnic groups were represented. In all, our study included 10,047 people worldwide.
This study, the largest ever undertaken on human mating desires, was merely the beginning. The findings had implications that reached into every sphere of human mating life, from dating to marriage, extramarital affairs, and divorce. They were also relevant to major social issues such as sexual harassment, intimate partner violence, pornography, and patriarchy. To explore as many mating domains as possible, my lab subsequently launched over 100 new scientific studies, involving thousands of individuals. Included in these studies were men and women searching for a mate in singles bars and on college campuses, dating couples at various stages of commitment, newlywed couples in the first five years of marriage, and couples who ended up divorced. The studies explored phenomena ranging from acts of love to acts of sexual treachery.
The findings from all of these studies caused controversy and confusion among my colleagues because in many respects they contradicted conventional thinking. They forced a radical shift from the standard view of men’s and women’s sexual psychology. One of my aims in this book is to formulate from these diverse findings a unified theory of human mating, based not on romantic notions or outdated scientific theories but on current scientific evidence. Some of what I discovered about human mating is not nice. In the ruthless pursuit of sexual goals, for example, men and women derogate their rivals, deceive members of the opposite sex, and even subvert their own mates. These discoveries are disturbing to me; I would prefer that the competitive, conflictual, and manipulative aspects of human mating did not exist. But a scientist cannot wish away unpleasant findings. Ultimately, the disturbing side of human mating must be confronted if its harsh consequences are ever to be ameliorated.
Sexual Strategies
Strategies are methods for accomplishing goals, the means for solving problems. It may seem odd to view human mating, romance, sex, and love as inherently strategic. But humans, like other sexually reproducing species, do not choose mates randomly. We do not attract mates indiscriminately. We do not derogate our competitors out of boredom. Our mating is strategic, and our strategies are designed to solve particular problems in ways that lead to successful mating. Understanding how people solve those problems requires an analysis of sexual strategies.
Adaptations are evolved solutions to the problems posed by survival and reproduction. Over millions of years of evolution, natural selection has produced in us hunger mechanisms to solve the problem of providing nutrients; taste buds that are sensitive to fat and sugar to solve the problem of what to put into our mouths (fruit, meat, nuts, and berries, but not dirt or gravel); sweat glands and shivering mechanisms to solve the problems of extreme hot and cold; emotions such as fear and rage that motivate either flight or combat with predators or aggressive competitors; and a complex immune system to combat diseases and parasites. These adaptations are human solutions to the problems of existence posed by the hostile forces of nature—they are our survival strategies.
Correspondingly, sexual strategies are adaptive solutions to mating problems. Those in our evolutionary past who failed to mate successfully failed to become our ancestors. All of us descend from a long and unbroken line of ancestors who competed successfully for desirable mates, attracted mates who were reproductively valuable, retained mates long enough to reproduce, fended off interested rivals, and solved the problems that could have impeded reproductive success. We carry in us the sexual legacy of those success stories.
Each sexual strategy is tailored to a specific adaptive problem, such as identifying a desirable mate or besting competitors in attracting a mate. Underlying each sexual strategy are psychological adaptations, such as preferences for a particular mate, feelings of love, desire for sex, or turbulent emotions such as sexual jealousy. Each psychological mechanism is sensitive to information or cues from the external world, such as physical features, signs of sexual interest, or hints of potential infidelity. Our psychological adaptations are also sensitive to information about ourselves, such as our own mate value or ability to attract mates with certain levels of desirability. The goal of this book is to peel back the layers of adaptive problems that men and women have faced in the course of mating and uncover the complex sexual strategies they have evolved for solving them.
Although the term sexual strategies is a useful metaphor for thinking about solutions to mating problems, it is misleading in the sense that it connotes conscious intent. Sexual strategies do not require conscious planning or awareness. Our sweat glands are “strategies” for accomplishing the goal of thermal regulation, but we do not consciously sweat, nor are we aware of our bodies’ target thermal state. Indeed, just as a pianist’s sudden awareness of her hands may impede performance, most human sexual strategies are most successfully carried out without the awareness of the actor.
Selecting a Mate
Nowhere do people have an equal desire for all possible mates. Everywhere some potential mates are preferred, and others shunned. Our sexual desires have evolved in the same way as many other desires. Consider the survival problem of what food to eat. Humans are faced with a bewildering array of potential objects to ingest—berries, fruit, nuts, and fish, but also dirt, gravel, poisonous plants, twigs, and feces. If we had no taste preferences and ate objects from our environment randomly, some people would consume ripe fruit, fresh nuts, and other objects that provide caloric and nutritive sustenance. Others would eat rancid meat, rotten fruit, and toxins. Earlier humans whose preferences ever so slightly tilted them toward nutritious objects survived more often than their counterparts and hence passed on their eating proclivities to offspring.
Our actual food preferences bear out this evolutionary process. We show great fondness for substances rich in fat, sugar, protein, and salt and an aversion to substances that are bitter, sour, pathogenic, or toxic.5 These food preferences solve a basic problem of survival. We carry them with us today precisely because they solved critical adaptive problems for our ancestors.
Our desires in a mate serve analogous adaptive purposes, but their functions do not center simply on survival. Imagine living as our ancestors did long ago—struggling to keep warm by the fire; hunting meat for our kin; gathering nuts, berries, and herbs; and avoiding parasites, dangerous animals, and hostile humans. If we were to select a mate who failed to deliver the resources promised, who had affairs, who was lazy, who lacked hunting skills, or who heaped physical abuse on us, our survival would be tenuous, and our reproduction at risk. In contrast, a mate who provided abundant resources, who protected us and our children, and who devoted time, energy, and effort to our family would be a great asset. As a result of the powerful survival and reproductive advantages reaped by those who chose a mate wisely, clear desires in a mate evolved. As descendants of those successful maters, we carry their desires with us today.
Many other species have evolved mate preferences. The African village weaverbird provides a vivid illustration.6 When the male weaverbird spots a female in the vicinity, he displays his recently built nest by suspending himself upside down from the bottom and vigorously flapping his wings. The female watches. If the male passes her first visual inspection, the female approaches the nest, enters it, and examines the nest materials, poking and pulling them for as long as ten minutes. As she makes her inspection, the male sings to her from nearby. At any point in this sequence she may decide that the nest does not meet her standards and depart to inspect another male’s nest. A male whose nest is rejected by several females will often break it down and rebuild it from scratch. By exerting a preference for males who can build a superior nest, the female weaverbird solves the problems of protecting and provisioning her future chicks. Her preferences have evolved because they bestowed a reproductive advantage over other weaverbirds who had no preferences and who mated with any males who happened along, regardless of the quality of their nests.
Women, like female weaverbirds, prefer men with desirable “nests.” Consider one of the problems that women in evolutionary history had to face: selecting a man who would be willing to commit to a long-term relationship. A woman in our evolutionary past who chose to commit to mate with a man who was flighty, impulsive, philandering, or unable to sustain relationships found herself raising her children alone, without benefit of the resources, aid, and protection that another man might have offered. A woman who preferred to mate with a reliable man, one willing to commit to her over the long run, was more likely to have children who survived and thrived. Over thousands of generations, a preference for men who showed signs of being willing and able to commit to them evolved in women, just as preferences for mates with adequate nests evolved in weaverbirds. This preference solved key reproductive problems, just as food preferences solved key survival problems.
People do not always desire the commitment required of long-term mating. Men and women sometimes deliberately pursue a short-term sexual strategy—a brief fling, a one-night hookup, a weekend liaison, or a casual affair. And when they do, their preferences shift, sometimes dramatically. One of the crucial decisions for humans in selecting a mate is whether they are seeking a short-term mate or a long-term partner, a partner in whom they invest little or a partner to whom they commit a lot. The sexual strategies pursued hinge on this decision. This book documents the universal preferences that men and women display for particular characteristics in a mate, reveals the evolutionary logic behind the different desires of each gender, and explores the changes that occur when people shift their goal from casual sex to a committed relationship.
Attracting a Mate
People high in mate value, those who possess desirable characteristics, are in great demand. Appreciating their traits is not enough for successful mating, however, just as spying a ripe berry bush down a steep and treacherous ravine is not enough for successful eating. The next step in mating is to compete successfully for a desirable mate.
Among the elephant seals on the coast of California, males during the mating season use their sharp tusks to fight rival males in head-to-head physical combat.7 Often their contests and bellowing continue day and night. The losers lie scarred and injured on the beach, exhausted victims of this brutal competition. But the winner’s job is not yet over. He must roam the perimeter of his harem, which contains a dozen or more females. This dominant male must hold his place in life’s reproductive cycle by herding stray females back into the harem and repelling “mate poachers” who attempt sneak copulations.
Over many generations, male elephant seals who were stronger, larger, more ferocious, and more cunning succeeded in securing mates. The larger, more aggressive males controlled sexual access to females and so passed on to their sons the genes conferring these qualities. Indeed, males now weigh roughly 4,000 pounds, or four times the weight of females, who appear to human observers to risk getting crushed during copulation.
Female elephant seals prefer to mate with the victors, and they pass on the genes conferring this preference to their daughters. But by choosing the larger, stronger winners, they also determine the genes for size and fighting abilities that will live on in their sons. The smaller, weaker, and more timid males fail to mate entirely. They become evolutionary dead ends. Because only 5 percent of the males monopolize 85 percent of the females, sexual selection pressures remain intense even today.
Male elephant seals must fight not just to beat other males but also to be chosen by females. A female emits loud bellowing sounds when a smaller male tries to mate with her. The alerted dominant male comes bounding toward them, rears his head in threat, and exposes a massive chest. This gesture is usually enough to send the smaller male scurrying for cover. Female preferences are one key to establishing competition among the males. If females did not mind mating with smaller, weaker males, then they would not alert the dominant male, and there would be less intense selection pressure for size and strength. Female preferences, in short, determine many of the ground rules of the male contests.
People are not like elephant seals in most of these mating behaviors. For example, whereas only 5 percent of the male elephant seals do 85 percent of the mating, more than 90 percent of men are able to find a mate at some point in their lives.8 Male elephant seals strive to monopolize harems of females, and the winners remain victorious for only a season or two, whereas many humans form enduring unions that last for years and decades. But men and male elephant seals share a key characteristic: both must compete to attract females. Males who fail to attract females risk being shut out of mating.
Throughout the animal world, males typically compete more fiercely than females for mates, and in many species males are certainly more ostentatious and obvious in their competition. But competition among females is also intense in many species. Among patas monkeys and gelada baboons, for instance, females harass copulating pairs in order to interfere with the mating success of rival females. Among wild rhesus monkeys, females use aggression to interrupt sexual contact between other females and males, occasionally winning the male consort for themselves. And among savanna baboons, female competition over mates serves not merely to secure sexual access but also to develop long-term social relationships that provide physical protection.9
Competition among women, though typically less noisy and violent than competition among men, pervades human mating systems. The writer H. L. Mencken noted: “When women kiss, it always reminds one of prize fighters shaking hands.” This book shows how members of each gender compete with each other for access to desirable mates. The tactics they use to compete are often dictated by the preferences of those they are trying to attract. Those who do not have what mate seekers desire risk remaining on the sidelines in the complicated dance of mating.
Keeping a Mate
Keeping a mate is another important adaptive problem; mates may continue to be desirable to rivals, who may poach, thereby undoing all the effort devoted to attracting, courting, and committing to the mate. Furthermore, one mate may break up a relationship because of the failure of the other to fulfill key needs and wants, or simply because someone fresher, more compelling, or more beautiful arrives. Mates, once gained, must be retained.
Consider the Plecia nearctica, an insect known as the lovebug. Male lovebugs swarm during the early morning and hover a foot or two off the ground, waiting for the chance to mate with a female.10 Female lovebugs do not swarm or hover. Instead, they emerge in the morning from the vegetation and enter the swarm of males. Sometimes a male captures a female before she can take flight. Males often wrestle with other males. As many as ten males may cluster around a single female.
The successful male departs from the swarm with his mate. Then the couple glides to the ground to copulate. Perhaps because other males continue to attempt to mate with her, the male retains his copulatory embrace for as long as three full days—hence the nickname “lovebug.” The prolonged copulation itself functions as a way of guarding the mate. By remaining attached to the female until she is ready to deposit her eggs, the male lovebug prevents other males from fertilizing her eggs. In reproductive currency, his ability to compete with other males and attract a female would be for naught if he failed to solve the problem of retaining his mate.
Different species solve this problem by different means. Humans do not engage in continuous copulatory embraces for days, but everyone who seeks a long-term relationship confronts the problem of holding on to a mate. In our evolutionary past, men who were indifferent to the sexual infidelities of their mates risked compromising their paternity. They risked investing time, energy, and effort in children who were not their own. Ancestral women, in contrast, did not risk the loss of parenthood if their mates had affairs, because maternity has always been 100 percent certain. But a woman with a philandering husband risked losing his resources, his commitment, and his investment in her and her children. One psychological strategy that evolved to combat infidelity was jealousy. Ancestral people who became enraged at signs of their mate’s potential defection and who acted to prevent it had a selective advantage over their nonjealous peers. People who failed to prevent a mate’s infidelity had less reproductive success.11
The emotion of jealousy motivates multiple actions in response to a threat to the relationship. Sexual jealousy, for example, may produce either of two radically different tactics, vigilance or violence. Using vigilance, a jealous man might follow his lover when she goes out, call her unexpectedly to see whether she is where she said she would be, keep an eye on her at a party, or read her text messages or email. Using violence, a man might threaten a rival discovered flirting with his lover, attack the rival with his fists, get his friends to beat up the rival, or throw a brick through the rival’s window. Both mate retention tactics, vigilance and violence, are different manifestations of the same psychological adaptation of jealousy. They represent alternative ways of solving the problem of a partner’s infidelity or defection.
Jealousy is not a rigid, invariant instinct that drives robotlike, mechanical action. It is highly sensitive to context and environment, including the formidability of the rival, differences in mate value between the two partners, and the alternative mating options available to the guarder. The many other behavioral options available to serve the strategy of jealousy give humans a flexibility in tailoring their responses to the nuances of a situation. This book documents the range of actions that are triggered by jealousy and the contexts in which they occur.
Replacing a Mate
Not all mates gained can be retained. Nor should they be. Sometimes there are compelling reasons to get rid of a mate, such as when a mate stops providing support, withdraws sex, or becomes physically or psychologically abusive. Those who remain with a mate through economic hardship, sexual infidelity, and cruelty may win our admiration for their loyalty today. But staying with a bad mate generally would not have helped ancestral humans to survive and reproduce successfully. We are the descendants of those who knew when to cut their losses.
Getting rid of a mate has precedent in the animal world. Ring doves, for example, are generally monogamous from one breeding season to the next, but they break up under certain circumstances. The doves experience a divorce rate of about 25 percent every season. The major reason for breaking their bond is infertility.12 When ring doves fail to produce chicks with one partner during a breeding season, they leave the mate and search for another. Breaking up with an infertile mate aids the reproduction of ring doves, while remaining in a barren union does not.
Just as we have evolved sexual strategies to select, attract, and keep a good mate, we have also evolved strategies for jettisoning a bad mate. Divorce occurs in all known human cultures.13 Our separation or “mate ejection” strategies involve a variety of psychological mechanisms. We assess whether the costs inflicted by a mate outweigh the benefits provided. We size up other potential partners and evaluate whether they might offer more than our current mate. We gauge the likelihood of successfully attracting more desirable partners. We calculate the potential damage that might be caused to ourselves, our children, and our kin by the breakup. And we combine all this information into a decision to stay or leave.
Once a mate decides to leave, another set of psychological adaptations is activated. Because these decisions have complex consequences for two sets of extended kin who often have keen interests in the union, breaking up is neither simple nor effortless. Complex social relationships must be negotiated and the breakup justified. The range of tactical options within the human repertoire is enormous, from simply packing one’s bags and walking away to provoking a rift by revealing an infidelity. There are indeed at least fifty ways to leave a lover.
Breaking up is a solution to the problem of a bad mate, but it opens up the new problem of replacing that mate. Like most mammals, humans typically do not mate with a single person for an entire lifetime. Humans often reenter the mating market and repeat the cycle of selection, attraction, and retention. But starting over after a breakup poses its own unique problems. People reenter the mating market at a different age and with different assets and liabilities. Increased status and resources may help a person to attract a mate who was previously out of range. Alternatively, older age, the presence of children, or psychological baggage from a previous mateship may detract from a person’s ability to attract a new mate.
Men and women undergo predictably different changes as they divorce and reenter the mating market. If there are children, women often take primary responsibility for child rearing, although this may be changing as some men step up to the plate. Because children from previous unions are usually seen as burdens rather than benefits when it comes to mating, a woman’s ability to attract a desirable mate often suffers more than a man’s. Consequently, fewer divorced women than men remarry, and this disparity gets larger with increasing age. This book documents the changing patterns of human mating over a lifetime and identifies circumstances that affect the likelihood of remating for men and women.
Conflict Between the Sexes
The sexual strategies that one sex pursues to select, attract, keep, or replace a mate often have the unfortunate consequence of creating a conflict with some members of the other sex. Among the scorpionfly, a female refuses to copulate with a courting male unless he brings her a substantial nuptial gift, typically a dead insect to be eaten.14 While the female eats the nuptial gift, the male copulates with her. During copulation, the male maintains a loose grasp on the food, as if to prevent the female from absconding with it before copulation is complete (sometimes a female sexual exploitation strategy). It takes the male twenty minutes of continuous copulation to deposit all his sperm into the female. Male scorpionflies have evolved the ability to select a nuptial gift that takes the female approximately twenty minutes to consume. If the gift is smaller and is consumed before copulation is completed, the female casts off the male before he has deposited all his sperm. If the gift is larger and takes the female more than twenty minutes to consume, the male completes copulation, and the two then fight over the leftovers. Conflict between male and female scorpionflies thus occurs over whether he gets to complete copulation when the gift is too small and over who gets to consume the residual food when the gift is larger than needed.
Men and women also clash over resources and sexual access. In the evolutionary psychology of human mating, the sexual strategy adopted by one sex can trip up and conflict with the strategy adopted by the other sex. I call these phenomena strategic interference. Consider the differences in men’s and women’s proclivities to seek casual short-term sex. Men and women typically differ in how long and how well they need to know someone before they consent to have sex. Although there are many exceptions and individual differences, men generally have lower thresholds for engaging in sex.15 For example, men often express the desire and willingness to have sex with an attractive stranger, whereas most women refuse anonymous encounters and prefer to know something about the potential mate prior to sex.
There is a fundamental conflict between these different sexual strategies: men cannot fulfill their short-term wishes without simultaneously interfering with women’s long-term goals. An insistence on immediate sex interferes with the goal of a longer courtship phase. The interference is reciprocal, since any delay also obstructs the goal of those seeking short-term sex. Whenever the strategy adopted by one sex interferes with the strategy adopted by the other sex, strategic interference and conflict ensue.
Conflicts do not stop with a couple’s commitment. Married women sometimes complain that their husbands are condescending, emotionally constricted, and unreliable. Married men sometimes complain that their wives are moody, overly dependent, and sexually withholding. Both sexes complain about infidelities, ranging from mild flirtations to serious affairs. All of these conflicts become understandable in the context of our evolved mating strategies.
Although conflict between the sexes is pervasive, it is not inevitable. There are conditions that minimize conflict and produce harmony between the sexes. Knowledge of our evolved sexual strategies gives us tremendous power to better our own lives by choosing actions and circumstances that activate some strategies and deactivate others. Indeed, understanding sexual strategies, including the cues that trigger them, is one step toward reducing conflict between men and women. This book explores the nature of sexual conflict and offers some solutions for fostering harmony between the sexes.
Sexual Orientation
“Heterosexual orientation is a paradigmatic psychological adaptation,” writes Michael Bailey, one of the world’s most prominent experts on sexual orientation.16 His reasoning is compelling. Among sexually reproducing species, males and females must mate with each other for successful reproduction. Any orientation that lowers the likelihood of successful reproduction will be ruthlessly weeded out. Although controversy surrounds estimates, most scientists converge on the finding that roughly 96 to 97 percent of all men and 98 to 99 percent of all women have a primary orientation toward heterosexuality.
The persistence of a small percentage of primarily or exclusively homosexual men and women, however, poses a genuine evolutionary puzzle. In the several hundred public lectures I’ve given on human sexual strategies, the question “What about homosexuality?” is by far the most frequently asked. It’s a mystery of human mating and an empirical enigma for evolutionary theory.17 The riddle is made more intriguing by two known facts. First, a number of twin studies show that sexual orientation is moderately heritable, suggesting a partial genetic basis.18 Second, a handful of other studies show beyond a reasonable doubt that homosexual men have a decisively lower rate of reproduction than heterosexual men.19 How can a sexual orientation that is partly inherited continue to persist in the face of continual evolutionary selection against it?
We will explore some of these issues later in the book and discuss scientific findings about the links between sexual orientation and mate preferences and sexuality, but several key conceptual issues are worth noting here. First, there are at least three different senses of the phrase “sexual orientation.” One can be called primary sexual orientation and refers to whom one is sexually attracted to—men, women, both (bisexual), or neither (asexual). Another is gender identity—whether one subjectively feels like a man or woman, feels like both, or neither. Still another is sexual behavior, referring to the gender of the individuals with whom one actually has sex. These distinctions are critical, since we witness many combinations and permutations in individual people. For example, some individuals may be primarily attracted to one sex but engage in sexual behavior with the other sex out of curiosity (sexual experimentation) or social constraint (lack of available sex partners corresponding to one’s primary sexual orientation).
Another critical distinction is that male and female sexual orientation have different natures and developmental trajectories. Male sexual orientation tends to appear early in development and rarely changes dramatically over time, whereas female sexuality appears to be far more flexible and fluid over the life span. For example, male sexual orientation tends to be bimodally distributed, with most men either strongly heterosexual or strongly homosexual—there are relatively few bisexual men. Women’s sexual orientation, by contrast, varies more smoothly along a continuum from highly heterosexual through a series of bisexual gradations to a nearly exclusive preference for same-sex partners.
Another difference is that women appear able to switch orientations more easily, evidence of the greater flexibility of their sexuality. Anecdotally, there is the “LUG” phenomenon found in women’s colleges—Lesbian Until Graduation. The actress Anne Heche lived for several years in a lesbian relationship with comedienne and actress Ellen Degeneres. After they broke up, Heche married a man and had a child with him. Similarly, some women marry when they are young, have children, and then in middle age switch to a lesbian lifestyle. Although some men “come out of the closet” after a socially prescribed marriage to someone to whom they are not sexually attracted, it is still very likely that their primary sexual orientation was set relatively early in life and had never really changed.
Once we recognize that sexual orientation is not singular and that there are important differences between sexual attraction, sexual identity, and sexual behavior, scientific understanding of variations in human sexuality is likely to accelerate. We must also recognize that there is probably no single theory that can explain the many varieties of human sexuality, including gay males, lesbians, bisexuals, transgendered individuals, and asexuals, much less one that can explain the profound individual differences among those with these different orientations. We delve into the origins and nature of sexual orientation in greater detail in Chapters 2, 3, and 4, with a special focus on mate preferences, sexual motivation, and preferred mating strategies.
Culture and Context
Although ancestral selection pressures are responsible for creating the mating strategies we use today, our current conditions differ from historical ones in critical ways. Ancestral people got their fruit and vegetables from gathering and their meat from hunting; most modern people get their food from supermarkets and restaurants. Modern urban people today deploy their mating strategies on Internet dating sites and in bars rather than on the savanna. Nevertheless, the same sexual strategies used by our ancestors operate today with unbridled force. Our evolved psychology of mating, after all, plays out in the modern world because it is the only mating psychology we mortals possess.
Consider the foods consumed in massive quantities at fast-food chains. We have not evolved adaptations specifically for burgers or pizza, but the foods we eat reveal the ancestral strategies for survival we carry with us today.20 We consume vast quantities of fat, sugar, protein, and salt in the form of burgers, shakes, fries, and pies. Fast-food chains are popular precisely because they serve these nutritional elements in concentrated quantities. They reveal the food preferences that evolved in a past environment of scarcity. Today, however, we overconsume these elements because of their unprecedented abundance, and the old survival strategies now hurt our health. Because evolution works on a time scale too slow to keep up with the radical changes of the past several hundred years, we are stuck with taste preferences that evolved under different conditions. Although we cannot go back in time and observe directly what those ancestral conditions were, our current taste preferences, like our fear of snakes and our fondness for children, provide a window for viewing what those conditions must have been. We carry with us equipment that was designed for an ancient world.
Our evolved mating strategies, just like our survival strategies, may now be maladaptive in some ways with respect to survival and reproduction. The increase in sexually transmitted infections, for example, renders casual sex more dangerous than it was under ancestral conditions. The dramatic opportunities to evaluate thousands of potential mates online sometimes paralyze our ability to decide on “the one.” Only with a deep understanding of our evolved sexual strategies, their origins, and the conditions they were designed to deal with can we hope to solve the problems of mating posed by these novel environments.
One impressive advantage humans have over many other species is a repertoire of mating strategies that is large and highly sensitive to context. Consider the problem of being in an unhappy marriage and contemplating whether to get divorced. This decision depends on many complex factors, including the amount of conflict within the marriage, whether one’s mate is unfaithful, the pressure applied by relatives on both sides of the family, the presence of children, the ages and needs of the children, and the prospects for attracting another mate. Humans have evolved psychological adaptations that consider and weigh the costs and benefits of these crucial features of context.
Cultural circumstances also vary in ways that are critical for activating particular sexual strategies from our complex menu of mating. Some cultures have mating systems that are polygynous, allowing men to have multiple wives. Other cultures are polyandrous, allowing women to take two or more husbands. Still others are monogamous—on the surface at least—and restrict both women and men to one marriage partner at a time. Others are promiscuous, with high rates of mate switching, or polyamorous, openly allowing love and sex with multiple partners. Our evolved strategies of mating are highly sensitive to these social, legal, and cultural patterns. In polygynous mating systems, for example, parents place tremendous pressure on their sons to compete for the status and resources needed to attract women so as to avoid the matelessness that plagues some men when others monopolize multiple women.21 In monogamous mating cultures, in contrast, parents put less pressure on their sons.
Another key circumstance is the ratio of the sexes, or the number of available men relative to the number of available women in the mating pool. When there is a surplus of women, such as among the Ache Indians of Paraguay or in some urban centers such as Manhattan, men become more reluctant to commit to one woman, preferring instead to pursue many casual relationships. When there is a surplus of men, such as in contemporary cities of China and among the Hiwi tribe of Venezuela, monogamous marriage is the rule and divorce rates plummet.22 As men’s sexual strategies shift, so must women’s. As women’s sexual strategies shift, so must men’s. The two coexist in a complex reciprocal relation, based in part on the crucial sex ratio.
From one perspective, context is everything. Contexts that recurred over evolutionary time created the strategies we carry with us now. Current contexts and cultural conditions determine which strategies get activated and which lie dormant. To understand human sexual strategies, this book identifies the recurrent selection pressures or adaptive challenges of the past, the psychological adaptations or strategic solutions they created, and the current contexts that activate some solutions rather than others.
Barriers to Understanding Human Sexuality
Evolutionary theory has appalled and upset people since Darwin first proposed it in 1859 to explain the creation of new species and the adaptations that characterize their component parts. The wife of the Bishop of Worcester, his contemporary, is reported to have remarked upon hearing about his theory of our descent from nonhuman primates: “Let’s hope that it’s not true; but if it is, let’s pray that it does not become generally known.”23 Strenuous resistance to evolutionary theory continues to this day. These barriers to understanding must be removed if we are to gain real insight into our sexuality.
One barrier is perceptual. Our cognitive and perceptual mechanisms have been designed by natural selection to perceive and think about events that occur in a relatively limited time span—over seconds, minutes, hours, days, sometimes months, and occasionally years. Ancestral humans spent most of their time solving immediate problems, such as finding food, maintaining a shelter, keeping warm, selecting and competing for partners, protecting children, forming alliances, striving for status, and defending against marauding males, so there was intense pressure to think in the short term. Evolution, in contrast, occurs gradually over thousands of generations in tiny increments that we cannot observe directly. To understand events that occur on time scales this large requires a leap of the imagination, much like the cognitive feats of physicists who theorize and infer from evidence black holes, dark matter, and eleven-dimensional universes they cannot see.
Another barrier to understanding the evolutionary psychology of human mating is ideological. From Spencer’s theory of social Darwinism onward, biological theories have sometimes been used for terrible political ends—to justify oppression or to argue for racial or sexual superiority. We must be vigilant about not repeating this history of misusing biological explanations of human behavior. At the same time, we cannot be misled by this history into ignoring the most powerful theory of organic life we have—evolution by selection. As the Harvard evolutionary psychologist Steven Pinker has noted, evolutionary psychology provides powerful theories to explain aggression and cooperation as well as human sexuality and mating. Understanding human mating requires that we face our evolutionary heritage boldly and understand ourselves as products of those prior forces of natural and sexual selection.
Another basis of resistance to evolutionary psychology is the naturalistic fallacy, which maintains that whatever exists should exist. The naturalistic fallacy confuses a scientific description of human behavior with a moral prescription for that behavior. In nature, however, there are diseases, plagues, parasites, infant mortality, and a host of other natural events that we try to eliminate or reduce. The fact that they do exist in nature does not imply that they should exist.
Similarly, male sexual jealousy, which evolved in part as an adaptation to protect men’s certainty of their paternity, is known to damage women worldwide in the form of intimate partner violence, stalking, and occasionally murder.24 As a society, we may eventually develop methods for reducing male sexual jealousy and its dangerous manifestations. Because there is an evolutionary origin for male sexual jealousy does not mean that we must passively accept it or its dangerous expressions.
The naturalistic fallacy applied in the reverse direction takes the form of the romantic fallacy. Some people have exalted visions of what it means to be human. According to one of these views, “natural” humans are at one with nature, peacefully coexisting with plants, animals, and each other. War, aggression, and competition are seen as corruptions of this essentially peaceful human nature by current conditions, such as patriarchy, culture, or capitalism. Despite the evidence, some people cling to these illusions. When the anthropologist Napoleon Chagnon documented that 25 to 30 percent of all Yanomamö men die violent deaths at the hands of other Yanomamö men, his work was bitterly denounced by those who had presumed that the group lived in harmony.25 The romantic fallacy occurs when we see ourselves through the lens of utopian visions of what we want people to be.
Opposition also arises to the presumed implications of evolutionary psychology for change. If a mating strategy is rooted in evolutionary biology, some people mistakenly think it is immutable, intractable, and unchangeable. We are therefore doomed, according to this view, to follow the dictates of our biological mandate, like blind, unthinking robots. This belief mistakenly divides human behavior into two separate categories, one biologically determined and the other environmentally determined. In fact, human action is inexorably a product of both. Every strand of DNA unfolds within a particular environmental and cultural context. Within each person’s life, social and physical environments provide input to both the development and activation of evolved psychological adaptations. Every behavior is without exception a joint product of those mechanisms and their environmental influences. In identifying the historical, developmental, cultural, and situational features that formed human psychology and guide that psychology today, evolutionary psychology represents a true interactionist view.
All behavior patterns can in principle be altered by environmental intervention. The fact that currently we can alter some patterns and not others is a problem only of knowledge and technology. Advances in knowledge bring about new possibilities for change, if change is desired. Humans are extraordinarily sensitive to changes in their environment, because natural selection did not create in humans invariant instincts that manifest themselves in behavior regardless of context. It produced psychological adaptations precisely to solve the problems posed by varying contexts. Identifying the roots of mating in evolutionary biology does not doom us to an unalterable fate.
Another form of resistance to evolutionary psychology comes from the worry that evolutionary explanations might imply an inequality between the genders, support restrictions on the roles that men and women can adopt, encourage stereotypes about the genders, perpetuate the exclusion of women from power and resources, and foster pessimism about the possibilities for changing the status quo. On closer examination, however, evolutionary psychology does not carry these feared implications for human mating. In evolutionary terms, men and women are similar in many or most domains. They differ only in the circumscribed domains in which they have faced recurrently different adaptive problems over the course of human evolutionary history. For example, they diverge primarily in their preference for a particular sexual strategy, not in their innate ability to exercise the full range of human sexual strategies. Evolutionary psychology strives to illuminate the evolved mating strategies of men and women, not to prescribe what the genders could be or should be. Nor does it offer prescriptions for appropriate gender roles. It has no political agenda.
A final source of resistance to evolutionary psychology comes from the idealistic views of romance, sexual harmony, and lifelong love to which we all cling. I cleave tightly to these views myself, believing that love has a central place in human sexual psychology. I penned an essay titled “True Love” that prompted some of my graduate students to think I’d gone off the rails. But mating relationships provide some of life’s deepest satisfactions. Without them, life would seem empty. After all, some people do manage to live and mate happily and harmoniously. But we have ignored the truth about human mating for too long. Conflict, competition, and manipulation also pervade human mating, and we must lift our collective heads from the sand to see them if we are to understand life’s most engrossing relationships.