The world is full of complainers. But the fact is—nothing comes with a guarantee.
—DETECTIVE IN THE FILM Blood Simple
AMONG THE CHIMPANZEES at the large zoo colony in Arnhem, the Netherlands, Yeroen reigned as the dominant adult male.1 He walked in an exaggeratedly heavy manner, and he looked larger than he really was. Only occasionally did he need to demonstrate his dominance, raising his hair on end and running full speed at the other apes, who scattered in all directions at his charge. Yeroen’s dominance extended to sex. Although there were four adult males in the troop, Yeroen was responsible for nearly 75 percent of all matings when the females came into estrus.
As Yeroen grew older, however, things began to change. A younger male, Luit, experienced a sudden growth spurt and started to challenge Yeroen’s status. Luit gradually stopped displaying the submissive greeting to Yeroen, brazenly showing his fearlessness. Once, Luit approached Yeroen and smacked him hard, and another time Luit used his potentially lethal canines to draw blood. Most of the time, however, the battles were more symbolic, with threats and bluffs in the place of bloodshed. Initially, all the females sided with Yeroen, allowing him to maintain his status. One by one they defected to Luit, however, as the tide turned. After two months, the transition was complete. Yeroen was dethroned and began displaying the submissive greeting to Luit. Mating changes followed. While Luit achieved only 25 percent of the matings during Yeroen’s reign of power, his sexual access doubled to 50 percent when he took over. Yeroen’s sexual access to females dropped to zero.
Although ousted from power and lacking sexual access, Yeroen’s life was not over. Gradually, he formed an alliance with an upcoming male named Nikkie. Although neither Yeroen nor Nikkie dared to challenge Luit alone, together they made a formidable coalition. Over several weeks, they grew bolder in challenging Luit. Eventually, a physical fight erupted. Although all the chimpanzees involved sustained injuries, the alliance of Nikkie and Yeroen triumphed. Following this victory, Nikkie secured 50 percent of the matings, and Yeroen, because of his friendship with Nikkie, now enjoyed 25 percent of the matings. His banishment from females had been temporary. Although he never again regained the top alpha position, he had rallied from the setback sufficiently to remain a contender in the troop.
With humans as with chimpanzees, nothing in mating remains static over a lifetime. An individual’s value as a mate changes, depending on gender and circumstances. Because many of the changes individuals experience have occurred repeatedly over human evolutionary history, we have evolved psychological adaptations designed to deal with them. A person who steadily ascends a status hierarchy may suddenly be passed by a more talented newcomer. A hunter’s promise may be cut suddenly short by a debilitating injury. An older woman’s son may become the chief of her tribe. An ignored introvert, long regarded as occupying the bottom rungs of desirability as a mate, may achieve renown through a dazzling invention that is useful to the group. A young married couple bursting with health may tragically discover that one of them is infertile. Ignoring change would have been maladaptive, impeding solutions to critical challenges. We have evolved psychological mechanisms designed to alert us to these changes and motivate us to take problem-solving action.
In a sense, all mating behavior entails changes over time, from the early hormonal stirrings triggered by puberty to grandparents’ attempts to influence the mating decisions of their kin. Clarifying one’s mating desires takes time. Honing the skills of attraction takes practice. Mating is never static through life. The goal of this chapter is to describe some of the broader changes that occur among men and women over the course of their mating lives—the losses and the triumphs, the uncertainties and the inevitabilities.
Changes in a Woman’s Mate Value
Because a woman’s desirability as a mate is strongly determined by cues to her reproductivity, that value generally diminishes as she gets older. The woman who attracts a highly desirable husband at age twenty will typically attract a less desirable husband at age forty. This downturn is shown in societies where women are literally purchased by men in return for a bride-price, as occurs among the Kipsigis in Kenya.2 The bride-price consists of quantities of cows, goats, sheep, and Kenyan shillings that a groom or his family pays to the bride’s family in exchange for the bride. A prospective groom’s father initiates negotiations with the father of the prospective bride, making an initial offer. The bride’s father considers all competing offers. He then counters by demanding a higher bride-price than was offered by any of the suitors. Negotiations can last several months. A final suitor is selected by the bride’s father, and a final price is set, depending on the perceived quality of the bride. The higher the reproductive value of the bride, the greater the bride-price she is able to command. Older women, even if older by only four or five years, command a lower bride-price. Several other factors lower a woman’s value to a prospective husband and hence lower her price as a potential bride, such as poor physical condition or a physical handicap, pregnancy, and the prior birth of children by another man.
The Kipsigis’ custom of placing a premium on the youth and physical condition of a woman is not unique. In Tanzania, for example, the Turu refund a portion of the bride-price in the event of a divorce, and older wives command less of a refund owing to the physical “depreciation of the wife’s body.”3 In Uganda, the Sebei pay more for young widows than for old widows, stating explicitly that an older widow has fewer reproductive years left.4
The effect of aging on a woman’s mate value shows up in the changing perceptions of attractiveness through life. In one study in Germany, thirty-two photographs were taken of women ranging in age from eighteen to sixty-four.5 A group of 252 men and women, from sixteen to sixty years of age, then rated each photograph for its attractiveness on a 9-point scale. The age of the subjects of the photographs strongly determined judgments of female attractiveness, regardless of the age or sex of the rater. Young women drew the highest ratings, old women the lowest. These age effects are even more pronounced when men do the ratings. The change in the perceived attractiveness of women as they move through life is not an arbitrary aspect of a particularly sexist culture. Rather, this change in perceptions reflects the universal psychological adaptations in men that equate cues to a woman’s youth with her value as a mate.
There are many exceptions, of course. Some women, because of their status, fame, money, personality, or social networks, are able to remain desirable as they age. The American supermodel Cindy Crawford strikes many as looking more desirable at age fifty than most women at age twenty. The averages mask a wide variability in individual circumstances. Ultimately, a person’s value as a mate is an individual matter and is determined by the particular needs, values, and circumstances of the individual making the selection. Consider the real-life case of a highly successful fifty-year-old business executive who had six children with his wife. She developed a debilitating disease and died young. He subsequently married a woman three years older than himself, and his new wife devoted a major share of her effort to raising his children. To this man, a younger woman who had less experience in child rearing and who wanted children of her own would have been less valuable and might have interfered with his goal of raising his own children. A fifty-three-year-old woman may be especially valuable to a man with children and less valuable to a man with no children who wants to start a family. To the individual selecting a mate, averages are less important than particular circumstances.
The same woman can have a different value to a man when his circumstances change. In the case of the business executive, after his children reached college age, he divorced the woman who had helped raised them, married a twenty-three-year-old Japanese woman, and started a second family. His behavior may have been ruthless and not very admirable, but his circumstances had changed. From his individual perspective, the value of his second wife decreased precipitously when his children were grown, and the attractiveness of the younger woman as his third wife increased to accompany his new circumstances.
Although averages can obscure individual circumstances, they do give the broad outlines of the lifetime trends of many people. Furthermore, they suggest the adaptive problems that have shaped the human psychology of mating. From the wife’s perspective, as her direct reproductive value declines with age, her reproductive success becomes increasingly linked with nurturing her children, the vehicles that transport her genes into the future. From her husband’s perspective, her parenting skills constitute a valuable and virtually irreplaceable resource. Women often continue to provide economic resources, domestic labor, social status, and other resources, many of which decline less dramatically with age than her reproductive capacity and some of which increase. Among the Tiwi tribe, for example, older women can become powerful political allies of their mates, offering access to an extended network of social alliances and even helping their husbands acquire additional wives.6 But from the perspective of other men on the mating market, an older woman’s desirability as a prospective mate is generally low, not only because her direct reproductive value has declined but also because her efforts may already be monopolized by the care of her existing children and eventually her grandchildren.
Changes in Sexual Desire
One of the most prominent changes within marriage over time occurs in the realm of sex. Among newlywed couples, with each passing year men increasingly complain that their wives withhold sex. Although only 14 percent of men complain that their newlywed brides have refused to have sex during the first year of marriage, 43 percent express this feeling four years later. Women’s complaints that their husbands refuse to have sex with them increase from 4 percent in the first year to 18 percent in the fifth year. Both men and women increasingly charge their partner with refusing sex, although more than twice as many men as women voice this complaint.7
One indication of the lower sexual involvement of married people over time is the decline in the frequency of intercourse. When married women are less than nineteen years old, intercourse occurs roughly eleven or twelve times per month.8 By age thirty, this frequency drops to nine times per month, and by age forty-two to six times per month, or half the frequency of married women half their age. Past age fifty, the average frequency of intercourse among married couples drops to once a week. These results may reflect a lessened interest by women, by men, or most likely by both.
Another indication of reduced sexual involvement with age comes from a Gallup poll that measured the extent of sexual satisfaction and the frequency of sexual intercourse over time among married couples.9 The percentage of couples having intercourse at least once a week declined from nearly 80 percent at age thirty to roughly 40 percent by age sixty. Sexual satisfaction showed a similar decline. Nearly 40 percent of the couples reported “very great satisfaction” with their sex lives at age thirty, but only 20 percent voiced this level of satisfaction by age sixty.
The arrival of a baby has a significant impact on the frequency of sex. In one study, twenty-one couples kept daily records of the frequency of intercourse over a period of three years, starting with the first day of marriage.10 The rates of intercourse a year after the marriage were half what they had been during the first month. The arrival of a baby depressed the frequency of sex even more: after the birth, the rate of intercourse averaged about one-third of what it had been during the first month of marriage. Although more extensive studies over longer time periods are needed to confirm this finding, it suggests that the birth of a baby has a long-lasting effect on marital sex, as mating effort shifts to parental effort.
The effect of the length of a marriage on sexual intercourse appears to be influenced by a woman’s physical appearance. According to a study of more than 1,500 married individuals, men and women respond differently to the normal changes in physical appearance that accompany aging.11 As women age, husbands show less sexual interest in them and experience less happiness with their sexual relationship. Men who perceive their wives as quite attractive, however, maintain high frequencies of sex and higher levels of sexual satisfaction. Other research confirms that after the early years of marriage, husbands lose more sexual interest in their wives than wives do in their husbands.12 Although it is somewhat of a cliché that men want sex more than their partners do, over time this gender difference sometimes flips. These changes may be more a function of the length of the relationship than of age per se. Switching to a new mate typically brings a resurgence of sexual desire.
Changes in Commitment
Women and men become increasingly distressed by their partner’s failure to show affection and attention, which suggests a lowered commitment to the relationship. Women are more distressed than men by declining affection. Whereas only 8 percent of newlywed women complain about their partner’s failure to express love, 18 percent of women voice this complaint by the time they are four years into the marriage.13 In comparison, only 4 percent of newlywed men are upset about their wives’ failure to express love, which doubles to 8 percent by the fourth year of marriage. Whereas 64 percent of newlywed women complain that their husbands sometimes fail to pay attention when they speak, 80 percent of women are disturbed by this behavior by the fourth and fifth years of marriage. Fewer husbands overall show distress about their partners’ inattentiveness, but the increase in this complaint over time parallels that of their wives, rising from 18 percent to34 percent during the first four years of marriage.
Another indication of the withdrawal of commitment over time is one spouse ignoring the other’s feelings. Among newlywed women, 35 percent express distress about having their feelings ignored, whereas four years later this figure has jumped to 57 percent. The comparable figures for complaints by men are 12 percent in the first year and 32 percent in the fourth. These changes signify a gradual diminution of commitment to a spouse over time, which occurs for both sexes but is more upsetting to women than to men.
While women are more disturbed about men’s increasing failure to show commitment through affection and attention, men are more distressed by their wives’ growing demands for commitment. Whereas 22 percent of newlywed men complain that their wives demand too much of their time, 36 percent of husbands express upset about this demand by the fourth year of marriage. The comparable figures for women are only 2 percent and 7 percent. Similarly, 16 percent of newlywed men express distress over their wives’ demands for attention, whereas 29 percent voice this complaint in the fourth marital year. The comparable figures for women are only 3 percent and 8 percent. Thus, although both genders show increasing distress about their partners’ demands for commitment, more men than women are troubled by these changes.
These changes are accompanied by a shift in the effort that men allocate to mate guarding—another index of commitment. In evolutionary terms, a man’s efforts to guard his mate should be most intense when his mate is youngest and hence most reproductively valuable, because failure to retain a mate carries the most severe reproductive penalties when the woman has the highest value. The age of a husband, however, would not necessarily govern the intensity of a woman’s efforts to keep him. The mate value of a man does not necessarily decline from age twenty to forty, as it does for a woman, because his capacity to accrue resources often increases with age. Thus, the intensity of a woman’s efforts to retain a mate should be linked less to a man’s age than to his effectiveness at providing her with valuable resources.
My lab confirmed these predictions in a study of the tactics that husbands and wives use to retain their mates.14 Using newlywed couples ranging in age from twenty to forty, we explored the frequency of nineteen tactics, which ranged from positive inducements, such as bestowing gifts and lavishing attention, to negative inducements, such as threats and violence. We then correlated tactics with the age of the tactician, the age of the mate, and the length of the relationship. We found that the frequency and intensity of the husbands’ efforts were a direct function of the age of their wives. Men guarded wives in their middle to late thirties significantly less intensely than wives in their early to middle twenties. Men married to younger wives tended especially to perform acts that signaled to other men to stay away—telling other men directly that their wives were already taken, showing physical affection when other men were around, and asking their wives to wear rings and other ornaments that signaled their committed status. Husbands of younger women were more likely to glare at other men who paid attention to their wives and sometimes threatened them with bodily harm. In contrast, wives’ efforts to keep older husbands were just as frequent as their efforts devoted to keeping younger husbands. Regardless of the husband’s age, there was no difference in women’s vigilance, monopolization of time, and appearance enhancement tactics. The intensity of women’s efforts to guard their mates is unrelated to the age of the man, showing a marked contrast to men’s reliance on a woman’s age to calibrate the intensity of their guarding.
The most plausible explanation for this sex difference is the decrease in a woman’s reproductive capacity with age. If declines in mate guarding were related to the fact that people simply get tired or complacent when they get older, as all of their functions senesce, then the degree of mate guarding would be directly related to the age of the person doing the guarding. But neither the age of the man nor the age of the woman is a good indicator of their efforts to hold on to their mates. And if the intensity of men’s guarding zeal were related to the length of the relationship, that zeal would dwindle as the relationship got older. But the study showed instead that the length of the relationship is not related to the intensity of the guarding efforts. In short, the most plausible reason for the effect of a woman’s age on the intensity of a man’s efforts to guard her is that women of differing ages differ in their overall desirability and men devote less effort to guarding an older wife than a younger wife.
The population of the Caribbean island of Trinidad illustrates this pattern of mate guarding.15 His observations of 480 individuals at regular intervals showed the anthropologist Mark Flinn that men whose wives are fecund (young and not pregnant at the time) spend more time with their mates and get into more fights with rival men. In contrast, men whose wives are infecund (older, pregnant, or having just given birth) spend less time with their mates and get along better with other men. Flinn concludes that the reproductive potential of a man’s mate is the key determinant of the intensity of his mate guarding.
In Middle Eastern societies that encourage the practice of sequestering women, postpubescent women are veiled and concealed most heavily when they are youngest, and these practices relax as women age.16 Homicidal rages of husbands over real or suspected infidelities occur worldwide and most often if they have young wives, regardless of the age of the husband. Wives who are less than twenty years old are more than twice as likely as women who are more than twenty to be killed by a husband in a jealous rage.17 These are just a few of the extreme strategies that men use to prevent other men from gaining sexual access to young wives. As their wives get older, men’s efforts to control them become less intense.
Changes in Frequency of Extramarital Affairs
As men’s intense mate guarding lessens, women become less constrained by their husbands in their sexual behavior with other men. It has been said in a humorous vein that “monogamy is the Western custom of one wife and hardly any mistresses.”18 Reliable information on extramarital affairs is difficult to come by. The question on this subject caused more people to decline to participate in Alfred Kinsey’s study of sex than did any other question, and more of those who did participate refused to answer it than any other question. A shroud of secrecy surrounds extramarital sex, despite the multitude of studies on the subject.
The statistics on the incidence of extramarital sex must therefore be regarded as conservative, in that extramarital affairs tend to be underreported. The Kinsey report suggested that the actual incidence of affairs is probably at least 10 percent higher than reported.19 Another study of 750 spouses found that the incidence may be even higher. Whereas only 30 percent of these people initially admitted to extramarital affairs, under subsequent intensive questioning an additional 30 percent revealed that they had had extramarital sex, bringing the total to approximately 60 percent.20
Women’s extramarital affairs change dramatically with age. Affairs are rare among the youngest wives, being acknowledged by only 6 percent of wives at ages sixteen to twenty and about 9 percent at ages twenty-one to twenty-five. The incidence of extramarital affairs goes up to 14 percent of women at ages twenty-six to thirty and hits a peak of 17 percent of women between ages thirty-one and forty. After the late thirties and early forties, extramarital sex by women declines steadily, being acknowledged by 6 percent of women at ages fifty-one to fifty-five and only 4 percent of them at ages fifty-six to sixty. Thus, there is a curvilinear relationship between age and affairs for women: women have few affairs when they are both most and least reproductively valuable, but many more toward the end of their reproductive years.
A similar curvilinear age trend is found for women’s orgasms from extramarital affairs. Kinsey tabulated the percentage of women’s total sexual activity to orgasm, whatever the source, including marital sex, masturbation, and affairs. Women’s orgasms from extramarital affairs represent only 3 percent of women’s total orgasms between ages twenty-one and twenty-five, nearly triple to 11 percent toward the end of women’s reproductive years at ages thirty-six to forty-five, and drop again to only 4 percent after menopause from ages fifty-six to sixty.
There may be several reasons for why women’s extramarital affairs and orgasms peak toward the end of their reproductive years. Women at this time are guarded less intensely by their husbands and thus are better able to take advantage of existing sexual opportunities than more heavily guarded younger women. Older women also suffer fewer costs inflicted at the hands of a jealous husband, and therefore the deterrents to a tempting extramarital involvement might be less powerful.21 Because the penalties for being caught are lower, older women may feel freer to pursue their extramarital desires. They may also be attempting to produce one last child before their fertility drops to zero—a phenomenon that evolutionary psychologist Judith Easton has called reproduction expediting.22 Support for the reproduction expediting explanation also comes from the fact that women experience a surge in sexual fantasies and sex drive as they enter their thirties and the proverbial biological clock starts to tick more loudly.
Affairs may also signal an effort by women to switch mates before their own reproductive value has plummeted. Support for this idea comes from a study of 205 married individuals who had affairs. Fully 72 percent of women but only 51 percent of men were motivated by emotional commitment or long-term love rather than sexual desires in their extramarital dalliances.23 Another study found that men who had affairs were twice as likely as women to think of the involvement as purely sexual, devoid of emotional attachments.24 Yet another study found that only 33 percent of women who had affairs believed that their marriages were happy, whereas 56 percent of men who had extramarital sex considered their marriages to be happy.25 More men than women who are happily married can engage in extramarital sex without emotional involvement and without feeling that their marriages are unsatisfactory. The fact that women who have affairs are more likely to be unhappy in their marriages and more likely to be emotionally involved with the extramarital partner suggests that they may be using their affairs for the purpose of changing mates.
Men’s patterns of extramarital sex differ from those of women. Men engage in sex outside marriage both more often and more consistently than women over their lifetime. The desires of married people provide a window on men’s greater desire for extramarital sex. In one study, 48 percent of American men expressed a desire to engage in extramarital sex; the comparable figure for women was only 5 percent.26 In another study of marital happiness among 769 American men and 770 American women, 72 percent of men, but only 27 percent of women, admitted that they sometimes experienced a desire for extramarital intercourse.27 A study of working-class Germans reveals similar tendencies: 46 percent of married men but only 6 percent of married women acknowledged that they would take advantage of a casual sexual opportunity with someone attractive if it was provided.28
These desires often translate into actual affairs. In the Kinsey report on the lifetime incidence of extramarital coitus from age sixteen through age sixty, affairs by husbands surpassed those by wives at every age.29 Fully 37 percent of married men in the youngest age bracket of sixteen to twenty reported at least one affair, in contrast to a mere 6 percent of comparably aged wives. The incidence of affairs by husbands remained relatively constant over the years, with only a slight downward trend in the later years.
These affairs are not occasional trifles. Instead, affairs make up a significant proportion of men’s sexual outlets at every age throughout their life. Extramarital sex comprises about one-fifth of these men’s sexual outlets between ages sixteen and thirty-five. It rises steadily to 26 percent at ages thirty-six to forty, 30 percent at ages forty-one to forty-five, and 35 percent at ages forty-six to fifty.30 For men who engage in extramarital sex with companions and prostitutes, these forms of sex become increasingly important with age and occur at the expense of sex with their wives, which becomes a smaller and smaller fraction of their total. Given our knowledge of men’s evolved sexual psychology, these patterns reflect boredom on the part of both spouses at repeating sex with the same person or the decreasing sexual attractiveness of wives to their husbands as a result of their increasing age.
The proportion of men and women who have affairs over their lifetime depends on the culture’s mating system. In polygamous cultures, for example, where many men are left mateless and most fertile women are married, the percentages of men and women having affairs would naturally be different from the percentages in presumptively monogamous societies. Bachelors who seek sex have only married women to choose from. Furthermore, it is historically and cross-culturally common for a few high-ranking men to cuckold a large number of low-ranking men, as when Roman emperors such as Julius Caesar were permitted by law to have sex with other men’s wives.31 Under these conditions, the percentage of women having affairs would necessarily be greater than the percentage of men having affairs.
The main point about our evolved sexual strategies is not that men inevitably have more affairs than women or that infidelity is invariably expressed in men’s behavior. Rather, men’s sexual psychology disposes them to seek sexual variety, and men seek extramarital sex when the costs and risks are low. Some women also seek short-term sex, including extramarital sex, and these affairs may serve reproduction-expediting or mate-switching functions. Nonetheless, it is also true that women’s desires, fantasies, and motivations for this form of sex are less intense on average than are men’s. Mark Twain observed that “many men are goats and can’t help committing adultery when they get a chance; whereas there are numbers of men who, by temperament, can keep their purity and let an opportunity go by if the woman lacks in attractiveness.”32 Extramarital sex remains a larger component of men’s desires than women’s throughout their lives, although many men refrain from translating that desire into infidelity.
Menopause—The Last Tick of the Biological Clock
A woman’s capacity for reproduction reaches zero when menopause is complete. One of the extraordinary facts about women’s lifetime development is that menopause occurs so long before life is over. Reproduction completely ends for most women by the time they reach fifty, even though many women live well into their seventies, eighties, or nineties. This situation contrasts sharply with that of all other primate species. Even in long-lived mammals, the post-reproductive phase for females represents only 10 percent or less of their total life span. Only 5 percent of elephants, for example, reach age fifty-five, but female fertility at that age is still 50 percent of the maximum observed at the peak of fertility.33
Other female functions decline gradually with age. Heart and lung efficiency, for example, is nearly 100 percent of capacity in the early twenties but declines to only 80 percent by the age of fifty.34 In contrast, fertility peaks in the midtwenties but is close to 0 percent by the time a woman reaches fifty. The steep decline in women’s fertility, in contrast to all other bodily functions, calls out for an explanation.
At one point in history, women themselves were blamed for menopause, owing to “many excesses introduced by luxury, and the irregularities of the passions.”35 Most people today see that as a sexist and antiquated notion. One current theory to account for the puzzling phenomenon of menopause is that women’s post-reproductive phase has been artificially lengthened as a result of better nutrition and health care. According to this view, our human ancestors would have rarely lived long past menopause, if they reached it at all. This explanation appears highly unlikely, however, because the increase in the average human life span is due mainly to a decline in infant mortality. Ancestral people who lived to age twenty typically enjoyed a maximum life span close to our own, or roughly seventy to eighty years. Indeed, there is little evidence that medical technology has altered the maximum lifetime of humans at all.36 The view that menopause is an incidental by-product of longer lives also cannot explain why women’s reproductive function declines so sharply, whereas all of women’s other vital capacities decline gradually, as if they were designed for a longer lifetime. Selection would be unlikely to favor efficient body functions into the fifties and sixties if ancestral humans did not live beyond fifty. Moreover, the longer-life view cannot explain the differences between the sexes whereby men’s fertility fades only gradually, while women’s declines precipitously.37
A more likely explanation for women’s long post-reproductive phase is that menopause is a female adaptation that prompts the shift from mating and direct reproduction to parenting, grandparenting, and other forms of investing in kin. This explanation, often called the grandmother hypothesis, depends on the assumption that continuing to produce children would actually have interfered with an ancestral woman’s reproductive success compared to investing in her existing children, grandchildren, and other genetic relatives. It also assumes that older women would have been particularly valuable to their children and grandchildren. Older women, for example, tend to acquire wisdom and knowledge about health practices, kin relations, and stress management that younger women may lack. They also tend to increase their control over resources and their ability to influence other people. These increased powers and skills can be channeled toward children, grandchildren, and the entire extended network of a woman’s genetic clan.38
One early test of the grandmother hypothesis among the Ache of Paraguay suggested that, for this group, the reproductive benefits provided by the shift from direct reproduction to grandparental investment may not be great enough to outweigh the reproductive costs to women of their lost capacity to produce children directly.39 More recent tests show a bit more promising support for the grandmother hypothesis. A study of traditional Gambians found that the presence of maternal grandmothers, but not paternal grandmothers, increased a grandchild’s survival for the first two years of life.40 A study of eighteenth- and nineteenth-century Finnish peoples found that the longer the postmenopausal phase of a woman’s life, the higher the probability that her grandchildren would survive.41
Another hypothesis for women’s menopause is that there is a trade-off between rapid reproduction relatively early in life and more extended reproduction over the life span. Producing many high-quality children early may in effect wear out a woman’s reproductive machinery, so that menopause is not in itself an adaptation but rather an incidental by-product of early and rapid breeding.42 In this view, it becomes critical to identify the conditions that would have allowed ancestral women the opportunity to reproduce early and rapidly.
Early reproduction and births at short intervals, or at three to four years on average, may occur in women because ancestral women could often rely on food and protection offered by an investing mate. The tremendous parental resources that men channel to their children and mates may have created the favorable conditions for early and rapid reproduction. Chimpanzee and gorilla females, in contrast, must do all the provisioning by themselves and so cannot space offspring so closely. In these species, females space out their reproduction over nearly all of their adult lives by having one birth every five or six years. The change in women’s lives that produces a cessation of direct reproduction and a shift to investing in genetic relatives may therefore be directly linked to the high levels of parental investment by men. Since men’s investment can be traced, in turn, to the active choosing by women of men who show the ability and willingness to invest, the reproductive changes that occur over women’s lives are intimately linked with the mating decisions that occur between the sexes.
Changes in Men’s Mate Value
While women’s desirability as mates declines predictably with age, the same does not apply to men’s. The reason is that many of the key qualities that contribute to a man’s value are not as closely or as predictably linked with age. These components include a man’s intelligence, cooperativeness, parenting proclivities, political alliances, kin networks, coalitions, and, importantly, ability and willingness to provide resources to a woman and her children.
Men’s value in supplying resources, indicated by cues such as income and social status, shows markedly different changes with age than women’s reproductive value. There are two important differences: men’s resources and social status typically peak much later in life than women’s reproductive value, and men differ more markedly from one another in the resources and social status they accrue. Men’s resources and status sometimes plummet, sometimes remain constant, and sometimes skyrocket with increasing age, whereas women’s reproductive value declines steadily and inexorably with age.
For men, a distinction must be drawn between social status and the accrual of resources to understand their lifetime value as mates. In ancestral hunter-gatherer societies, limited hunting capacities and the short shelf life of killed game constrained how much meat men could accumulate. Furthermore, men in current hunter-gatherer societies do not vary widely in the amount of land they hold or the amount of meat they store.43 Indeed, although men vary in hunting ability, some groups, such as the Ache of Paraguay, share their meat communally, so that individual men do not vary widely in the direct resources they derive from the hunt.
In societies where meat is shared communally, however, skillful hunters do experience a greater reproductive success than poor hunters. This can happen for two reasons. Men who are good hunters are attractive to women and consequently secure more extramarital matings than men who are poor hunters. Women prefer to have sex with the better hunters. The children of good hunters are better nurtured by other members of the group than are the children of poor hunters. Although Ache men do not vary in their meat resources per se, they do vary in their social status derived from hunting, which gives them sexual access to desirable women and better care for their children.44 Thus, status and resources are somewhat separate qualities.
The advent of agriculture roughly 10,000 to 15,000 years ago and the invention of cash economies permitted the stockpiling of resources far beyond what was possible among our hunter-gatherer ancestors. The differences in tangible resources between someone like Facebook founder Mark Zuckerberg and a homeless person are much greater than those between the highest-ranked head man among the Ache and the lowest-ranked older male who is no longer able to hunt. The same may not be true for social status. Although cash economies have amplified the differences in men’s resources, the status differences of contemporary men are not necessarily greater than the status differences among our ancestors.
Although social status is harder to measure than income, contemporary hunter-gatherer societies around the world provide clues to the distribution of social status by age. In no known culture do teenage boys enjoy the highest status. Among the Tiwi tribe, men are typically at least thirty years old—and often middle-aged—before they are in a position of sufficient status to acquire a wife or two.45 Young Tiwi men lack the political alliances to garner much status.
Among the !Kung, the decade of the twenties is spent refining skills and acquiring knowledge and wisdom about hunting.46 Not until a !Kung man is in his thirties does he come into his own in taking down large game for the group. Among the Ache of Paraguay, male prestige is also linked to hunting ability, which does not peak until the late twenties or early thirties and carries well into the late forties.47 Among both the !Kung and Ache, men older than sixty typically become unable to hunt successfully, stop carrying bows and arrows, and show a considerable decline in their political status and ability to attract younger wives. Status among the Ache males may peak somewhere between twenty-five and fifty, corresponding closely with their hunting prowess.48 Older Ache, Yanomamö, and Tiwi men command respect, status, and awe from younger men because they have survived so many club fights, spear fights, and ax fights. Men maintain status well into middle age if they manage to survive the onslaught of aggression from other men that long.
Similar trends tied to age are observed in contemporary Western societies. One indication of men’s resources over their lifetime in contemporary Western society is actual monetary income. Unfortunately, no worldwide statistics are available on men’s and women’s resources as a function of age. A particular income distribution by age in the United States, however, has been found repeatedly over the years. The distribution of men’s average income in the United States, broken down by age, shows that income tends to be quite low among men in their teens and early twenties. In the decade between the ages of twenty-five and thirty-four, men’s income attains only two-thirds of its eventual peak. Not until the decades from ages thirty-five to fifty-four does men’s income in the United States achieve its peak. From age fifty-five on, men’s income declines, undoubtedly because some men retire, become incapacitated, or lose the ability to command their previous salaries.49 These income averages conceal great variability, because some men’s resources continue to increase throughout their old age, whereas other men remain poor throughout their lives.
Because older men tend to have more status and resources than younger men, men and women of the same age differ on average in their value as mates. In the same decade between the ages of sixteen and twenty-five when women peak in fertility and reproductive value, men’s income and status are typically the lowest that they will be in their adult lives. When most women between the ages of thirty-five and forty-four are rapidly approaching the end of their reproductive years, most men in the same decade are just approaching the peak of their earning capacity. To the extent that the central ingredients of desirability are a woman’s reproductive value and a man’s resource capacity, men and women of comparable age are not typically comparable in desirability.
Greater variability, which is the other critical difference between the value of women and men as mates at different ages, renders age per se a less important factor for men in mating. Men’s occupational status in Western societies ranges from janitor or burger flipper to CEO, college president, or successful entrepreneur. Men at the same age vary in income from the nickels and dimes of a homeless person to the billions of a Bill Gates, Mark Zuckerberg, or Warren Buffett. Between the ages of twenty and forty, men diverge dramatically in their ability to accrue resources.
These trends fail, however, to reveal the tremendous variability in the individual circumstances of women who do the choosing. From a woman’s perspective, her particular circumstances, not the averages, carry the most weight. Some middle-aged women prefer older men not because of their resources but because they believe that older men value them more than do men their own age. Among the Aka of Africa, for example, men who achieve high status and garner many resources during their lives contribute little to the direct care of their children when they marry. In contrast, Aka men who attain only low status and few resources for a wife and children compensate by spending more time directly caring for the children.50 One key indicator of a father’s investment, for example, is how many minutes a day he spends holding an infant, which is an expensive activity in terms of both calories consumed and other activities forgone. Holding protects an infant from environmental dangers, temperature changes, accidents, and aggression from others. Aka men who maintain positions of status in the group hold their infants an average of thirty minutes per day. Men who lack positions of status, in contrast, hold their infants more than seventy minutes per day. Although women typically prefer men with status and resources, a man’s willingness to parent constitutes a valuable resource that can partially compensate for the lack of other qualities.
Some women, because of the tremendous economic resources they command, may not need to select a man based on his external acquisitions. The desirability of men must be evaluated by means of the psychological adaptations of women, and these mechanisms are highly sensitive to circumstances. This is not to deny the importance of average trends; indeed, selection has produced such trends over thousands of generations of human evolutionary history. Our evolved psychological mechanisms include not only those that promote mate choices that are specific and typical of each sex but also adaptations that tailor our choices over our lifetime to the individual circumstances in which we find ourselves.
Earlier Death of Men
Human mating mechanisms account for the puzzling finding that men die faster and earlier than women in all societies. Selection has been harder on men than on women in this respect. Men live shorter lives than women and die in greater numbers of more causes at every point in the life cycle. In the United States, for example, men die on average four to six years earlier than women. Men are susceptible to more infections than women and die of a greater variety of diseases than women. Men have more accidents than women, including falls, accidental poisonings, drownings, firearm accidents, car crashes, fires, and explosions. Males suffer a 30 percent higher mortality rate from accidents during the first four years of life and a 400 percent higher mortality from accidents by the time they reach adulthood.51 Men are murdered nearly three times as often as women. Men die taking risks more often than women. They also commit suicide roughly three times more often than women. The ages between sixteen and twenty-eight, when mate competition reaches a strident pitch, seem especially bad for men: they suffer a mortality rate nearly 200 percent higher than women at this time in their lives.
The reason for men’s higher mortality, like that of males of many mammalian species, stems directly from their sexual psychology, and in particular from their competition for mates. The use of risky tactics of competition becomes greater as the differences in reproductive outcome become greater. Where some males monopolize more than one female, there are tremendous reproductive benefits to being a winner and tremendous reproductive penalties for being a loser. The red deer is a case in point. Male deer who grow larger bodies and larger antlers experience greater mating success on average than their smaller counterparts. They are able to beat their rivals in head-to-head competition. But their success comes at a cost to their survival. Precisely the same traits that give them their mating success lead to a greater likelihood of dying. During a cold winter with scarce resources, for example, the male is more likely to die because of a failure to obtain enough food for his larger body. Larger size may also make the male more susceptible to predation and less agile at escape. To these possibilities must be added the risk of dying directly through intrasexual combat. All these risks follow from the sexual strategies of red deer, which pay off on average in the competition for mates but also generally result in a shorter lifetime.
As a rule, throughout the animal kingdom, the more polygynous the mating system, the greater the differences between the sexes in terms of mortality.52 Polygynous mating selects for males who take risks—risks in competing with other males, risks in securing the resources desired by females, and risks in exposing themselves to dangers while pursuing and courting females. In a mildly polygynous mating system like our own, some men acquire multiple partners through serial marriage and affairs and others are left mateless. Competition among men and selection by women of men high in status and resources are ultimately responsible for the evolution in males of risk-taking traits that lead to successful mating at the expense of a long life.
Because the reproductive stakes are higher for men than for women, more men than women risk being shut out of mating entirely. Men who are mateless for life are more numerous than similarly mateless women in every society. In the United States in 2015, for example, 67 percent of men but only 54 percent of women in the twenty-five- to twenty-nine-year-old age bracket had never been married.53 In the thirty- to thirty-four-year-old age bracket, 41 percent of men but only 31 percent of women had never been married. These gender differences reach extremes in highly polygynous cultures such as the Tiwi, where literally all women are married, a few men have as many as twenty-nine wives, and therefore many men are relegated to bachelorhood.54
This adaptive logic suggests that the greater risk taking—and hence greater death rate—should occur among men who are at the bottom of the mating pool and who therefore risk getting shut out entirely. Men who are unemployed, unmarried, and young are greatly overrepresented in risky activities, ranging from gambling to lethal fights.55 Among homicides in Detroit in 1972, for example, 41 percent of adult male offenders were unemployed, compared with an unemployment rate of 11 percent for the whole city. Sixty-nine percent of the male victims and 73 percent of the male perpetrators were unmarried, compared with an unmarried rate of 43 percent in the entire city. These homicides were also disproportionately concentrated between the ages of sixteen and thirty. In short, men low in desirability, as indicated by being unemployed, unmarried, and young, seem especially prone to risk taking, which sometimes becomes lethal. The point is not that killing per se is necessarily an adaptation but rather that men’s evolved sexual psychologies are designed to respond to dire mating conditions by increasing the amount of risk they are willing to take.
In ancestral times, the great reproductive gains that risk-taking men generally achieved and the reproductive dead ends that usually awaited more cautious men have favored traits that yield success in competition among males at the expense of success at longevity. In the currency of sheer survival, selection through mate competition has been hard on men.
A Mating Crisis—Especially for Educated Women
The earlier death of men is one critical factor among several that produces a serious imbalance between the number of men relative to the number of women on the mating market—a disparity that gets more severe with time. This phenomenon is sometimes referred to as “the marriage squeeze,” although it occurs whether or not people seek marriage per se. Many factors affect the relative numbers. Rates of infant, childhood, adolescent, and adult mortality differ, with males dying at a faster rate throughout the life span. Men emigrate more often than women, leaving behind a sexual imbalance. Baby booms also cause imbalances because women typically select men older than they are and there are fewer men for the many women born during the boom to choose from the smaller cohort born before the baby boom. From men’s perspective, those born prior to the baby boom have a relatively large pool of women to select from, since they tend to choose younger women who were born during the boom period. Far more men than women are imprisoned, creating even more imbalance in the ratio between the sexes on the mating market. And wars end men’s lives far more often than women’s lives, creating a surplus of women on subsequent mating markets.
Divorce and remarriage patterns over the life span are other key causes of the marriage squeeze. Men who divorce tend to remarry women who are increasingly younger than they are. A 2013 study, for example, found that among first-time married men, only 10 percent married women ten or more years younger than they were and 5 percent married women who were six to nine years younger.56 Upon remarriage, these figures jumped to 20 percent and 18 percent, so that fully 38 percent of remarried men had brides six or more years younger. It may be a cliché that men marry women increasingly younger as they age and remarry, but in this case the stereotype is verified by the statistics.
These remarriage patterns are not quirks of North American countries but rather emerge in every country for which there is adequate information. In one study of forty-seven countries, age affected women’s chances of remarriage more than men’s.57 For the ages of twenty-five to twenty-nine, the differences in remarriage by sex were slight, because young women maintain high desirability at those ages as potential mates. By the ages of fifty to fifty-four, however, the sexes diverge dramatically in their remarriage rates. In that age bracket in Egypt, for example, four times as many men as women remarry; in Ecuador, nine times as many men as women remarry; and in Tunisia, nineteen times as many men as women remarry.
The mating crisis is especially pronounced among educated women. Every year more women than men become college-educated. The disparity is already prevalent across North America and Europe, and the trend is beginning to spread across the world more widely. At the University of Texas at Austin where I teach, the 2016 student body consisted of 54 percent women to 46 percent men. This imbalance may not seem large at first blush. But if you do the math correctly, it translates into a hefty 17 percent more women than men in the local mating pool. A key cause of the broader mating crisis for educated women is that women seek certain qualities in committed mateships. Most women are unwilling to settle for men who are less educated, less intelligent, and less professionally successful than they are. Men are less exacting on precisely these dimensions, choosing to prioritize, for better or worse, other evolved criteria such as youth and appearance. So the initial sex ratio imbalance within the college-educated group gets worse for high-achieving women. They end up being forced to compete for the limited pool of educated men not just with their more numerous educated rivals, but also with less educated women who men find desirable on other dimensions. The good news is that educated women and men who choose each other tend to have happier, more stable, and more affluent marriages.
The sex ratio imbalance as women age is largely an outcome of the sexual psychology of men and women. At the heart of this squeeze is the decline in female reproductive value with age, which caused selection to favor ancestral men who preferred younger women as mates and to favor ancestral women who preferred somewhat older men with status and resources as mates. In the modern environment, intelligence and education predict upward mobility. Young, healthy, and attractive women act on their desires for somewhat older, high-prestige mates, attracting men who might otherwise become mates for older women. Men with status and relative wealth try to fulfill their preferences for youthful, healthy, attractive women. And because ancestral women’s preferences for men with resources created a selection pressure for greater male competitiveness and risk taking, men die at a faster rate than women, exacerbating the shortage of men.
Changes in the proportion of men to women throughout life cause predictable changes in their sexual strategies. The degree of selectivity is the first strategy to shift. When there is a surplus of men, fewer men can be highly choosy, and they must settle for a less desirable mate than they would otherwise attract if the sexes were more in balance. A low sex ratio, in contrast, restricts women’s selectivity, because there are fewer men from whom to choose. These ratios affect the degree to which both sexes can translate their ideal preferences into actual mateships.
Low proportions of men also cause a destabilization of marriage. A surplus of women makes many of them unable to secure strong commitments. Men with many available women can pursue casual sexual liaisons with aplomb. The current rise of the hookup culture on college campuses can be traced, in part, to the surplus of women. Changes in the ratios of men to women within the United States throughout history support this explanation, because periods of increasing divorce, as between 1970 and 1980, correspond closely to periods when there was a surplus of women on the mating market.58
In the late 1980s, in contrast, divorce rates for new marriages were lower than in the previous decade, coinciding with an increase in the sex ratio.59 At that time American women’s marital happiness was also higher than their husbands’, whereas it had fallen below their husbands’ marital happiness during the preceding fifteen years, when there was a shortage of men.60 The number of men pursuing business careers doubled between 1973 and the late 1980s, coinciding with the shift from a low to a high ratio of males and suggesting that men were becoming more concerned with their economic success. Men’s willingness to invest directly in care for their children can also be expected to increase at such times, though no evidence yet exists on this point. Men may strive to become kinder and gentler to fulfill women’s mating preferences when there are relatively few available women.
A shortage of available men also causes women to take greater responsibility for providing resources. One reason is that women are not able to count on provisioning from men. Furthermore, increasing economic assets may represent a woman’s strategy to increase her desirability, analogous to the dowry competition in traditional societies. Throughout history, female participation in paid employment has increased during periods of low ratios of men to women. During the 1920s, foreign-born women in the United States outnumbered foreign-born men because of restrictive immigration laws; the participation of these women in the labor force abruptly rose.61 The existence of fewer investing men causes women to take greater responsibility for securing their own resources.
Women in mating markets of few men also intensify their competition with each other by enhancing their appearance, increasing their health-promoting behavior, and even offering sexual resources to attract men. In the sexual revolution in the United States in the late 1960s and the 1970s, for example, many women abandoned their sexual reserve and engaged in sexual relationships without requiring serious male commitment. This shift in sexual mores coincided with a period of low numbers of optimally older men for women of the baby boom. Increased competition among females with regard to their appearance, as shown by such trends as the rise of the diet industries, the mushrooming of the women’s makeup and make-over industries, and the increase in cosmetic plastic surgery—including tummy tucks, liposuction, breast implants, and facelifts—also occurred in this time of a shortage of men.
When there are more men competing for fewer women, the balance of power shifts to women. Women can more easily command what they want from men, and men in turn become more competitive with one another to attract and retain desirable women. Marriages and other long-term committed relationships are more stable, because men are more willing to offer commitment and are less willing to leave. Men have fewer available alternatives and cannot easily pursue casual sexual goals when women are scarce. Men therefore increasingly compete to fulfill women’s preferences for a long-term mate, especially by striving for position and showing a willingness to invest parentally.
Not all changes that occur during periods of high ratios of men, however, benefit women. An important drawback is the potential at these times for increasing violence toward women. During periods of male surplus, great numbers of men are excluded from mating because there are not enough women to go around. Furthermore, men who can attract women under these conditions jealously guard them against rivals. Married women in turn have more alternatives, and so the threat of their leaving gains greater credibility. This circumstance may evoke sexual jealousy in husbands, promoting threats and violence to control wives and increased violence against men who threaten to lure a mate away.62
The existence of large numbers of men who are unable to attract a mate may also increase sexual aggression and rape. Violence often becomes the strategy of people who lack resources that would otherwise elicit voluntary compliance with their wishes.63 Rape is sometimes perpetrated by marginal men who lack the status and resources that women seek in long-term mates.64 Furthermore, the likelihood of war is apparently higher in societies with a high ratio of males than in societies with a low ratio of males, supporting the theory that competition among males intensifies at times of a surplus of males.65
Changes in the ratio of men to women throughout life cause corresponding shifts in mating strategies. Adolescent men often live in a world where available women are in scarce supply, because women prefer mature men with position and affluence. Young men’s strategies reflect these local conditions of female scarcity, because they engage in highly risky competition strategies, committing the vast majority of violent crimes of sexual coercion, robbery, battery, and murder.66 In one study, for example, 71 percent of the men arrested for rape were between the ages of fifteen and twenty-nine.67 These are crimes of coercion against women whom men cannot attract or control through positive incentives.
As men mature into their thirties and forties, the ratio between the sexes typically tilts in their favor, if they have survived the risks and attained positions of reasonable status. They have a wider pool of potential women to choose from, and they enjoy a higher value on the mating market than they did in their youth. They are better able to attract multiple mates, whether through casual sex, extramarital sex, serial marriage, or polygyny. Men of any age who have little desirability as mates, however, do not enjoy this advantage, and some men are shut out of mating entirely. Women experience an increasingly skewed sex ratio as they age and are more often forced to compromise their mating strategies by lowering their standards, increasing their level of intrasexual competition, securing more resources on their own, or sometimes just opting out of the mating market. These changes over time are all products of our evolved mating strategies.
The Prospects for Lifetime Mating
Human mating changes over a lifetime, from the internal stirrings of puberty through the final bequest of inheritance to a surviving spouse. Both sexes have evolved psychological mechanisms designed to solve the problems posed by change over time—adaptations sensitive to shifts in reproductive value, status and resources, sex ratio, and mating opportunities. The changes affect women and men differently, and some of these changes are unpleasant. Women begin puberty two years earlier than men, but their capacity for reproduction stops two or three decades before men’s. The urgency that some childless women feel as their remaining years of potential reproduction wane—the increasingly loud ticking of the biological clock—is not caused by an arbitrary custom dictated by a particular culture, but rather reflects a psychological adaptation attuned to a reproductive reality.
A woman’s reproductive value over time affects not only her own sexual strategies but those of the men in her social environment, including her regular mate and other potential mates. When women are young, their partners guard them intensely, clinging tightly to the valuable reproductive resource they have successfully secured. The intense guarding closes off a woman’s opportunities for affairs and women see it as a sign of a man’s commitment or insecurity depending on circumstances. The sex lives of many couples are initially electrifying, made more so by the presence of interested rivals. With each passing year, however, the frequency of intercourse declines as women’s reproductive value declines. Episodes of intense jealousy gradually wane. Men become increasingly dissatisfied, and they show less affection to their wives. Women dislike this diminished attention from their mates and become increasingly irritated and upset about being neglected. Simultaneously, men express mounting distress about the demands of their mates for time and attention.
As women get older, men loosen the grip of guarding, and a higher and higher proportion of women pursue extramarital affairs, reaching a maximum as women approach the end of their reproductive years. Whereas for men affairs are often motivated by the desire for sexual variety, for women affairs are motivated more by emotional goals and may represent an effort to switch mates while they are still reproductively vibrant. Women seem to know that their desirability on the mating market will be higher if they leave their husbands sooner rather than later. After menopause, women shift their effort toward parenting and grandparenting, aiding the survival and reproduction of their descendants rather than continuing to reproduce directly. Women pay for their reproductive strategy of early and rapid reproduction in the currency of a shorter period of fertility.
Changes in men over a lifetime, like those of male chimpanzees, are more variable in the currencies of mating success. Men who increase their status and prestige remain highly desirable over the years. Men who fail to accrue resources and status become increasingly sidelined in the field of mating. Roughly half of all married men pursue some extramarital mating over their lifetime, and for those who do, liaisons occur at the expense of sex with their wives. Some men continue throughout life to compete for new mates, divorcing older wives and marrying younger women. Long attributed by traditional scientists to the fragile male ego, to psychosexual immaturity, to “male menopause,” or to a culture of youth, men’s effort to mate with younger women as they age instead reflects a universal evolved desire that does not go away.
One startling by-product of the differences in mating strategies of the sexes over the lifetime is that men die at an earlier age than women. This is a predictable consequence of the greater risk taking and intrasexual competition of men as they pursue the status and resources that bring about success in mating. With increasing age, the ratio of men to women becomes increasingly skewed, resulting in a surplus of women, especially among those with higher education. For women who reenter the mating market, the sex ratio imbalance becomes worse with each passing year. Both sexes have evolved mechanisms designed to shift strategies depending on changes in the sex ratio.
Given all the changes that befall men and women over their lifetimes, it is remarkable that in fact 50 percent of them manage to remain together through thick and thin. The lifelong convergence of interests between two genetically unrelated individuals may be the most extraordinary feat in the evolutionary story of human mating. Just as we have evolved mechanisms that draw us into conflict, we have adaptations that enable us to live harmoniously with the other sex. My lab’s massive cross-cultural study, for example, found that as men and women age they place less value on physical appearance in a mate and more value on enduring qualities such as dependability and having a pleasing disposition—qualities important for long-term mating success. The adaptations that promote this strategic harmony between the sexes, just as much as the mechanisms that produce strife, stem from the adaptive logic of human mating.