LOVE AND SEXUALITY ARE FAR AND AWAY THE MOST IMPORTANT emotional phenomena for our direct genetic survival. It is no surprise that nearly 80 percent of people surveyed by Daniel Kahneman and his colleagues in the course of their research on happiness reported that sexuality and love are the most decisive factors in their lives for achieving happiness.1 The other rational emotions discussed in this book are important for evolutionary survival because they increase our fitness to our environment and our personal chances for survival. But love and sexuality directly contribute to our genetic survival by enabling us to reproduce and raise offspring.
Love is not a mechanism that is needed for reproduction in most animals, for whom sexual relations alone suffice. These typically involve brief sexual encounters, often only once with each mate, with males taking on little or no responsibility for caring for their offspring.
Many of us may also know humans who fit this description in their attitudes toward sexual relations. But most of humanity exhibits a different pattern of sexual behavior. The institution of marriage, a nearly universal cultural phenomenon, is a strong expression of the more typical human attitude toward love and sexuality. This distinction between human sexuality and that of most animals is related to the fact that raising a human child is a very long and complex process requiring the involvement of more than one parent.
While humans wait patiently for up to a full year or more for infants to learn to walk after their births, newborn gazelles are up and walking within two days of their births. Equine mares watch their newborn foals take their first steps within half a day of birth.
The life expectancy of gazelles and horses is shorter than that of human beings, but it still ranges up to about thirty years. Raising a human child to the point of complete independence from adult care and supervision takes about 20 percent of modern human life expectancy. Until about two hundred years ago, it required as much as 30 percent of life expectancy. There are virtually no other animals that go through such a lengthy juvenile period relative to their life expectancies.
From the evolutionary perspective there is no point in having offspring unless those offspring in turn have offspring of their own. Only a child who has reached independent adulthood can contribute to the genetic survival of his or her parents. If childhood were sufficiently short relative to the life span of a single parent, and demanded relatively few resources, mothers could reasonably care for their offspring on their own. The longer childhood lasts and the more one needs to invest resources in raising a child, the more important it becomes for the father, who also benefits (genetically) from having offspring who successfully reach adulthood, to share in the burden of raising the child.
Previous chapters looked into the roles that social emotions play in creating commitment. Anger, for example, helps us create credible threats. Love, in contrast, creates credible commitment for altruistic behavior toward mates, a commitment that is a precondition for parental cooperation in caring for offspring. From the male perspective, the commitment arising from love within a couple increases the chances that the child he is helping to raise is indeed his child, carrying genes that are similar to his, and not the child of another man with whom his spouse has had relations. Love and social structures that are built on stable monogamous relationships are the result of the large amount of parental energy humans need to invest for the successful survival of their offspring.
Human parents generally care simultaneously for children who were born in different pregnancies. This is not a phenomenon that characterizes other animals, whose offspring leave their parental nests before their mothers reproduce again. My colleague Motty Perry coauthored an excellent paper that used models of game theory to show that this phenomenon is responsible for the familiar structure of the human family, in addition to the commitments that members of couples exhibit toward each other.2 Without these commitments, men would never know if the food that they have worked so hard to obtain and give to their spouses will be passed on to feed their children, as opposed to the children of other men from previous pregnancies.
Human childhood is very lengthy because human children need to learn complex social skills, over and above the physical and cognitive growth that all animals undergo as juveniles. Very few animals form long-term stable couplings with a single mate (hamsters and foxes are two noteworthy exceptions). The vast majority of animals have what we humans might call far more “steamy sex lives,” based on casual sexual encounters. The sole purpose of their sexual interactions is procreation. Sexuality in these species is based on intense and sometimes violent “sperm competition” between males, along with selective female receptivity to the mating efforts of the males, with only the males deemed most fit on the part of the females succeeding in mating.
The specific characteristics of sperm competition between males vary from one species to another, depending on evolutionary developments. Competition between drones (male bees), for example, comes down to a total of about ten minutes out of their very brief lives. When a virgin queen bee is ready to mate, she enters a vigorous dancing state, drawing a swarm of drones. Only the strongest and quickest drones can succeed in mounting the larger queen bee and inserting their sperm into her. The drones die shortly afterward, while the queen bee stores their sperm for the rest of her life (up to thirty years) for use in fertilizing the millions of ova she produces.
Sperm competition between male mice is no less interesting. Its main expression comes after the act of mating has been completed. After inserting his sperm into a receptive female, the male secretes a sticky substance that essentially blocks the female’s reproductive tract to prevent other males from successfully mating with her until his sperm has been fully absorbed inside the female. This strategy, reminiscent of the chastity belts that the knights of the Middle Ages once locked their wives in before going out to battle, increases the male’s chances of successfully fertilizing a female with whom he mates and also incentivizes him to care for her offspring because he has greater certainty that her offspring are his.
Sperm competition strategies vary widely between species, but generally it is one of two kinds of evolutionary strategies for ensuring the survival of one’s DNA. The other is a “marketing strategy” (think of the peacock’s tail and other characteristics and behaviors that can be explained using the handicap principle) used to increase the attractiveness of individual males in the eyes of females.
Men and women have evolved differences in their emotional and sexual behavior due to physiological differences related to reproduction between the two sexes. Reproductive asymmetries between men and women are expressed in three main ways:
1. The maximal number of children that a woman can bear in a lifetime is well below one hundred. (The best documented historical record of the greatest number of children borne by one woman is held by a Russian peasant woman who lived in the eighteenth century and gave birth to sixty-four children through twenty-seven pregnancies.) In contrast, a man can theoretically father 100,000 children. Similarly, while a woman can reach her maximal reproductive potential by mating with only one man throughout her life, a man would need about a thousand women to attain his maximal reproductive potential.
2. A woman knows with exact certainty who her biological children are: the children emerging from her womb. A man can never be certain whether the children borne by his spouse are indeed his biological children.
3. In the reproductive process itself mothers invest far more resources than fathers because mothers carry fetuses within them for nine months of pregnancy.
In addition to these three differences, men and women differ in one more relevant physiological actor: men on average have greater muscle mass than women.
To get an idea of the extent to which these physiological distinctions influence differences in emotional reactions and sexual behaviors between men and women, I will review several widespread clichés, taking a close look at each one. Keep in mind that the evolutionary forces that have been shaping differences between the sexes long predate the feminist revolution and the modern era. They existed before human civilization arose, under conditions of a daily struggle for survival in which lack of close care for a child on the part of both parents meant almost certain death for the child.
A brief discussion at the end of the chapter will also look into why evolutionary gender differences in emotional and sexual behavior stubbornly persist even in our modern world.
Cliché 1: Men are far more likely than women to agree to brief one-time sexual encounters without emotional commitments.
The facts: A man can theoretically father a thousand times as many children as any one woman can bear. In practice, men and women have the same number of children on average for the simple reason that each child has precisely two biological parents. This brings about a situation in which men are in perpetual competition with other men in the race for greater fertility. From this perspective, a long-term commitment to one partner reduces a man’s genetic survival potential because it limits the number of children he can have to the upper limit of children that his partner can bear for him. In contrast, women need only one man to attain their maximal fertility, and gain no advantage in having multiple sexual partners.
Cliché 2: Women have a greater need than men to express love.
The facts: As noted above, having sexual relations with multiple partners without any emotional commitment has no effect on the number of children a woman can bear. On the other hand, it does reduce her children’s chances of survival, because if she has no partner with an emotional commitment to her and her children, then none of the fathers of her children is likely to contribute to the burden of raising the children. If she is alone in the task of providing for her children, they are likely to have less protection and less food than they would if they had a father helping to raise them. Procreation in general is more resource-demanding for women than men because a woman can have only one child every nine months, during which she needs to invest a great amount of energy in pregnancy and childbirth. As a result, women need to be much choosier than men in mating, and they need to ascertain that their mates will be committed to them and to their children.
Cliché 3: Women are more anxious than men when it comes to their health and the well-being of their children, while men become more nervous than women when their health shows signs of failing.
The facts: The image and stereotype of the “caring and worrying” mother is common in many cultures, and for good reason. Because women are more limited than men in the number of children they can have, they need to invest more resources than men in protecting the children that they already have. This is the evolutionary source of the “caring and worrying mother” figure. When all her children have achieved adulthood and her years of fertility are behind her, usually when she is in her fifties, a woman’s task in directly ensuring her genetic survival is over. But a man at that age can still contribute to his genetic survival by fathering more children. Only death or disease can limit his further fertility. In other words, from the perspective of genetic survival, from age fifty and above only men have “something to lose,” which may be the source of male hypochondria in their later years.
Cliché 4: Women are more jealous and suspicious than men of their partners.
The facts: It is nearly impossible to check this empirically. On the other hand, evolutionary explanations do not support the claim. Both sexes have good reasons to be jealous. A man needs to ensure that the children his partner bears, whom he is committed to supporting, are indeed his biological children. A woman needs to ensure that her partner will not leave her and commit himself to another woman in her place, leaving her children bereft of his protection and support.
But these evolutionary sources of jealousy differ between men and women, leading to differences in behavior. Several studies, including one by Monica T. Whitty and Laura Lee Quigley, have found that men are emotionally hurt most by sexual infidelity on the part of their partners, while women are more anxious to preserve emotional fidelity.3 Interestingly, differences in emotional responses to infidelity between men and women are also expressed when they are the ones doing the cheating. Women who have intense emotional (but not sexual) relations with men who are not their partners feel stronger pangs of guilt than women who have extramarital sexual relations that do not involve emotional commitments. In contrast, men feel guiltier about sexual relations they have with women who are not their partners than about emotional relations. This can cause many couples to disagree about whether one of the partners has cheated, or whether jealousy is justified at all, even when they agree about the facts.
Cliché 5: Men are more likely than women to cheat on their partners.
The facts: An interesting research study conducted in the United States several years ago using DNA tests performed on newborn infants revealed that 5 to 10 percent of newborns are not the biological children of the men who are listed as their fathers.4 Most of those men are completely ignorant of the fact that they are raising another man’s biological child. This statistic, however, does not answer the question of whether more men than women cheat on their partners. The fact that men need more sexual partners than women to achieve their maximal fertility potential might lead men to be more receptive to opportunities for cheating, but that does not necessarily translate into more cheating in practice.
Imagine listing all the men in a particular town by their attractiveness to women, from the most attractive to the most slovenly and unappealing man you have ever seen. Although it is clearly not realistic, for the purposes of this thought experiment assume that all women would have the same preferences regarding the attractiveness of these men. Again, for the sake of the argument, suppose that in this virtual town each man is married to one woman and each woman is married to one man.
Now ask yourself which of these men has the best chance of conducting extramarital affairs with several women. The answer is obviously the men who are highest up in the attractiveness ranking. They can offer most of the women around them an opportunity for much “better” mating than the men to whom they are married. Women do not physically increase the number of children they can bear by increasing the number of sexual partners they have. What they do gain, however, is the opportunity to improve the genetic legacy they can give their children if they have relations with a more attractive man than their spouse. A man who is only slightly more attractive than her husband is unlikely to tempt a woman to cheat on her marriage, but George Clooney stands a good chance. Men, in contrast, can gain more by stressing quantity over quality, hence they will tend to be less choosy. It doesn’t take a supermodel to tempt them to cheat.
What percentage of men, then, will manage to realize their dream of having an extramarital affair? The answer to that question depends on two variables. One is the distribution of “grades” that women give to the men around them for attractiveness, and the other is the extent to which women gain an advantage by remaining faithful to their husbands.
Suppose, for example, that the most attractive man in town is a perfect 10 in the rankings while all the other men are rated 5, and furthermore suppose that the advantage for remaining faithful to one’s husband is low (which is the case in wealthy societies, in which women are not dependent on men contributing resources for the raising of their children). In this case the “adultery market” would be very simple. Nearly all the men (except for the top-ranked man) will be faithful to their wives while every woman except one will cheat on her husband (all of them with the same highly ranked man). In this case, despite the advantage that men clearly gain from having multiple partners, adultery would be mostly a female pursuit. This seemingly paradoxical situation arises from the market forces described in the example. All the men want to commit adultery but only one actually does so, while all but one of the women cheat on their husbands but only with the most attractive man in town.
This example is admittedly extreme, but it can be generalized. In any situation in which there is a small number of “stars” at the top of the attractiveness ranking who are far and away more preferred than their nearest competitors, there will be more women committing adultery than men. This may describe, to a certain extent, the true situation in wealthy and liberal modern societies with relatively weak economic anchors to maintain the traditional family structure. In traditional and religious societies individuals who cheat on their spouses pay a heavy price for their infidelity, with women usually punished more than men. The punishments can range from social ostracism all the way to execution. They significantly reduce the incentive for infidelity.
Cliché 6: Men are more competitive than women.
The facts: The Hebrew University of Jerusalem conducted a wide-ranging survey in 2003 to study the sex ratio of men to women at all ranks and levels, from students to full professors. The study produced an interesting set of data. A majority of students awarded the university’s bachelor’s degrees, 61 percent, were women. Among master’s students women comprised an even larger majority, 62.5 percent. But the percentage of women obtaining PhD degrees placed them in the minority, at 46 percent. The representation of women among faculty members was even lower, 33 percent. Finally, the percentage of women who were full professors (the highest faculty rank at the university) was so low it was embarrassing—only 11 percent. These numbers did not surprise most people familiar with the composition of the faculty, but they did spark an intense discussion on the question of why the percentage of women drops so dramatically from one academic rank to the next.
A similar discussion at Harvard University a few years ago led to the firing of university president Larry Summers after remarks he made on the subject set off an uproar. Summers merely speculated that the lack of women in faculty positions in the sciences is related to differences in the competiveness exhibited by women and men. The Hebrew University discussion was less stormy. The data on the ratio of women to men completing bachelor’s and master’s degrees and the grades women were attaining in their coursework left no doubt that women are as intellectually capable as their male colleagues. Why, then, are women dropping out the higher up one looks on the academic ladder?
Some blamed the heavy burden that raising children places on women, a lack of day care opportunities for small children, and difficult hurdles that faculty members need to overcome for university promotion, which disadvantage mothers of newborns. Some accused the university of conscious or subconscious discrimination against women, claiming that men feel more comfortable in all-male working environments.
Pointing accusatory fingers at particular individuals or policies and blaming them for unbalanced sex ratios in corporations and institutions is convenient, but in my opinion this is an inefficient approach. It is convenient because it gives the mistaken impression that drastic changes can be immediately obtained if only aggressively enforced affirmative action policies are brought to bear. It is inefficient because it deals only with the supply side of senior jobs positions and not the demand side.
Several research studies conducted by behavioral economists in recent years have added to our insight in this subject. One such study, published by Uri Gneezy and Aldo Rustichini, revealed that men and women behave differently in competitive conditions.5 The researchers gave men and women monetary rewards for solving maze problems on a computer. In the first stage of the study the participants received a set, uniform payment for every maze that was successfully solved. In this stage there were no sex-related differences evident—women and men were equally successful in solving the mazes.
In the second stage the offered payments terms were changed. Instead of a uniform payment for each successful solution of a maze, payments were based on the results of a competitive tournament. In other words, the participants were ranked in relation to others, with the payments they received depending on how high they were ranked. The money received by each participant now depended not only on his or her performance but also on the performance of others. In this stage men attained significantly better results than women. Not only that, women performed better in the noncompetitive stage of the study than in the competitive stage, managing to solve more mazes.
It is still unclear why the women performed worse in the competitive stage. One possible explanation is that they felt less motivated to make an effort to solve the mazes when the payments were based on tournament results. But another explanation is that the stress that was induced by the competitive environment of the second stage affected their abilities. Gneezy and Rustichini concluded that men perform better than women in competitive situations.
Another pair of researchers, Muriel Niederle from Stanford University and Lise Vesterlund from the University of Pittsburgh, also studied gender-based differences in competitive situations.6 Participants in their study were paid to solve tasks requiring cognitive efforts—summing five two-digit numbers. This time, however, the participants had the option of receiving either a uniform payment based on their performance alone or a payment based on their performance in competition with others. A majority of male participants, 73 percent, chose the competitive payment method compared to only 35 percent of female participants who preferred that option. That large gap was independent of the relative performances of men and women in accomplishing the tasks in the experiment. Part of the gap stemmed from the simple fact that many of the female participants felt less comfortable being in a competitive situation, no matter how good they were at the task of summing five numbers. This is one of the most important points that emerged from the study: even women who were very good at the task and could have attained higher payments by choosing the competitive payment method preferred the noncompetitive method.
Several other studies, in addition to the two described in detail here, also indicate that men and women differ in their attitudes toward competition. There are also studies showing that women prefer avoiding negotiating situations much more than men.
Gender-based differences in attitudes toward competition may, if only partially, help explain the imbalance between men and women in senior jobs. Sherwin Rosen and Edward Lazear of the University of Chicago composed a very influential article in the 1980s comparing the promotion process in large organizations to sports tournaments.7 An employee who wants a promotion in an organization needs to “defeat” several rivals in order to advance to the next level, just like a tennis player at Wimbledon. The higher one climbs in the hierarchy, the closer one gets to the spire of the pyramid. At each successive level the competition gets fiercer.
Rosen and Lazear give a very interesting explanation for the fact that the greatest leap in salary typically occurs between the penultimate level of the pyramid and its apex. At every other stage of the competition, they explain, if you get promoted, not only do you get a higher salary and more prestige, you also get another important prize, namely the right to compete for the next level in the hierarchy, where you will get even more money and prestige. If you get to the very top of the pyramid, you cannot receive this added prize, simply because it does not exist. There are no more levels to climb. The compensation for this comes in the form of a greater increase in salary in the move from second-in-command to the top position than the salary increases in all the other promotions. Otherwise, organizations would be reducing the incentive for promotion at the highest level of competition, hurting their chances of getting the best person for the top job.
Workplace promotion competition is usually not as transparent and blunt as in Rosen and Lazear’s model. But it definitely exists, and the competition unquestionably gets tougher the higher up you climb in the hierarchy. That may be the reason that women, who on average avoid competitive environments more than men, often decide to bow out of the competition at a certain stage even when their talents and chances for promotion are equal to those of the men against whom they are competing. This is why gender-based affirmative action in general is unlikely to be the right policy to use for the goal of increasing the representation of women in senior positions in organizations and corporations.
In Rosen and Lazear’s model, affirmative action is akin to lowering the bar by half a foot in a high-jump competition when the jumper is a woman. Doing so will not change the fact that there is a competition in the first place. It won’t make women who prefer avoiding competition altogether feel any better about the process. In fact, it could have the opposite effect. Knowing that they are being judged by different criteria than those applied to men may harm their self-image and reduce the satisfaction they would otherwise get from winning the competition, reducing women’s incentives to participate from the start.
A more efficient policy to adopt would be one that judges men and women using equal criteria but gives women a greater incentive to agreeing to compete in the first place. Possible incentives include giving women a “prize” for participating in the competition, even before the winner is announced, or offering a bigger prize for women who win the competition (which would translate into a higher salary or bonus given to women who attain promotions).
Sex-based differences in attitudes to competition undoubtedly developed during the course of evolution. Competitiveness gave males a greater survival advantage than it gave females. Competition between males for female mates is characteristic of many animals. Competitiveness gave human males an evolutionary advantage in genetic propagation. Acquiring food resources, hunting, and protecting families against predators and enemies are inherently masculine pursuits (given the more muscular frames men generally have in relation to women). They require a good deal of competitiveness. In a hostile environment, with scarce food resources that are difficult to obtain, a man who avoids competition risks death for himself and his family.
Cliché 7: Men are more likely than women to take risks.
The facts: Medical researchers studying the male hormone testosterone discovered an incredible relationship several years ago between the concentration of the hormone in the human body and the structure of the fingers of the hands. It is a very simple relationship that anyone can easily check by looking at his or her own hands. Place your right hand flat and spread open on a table top. Measure the length of your index finger, followed by the length of your ring finger, and calculate their ratio. In most men the index finger is shorter than the ring finger, giving a ratio of less than one. The smaller the ratio, the greater the concentration of testosterone in the body. This is a statistical relation that is not necessarily always true but it does occur in the vast majority of cases in a statistically significant manner.
High concentrations of testosterone are also statistically correlated with increased sex drive, stronger levels of concentration, and greater muscle mass. The hormone also has positive health effects, cutting down the concentration of lipids in the body and reducing heart attack risk.
On the other hand, testosterone is also linked to several negative phenomena, including many undesirable behavioral traits. People with elevated testosterone levels tend to be attracted to smoking and alcohol abuse. The chances that a man with high testosterone levels will develop a smoking habit are nearly twice as high as those of a man with relatively low testosterone. High-testosterone men also exhibit tendencies toward violent behavior and danger-seeking.
But that’s not the end of the tale of the ring finger. Economists at the University of Cambridge compared the finger lengths of hundreds of financial “day traders.”8 Day traders, usually agents of investment houses and trust funds, buy and sell stocks at torrid paces. In many cases, using a method called “shaving” in the day-trading jargon, shares in a stock may be bought, held, and then sold in under a minute, sometimes within seconds.
Nearly all day traders are young men who work for only short periods of time for any one employer before being replaced. The Cambridge researchers tracked the work performances of several day traders and came to a startling conclusion: the lower the ratio of index finger to ring finger, the more likely a trader is to take risks in buying and selling stocks, and the higher the average profits he or she brings in. Even neophyte investors know that taking bigger risks can lead to higher average profits, but predicting the statistical likelihood that a trader will be willing to run great risks in the hope of netting large profits by looking at the lengths of fingers sounds completely ludicrous. Yet it is scientifically confirmed.
There are many additional research findings indicating that men and women have different attitudes to risk. An interesting series of studies trying to understand youth behavior were conducted in recent years. They focused, in particular, on the question of why obsessive thrill-seeking, provocative behavior, and thoughtless risk-taking are so prevalent among youths aged thirteen to twenty-three. Parents of children in that age range often find it difficult to understand their children’s behaviors, forgetting that they themselves did the same when they were younger.
Research studies have shown that the brain of a youth over those ten years is still “a work in progress,” during which new experiences, including extreme situations, are important for the development of an adult personality.
Significant differences were noted between the attitudes of male and female youths with regard to risk-taking. Young males take much greater risks than females in the same age range, and more risks than older men. This is a major reason that throughout history most of the blood spilled in battles has been the blood of young men.
The differences in risk attitudes between the sexes are also due to evolutionary developments related to competition between males over female mates. They can be explained by Zahavi’s “handicap principle” mentioned in Chapter 11. Risk-taking by males broadcasts courage to females, a behavioral trait that indicates greater chances of success in protecting offspring from danger and obtaining food sources. This gives men who boast about their willingness to take risks in the presence of females an evolutionary advantage.
But the presence of another man also pushes men to greater risk-taking. Experiments studying the reactions of men in car race simulators indicate that the extent to which they are willing to take greater risks increases significantly when there is another man in the vicinity. Parents of teenage children who feel nervous every time their hormone-filled son takes the keys to the family car on weekends should feel calmer when their son is alone in the car than when it fills up with friends his age.
Natural selection has a role to play here as well. Displays of willingness to take risks in the presence of one or more other males are intended to intimidate potential rivals for mates. In the nineteenth century this trait became so pronounced that many young men lost their lives in armed duels fought over petty insults, all conducted with the approval of the establishment without anyone ever brought to trial.
Cliché 8: Men seek younger women, while women place less importance on the age of their mates.
The facts: Clear and incontrovertible statistical evidence shows that in most marriages husbands are older than their wives. But does this reflect biological or cultural preferences?
Two main elements have influenced social norms with regard to age differences in couples. The first is the gap in fertility ages between men and women and the second is the fact that human sexuality is characterized by long-term stable relationships, as detailed previously in this book. In societies in which sexual encounters are casual one-off events there is no reason for a man to prefer a younger woman to an older woman, assuming both of the women are fertile. In long-term monogamous relationships this is no longer the case. From the perspective of achieving maximal fertility, a man who is limited to one partner in a long-term relationship will prefer as young a woman as possible (assuming she is fertile) to ensure the greatest number of children over time.
Several years ago an interesting study was conducted in Finland in an effort to ascertain the optimal age difference between men and women in marriages for the purpose of maximizing the number of children reaching adulthood successfully.9 The authors of the study based their findings on historical records in the Sami population between the seventeenth to nineteenth centuries. The Sami, native to northern Scandinavia, were chosen for this study, as was the range of years in the historical records, in order to identify the optimal age gap in an entirely natural environment unaffected by modern medicine. The researchers’ conclusions grant Hugh Hefner and Woody Allen a bit of legitimacy in their choices of mates: the optimal age difference was greater than fifteen years. The couples included in the study exhibited a wage range of age gaps, from men who married women twenty years older to men who married women twenty-five years their juniors. The precise optimal age gap for having the greatest number of healthy children was found in couples in which husbands were 16.4 years older than their wives.
A follow-up study that focused on couples in modern Sweden, who obviously benefit from the latest in medical advances, concluded that the optimal age gap had narrowed to six years. But even in contemporary Western societies it is not extremely rare to find couples in which the age gap is as much as twenty years or more. It is no coincidence that large age gaps are particularly noticeable among celebrities and their wives, largely for social reasons. These couples usually form as a result of a “trade” in which the older man receives social credit for exhibiting vitality and youthful fervor while the younger woman receives in exchange social status, money, and fame. Television personality Larry King was once asked about the twenty-six year age difference between him and his wife Shawn.
“I know what you’re thinking,” replied King, “that when people look at Shawn and me, the first thing they notice is the age difference. But I’m here to say, if she dies, she dies.”
Cliché 9: Men, more than women, seek physically attractive mates. Women, more than men, seek professionally successful mates.
The facts: Outward physical attractiveness in mates is important for both sexes to some extent, because in the past it was a marker indicating health and fertility. On the other hand, what is considered attractive in humans is very culturally specific and far from universal (except for some measures of facial symmetry, which have been shown to play a remarkably universal role in defining beauty). The attraction people feel to whatever is considered fashionably beautiful in a specific culture is mainly related to the social credit accruing from attaining a desirable mate in the mating market. That is also the reason that men tend to brag more than women about their romantic escapades.
When it comes to seeking professional success in mates, the picture is different. In prehistoric societies professional success was expressed in hunting skills. Good hunting skills improved the attractiveness of a mate in two ways. It increased the chances of feeding a large family of children. But perhaps even more importantly, since good hunting skills are to some extent inherited in successive generations, it also increased the chances of having successful offspring over several generations, a significant factor in improving the overall genetic success of the woman.
By this reasoning, a woman’s professional success should also be important for men seeking mates. But men and women are not symmetric in their “reproductive strategies.” As already noted, men have evolutionary grounds for stressing quantity (meaning absolute numbers of offspring) whereas women stress quality. This is apparently the evolutionary reason that professional success in mates is more important for women than it is for men.
Cliché 10: Women are more talkative than men.
The facts: Luann Brizendine published a book in 2006 titled The Female Brain, which provided the ultimate explanation for the ever-present tension so many of us experience in our marriages: women, claimed Brizendine, talk three times as much as men!10 Using data collected in her clinic, Brizendine concluded that women express on average 20,000 words per day compared to an equivalent male statistic of only 7,000 words per day. Brizendine compared the female brain to a highway for emotional processing. The male brain in this metaphor is more like a dirt road. These differences, she claimed, are due to the effects of testosterone, which cause men to think about sex so much that it blocks their ability to express emotions.
Though many men may think their wife or girlfriend is a shining example of this phenomenon, Brizendine is in fact wrong. About a year after she published her book, a thorough and wide-ranging research study was conducted on the subject of talkativeness in men and women by Matthew Mehl and several of his colleagues from the Department of Psychology at the University of Arizona.11 Their conclusions were published in an article in the prestigious journal Science. According to the article, there is no difference in the number of words used by men and women. Members of both sexes express about 16,000 words per day on average. This finding was based on research using tape-recording devices attached to a large population sample. The three most talkative participants in the experiment were men, with the man topping the list clocking 47,000 words per day on average. The most important aspect here, however, is not the specifics of Brizendine’s or Mehl’s research claims, but the fact that so many people, male and female, are convinced (with slight exaggeration) that women are obsessive talkers, while men, in contrast, are imagined to be closer to monks who have taken vows of silence.
Why is there a large gap here between reality and the popular perception? One of the most talked about phenomena in the professional psychology literature on relationships is what is called demand/withdrawal, a situation in which one partner asks (or demands) to talk about problems in the relationship while the other partner seeks ways to avoid (or withdraw from) such conversations. Demand/withdrawal apparently plays an important role in the stigma of women as being overly talkative. A thorough study of the phenomenon conducted by UCLA researchers in 1990 showed that in most demand/withdrawal situations, it is women who are doing the demanding while men respond either with passivity or withdrawal.12
The UCLA study spurred efforts by several researchers to explain the different roles men and women play in demand/withdrawal situations. Some claimed that the demands expressed by women and the withdrawal exhibited by men were due to different ways in which men and women process emotions. But further research into the subject gradually showed that this is not the case. One such study showed that the active and passive roles in demand/withdrawal situations are determined not by the sex of the partners but by which partner initiates the conversation.13 In general, the initiating partner is active while the other partner is the withdrawer, independently of the sex of the initiator. Another study, published in 2010, showed that demand/withdrawal occurs between homosexual partners (both male homosexuals and lesbians) to the same extent that it occurs among heterosexuals.14 Finally, a 2006 paper showed that there is a significant cultural factor in the behavioral patterns exhibited in demand/withdrawal situations.15 In Pakistani couples, for example, the roles we normally assign to men versus women are reversed. Taken together, these studies indicate that the role of women as the demanders in demand/withdrawal situations is not the result of different mechanisms for processing emotions. Apparently, women in relationships more often seek change, while men prefer to maintain the status quo.
This still leaves two questions relating to the phenomenon of demand/withdrawal. First of all, why do women seek change in relationships more than men? Secondly, why does the partner who is the receiver of the “demand” (whether man or woman) so often choose the passive “no comment” role, avoiding conflict instead of “firing back” or entering into a discussion of the issues raised by the demander? After all, we are usually very active in responding to demands we dislike when they come from people who are not our spouses.
We have, actually, already answered the first question when we discussed the evolutionary reason that women require emotional input and commitment from their male partners. Demand/withdrawal often occurs when one of the partners in a relationship (usually the woman) is complaining about a lack of commitment and involvement on the part of the other partner.
To answer the second question we will use some simple insights from game theory. Why does the partner who is the recipient of the demand withdraw? It has nothing to do with gender. In fact it has nothing to do with monogamous relationships at all. This phenomenon is typical of many intensive and long-term interactions. Demand/withdrawal is common, for example, between parents and their children (with the parent playing the role of the demander and the child withdrawing). The behavior associated with demand/withdrawal situations creates equilibrium between the partners to the interaction. In most cases demand/withdrawal is part of a long-running negotiation between the partners, where one of the partners is demanding a change that is costly to the other partner.
A strategy of passivity in response to demands does not necessarily imply lack of interest in the other partner’s desires. Its goal is creating balance between accepting some of the demands without fully committing to all the changes asked for. In repeated interactions, this “no comment” strategy can be part of an equilibrium. Sometimes, silence is golden.
The last cliché relates to a commonly heard claim that is not directly connected to differences between the sexes but is relevant to the general subject of this chapter.
Cliché 11: Homosexuality endangers the survivability of the human race.
The facts: This claim is frequently raised by clergymen of nearly all the major religions who claim, “the creator favors the furtherance of the human race and homosexual sex can never be reproductive and therefore must be against god’s will.” Interestingly, some of the most secular individuals who believe in evolution would tend to argue the same, saying, “the forces of evolution favor the furtherance and reproduction and homosexual sex can never be reproductive.”
This claim is true but reflects a shallow understanding of “kin selection,” the evolutionary survival of a genetic line. The survival of the species is enhanced not only by those who produce new offspring but by those who ensure the survival of offspring with similar DNA (i.e., family members). Worker bees and ants, for instance, forgo reproduction and devote themselves to caring for the offspring of their queen, thus ensuring that her line continues to propagate. The phenomenon is not limited to social insects alone. The evolutionary advantage gained by avoiding direct sexual reproduction is that the “passive” individual, freed from the burden of caring for his or her offspring, can invest resources in caring for the offspring of others with a similar genetic inheritance, such as a brother or niece, thus increasing their chances of survival.
Empirical support for this explanation can be found in an article published in 2006 in the prestigious Proceedings of the National Academy of Sciences of the United States of America.16 The article’s authors reported that youths who have older brothers develop homosexual tendencies to a significantly greater extent than their peers who do not have older brothers. In addition, it was found that the same increased homosexual tendencies are not expressed when the older brothers are not biologically related (as a result of adoption or divorce and remarriage on the part of parents of the children). This implies that the source of the increased homosexual tendencies is biological, not social influences. (How a mother’s second or third child might differ biologically from her first is not known; but, for instance, her eggs might change after her first has been fertilized.) In many cases the older brothers had children of their own to care for, and were helped in bearing this burden by their younger brothers.
Note that this explanation is independent of whether or not homosexuals in the modern world tend to care for their nieces and nephews more than heterosexuals; evolutionary pressures influenced these tendencies tens of thousands of years ago. It is therefore plausible that evolution selected for homosexuality in those cases in which having that trait conferred evolutionary advantages.
DIFFERENCES BETWEEN THE SEXES DUE TO EVOLUTION WERE established at the dawn of human civilization, in a physical environment that was very different from the environment in which we live today. Many of those differences stopped giving individuals evolutionary advantages hundreds of years ago, if not earlier. Social mechanisms that adapted human characteristics to new environments undoubtedly changed many of the components of our personalities and our emotional reactions.
Why, then, have so many differences between the sexes continued to persist in our modern and advanced societies despite a century of feminism and policies directly intended to blur the distinctions? There may be more than one answer to that question, but I believe that there is one decisive answer: although some of the specific traits distinguishing men from women may not provide any evolutionary advantages in our day and age, the very fact that there are differences between the sexes is still a tremendous evolutionary advantage for the human race and for both sexes. Our sexuality is enhanced by the differences between men and women, encouraging sexual attraction and therefore reproduction. Men who blur their masculinity and women who blur their femininity reduce their chances of successfully competing for mates of the opposite sex.
Even in situations that have nothing to do with finding romantic partners, people consider stressing masculinity in men and femininity in women to be aesthetic and attractive. That is why instead of blurring gender differences in our outward appearances, we continue to stress them. Many of the most liberal and enlightened individuals in our societies still put on make-up (if they are women) or wear masculine-looking clothes (if they are men).
We often stress gender differences in behaviors for the same reason we stress them in outward appearances: consider how many couples you know in which the woman is more often in the driver’s seat when both of them are in the car versus the number of couples in which it is the man who is more likely to be the driver. How about the number of men you know who do most of the cooking in their families versus the number of women?
Minor gender differences based on ancient evolutionary conditions can grow and become more prominent over time, instead of disappearing. That is why breast enlargement surgery became popular at a time when few women were breastfeeding their infants, and why men are still attracted to body-building gyms even though technological and economic advances have almost entirely eliminated the usefulness of physical strength in obtaining food and shelter for their children.