Most Women Benefit from Polygyny, Most Men Benefit from Monogamy
When there is resource in equality among men (which there always is in every human society), most women benefit from polygyny. This is because under polygyny, women can share a wealthy man, whereas under monogamy, they are stuck with marrying a poorer man. If the resource in equality is large enough, then a fraction of a wealthy man is bigger and thus better than a whole of a poor man.31
The only exceptions are extremely desirable women. These women can marry the most desirable, wealthiest men under any circumstance (polygyny or monogamy). Under monogamy, they can monopolize the wealthiest men, whereas under polygyny, they must share them with other, less desirable women. So the most desirable women benefit from monogamy, but all other women benefit from polygyny.
The situation is exactly opposite for men. Most men benefit from monogamy, because it guarantees that every man can find a wife. True, less desirable men can only marry less desirable women, but marrying a less desirable woman is much better than not marrying anyone at all.
Once again, extremely desirable men are the exceptions. Such men can have multiple wives under polygyny, whereas they are limited to only one wife (albeit an extremely desirable one) under monogamy. So extremely desirable men benefit from polygyny, but all other men benefit from monogamy.
When men in monogamous societies imagine what their life might be like under polygyny, they imagine themselves with multiple wives. So they may think they would be better off under polygyny. What they don’t realize is that for most men, who are not extremely desirable, polygyny means no wife at all, or, if they are lucky, one wife who is much less desirable than one they could get under monogamy (because under polygyny, more desirable wives are taken by men who are more desirable than them). If they do the math, they will come to the right conclusion that most of them are better off under monogamy than under polygyny.
Q. Why Does Having Sons Reduce the Likelihood of Divorce?
Sociologists and demographers have discovered that the presence of sons decreases the probability of divorce.31 Couples who have at least one son face a significantly lower risk of divorce than couples who have only daughters. Why is this?
Remember from chapter 3 that a man’s mate value is largely determined by his wealth, status, and power, whereas a woman’s mate value is largely determined by her youth and physical attractiveness. This means that the father has to make sure that his son will inherit his wealth, status, and power, regardless of how much or how little of these resources he has. A working-class father still has to make sure that his son will inherit what little wealth he has, because the more the son inherits, the greater his expected reproductive success. In sharp contrast, there is relatively little that a father (or mother) can do to affect the daughter’s expected reproductive success; once she is born, there is very little parents can do to keep her youthful or make her more physically attractive.
The evolutionary psychological logic therefore predicts that the continued presence of (and investment by) the father is important for the son, but not as much for the daughter. Strictly in reproductive terms, there is very little fathers (or anyone else) can do for daughters beyond keeping them alive and healthy. The presence of sons therefore deters divorce and departure of the father from the family more than the presence of daughters, and this effect should be stronger among wealthy families.
Of course, strongly wedded to the Standard Social Science Model as they are, the sociologists and demographers who discover that the presence of sons decreases the probability of divorce explain this finding by saying that fathers are considered to be more important for their sons’ lives than for their daughters’, and the presence of sons encourages fathers to get more involved in child rearing, thereby lowering the likelihood of divorce. Of course, they are right; fathers are generally considered more important for sons than for daughters, and the presence of sons does encourage fathers to get more involved. But the Standard Social Science Model cannot explain why this is so; evolutionary psychology can.
Q. Why Are Diamonds a Girl’s Best Friend?
Because women make disproportionately greater parental investment in children than men do, their primary task is to discriminate between “dads” and “cads”33 among male suitors. Dads are males who are willing to invest in a woman and her offspring in the long run; cads are those who are only looking for cheap thrills for the night and are likely to desert her after having sex. Given that women can have only so many children in their lifetimes and that they must invest much more in each child, the reproductive consequences faced by a woman for failing to discriminate between dads and cads are very large.
How might a woman accomplish this task? How would she know which men will invest resources in her and her offspring? A good dad must possess two qualities: the ability to acquire and accumulate resources, and the willingness to invest them in her and her children. A good way to screen for men who are simultaneously able and willing to invest is to demand an expensive gift; only men who are capable of acquiring resources and willing to invest them can afford to give a woman expensive gifts, which are known as courtship gifts or nuptial gifts in evolutionary biology.34 (Yes, females of other species demand these gifts before they agree to have sex with the males.) Would any expensive gifts do? A Mercedes-Benz? A house in the suburbs?
No, these gifts will not do. A man who is intrinsically interested in luxury European cars might buy her a Mercedes. A man who is intrinsically interested in real estate might buy her a house in the suburbs. In either case, his gift is not an unequivocal and pure indicator of his general and universal willingness to invest resources in her and her offspring. The courtship gift for the purpose of screening dads from cads must not only be costly but also lack intrinsic value.
Diamonds make excellent courtship gifts from this perspective because they are simultaneously very expensive and lack intrinsic value. No man (or woman) can be inherently interested in diamonds; you cannot drive them, you cannot live in them, you cannot do anything with them. Any man who would buy diamonds for a woman must be interested in making an investment in her. Flowers, another favored gift for women, are also relatively expensive and lack intrinsic value. Of course, diamonds and flowers are beautiful, but they are beautiful precisely because they are expensive and lack intrinsic value, which is why it is mostly women who think flowers and diamonds are beautiful. Their beauty lies in their inherent uselessness; this is why Volvos and potatoes are not beautiful.
Consistent with this evolutionary psychological logic, a recent analysis using game theory demonstrates that what the researchers call “extravagant” gifts—gifts to women that are “costly but worthless”—facilitate courtship.35 The researchers note that such extravagant gifts have the added benefit for men of deterring “gold diggers,” women who promise to mate in exchange for a gift but then desert without mating after receiving it. (Once again, yes, there are such “gold diggers” among other species as well.) It appears that women are not the only ones who must screen their mates very carefully.
Q. Why Might Handsome Men Make Bad Husbands?
Recall from chapter 3 that beauty is not in the eye of the beholder or skin-deep. Beautiful people are genetically and developmentally healthier than are unattractive people. So how are handsome men different from unattractive men as husbands? Why would healthier men not make better husbands?
Two leading evolutionary psychologists, Steven W. Gangestad and Jeffry A. Simpson, suggest one answer.36 Gangestad and Simpson observe that men can maximize their reproductive success by pursuing one of two different strategies: Seek a long-term mate, stay with her, and invest in their joint offspring (the “dad” strategy); or seek a large number of short-term mates without investing in any of the resulting offspring (the “cad” strategy).37
All men may want to pursue the cad strategy; however, their choice of the mating strategy is constrained by female choice. Men do not get to decide with whom to have sex; wome
n do.38 And women disproportionately seek out handsome men for their short-term mates for their good genes. Even women who are already married would benefit from short-term mating with handsome men if they could successfully fool their husbands into investing in the resulting offspring. The women then get the best of both worlds: Their children carry the high-quality genes of their handsome lover and the parental investment of their unknowingly cuckolded but resourceful husband.
Thus, handsome men get a disproportionate number of opportunities for short-term mating and are therefore able to engage in the cad strategy. Ugly men have no choice. Since women do not choose them as short-term mates, their only option for achieving any reproductive success is to find one long-term mate and invest heavily in their children—the dad strategy.
Consistent with Gangestad and Simpson’s theory, a study shows that more attractive men have a larger number of extra-pair sex partners (sex partners other than their long-term mates).39 Another study shows that more attractive men have more short-term mates than long-term mates, while more attractive women have more long-term mates than short-term mates.40 More important, handsome men invest less in their exclusive relationships than ugly men. They are less honest with and less attentive to their partners.41
We hasten to add that “good” and “bad” are value judgments that we promised not to make in this book. (See “Two Errors in Thinking That We Must Avoid” in the introduction.) However, empirical data do demonstrate that handsome men have more extramarital affairs and are not as committed to their marriages, which many wives may consider undesirable. In this sense, handsome men make better lovers than husbands.
5
Some Things Are More Important Than Money
THE EVOLUTIONARY PSYCHOLOGY OF THE FAMILY
While the topic of the family receives somewhat less attention in evolutionary psychology than, say, sex and mating do, evolutionary psychologists have nonetheless made significant contributions toward our understanding of the human family. Two of the early pioneers of modern evolutionary psychology, Martin Daly and Margo Wilson, for example, conducted a study in Canada and the United States demonstrating the dangers of stepparents—stepfathers in particular—to children.1 Infants and children who do not live with two biological parents face 40 to 100 times as great a chance of being injured or killed within the family as those who live with both biological parents. In a sense, Daly and Wilson provided an evolutionary psychological explanation for the “Cinderella Effect.”2
Family is the context for parental investment; it is where children are born and raised by biological and not-so-biological parents (who believe themselves to be biological parents but really are not). While much of parental investment in children is made consciously by the parents, one of the great and surprising discoveries of evolutionary psychology is that some forms of parental investment are unconsciously made.
For example, parents may invest more or less into sons or daughters simply by having more children of one sex over the other. The sex of the child is not consciously decided by the parents (outside of sex-selective abortion). While parents may wish to have a boy or a girl, they cannot consciously choose to have one or the other. Yet evidence shows that the sex of the child can be predicted by certain features of the parents that are important in evolutionary psychological terms.
That’s where our story begins….
Q. Boy or Girl? What Influences the Sex of Your Child?
It is commonly believed that whether parents conceive a boy or a girl is entirely up to chance. Close enough, but not quite; it is largely up to chance, but there are factors that very subtly influence the sex of an offspring. It is also commonly believed that exactly half the babies born are boys and the other half are girls. Close enough, but not quite; the normal sex ratio at birth is 0.5122—that is, 105 boys born for every 100 girls. But the sex ratio varies slightly in different circumstances and for different families. So what factors affect the sex of the child?
The Genius of Robert L. Trivers
Any discussion of sex ratio at birth must begin with the work of Robert L. Trivers, who is one of the greatest evolutionary biologists of the last century. In 1973, Trivers teamed up with a mathematician, Dan E. Willard, to formulate one of the most celebrated principles in evolutionary biology, called the Trivers-Willard hypothesis.3 The hypothesis states that wealthy parents of high status have more sons, while poor parents of low status have more daughters. This is because children generally inherit the wealth and social status of their parents. Sons from wealthy families, who themselves become wealthy, have, throughout most of evolutionary history, been able to expect to have a large number of wives, mistresses, and concubines, and produce dozens or hundreds of children,4 whereas their equally wealthy sisters can have only so many children. So wealthy parents should “bet” on sons rather than daughters.
Conversely, poor sons can expect to be completely excluded from the reproductive game, because no women would choose them as their mates. But their equally poor sisters can still expect to have some children if they are young and beautiful. (Recall from chapter 2 that the “fitness ceiling”—the best one can do—is much higher for men than for women, while the “fitness floor”—the worst one can do—is much higher for women than for men.) So natural selection designs parents to have a biased sex ratio at birth depending upon their economic circumstances—more boys if they are wealthy, more girls if they are poor.
There is evidence for this hypothesis throughout human societies. American Presidents, Vice Presidents, and cabinet secretaries have more sons than daughters.5 Poor Mukogodo herders in East Africa have more daughters than sons, both at birth and in the zero to four age group.6 Church parish records from the seventeenth and eighteenth centuries in Germany show that wealthy landowners in Leezen, Schleswig-Holstein, had more sons than daughters, while farm laborers and tradesmen without property had more daughters than sons.7 Among the Cheyenne Indians on the American Plains, prestigious, high-status “peace chiefs” have more sons than daughters, while poor and marginal “war chiefs” have more daughters than sons in the zero to four age group.8 In the contemporary United States and Germany, the elite—judged by the listing in their respective country’s Who’s Who—have a greater proportion of sons among their offspring than does the population in general.9 In an international survey of a large number of respondents from forty-six different nations, more wealthy individuals are more likely to indicate a preference for sons if they could only have one child, whereas less wealthy individuals are more likely to indicate a preference for daughters.10 While there is some counterevidence,11 most evidence is in support of the Trivers-Willard hypothesis.12
Extending Trivers’s Genius
Recently, there has been a theoretical extension of the original Trivers-Willard hypothesis, called the generalized Trivers-Willard hypothesis.13 The idea behind the new hypothesis is the same as that behind the old one, but it extends the idea to many other factors besides the family’s wealth and status. The new hypothesis suggests that if parents have any trait they can pass on to their children that is better for sons than for daughters, then they will have more boys. Conversely, if parents have any trait they can pass on to their children that is better for daughters than for sons, then they will have more girls. Parental wealth and status are just two of the traits they can pass on to their children that are more beneficial for sons than for daughters, but there are many other factors.
Brain types are another example of such heritable traits. Strong “male brains,” which are good at systematizing (figuring things out), are more beneficial for sons than for daughters, while strong “female brains,” which are good at empathizing (relating to people), are more beneficial for daughters than for sons.14 Since brain types are heritable, the generalized Trivers-Willard hypothesis would predict that parents with strong male brains, such as engineers, mathematicians, and scientists, are more likely to have sons, while those with strong female brains, such as nurses, social workers,
and school teachers, are more likely to have daughters. This is indeed the case.15 While the sex ratio at birth among the general population is 0.5122—that is, 105 boys for every 100 girls—the study shows that the sex ratio among engineers and other systemizers is 0.5833—that is, 140 boys for every 100 girls. The comparable sex ratio among nurses and other empathizers is 0.4255—that is, 140 girls for every 100 boys.[16]
By the same token, tall and big parents have more sons and produce more male fetuses (because size was a distinct advantage in male competition for mates in the ancestral environment, while body size has no particular advantage for women), and short and small parents have more daughters and produce more female fetuses.17 Because violence was probably a routine means in the male competition for mates in the ancestral environment18 (as it is among our primate cousins),19 tendency toward violence was adaptive for ancestral men but not for ancestral women. Accordingly, violent men have more sons, both in the United States and the United Kingdom.20
Why Beautiful People Have More Daughters…
Why Beautiful People Have More Daughters: From Dating, Shopping, and Praying to Going to War and Becoming a Billionaire–Two Evolutionary Psychologists Explain Why We Do What We Do Page 10