Dollars and Sex (31 page)

This is because decisions are made based on the likelihood of a bad outcome, not based on the certainty of a bad outcome. If everyone who cheated knew with certainty that they would be caught, knew with certainty that their spouse and community would respond negatively, and knew with certainty the costs they would incur as a result, I think you would agree with me that there would be significantly less marital infidelity than there currently is.

THE MYTH OF MONOGAMY

Humans, like other mammals, are not naturally monogamous; even the overly romanticized female sloth, rumored to be the most monogamous of all the primates, will sneak out for a night of coitus with a nearby sloth if she gets the chance. Understanding the benefit side of the cost-benefit analysis that determines whether or not a man or woman cheats requires an understanding of the biological payoff to giving into the desire to have a sexual relationship outside of marriage.

As we discussed in
chapter 2
, the males of our species demonstrate a biological desire for multiple sex partners. The best descriptor of this male trait, in my mind, is called the Coolidge Effect. The Coolidge Effect describes how males of any mammalian species, including humans, who are sexually receptive to a sexual partner, will, eventually, lose interest in copulation completely unless a new partner is introduced; males are hardwired not to invest in repeatedly inseminating a female that they have already inseminated.

Psychologists Frank Beach and Lisbeth Jordan tested this effect in laboratories in the 1950s by placing male and female rats in a container and allowing them to copulate until the male was exhausted. At the point of exhaustion, the male lost all interest in copulation, despite persistent attempts by the female rats to encourage him to continue (this scenario may sound familiar to some of you). When the researchers introduced a new female rat into the container, however, the male rat regained his interest in copulation and proceeded to inseminate the new female rat.

Just in case you are either a sexually frustrated women who is tempted to think that introducing another woman to your bed will stimulate your male partner's sexual interest, or a sexually bored man who thinks this is convincing argument to share with your partner, you should know that the introduction of the new female did not renew the male's sexual interest in the original female rat—just the new one that was introduced.

The popular theory for why males behave this way is that, throughout evolutionary history, the men
who have had the most sexual partners (we can call him Australo-promiscuous, if you like) were the same men who had the most children. We are descendants of the most promiscuous males, meaning that modern-day men are hardwired to desire multiple sexual partners.

Females are more restricted in the number of children they can produce and having multiple sexual partners does not increase the quantity of children they will bear over their lifetime. It can, however, improve the quality of their children. Children who are taller and healthier are more likely to survive to adulthood and have children of their own. As a result, we are descendants of the women who sought out the tallest and healthiest sexual partners to be the fathers of their children.

Some evidence that women are hardwired to seek high-quality sexual partners for the purpose of fertility can be found in studies that show that women change their preference for sexual partners depending on where they are in their menstrual cycle. For example, evolutionary psychologists Martie Haselton and Geoffrey Miller found that when the participants in their study were ovulating, 93 percent stated that they would prefer a poor yet creative man for a short-term sexual relationship to a financially successful but uncreative man. When this exercise was repeated with participants who were not ovulating, only 58 percent of women preferred the poor yet creative man as a short-term sexual partner.

These effects of ovulation on mate choice were not found when women were asked about long-term relationships. You might be tempted to predict that wealth matters more for long-term relationships than it does for short-term relationships where women are looking for good providers instead of good genes. However, in this particular study when the choice of long-term partner was a poor yet creative artist or a wealthy yet uncreative artist, approximately 84 percent of both ovulating and non-ovulating women expressed a preference for the poor artist.

Another study, by evolutionary psychologists Elizabeth Pillsworth and Martie Haselton, is even more to our point. It finds that women who are married to less-attractive men were more likely to seek extramarital relationships when they are ovulating than are women who are married to more-attractive men. Those same women, who were more inclined to seek an extramarital sexual partner, also reported that their husbands were more attentive and affectionate when they were most fertile; less attractive men seem to realize on some level that they must protect their wives from extramarital relationships by rewarding them for their fidelity through affection.

The point of this evidence on human biology is that it tells us that the benefits of being unfaithful to one's partner are different for women than they are for men.

For example, it implies that when a man cheats, it is because he is desirable enough to persuade a woman, other than his wife, to have extramarital sex with him. He can do this because the benefits to a short-term relationship with a man who has good genes, measured in the quality of her children, is high for the woman he attracts.

It also implies that when a woman cheats, it is not because she is highly desirable but because her husband is less desirable than the men who are willing to have extramarital sex with her. She will do this because there is a benefit, measured in the quality of her children, to having a short-term relationship with a man who has good genes.

IT'S NOT YOU; IT'S ME

This idea that a man's willingness to cheat is a function of his own quality and a woman's willingness to cheat is a function of her husband's quality is a testable hypothesis that was taken on by Bruce Elmslie and Edinaldo Tebaldi, whose research we discussed earlier in this chapter.

The idea that infidelity is related to fertility is supported by their research. Men are fertile for a longer period of their lives; men are more likely to be unfaithful to their wives as they themselves age, but only up to the age of age of 55, after which point the likelihood that they will cheat drops off. The relationship between women's infidelity and age has a similar pattern (increasing and then decreasing), but with a peak in the likelihood of infidelity occurring much earlier—around the age of 45—when a woman's ability to reproduce is in decline. It is at this point that the reproductive benefits to a woman of having extramarital sex end since she is unlikely to have any other children.

Using educational achievement as an indicator of gene quality, they find no evidence that educated men are more likely to have extramarital sex than are less-educated men—in fact they find that men who have only a high school diploma or less are about 3 percent more likely to cheat than are men with a college or graduate degree. This evidence seems to refute the hypothesis that high-quality men are more able to cheat than are low-quality men. The authors attribute this result to the fact that some men are having sex with prostitutes and that gene quality does not determine a sex worker's willingness to have sex with a married man.

If women are seeking short-term sexual partners based on gene quality, however, because they have been hardwired by years of evolutionary forces to select fathers who will give their children the greatest chance of survival, then is a university degree what they are really looking for?

As a woman myself, I have to say that to me the ideal short-term sex partner looks more like someone who would scale a cliff to tackle a tiger on my behalf, rather than a man who can solve systems of equations. I suspect it is their measurement of attractiveness (i.e., education) that has made it difficult to prove their hypothesis that men with high gene quality are more likely to cheat.

Having said that, women whose husbands have a college or graduate degree are 3 percent less likely to cheat than are women whose husbands have only a high school diploma or less. Men don't seem to be more or less likely to cheat dependent on their wives' education. This does lend some evidence to support the hypothesis that for women it is their husband's characteristics that determine whether or not they cheat, but men's decisions are independent of that consideration.

That conclusion leaves something out, however: it assumes that a husband's low educational achievement increases a woman's likelihood of cheating because it increases the benefit of having sex with a superior man through the good-genes effect. This argument ignores the fact that a woman's decision to cheat is determined by the expected cost of cheating as well as the benefit, and we already know that the cost of cheating is partially measured in the income she will forgo if he divorces her.

IF I HAD A RICH MAN