Authors: Andrew Trees
Decoding Love (6 page)
As always when you find this sort of discrepancy in behavior, evolutionary thinking demands an explanation, particularly when there is an obvious downside to increasing the length of copulation. First, during the act, you are vulnerable to attack, and second, the longer you have sex, the more precious energy you are using. The answer lies in the pair-bond. It turns out that sex in humans is much more about developing a bond than it is about procreation. Not that procreation isn’t essential. Obviously, that’s what all this is about at the end of the day. But that is just an occasional by-product. In fact, if you looked at human sex from the standpoint of efficiency, it’s a disaster. Even during their most fertile years, many couples can take months to conceive.
Once you look at sexual activity primarily as a way to strengthen the pair-bond, though, you can begin to make sense of a variety of oddities about human beings. For instance, women have a tipped vagina, which promotes more intimate face-to-face copulation, and large breasts, which are on permanent display and act as a constant advertisement of sexual receptivity totally disconnected from ovulation. In contrast, most female mammals only develop enlarged breasts when they are pregnant. Ethologist Desmond Morris argues that various other features—fleshy earlobes, protruding noses, and everted lips—are also designed to promote face-to-face copulation. Even the loss of body hair was possibly a means of promoting the pair-bond.
Perhaps most important, women developed concealed ovulation, which makes it impossible for men to tell when it’s the ideal time to mate. This makes her distinct among primate females, all of which have visible displays of their fertility (think of certain primates in which the females buttocks turn bright red during estrus). Further confounding male efforts to determine the time of peak fertility, women do not limit their sexual activity to the time they are ovulating. These developments likely played a crucial role in cementing her bond with a man. Instead of guarding a woman jealously for a few days during ovulation, the man had to develop a long-term relationship to try to ensure that her offspring would also be his. Anthropologist Helen Fisher has called this the “sex contract” that evolved to secure women the help they needed to raise their children.
So, with all of these traits to promote pair-bonds, everything should be great when it comes to the relationship between a man and a woman, right? Unfortunately, no. To understand why, we need to explore the crucial role of two largely unmentioned participants in all of this pair-bonding, the sperm and the egg. It is at their fruitful conjunction that everything happens. But what they do to get there and how their carriers (i.e., men and women) feel about that journey makes all the difference.
It took a while for scientists to realize the significance of this. Although they were busy studying and refining Darwin’s arguments, sexual selection didn’t receive a lot of attention, particularly when it came to one particular segment of the animal kingdom—human beings. While happy to study the mating rituals of everything from slugs to lemurs, scientists proved reluctant to put humans under the microscope, albeit with a few high-profile exceptions such as Alfred Kinsey. That all began to change in 1972 when Robert Trivers published an essay entitled “Parental investment and sexual selection.” Despite the rather pedestrian title, that essay is possibly the single-most influential piece of evolutionary theory to come along since Darwin’s original concept of sexual selection. What Trivers discovered was no less than the key to sexual selection, the engine, as it were, that made the whole thing run. That engine was parental investment.
Trivers’s revolutionary insight was simple. The investment a parent makes in his or her offspring has a huge influence on how that parent will approach mating. The more investment a parent makes, the more selective that parent will be in choosing a mate. The less investment a parent makes, the more sexual competition there will be to attract a mate. Think of the many men who often crowd around an attractive woman at a bar, and you have a pretty good picture of this dynamic at work. Which brings us back to the sperm and the egg. You see, sperm are cheap. The average man’s ejaculate contains hundreds of millions of the little buggers (over his lifetime, he will produce two trillion). And although he has nowhere near the sexual ardor of a ram or even a chimpanzee, a young, healthy man can have sex several times a day. On top of all that, if the man is more interested in being a cad than a dad, he can walk away after planting his seed and never lift another finger, so his parental investment is potentially miniscule.
If a man could have sex with an unlimited number of women and conceive with all of them, he could theoretically father hundreds of children in one year, and some famous historical figures have indefatigably attempted to do just that. According to historical records, Moulay Ismael the Bloodthirsty, the emperor of Morocco from 1672 to 1727, fathered 888 children. Recent DNA evidence suggests that Genghis Khan might have fathered an even larger number, and according to research, a mere nineteen male lineages have played the dominant role in populating the world, a remarkable example of the multiplying power of sexual selection for successful males.
Now, consider the woman and her egg, which is a very precious commodity indeed. A woman ovulates once a month, and once she is pregnant, she must carry that child inside of her for nine months. Even after she has the baby, she will have to care for it, and she is unlikely to get pregnant again right away because breast-feeding makes it more difficult to conceive. Over the course of her lifetime, the typical woman will have approximately four hundred to five hundred ovulations. Compare that to the trillions of sperm men will produce over the course of their lifetime (of course, the egg is 85,000 times larger than an individual sperm). Let’s assume that she manages to have one baby a year during all of her fertile years. It’s possible she could crack twenty. The record is an astounding sixty-nine, which an eighteenth-century Russian achieved by repeatedly having twins (although this figure is possibly apocryphal). Even that extreme number—any woman who has been pregnant will shudder at the thought—pales in comparison to the number of children a man can father, even if he isn’t Ismael the Bloodthirsty. If you are still unconvinced, anthropological evidence also confirms that cheap sperm-precious egg distinction. Seventy percent of human societies involve a payment between the two families. Any guesses as to what percentage of those require a payment to the bride’s family? Ninety-six percent!
Trivers’s brilliant insight was to realize the enormous ramifications of this simple difference. For a man, the ideal approach from an evolutionary standpoint—passing along his genes to as many children as possible—is to sleep with as many women as possible. And he shouldn’t worry too much about the quality of those women. Ugly women, pretty women, women with no teeth, women who can’t spell unilateral—it doesn’t matter. Having sex with them costs him very little effort, and all of them provide an opportunity to pass along his DNA. For a woman, though, the ideal approach is to be as selective as possible. With so few opportunities in a lifetime, she wants to ensure that she gets quality genetic material from the father. So, for her, it makes a great deal of difference whether the father is a bright, attractive, funny guy who likes to read Jane Austen or a slack-jawed, humor-less oaf who mistreats his dog. Hence, the battle of the sexes—a constant war between men who want to seduce with as little work as possible and women who want to resist until they are sure that the potential father is genetically superior and committed to help. As one research team writes, evolution favors males who are “aggressive sexual advertisers” and females who are “coy, comparison shoppers.”
Ah, but wait! We have left out one crucial wrinkle: pair-bonding. In our case, the legal bond between man and wife, which changes the calculus considerably. With marriage, a man is tied to a woman for life. With divorce rates running at almost 50 percent, this isn’t really the case, but for theoretical purposes we’ll take the “until death do us part” seriously. So what happens to our Lothario under those conditions? It turns out that men become much more choosy as well—at least when it comes to long-term relationships (for short-term ones, most men are still pretty much willing to sleep with anyone). But that doesn’t undo all the evolutionary hardwiring related to the sperm and the egg. Even with the legal bond of marriage, men and women still find ample scope to express their natural inclinations: men as the promiscuous sperm producers and women as the precious egg holders. What this means is that conflict is built into the relationship between men and women, and pair-bonding is our attempt to contain that conflict.
Of course, Trivers’s theory should come as welcome news to any women currently on the dating scene, because it means that women are firmly in control when it comes to the courtship phase of mating. Harvard anthropologist Irven Devore has even called males “a vast breeding experiment run by women.” This goes a long way toward explaining why men (particularly low-status males) have a lower life expectancy—they have to take more risks in order to pass along their genes. Women are probably reading this and thinking to themselves that all this Darwinian theorizing is great, but they don’t feel like they have much control at all. And it’s true that there are some mitigating factors. Because marriage at least theoretically implies a lifetime commitment, men are also choosy. In addition, demographics and culture can undermine female ascendancy. If women vastly outnumber men, for example, men become the scarce and precious commodity. So, in order to see the underlying control that women exert, I ask you to imagine a simple way that women could change the rules of American dating and marriage: they could refuse to have sex until they were married. No more one-night stands or even any long-term cohabitations. If this happened, all female complaints about men refusing to commit would instantly disappear. While many men are happy to date a woman for years at a time if they can still have sex, they would not be willing to do so if those relationships remained entirely chaste.
Since Trivers’s revolutionary essay, study after study has demonstrated the significance of the sperm/egg distinction for human behavior (and all other creatures for that matter). Let’s start with sex. Given Trivers’s theory, you would expect to find extremely different attitudes about sex, and that is exactly what researchers have discovered. For any squeamish women reading this book who would like to believe that men are not the appalling sexual predators that they sometimes appear to be, I suggest that you skip the next few pages.
Simply put, men have a much lower threshold for having sex. If you don’t believe me, let’s try a little experiment. If you are an attractive woman, walk up to a man on the street and ask him if he wants to have sex with you. Chances are he will say yes. How do I know? Researchers conducted a study of exactly this question. An attractive woman approached a man on a college campus and asked him one of three questions:
1. Would you go out on a date tonight?
2. Would you go back to my apartment with me?
3. Would you have sex with me?
Fifty percent of the men said they would go out on a date that night, which might seem somewhat low given what I have just said about parental investment theory. But remember that a date takes a certain amount of time and money with no promise of any sexual activity. Notice what happens to the numbers for the next two questions. Sixty-nine percent of men were willing to go back to the woman’s apartment, and a whopping 75 percent were willing to have sex with the woman (and that last number is probably low—the study noted that men who declined to sleep with the woman were usually apologetic and would often ask for a rain check or offer a reason, such as having a fiancée). Researchers then had an attractive man approach women and ask them the same three questions. When it comes to a date, women are the same as the men, accepting 50 percent of the time. From there, though, the disparity could not be starker. Only 6 percent of women were willing to go back to the man’s apartment, and not a single woman was willing to have sex with the man.
I know some of the women reading this book are already thinking that the study isn’t valid because there is a fear factor for women accepting invitations from strangers that men don’t have to worry about. Well, the researchers realized the same thing and conducted a second study. This time, the men and women were contacted by a close personal friend who vouched for the stranger’s character. Then the friends asked one of two questions:
1. Will you go on a date with the stranger?
2. Will you go to bed with the stranger?
Under this scenario, 91 percent of women and 96 percent of men were willing to go on a date—again fairly similar. But only 5 percent of women were willing to sleep with the stranger, while fully half of the men were willing to do precisely that (sight unseen!). All of this is exactly what evolutionary theory would predict. If women are choosier in general, they should be particularly choosy when it comes to a one-night stand.
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