By: Dan Slater
NY Times, January 12, 2013

A COUPLE of evolutionary psychologists recently published a book about human sexual behavior in prehistory called “Sex at Dawn.” Upon hearing of the project, one colleague, dubious that a modern scholar could hope to know anything about that period, asked them, “So what do you do, close your eyes and dream?”

Actually, it’s a little more involved. Evolutionary psychologists who study mating behavior often begin with a hypothesis about how modern humans mate: say, that men think about sex more than women do. Then they gather evidence — from studies, statistics and surveys — to support that assumption. Finally, and here’s where the leap occurs, they construct an evolutionary theory to explain why men think about sex more than women, where that gender difference came from, what adaptive purpose it served in antiquity, and why we’re stuck with the consequences today.

Lately, however, a new cohort of scientists have been challenging the very existence of the gender differences in sexual behavior that Darwinians have spent the past 40 years trying to explain and justify on evolutionary grounds.

Of course, no fossilized record can really tell us how people behaved or thought back then, much less why they behaved or thought as they did. Nonetheless, something funny happens when social scientists claim that a behavior is rooted in our evolutionary past. Assumptions about that behavior take on the immutability of a physical trait — they come to seem as biologically rooted as opposable thumbs or ejaculation.

Using evolutionary psychology to back up these assumptions about men and women is nothing new. In “The Descent of Man, and Selection in Relation to Sex,” Charles Darwin gathered evidence for the notion that, through competition for mates and sustenance, natural selection had encouraged man’s “more inventive genius” while nurturing woman’s “greater tenderness.” In this way, he suggested that the gender differences he saw around him — men sought power and made money; women stayed at home — weren’t simply the way things were in Victorian England. They were the way things had always been.

A century later, a new batch of scientists began applying Darwinian doctrine to the conduct of mating, and specifically to three assumptions that endure to this day: men are less selective about whom they’ll sleep with; men like casual sex more than women; and men have more sexual partners over a lifetime.

In 1972, Robert L. Trivers, a graduate student at Harvard, addressed that first assumption in one of evolutionary psychology’s landmark studies, “Parental Investment and Sexual Selection.” He argued that women are more selective about whom they mate with because they’re biologically obliged to invest more in offspring. Given the relative paucity of ova and plenitude of sperm, as well as the unequal feeding duties that fall to women, men invest less in children. Therefore, men should be expected to be less discriminating and more aggressive in competing for females.

It was an elegant, powerful application of evolutionary theory to the mating game. The evolutionary psychologists of the 1980s and ’90s built on Mr. Trivers’s theory to explain a wide array of stereotypical gender differences in mating.

In 1993, David M. Buss and David P. Schmitt used parental investment theory to explain why men should be expected to “devote a larger proportion of their total mating effort to short-term mating.” Because men invested less time and effort in their offspring, they evolved toward promiscuity, while women evolved away from it. Promiscuity, the researchers hypothesized, would have been more damaging to the female reputation than to the male reputation. If a man mated with a promiscuous woman, he would never be able to ensure his paternity. Men, on the other hand, could potentially enhance their status by pursuing a short-term mating strategy. (Think Kennedy, Clinton, Spitzer, Letterman and so forth. My space is limited.)

One of the earliest critics of this kind of thinking was Stephen Jay Gould. He wrote in 1997 that parental investment theory “will not explain the full panoply of supposed sexual differences so dear to pop psychology.” Mr. Gould felt that the field had become overrun with “ultra-Darwinians,” and that evolutionary psychology would be a more fruitful science if it didn’t limit itself “to the blinkered view” that evolutionary explanations accounted for every difference.

BUT if evolution didn’t determine human behavior, what did? The most common explanation is the effect of cultural norms. That, for instance, society tends to view promiscuous men as normal and promiscuous women as troubled outliers, or that our “social script” requires men to approach women while the pickier women do the selecting. Over the past decade, sociocultural explanations have gained steam.

Take the question of promiscuity. Everyone has always assumed — and early research had shown — that women desired fewer sexual partners over a lifetime than men. But in 2003, two behavioral psychologists, Michele G. Alexander and Terri D. Fisher, published the results of a study that used a “bogus pipeline” — a fake lie detector. When asked about actual sexual partners, rather than just theoretical desires, the participants who were not attached to the fake lie detector displayed typical gender differences. Men reported having had more sexual partners than women. But when participants believed that lies about their sexual history would be revealed by the fake lie detector, gender differences in reported sexual partners vanished. In fact, women reported slightly more sexual partners (a mean of 4.4) than did men (a mean of 4.0).

In 2009, another long-assumed gender difference in mating — that women are choosier than men — also came under siege. In speed dating, as in life, the social norm instructs women to sit in one place, waiting to be approached, while the men rotate tables. But in one study of speed-dating behavior, the evolutionary psychologists Eli J. Finkel and Paul W. Eastwick switched the “rotator” role. The men remained seated and the women rotated. By manipulating this component of the gender script, the researchers discovered that women became less selective — they behaved more like stereotypical men — while men were more selective and behaved more like stereotypical women. The mere act of physically approaching a potential romantic partner, they argued, engendered more favorable assessments of that person.

Recently, a third pillar appeared to fall. To back up the assumption that an enormous gap exists between men’s and women’s attitudes toward casual sex, evolutionary psychologists typically cite a classic study published in 1989. Men and women on a college campus were approached in public and propositioned with offers of casual sex by “confederates” who worked for the study. The confederate would say: “I have been noticing you around campus and I find you to be very attractive.” The confederate would then ask one of three questions: (1) “Would you go out with me tonight?” (2) “Would you come over to my apartment tonight?” or (3) “Would you go to bed with me tonight?”

Roughly equal numbers of men and women agreed to the date. But women were much less likely to agree to go to the confederate’s apartment. As for going to bed with the confederate, zero women said yes, while about 70 percent of males agreed.

Those results seemed definitive — until a few years ago, when Terri D. Conley, a psychologist at the University of Michigan, set out to re-examine what she calls “one of the largest documented sexuality gender differences,” that men have a greater interest in casual sex than women.

Ms. Conley found the methodology of the 1989 paper to be less than ideal. “No one really comes up to you in the middle of the quad and asks, ‘Will you have sex with me?’ ” she told me recently. “So there needs to be a context for it. If you ask people what they would do in a specific situation, that’s a far more accurate way of getting responses.” In her study, when men and women considered offers of casual sex from famous people, or offers from close friends whom they were told were good in bed, the gender differences in acceptance of casual-sex proposals evaporated nearly to zero.

IN light of this new research, will Darwinians consider revising their theories to reflect the possibility that our mating behavior is less hard-wired than they had believed?

Probably not. In an article responding to the new studies last year, Mr. Schmitt, a leading voice among hard-line Darwinians, ceded no ground. Addressing Ms. Conley’s finding that women were more likely to agree to casual sex with a celebrity, Mr. Schmitt argued that this resulted from “women’s (but not men’s) short-term mating psychology being specially designed to obtain good genes from physically attractive short-term partners.” He continued: “When women’s short-term-mating aim is activated (perhaps, temporarily, because of, e.g., high-fertility ovulatory status or desire for an extramarital affair, or more chronically, because of , e.g., a female-biased local sex ratio or a history of insecure parent-child attachment), they appear to express relatively focused desires for genetic traits in ‘sexy men’ that would biologically benefit women when short-term mating.”

In other words: Nothing new here, it’s all evolution.

Steven Pinker, the Harvard psychologist and popular author, also backs the Darwinians, whom he says still have the weight of evidence on their side. “A study which shows you can push some phenomenon around a bit at the margins,” he wrote to me in an e-mail, “is of dubious relevance to whether the phenomenon exists.”

But the fact that some gender differences can be manipulated, if not eliminated, by controlling for cultural norms suggests that the explanatory power of evolution can’t sustain itself when applied to mating behavior. This wouldn’t be the first time we’ve pushed these theories too far. How many stereotypical racial and ethnic differences, once declared evolutionarily determined under the banner of science, have been revealed instead as vestiges of power dynamics from earlier societies?

Citing the speed-dating study, Mr. Pinker added, “The only reason this flawed paper was published was that it challenged an evolutionary hypothesis … in particular a sex difference — as the Larry Summers incident shows, claims about sex differences are still politically inflammatory in the academy.” Here, he was referring to the much criticized 2005 comments Mr. Summers made when he was Harvard’s president suggesting that women’s underrepresentation in science and engineering was attributable not to socialization but to “different availability of aptitude at the high end.”

Perhaps these phenomena exist. Perhaps men do, over all, pursue more short-term mating. But given new research, continued rigid reliance on evolution as an explanation seems to risk elevating a limited guide to teleological status — a way of thinking that scientists should abhor.

“Some sexual features are deeply rooted in evolutionary heritage, such as the sex response and how quickly it takes men and women to become aroused,” said Paul Eastwick, a co-author of the speed-dating study. “However, if you’re looking at features such as how men and women regulate themselves in society to achieve specific goals, I believe those features are unlikely to have evolved sex differences. I consider myself an evolutionary psychologist. But many evolutionary psychologists don’t think this way. They think these features are getting shaped and honed by natural selection all the time.” How far does Darwin go in explaining human behavior? 

The problem with sex from an existential perspective is that it’s inherently awesome and it’s inherently banal and cliche, and it’s both things at the same time. Hardline religious prohibitions against recreational fornication, for example, seem insanely anachronistic but also, undeniably, are based on a valid point: sex for the purpose of sex somehow seems spiritually empty. Reality, however, makes it manifestly true that everything that occurs in adulthood, especially the stuff we admire and celebrate, like art, skyscrapers, and getting decent at guitar, exists as a semi-conscious ploy to win some girl or guy’s favor. Studies consistently show significant negative correlations between sexual frustration and a more general existential frustration. And further, any acts that lack the promise of sexual reward - like say, attaching a solid fuel rocket to a car, moving to Montana, or becoming a Catholic priest - are not only pointless, they tend to make trouble.