For more than three decades evolutionary psychologists have advanced a simple theory of human sexuality: because men invest less reproductive effort in sperm than women do in eggs, men's and women's brains have been shaped differently by evolution. As a result, men are eager for sex whereas women are relatively choosy. But a steady stream of recent evidence suggests this paradigm could be in need of a makeover.
“The science is now getting to a point where there is good data to question some of the assumptions of evolutionary psychology,” says social psychologist Wendy Wood of the University of Southern California (U.S.C.).
The eager males–choosy females paradigm doesn't imply that men and women literally make conscious decisions about how much effort they should put into short- and long-term mating relative to their costs of reproduction—minutes versus months. Instead the idea is that during human history, men and women who happened to have the right biochemical makeup to be easy and choosy, respectively, would leave more offspring than their counterparts.
In 1993 psychologists David Buss and David Schmitt, then at the University of Michigan at Ann Arbor, used that idea to generate a series of predictions about men's and women's sexual behavior. As part of their study, Buss and Schmitt surveyed college students about their desire for short- and long-term mates (that is, one-night stands versus marriage partners), their ideal number of mates, how long they would have to know someone before being willing to have sex, and what standards a one-night stand would have to meet. In all categories the men opted for more sex than the women.
Although the study has been cited some 1,200 times, according to Google Scholar, there were “huge gaps from what I'm used to as a scientist,” says Lynn Carol Miller of U.S.C. Miller says that in order to evaluate the relative proportion of mating effort devoted to short- and long-term mating in the two sexes, the proper method is to use a scale such as time or money, which has the same interval between units, not the seven-point rating scale that Buss and Schmitt used.
In a study to be published in the journal Sex Roles: A Journal of Research, Miller and her colleagues carried out their own version of Buss and Schmitt's work, asking how much time and money college students spent in a typical week pursuing short-, intermediate- or long-term relationships. The proportion of mating effort dedicated to short-term mating was the same for men and women.