Darwin's Rape Whistle
Have women evolved to protect themselves from sexual assault?
Women, gather round, read carefully, because this gay man—who once, long ago, feigned sexual interest in your bodies—is about to shine a spotlight on some hidden truths about your natural design. It's by no means a perfect system, but evolution has endowed you with some extraordinary, almost preternatural abilities to prevent your own sexual assault. And these abilities are especially pronounced when you're ovulating.
Although it can certainly take other forms, rape will be defined throughout this article as the use of force, or threat of force, to achieve penile-vaginal penetration of a woman without her consent. Whether or not human males evolved to rape women is, to put it mildly, a controversial topic. The flames were fanned especially with the publication, about a decade ago, of Randy Thornhill and Craig Palmer's A Natural History of Rape, which presented evidence of what appear to be biological adaptations in human males (as well as males of many other species) specialized for forcibly coercing females into copulation. They argued that rape is an adaptive behavior in certain contexts; for example, when consensual partners are unavailable. There is some evidence that convicted rapists are physically unattractive, at least as judged by women on the basis of their mug shots. And spousal rape is most likely to occur when the husband finds out (or suspects) his wife has been unfaithful, suggesting that he is attempting to supplant another man's seed. (In fact, the distinctive, mushroom-capped shape of the human penis is designed to perform the specialized function of removing competitors' sperm, which indicates an ancestral history of females having sex with multiple males within a 24-hr period.) Furthermore, UCLA psychologist Neil Malamuth and his colleagues found that one-third of men admit that they would engage in some type of sexual coercion if they could be assured they would suffer no negative consequences, and many report having related masturbatory fantasies.
Thornhill and Palmer, Malamuth, and the many other investigators studying rape through an evolutionary lens, take great pains to point out that "adaptive" does not mean "justifiable," but rather only mechanistically viable. Yet dilettante followers may still be inclined to detect a misogyny in these investigations that simply is not there. As University of Michigan psychologist William McKibbin and his colleagues write in a 2008 piece for the Review of General Psychology, "No sensible person would argue that a scientist researching the causes of cancer is thereby justifying or promoting cancer. Yet some people argue that investigating rape from an evolutionary perspective justifies or legitimizes rape."
The unfortunate demonization of this brand of inquiry is rooted in the fallacy of biological determinism (according to which men are programmed by their genes to rape and have no free will to do otherwise) and the naturalistic fallacy (that because rape is natural it must be acceptable). These are resoundingly false assumptions that reveal a profound ignorance of evolutionary biology. Yet the purpose of the remaining article is not to belabor that tired ideological dispute, but to look at things from the female genetic point of view. We've heard the argument that men may have evolved to sexually assault women. Have women evolved to protect themselves from men?
While it's debatable that a rape module lurks in the male brain, there is absolutely no question that rape is a distressingly common occurrence in our species. One study from 1992 found that about 13 percent of American women are raped; the real number is almost certainly higher since so many sexual assaults go unreported. And aside from its self-evident harms, there is no question that rape seriously impairs a woman's reproductive interests. To say that rape pregnancies are costly to a woman's genetic success would be an enormous understatement. Not only do such conceptions completely undermine the female's mate selection—and so the quality of her offsprings' genes—but rapists are unlikely to stick around and help raise children, putting such children at a significant disadvantage. In short, it's a catastrophic mess from the vantage point of the mother's genes.
Given the enormity of this adaptive problem for ancestral women, it is plausible that human females would have evolved a set of counter-adaptations to protect them from being raped, and that these anti-rape adaptations would be activated, specifically, during the woman's most fertile period, the periovulatory phase of her reproductive cycle. So with the foregoing theoretical sketch in mind, I now present to you an up-to-date list of four empirically validated "phase dependent female rape-avoidance mechanisms:"
Jesse Bering is the author of The Belief Instinct and Why Is the Penis Shaped Like That? (July 2012). He is a frequent contributor to Slate and writes the "Bering in Mind" column for scientificamerican.com. His next book will be on the curiously scandalous science of human sexuality. Follow him at www.jessebering.com, on Twitter @JesseBering, or try adding him on Facebook.
The Rape of the Sabine Women painting by Pietro da Cortona is in the public domain.