Darwin's Rape Whistle: Jesse Bering responds to the critics.

The state of the universe.
Jan. 21 2011 4:09 PM

Darwin's Rape Whistle: The Morning After

A response to the critics.

(Continued from Page 1)

In his post, Myers uses my discussion of the evolution of the human penis as a prime example of the sloppy work being done in the study of evolution and human behavior. He pillories psychologist Gordon Gallup's famous "dildo study," which suggests that the distinctive mushroom-capped shape of the penis might serve to scoop a competitor's semen out of the vagina. (I described this work at long, intimate length in two prior articles in Scientific American.) Myers calls this penis study "tripe" because Gallup and his colleagues failed to show how variations in penis shape within a population—and variations in how the penis is used for coital thrusting—directly affect fertilization rates. Instead, the researchers relied on dildos of different designs, surveys of college students' detailing their sexual behaviors, and a batch of artificial semen.

Now, I can only assume that Myers has not had to face a university human-research ethics committee in the past several decades. If he had, he would realize that his suggested empirical approach would be unilaterally rejected by these conservative bureaucratic gatekeepers. Does Myers really believe that these seasoned investigators wouldn't rather have done the full experiment he describes—if only they lived in a less prudish and libellous university world? The fact of the matter is that research psychologists studying human sexuality are hamstrung by necessary ethical constraints when designing their studies. Perhaps Myers would be happy enough to allow investigators into his bedroom to examine the precise depth and vigor to which he plunges into his wife's vaginal canal after they've been separated for a week, but most couples would be a tad more reticent. Gallup's dildo study, and his related work on penis evolution, offered an ingenious—ingenious—way to get around some very real practical and ethical limitations. Is it perfect? No. Again, the perfect study, conceptually speaking, is often the least ethical one, at least as deemed by research ethics committees. But was it driven by clear, testable, evolutionary hypotheses? Yes. And it offered useful information that was otherwise unknown.

As for his concerns about the researchers' failing to examine genes for better-scooping penises, I don't know what Myers' penis looks like, so perhaps he's working with a different set of assumptions. But the key point in Gallup's theory is that the heritability of standard penis morphology at this stage of human evolution would be close to zero. Sure, there are some quirky, superficial penile traits that can be passed down through the generations (I'll spare you the examples, but suffice it to say that your penis looks more like your father's penis than it does mine); but all human penises, just like all human fingers, have the same basic design. And our members are very distinctive compared to those of other primates, which, as Gallup argues convincingly, likely reflects ancestral women's having sex with multiple males (at least two different males) within a relatively short period of time.


Jerry Coyne, for his part, claims—after much throat-clearing and philosophical prevarication—that he is perfectly agreeable to the idea of studying human behavior through an evolutionary lens, but that evolutionary psychology happens to be a wobbly discipline that requires "policing." (That's absolutely true, incidentally, just as it is for any other field, including Coyne's own—evolutionary biology.) And who should do that admirable, tireless work of keeping the psychologists in check? Well, Coyne himself, apparently. "If you policed your own discipline better," Coyne wags his finger at misbehaving scientists, "I wouldn't have to." Now why on earth would Jerry Coyne, who is not a psychologist and is indisputably unqualified to evaluate studies in any psychological science, ever think he's the man to be sheriff of this town? (See, again, Kurzban's thoughtful rejoinder.)

Coyne expresses big-brotherly concern, especially, over the lax standards for communicating evolutionary psychology theories and findings to the public. After taking David Brooks to task for his recent feature in the New Yorker, Coyne admonishes me for not having "known better" than to have shared with you, the gullible masses, those findings on adaptations to prevent rape. Or at least I should have provided you with a caveat emptor about the theoretical wares I was peddling. Well, perhaps. But that's a judgement call. And I suppose I have enough faith in the Slate audience to assume my readers will understand that my own voice and interpretation are overlaid on whatever science topics I happen to discuss. (That's why I include links to the original articles covered in my word-limited posts—so interested readers can explore the various intellectual debates and methodological sundries involved.)

Of more concern than these broad disputes among academic fields is the question of whether the studies I cited in my last column were valid and believable. Do women really become stronger when they ovulate? Do they become more fearful of strange men, or more likely to avoid dangerous situations, or even more racist? Coyne and others point out that the data in support of these findings were gleaned from a rather limited and specific group of people: Female undergraduates studying psychology. They're right, of course, that we shouldn't be so keen to assume that such findings would apply neatly to an entire human demographic. "It takes more than a small study on American college women at a single school," laments Coyne, "to convince me that a behavior is an evolved adaptation to prevent rape." As well it should. But his implication that evolutionary psychologists are naïve about this problem of generalizability, or that they dismiss it out of hand, shows just how out of touch Coyne is with contemporary work in the field. As with all good studies in psychology, there's enough explanatory hedging about this problem to cover the entire state of Maine. And any evolutionary psychologist worth his or her salt is chomping at the bit to do cross-cultural replications. Many already have.

Still, let's use our common sense here. Consider the set of findings showing that female handgrip strength increased among ovulating participants who'd just read a story about sexual assault, but did not increase among participants using contraceptives or those at other phases of their reproductive cycles who read the same story. And handgrip strength did not increase in ovulating women who'd read a neutral story rather than the rape vignette. These are the data, there's no debate about that. (Or is Coyne insinuating something more sinister? He does, after all, claim to have uncovered evidence of "unsavory fiddling with statistics" by Randy Thornhill and Craig Palmer, another pair of evolutionary psychologists who studied rape.)

Some critics of my essay suggest that these findings were somehow in conflict with work that had come before, studies showing that ovulating women did not exhibit increased strength. But Petralia and Gallup's handgrip study was notable precisely because it was better-designed than those earlier studies: While earlier work found no increase in strength, performance, or endurance among ovulating women in general, Petralia and Gallup narrowed their focus on the problem of rape, and found increased strength specifically in handgrip among ovulating women specifically thinking about rape.