Darwin’s Rape Whistle: The Morning After

A response to the critics.

Painting of Io and Zeus by Correggio.
Jupiter and Io, by Correggio Public domain

Oy vey. For my last piece here at Slate (“Darwin’s Rape Whistle“), I described a diverse set of scientific studies that were motivated by what I deem to be a very reasonable hypothesis: that women’s social cognition and behavior have been shaped by natural selection to pre-empt rape, and that these adaptations are likely to come into play at precisely the time when a woman’s mate choice and genetic interests would be most undermined by sexual assault. That is to say, the studies are predicated on the idea that women have evolved to avoid being raped when they’re ovulating. The article caused quite a stir.

This included a flurry of critical posts disputing the validity of the data I reported, my wide-eyed acceptance of them, and questioning—even if the data were valid—their ability to rid the world of the anathema that is rape. Jerry Coyne, biologist and author of Why Evolution is True, jumpstarted the debacle; Rob Kurzban, psychologist and author of Why Everyone Else is a Hypocrite, then responded in defense of his field. Then P.Z. Myers, prominent science blogger and professional firebrand, became nauseated by my essay and got all worked up about the evolution of penises. Kurzban did a one-two punch back at Myers. Amanda Marcotte, Emily Yoffe, and Amanda Schaffer of Slate’s DoubleX blog jumped into the ring, all of them weighing in on rape research by evolutionary psychologists. Coyne had some more to say, and John Rennie, former editor at Scientific American, agreed with the critics, and then he agreed some more. And that’s just part of the storm that’s followed in the wake of my anti-rape essay.

I must say, the whole affair has given me a bit of a headache, but I also realize that this prickly reaction presents a great opportunity for discussion. Strange, is it not, that such grievous concerns about the science of evolutionary psychology—in particular, whether its central hypotheses are falsifiable, whether reporters should be so enthusiastic in reporting its results, and whether its methods are adequate—seem to appear at some times but not others? Where were these same outraged critics, I wonder, when I wrote enthusiastically about the evolutionary psychology of humor, blushing, athletics, male body odor, suicide, and cannibalism? Yet whenever the issue at hand relates to female sexuality—whether it’s the prevention of rape or the evolution of female orgasm, the field’s most outspoken opponents turn up in droves. We do need to clear up a few misunderstandings about the science. But I would like to know what we are really, truly, talking about here. Is this a debate over quality control in a particular academic field or a battle over politics and ideology? I wish I could believe it were only about the science. When the skeptics chime in, I suspect they are egged on by politicized reactants.

I’ve been writing about evolutionary psychology, among other topics, for a while now, and I know that whenever I cover studies of women’s sexuality, I’m bound to receive comments, emails, tweets, and blog posts calling me a “mansplainer,” “douche-bag,” “rape apologist” or worse. (Once, for the reportorial sin of failing to mention transsexuality in a piece about sexual development, a disgruntled reader posted to Twitter: “Jesse Bering is a shining example of the kind of hateful f_ck who gleefully murders trans women.”) That’s fine. Well, I’m not exactly immune to such hostilities, mind you, but I do brace myself for them and think I can get my head around where they’re coming from, for better or worse. I can only say in reply to this brand of criticism that I write with a style of insouciance in a sign of solidarity with natural selection, which is completely indifferent to any ideology. I will confess, however, that I’m often at a loss to understand the more peculiar, and even more fervent, animosity toward evolutionary psychology shown by so many biologists. Take P.Z. Myers: It’s not just my little review article that has him in a state of vascular thrombosis; it’s the entire discipline. “Researchers in this field produce some of the most awesomely trivial drivel,” he says in disgust.

Perhaps, just perhaps, some biologists are besotted with a sense of ownership over the world of evolutionary theorizing—how dare these mere psychologists trespass on our grounds with their outrageous, “just-so” stories?

P.Z. Myers is not, of course, the undisputed public ambassador of his discipline (although I’ve no doubt he sees himself as such), and by no means does the following apply to all biologists, or even all those who are critical of evolutionary psychology. But Myers’ affect-laden views regarding evolutionary psychology do represent those of at least a significant and vocal minority. Critics are particularly irritated by the fact that evolutionary psychologists do not test for genetic inheritance of the very traits they argue are adaptive but instead rely on behavioral or self-report measures to evaluate their theories. They also believe that evolutionary psychologists take too many story-telling liberties in reconstructing the ancestral past, since we can never know for certain what life was like hundreds of thousands of years ago, when such traits would have, theoretically, been favored by natural selection. (This is a point also stressed by Rennie in his critique of my Slate essay.) According to Myers, the whole messy endeavor, therefore, “is a teetering pyramid of stacked ‘couldas’ and guesses that it woulda had an influence on evolution.”

I would recommend that you read Kurzban’s cool-headed critique of Myers’ hot-headed critique, if only because he’s done as good a job throwing water as I could hope to do here. But I will address one of Myers’ points myself.

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.

Incidentally, all four anti-rape experiments I addressed in the previous article were empirically cumulative—meaning they were, like any good reductionist science, extensions of hard work that came before them—and they were published in well-respected, peer-reviewed academic journals with high rejection rates. By the time I relayed them to you, a whole slew of specialists, many with backgrounds in biology and anthropology (and who have devoted their entire careers to perfecting their critical thinking abilities and separating the wheat from the chaff) had already pored over and vetted them. That doesn’t make the studies flawless or protected from criticism, of course, but for Coyne to say in response to this very work that “the field suffers from scientific lassitude” is supremely arrogant. And I say that for every editor and reviewer who sifted laboriously through these studies with a fine-toothed conceptual comb. If the data were poor, if the arguments were weak, these studies simply would not have made it through the editorial sieve of journals like Psychological Science.

How we interpret these data, of course, will be colored by our particular theories and beliefs. But if we hadn’t bothered to take an evolutionary perspective to the question of rape to begin with, it’s unclear how this fascinating and subtle effect would have ever been discovered. Sure, these particular findings await replication, but so do the vast, vast majority of findings from every imaginable discipline. Certainly the investigators would welcome any replication attempts, especially using subjects from other cultures. But given that we’ve got these intriguing data in hand, so to speak, it’s just plain difficult to interpret them in any framework besides a theory of adaptations to prevent rape. Isn’t that the most parsimonious, logical explanation available to evolutionary theorists? Maybe Coyne, et al., believe there’s something truly special about the nearly two hundred female students from the study. Something in the water in Albany, perhaps, or maybe something they teach all the girls in school there that renders ovulating women—and only ovulating women—extra-strong, but only after they’ve been thinking about rape? Or maybe they grant the possibility that the findings are universal (and again, the verdict is still out about that), but that rather than serving to reduce the likelihood of conception through sexual coercion, ovulating women’s handgrip strength increases when thinking about rape because—well, just because.

It’s rather unfortunate that folks like P.Z. Myers and Jerry Coyne think evolutionary psychologists are doing substandard work. But that’s about the extent of it. It’s just unfortunate. After all, my sympathies are aligned with theirs, and those of many of our readers, in the battle against general stupidity and ignorance. I cannot recommend strongly enough that anybody wishing to explore the subject of rape from an evolutionary perspective go straight to the primary literature. As one of my colleagues, Loyola Marymount University psychologist Michael Mills, told me recently: “When other scientists put forward a model of how the world works, it is called a ‘theory.’ When evolutionary psychologists do it, it is called ‘story telling.’ ” That is an unfortunate situation indeed, because anyone who swallows up the anti-evolutionary-psychology rhetoric will end up missing out on some extraordinarily innovative, important, and clean science.

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