Another Dingbat Sexual Selection Theory
Beware of evolutionary explanations that rest on what men find attractive.
Photo by Reuters
Update, Feb. 26, 2013: This story misrepresented the views of Joshua Akey. Corrections and a full explanation are below.
On Valentine’s Day, the New York Times ran an article in its science section linking physical traits common in East Asians—thick hair, distinctively-shaped teeth, small breasts, and extra sweat glands—to a 35,000-year-old mutation in a gene called EDAR. Researchers reproduced the mutation, which is carried by East Asians but not Africans or Europeans, in mice. The animals had more lustrous fur, more sweat glands, and smaller chests.
The article, by Nicholas Wade, starts off with plausible explanations for why natural selection might have favored the deviation in EDAR when it emerged thousands of years ago in central China. One or two of the traits influenced by the gene may have been advantageous for survival; as those features persisted in the population, the other attributes came along for the ride. And he tracks down a reasonable hypothesis about which characteristic made EDAR so valuable: the sweat glands. For people hunting and gathering in China’s formerly warm and soupy climate, staying cool was crucial.
Fine. But then Wade derails the whole thing with a perfectly silly evolutionary biology just-so story. He spoke Joshua Akey, a geneticist at the University of Washington in Seattle.
As Wade summarizes Akey's point: “thick hair and small breasts are visible sexual signals which, if preferred by men, could quickly become more common as the carriers had more children.” In fact, as Wade paraphrases Akey, “the sexually visible effects of EDAR are likely to have been stronger drivers of natural selection than sweat glands.”*
Basically, in my understanding, the genetic mutation flourished because men wanted to do the no-no-cha-cha with women who carried it. Oops, I’d forgotten that science, the world, etc., revolves around what males find attractive. Never mind that this assumes an alarming passivity on the part of the females. Did they have no say in their mating partner? (That’s a rhetorical question: Studies throughout the animal kingdom show that it’s usually the females who decide who gets action and who doesn’t.) And even supposing that the women had no agency, were prehistoric East Asian men really so very picky? Did they typically refuse intercourse with large-breasted or fine-haired women? I am trying to imagine a caveman turning down a willing sexual partner on account of a triviality like insufficiently luxuriant tresses, and not just one caveman but the entire sperm-producing Pleistocene population.
To be fair, the paper itself, written by a team led by Yana G. Kamberov and Pardis C. Sabeti at the Broad Institute in Cambridge, Mass., largely avoids speculating about how the EDAR mutation perpetuated. “The problem with all selection, but especially sexual selection, is that it’s impossible to test on humans,” co-author Daniel Lieberman told me. “We were careful not to make assumptions about the selective benefits of the gene.” When I asked him whether he found the hypothesis plausible that male preference led to the prevalence of the gene, he replied, “Frankly, no.”*
He’s not alone. The variability of erotic desire is just one reason many biologists believe that sexual selection played a relatively small role in the evolution of human appearance. Other factors proved much more crucial for survival and only incidentally influenced what we look like today. For instance, populations that migrated north had less exposure to ultraviolet light and thus risked vitamin D deficiency; light skin, which makes it easier to produce vitamin D, evolved independently several times. Efficient fat storage allowed humans to weather periods of famine.
Jerry Coyne, an evolutionary geneticist at the University of Chicago who blogs at Why Evolution Is True, describes the hair-and-breast theory as “extremely dubious.”* He says that sexually selected traits tend to arise in one sex only, as the choosier adults—usually the females, not the males—mate with partners on the basis of a characteristic that is otherwise less than optimal. That feature would normally disappear from a population, except that the picky sex keeps selecting for it. (The less picky sex, on the other hand, generally just reproduces with whoever is around, which happen to be the fittest animals. Hence, male birds often boast showy, unwieldy tails that females prefer; female birds have shorter, practical tails that neither hamper flight nor lure suitors.)
Coyne also takes issue with the study in general. He wonders how the researchers concluded that the variant EDAR gene shrinks breasts at all, given that mice don’t have breasts—at least, they don’t have pronounced lumps on their chests the way people do. (Daniel Lieberman answered this criticism on the phone by noting that the animals’ mammary tissue was carefully weighed, but even then, anatomical differences make it hard to extrapolate from rodents to humans.) The entire effort, Coyne says, shows “evolutionists indulging in their favorite game—adaptionism—by imagining scenarios of evolution fixing various things, regardless of evidence.”
Yet in some circles (ones that get print space in the New York Times), the explanatory power of the primordial dude surveying his pack of womenz and picking the hottest one apparently remains unequalled. As our distant great grandmothers might say, ugh.
Correction, Feb. 26, 2013: Joshua Akey was not contacted prior to publication of this article. This article incorrectly attributed ideas to him. Some of these ideas were paraphrased in the New York Times and were then misinterpreted by the author. Akey did not speculate that sexual selection of the EDAR genetic mutation was influenced by male preference for small breasts, and this article should not have attributed this idea to him. The implication that sexual selection of EDAR required female passivity or male pickiness was the author’s own interpretation. We apologize for misrepresenting Akey’s position.
Corrections, Feb. 24, 2013: This article originally implied that statements attributed to Joshua Akey were direct quotes. In fact, the quoted lines were paraphrased by the New York Times. The article should not have referred to the idea that males preferred small breast size as "Akey's theory." Feb. 26, 2013: This article has been further corrected to clarify that the ideas presented here are the author’s interpretation of language that appeared in the New York Times.
Katy Waldman is a Slate assistant editor.