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Ahead of the Curve

by Anna Weinberg
May/June 2007

Peter Paul Reubens/Getty Images

“Only human females seem to be blessed with a more ample backside than their male counterparts.”

From the Venus de Milo to Sophia Loren, the appeal of an hourglass figure is legend. In 1992, appreciation for the ample female form even became a populist anthem: “I like big butts,” rapped Sir Mix-a-Lot, “And I cannot lie.” There has been much discussion about the “ideal” female figure—the figure with a low waist-to-hip ratio (WHR). But few would argue that the appeal of J. Lo’s booty is that it holds the key to building a better infant brain.

Enter Dr. Steven Gaulin, a professor of anthropology at UC Santa Barbara who studies the evolutionary forces driving male preference for the generous female figure. Gaulin, with collaborator William Lassek, is working on what he calls “the string theory of fat” to explain some pressing questions: “Why are women fattier? Why do they have the fat distribution they do? And why do men care? Why do they spend money to look at women with favorable waist-to-hip ratios?”

For years, it was assumed that women have more overall body fat than men because of the calorically demanding activities of gestation and lactation. But, Gaulin points out, these events happen in all female mammals. If childbearing were enough to explain the specialized distribution of fat on the human female body, then we should see female otters and hippopotami laden with saddlebags. But we don’t. Human females alone seem to be blessed with a more ample backside than their male counterparts.

Only human females seem to be blessed with a more ample backside than their male counterparts."

“Most body fat is like a checking account,” says Gaulin, “where you make regular deposits and withdrawals. But hip and thigh fat is more like a certificate of deposit; you can’t just take it out whenever you want. It’s … event dependent.” The event this fat is waiting for is the third trimester of pregnancy, when the fetal brain begins its most exuberant period of growth, and which also seems to be the only time in life when women easily lose this fat.

“The brain is 20 percent fat,” says Gaulin. “And not just any old fat—not French-fry fat. The brain is made up of arachidonic acid and docosahexaenoic acid. These two fatty acids can’t be substituted; brains are literally built out of those two things, and women store those in the hips and thighs.” The more of this crucial material available to the developing brain, the better that brain should be. In a species experiencing such rapid neural growth as humans, where the demand for specialized fats is highest, “selection on women to acquire and store these fats and selection on men to recognize which women have more of them would be especially intense,” says Gaulin.

Gaulin and Lassek are not ready to make a direct connection between maternal WHR and offspring intelligence—yet. But they are conducting studies comparing cognitive function and maternal WHR. They are also examining evidence that the kind of fat stored around the midsection—tummy pudge—actually inhibits production of the kinds of fats the brain needs. Thus, that pudge-free waist, combined with fatty nether regions, has come over the long arc of evolution to be considered the more attractive body shape. “I’m not saying men look at Playboy and say, ‘Hmmm, she’s got an adaptive WHR,’” says Gaulin. “We don’t have conscious access to that, just to the perceptual pleasure, because we’re not designed to understand evolution. We’re just designed to do the things that promote fitness.”