We Asked: Viren Swami, Ph.D., YouBeauty Attraction Expert and Reader in Psychology at the University of Westminster in London, England.

The Answer: They stare, they ogle, they pat and they pinch. But what is it that draws some men so intensely to the female behind? The long held theory that an hourglass figure, including a full lower body, is attractive because it suggests health and fertility has been largely discredited. It has yet to be replaced by a convincing alternative.

What we do know is that a booty is a uniquely female trait-and therefore uniquely feminine. After puberty, sex hormones begin to dictate the distribution of fat on the body. In men, fat accumulation is stimulated around the gut and inhibited in the seat. It’s the opposite for women, who tend to carry fat in their gluteofemoral region, that is, the butt and thighs.

That doesn’t mean that males everywhere are universally attracted to a round rump. Body weight, in general, seems to hold more sway, but preferences vary between cultures. For instance, one study suggested that while British, Spanish and Portuguese men all favored slender women, the Latin lovers were more interested in curvier bodies with bigger hips and smaller waists. Another study found that among white, British men, breast size played a large role in attraction, while butt size failed to factor in.

Indeed, if it seems like there are two types of guys-boob men and butt men-that’s because there probably are. A 2012 study in the Archives of Sexual Behavior found that Argentinian men self-reported as preferring either the breasts or the butt, but not both equally. (Consistent with the above, they leaned more toward butts.) And when the researchers tracked their eye movements as they sized up two women, their gazes systematically started and ended at their favorite part.

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