A new study finds that there's an evolutionary reason men prefer women with a "theoretically optimal angle of lumbar curvature." Another way of putting it? Even prehistoric guys probably liked a gal with a curvy backside. Researchers at the University of Texas at Austin ran a two-part study, published in Evolution and Human Behavior: In the first part, men rated the attractiveness of manipulated images of spinal curves; most best liked a 45.5-degree curve from back to buttocks. In the second part, men were shown pictures of women with different buttock sizes—and they still most preferred the ones whose spinal curvature was closest to the ideal, meaning it's the lumbar curvature they like, not just "big butts," researchers say in a press release. But "men may be directing their attention to the butt and obtaining information about women's spines, even if they are unaware that that is what their minds are doing," the lead researcher explains, per Medical Daily.
As for that evolutionary reason for the preference, researchers attribute it to "prehistoric influences." Explains the lead researcher, "This spinal structure would have enabled pregnant women to balance their weight over the hips. These women would have been more effective at foraging during pregnancy and less likely to suffer spinal injuries. In turn, men who preferred these women would have had mates who were better able to provide for fetus and offspring, and who would have been able to carry out multiple pregnancies without injury." Researchers note that this preference has evolved over thousands of years. "This adds to a growing body of evidence that beauty is not entirely arbitrary, or 'in the eyes of the beholder,'" says a co-author, "but rather has a coherent adaptive logic." (Another recent study uncovered the surprising reason we hate zits.)