The study, published online in Evolution and Human Behavior, investigated men’s mate preference for women with a “theoretically optimal angle of lumbar curvature,” a 45.5 degree curve from back to buttocks allowing ancestral women to better support, provide for, and carry out multiple pregnancies. “What’s fascinating about this research is that it is yet another scientific illustration of a close fit between a sex-differentiated feature of human morphology — in this case lumbar curvature — and an evolved standard of attractiveness,” said the study’s co-author David Buss, a UT Austin psychology professor. Results showed that the majority of the men were significantly more attracted to silhouettes of women who had a spine curvature of 45.5 degrees, suggesting that this ancestral preference for spinal curvature has persisted. “[The curve] would have enabled ancestral women to shift their center of mass back over their hips during pregnancy, a time during which there is a dramatic forward shift of their center of mass,” said lead researcher Dr. David Lewis, The Daily Mail reported. The Importance Of Spine Curvature 
 
 The curve at the bottom of a woman’s spine is something that she wouldn’t realize the importance of until it’s gone. “This tight fit between evolutionary pressures and modern humans’ psychology, including our standards of attractiveness, highlights the usefulness that an evolutionary approach can have for expanding our knowledge not just of the natural sciences, but also the social sciences,” Lewis said.
– 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.)