And it's one curve in particular
A new University of Texas study has found that men express a clear preference for women who have a pronounced back-to-buttock curve.
After asking around 100 men to rank the attractiveness of images of various females, researchers found that men strongly preferred women with a back-to-buttock curve of 45.5 degrees, which they described as the “theoretically optimal angle of lumbar curvature.”
They theorized that, in ancient times, such an angle meant that women were more likely to carry out successful pregnancies.
“This spinal structure would have enabled pregnant women to balance their weight over the hips,” said researcher David Lewis.
“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 conducted a second study to rule out if the spinal curvature preference was due to the buttock size rather than the spinal curvature angle itself. But they discovered that men repeatedly exhibited a preference for women with spinal-curvature angles closer to the optimum, even if the women had smaller buttocks.
“Beauty is not entirely arbitrary, or ‘in the eyes of the beholder’ as many in mainstream social science believed, but rather has a coherent adaptive logic,” Lewis added.