Why do most men prefer women with curvier bodies, especially sharp curvy hips? According to a fascinating research, modern man’s this preference has pre-historic evolutionary roots.

For a mate, man is inclined towards a woman 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, investigation by a team from the University of Texas (UT) at Austin and the UT – Arlington found.

"The findings enable us to conclusively show that men prefer women who exhibit specific angles of spinal curvature over buttock mass," said study’s co-author Eric Russell from the UT – Arlington in a paper published in the journal Evolution and Human Behavior.

This adds to a growing body of evidence that 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, added psychology professor David Buss from the UT Austin.

This research consisted of two studies. The first looked at vertebral wedging, an underlying spinal feature that can influence the actual curve in women’s lower backs.

About 100 men rated the attractiveness of several manipulated images displaying spinal curves ranging across the natural spectrum.

Men were most attracted to images of women exhibiting the hypothesised optimum of 45 degrees of lumbar curvature.

"This spinal structure would have enabled pregnant women to balance their weight over the hips," the authors noted.

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 foetus and offspring, and who would have been able to carry out multiple pregnancies without injury.

The second study addressed the question of whether men prefer this angle because it reflects larger buttocks, or whether it really can be attributed to the angle in the spine itself.

Approximately 200 men were presented with groups of images of women with differing buttock size and vertebral wedging, but maintaining a 45.5-degree curve.

Men consistently preferred women whose spinal curvature was closer to optimum regardless of buttock size.

This morphology and men’s psychological preference toward it have evolved over thousands of years, and they won’t disappear overnight, the authors concluded.