BEIJING (Xinhuanet) — Women evolved more flexible and supportive spines than men to keep them from toppling over under the weight of pregnancy, according to a new study published in Thursday's issue of the journal Nature.
"Pregnancy presents an enormous challenge for the female body. The body must change in dramatic ways to accommodate the baby, and these changes affect a woman's stability and posture," said Katherine Whitcome, an anthropologist at Harvard University, who led the study.
"It turns out that enhanced curvature and reinforcement of the lower spine are key to maintaining normal activities during pregnancy," Whitcome said.
Whitcome found two physical differences in male and female backs: One lower lumbar vertebra is wedged-shaped in women and more square in men; and a key hip joint is 14 percent larger in women than men when body size is taken into account.
The slight differences allow women to adjust their center of gravity.
"Without the adaptation, pregnancy would have placed a heavier burden on back muscles, causing considerable pain and fatigue and possibly limiting foraging capacity and the ability to escape from predators," said researcher Liza Shapiro, an anthropologist at the University of Texas at Austin.
Researchers found a similar trend in the vertebrae of early humans called Australopithecus, but not in those of chimpanzees.
The finding suggests these spine adaptations evolved at least two million years ago when human ancestors first began to walk upright.
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