Pregnant? Backache? Thank evolution

Pregnant? Backache? Thank evolution
Pregnant women may stand out a mile away with their characteristic backward-leaning stance, but that clumsy-looking position is a unique adaptation that evolved over millennia, anthropologists said on Wednesday. (Graphics/Reuters)WASHINGTON (Reuters) - Pregnant women may stand out a mileaway with their characteristic backward-leaning stance, butthat clumsy-looking position is a unique adaptation thatevolved over millennia, anthropologists said on Wednesday.
Pregnant pre-humans appeared to have stood the same way.And it may save women from even more back pain than theyalready have, the researchers report in this week's issue ofthe journal Nature.
The bodies of women do two things when they are pregnant --they adjust their stance to move the center of gravity toaccommodate the growing fetus, and the lower vertebrae haveevolved a distinct shape to allow this shifting to take placewithout damaging the spine, Katherine Whitcome of HarvardUniversity and colleagues found.
"It was one of these things like, 'Oh my god, no one's everthought of this,' and it looks so obvious," Liza Shapiro of theUniversity of Texas at Austin, who helped supervise the work,said in a telephone interview.
Whitcome and Shapiro followed 19 women through theirpregnancy, using digital cameras and motional analysisequipment to map the changes in stance and movement as themonths passed.
"What women do when their pregnancy reaches about half ofthe expected mass ... they shift backwards," Shapiro said.
"If you didn't have any of those mechanisms, the only wayto offset a load in front of you is to contract your backmuscles. The more you have to use your muscles, the morediscomfort you would have. It would be worse otherwise, andthere would be more potential damage to the vertebrae."
Without this change in shape, the vertebrae could besubject to shearing forces, with one sliding over another,damaging the fluid-filled discs in between or pulling onligaments and muscles.
"The shape of the vertebrae allows her to rotate the upperbody," Shapiro said.
When she moved to Harvard, Whitcome continued the study andlooked at the fossils of pre-humans known asaustralopithecenes, as well as at the bone structure of ournearest living relatives, the chimpanzees.
"These differences are absent in the chimpanzee. So thereis something unique about humans," Whitcome said. "We also seesome evidence for these adaptations in earlyaustralopithecenes."
Men do not have this adaptation, either, Shapiro said.
"We can only conclude that men can't resist the forces oftheir big bellies as well as women. They are at adisadvantage," she said.
"They probably lean back the same way to try and balancethat load, but they are kind of putting their vertebrae more atrisk. I am sure there has got to be a correlation betweenhaving a big beer gut and having back pain," Shapiro laughed.
(Editing by Will Dunham and Sandra Maler)