Fascinating

Even wonder what keeps a pregnant woman from toppling over from the additional 30+ lbs she's carrying front and center?
Harvard anthropology researcher Katherine Whitcome found two physical differences in male and female backs that until had gone unnoticed until now: 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. This engineering is seen only in female humans and our immediate ancestors who walked on two feet, but not in chimps and apes.
The researchers did engineering tests that show how those slight changes allow women to carry the additional and growing load without toppling over -- and typically without disabling back pain.
"When you think about it, women make it look so very damn easy," Whitcome said. "They are experiencing a pretty impressive challenge. Evolution has tinkered ... to the point where they can deal with the challenge. A little bit of tinkering can have a profound effect."
Of course, this does not mean that pregnancy is not hard on a woman's back and gestating females should still be granted full back and foot rub privileges.