www射-国产免费一级-欧美福利-亚洲成人福利-成人一区在线观看-亚州成人

   

Study: Why pregnant women don't topple

(Agencies)
Updated: 2007-12-13 08:19

WASHINGTON -- With all that growing weight up front, how is it that pregnant women don't lose their balance and topple over? Scientists think they've found the answer: There are slight differences between women and men in one lower back vertebrae and a joint in the hip, which allow women to adjust their center of gravity.


A pregnant model showcases a costume during a maternity fashion show organised by a newly launched company which caters to pregnant women in New Delhi August 25, 2007. [Agencies] 

This elegant evolutionary engineering is seen only in female humans and our immediate ancestors who walked on two feet, but not in chimps and apes, according to a study published in Thursday's journal Nature.

"That's a big load that's pulling you forward," said Liza Shapiro, an anthropology professor at the University of Texas and the only one of the study's three authors who has actually been pregnant. "You experience discomfort. Maybe it would be a lot worse if (the design changes) were not there."

Harvard anthropology researcher Katherine Whitcomb found two physical differences in male and female backs that until now had gone unnoticed: One lower lumbar vertebrae 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 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," Whitcomb said. "They are experiencing a pretty impressive challenge. Evolution has tinkered ... to the point where they can deal with the challenge.

"It's absolutely beautiful," she said. "A little bit of tinkering can have a profound effect."

Walking on two feet separates humans from most other animals. And while anthropologists still debate the evolutionary benefit of walking on two feet, there are notable costs, such as pain for pregnant females. Animals on all fours can better handle the extra belly weight.

The back changes appear to have evolved to overcome the cost of walking on two feet, said Harvard anthropology professor Daniel Lieberman.

When the researchers looked back at fossil records of human ancestors, including the oldest spines that go back 2 million years to our predecessor, Australopithecus, they found a male without the lower-back changes and a female with them.

But what about men with stomachs the size of babies or bigger? What keeps them from toppling over?

Their back muscles are used to compensate, but that probably means more back pain, theorized Shapiro, who added: "It would be a fun study to do to look at men with beer bellies to see if they shift their loads."



Top World News  
Today's Top News  
Most Commented/Read Stories in 48 Hours
主站蜘蛛池模板: 欧美中文字幕一区二区三区 | 国产一区二区免费不卡在线播放 | 九九在线精品视频播放 | 久久综合久久美利坚合众国 | 亚洲大片 | 成年男人午夜片免费观看 | 免费一级做a爰片久久毛片 免费一级做a爰片性色毛片 | 影音先锋色先锋女同另类 | 亚洲视频精品在线观看 | 99久久国产综合精品成人影院 | 久久久国产99久久国产首页 | 成人观看免费大片在线观看 | 国产成人aa在线视频 | 欧美一区二区三区久久综合 | 免费一级 一片一毛片 | 亲子乱子伦xxxxxinin | 久久91精品综合国产首页 | 久久精品国产99国产精品 | 精品国产成人综合久久小说 | 国产中文字幕在线播放 | 欧美精品亚洲精品日韩一区 | 亚洲国产99在线精品一区二区 | 亚洲欧美人妖另类激情综合区 | 国产激情一区二区三区在线观看 | 欧美在线精品一区二区三区 | 免费视频成人 | 国产性大片黄在线观看在线放 | 伊人不卡| 久久成人午夜 | 99久久免费看国产精品 | 成人欧美一区二区三区视频 | 免费人成观看在线网 | 国产资源免费 | 国产精品一区二区在线观看 | 国产免费播放一区二区 | 草草影院ccyy免费看片 | 999成人国产精品 | 国产精品亚洲综合久久 | 日韩欧美亚洲国产 | 麻豆国产 | 91久久国产口精品久久久久 |