And why don't pregnant women tip over? by Hero

REAL WORLD EVENT DISCUSSIONS

And why don't pregnant women tip over?

POSTED BY: HERO
UPDATED: Thursday, December 13, 2007 05:40
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Wednesday, December 12, 2007 11:26 AM

(I always thought it was because of the Weebles-wobble principal.)

Women Evolve More Spine to Carry Babies
by Jeanna Bryner
LiveScience Staff Writer
LiveScience.com

Like cushy baby strollers, women's bodies have evolved spines that are more flexible and supportive than men's to keep from tipping over while walking during pregnancy.

Pregnancy brings loads of hormonal changes as seeming biological wizardry transforms a woman's body into a baby incubator. As the fetus grows, so does a woman's belly. No surprise, the front cargo pulls her center of gravity off kilter.

If the body architecture failed to take counter measures, pregnant women would be tipping over left and right or walking around with even worse pain than they do. New research detailed in the Dec. 13 issue of the journal Nature shows lower-back vertebrae and joints in women have special features that accommodate the extra weight.

"The body must change in dramatic ways to accommodate the baby, and these changes affect a woman's stability and posture," said researcher Katherine Whitcome, an anthropologist at Harvard University. "It turns out that enhanced curvature and reinforcement of the lower spine are key to maintaining normal activities during pregnancy."

They found a similar trend in the vertebrae of early humans called Australopithecus, but not in those of chimpanzees (our crawling relatives). The finding suggests these spine adaptations evolved at least two million years ago when human ancestors first began to walk upright. Our four-legged ape ancestors didn't have to accomodate for the extra baby weight, because their bellies just hung lower and there was no significant shift in the center of gravity.

"Natural selection favored this adaptation because it reduces extra stress on a pregnant female's spine," said researcher Liza Shapiro, an anthropologist at the University of Texas at Austin. "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."

Whitcome, Shapiro and Harvard anthropologist Daniel Lieberman studied 19 pregnant women between the ages of 20 and 40 from their first trimester until after they gave birth. They found that when the mass of the developing baby reached about 40 percent of its full-term weight, the mother's posture began to change.

"They leaned back, and they did that by extending their upper body at the lower back," Whitcome told LiveScience. "And this happened when the position of their center of mass was changing."

The researchers also examined participants' spines and compared results with male spines. In both women and men, the curvature of the spine in the lower back, called the lordosis, stabilizes the upper body above the lower body. While male lordosis curves across just two vertebrae, the curvature extends across three vertebrae in women, Whitcome said.

"Loading across three vertebrae allows an expectant mother to increase her lordosis, re-aligning her center of gravity above her hips and offsetting the destabilizing weight of the baby," Whitcome said.

In addition, the female vertebral joints are relatively larger and extend more down the spine than those of males. The extra support helps to offset strain on the spine that occurs when a pregnant woman leans back to balance the weight of the fetus, the researchers say.

Ancient adaptations

The researchers also studied two hominid fossils about two million years old and found that one, which anthropologists have long suggested is female, had three lordosis vertebrae. The other fossil, which is thought to be male, had fewer such vertebrae. The angles and sizes of the vertebrae also followed the same male-female trend found in humans.

"Early human women lived very strenuous, active lives, and pregnant females were forced to cope with the discomfort of childbearing while foraging for food and escaping from predators," Lieberman said. "This evolution of the lower back helped early woman to remain more mobile during pregnancy, which would have been essential to survival, and appears to have been favored by natural selection."

They didn't find these gender-specific differences in the spines of chimpanzees, which walk on four legs, further supporting the idea that bipedalism led to the adaptations.

H

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Wednesday, December 12, 2007 11:34 AM

CITIZEN

Do you have a link to the source?

More insane ramblings by the people who brought you beeeer milkshakes!
No one can see their reflection in running water. It is only in still water that we can see.

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Wednesday, December 12, 2007 11:38 AM

GORRAMGROUPIE

There's a lead story link on Yahoo, probably other pages as well.

I want you now
tomorrow won't do
there's a burning inside
and it's showing through.

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Wednesday, December 12, 2007 11:48 AM

MAL4PREZ

I had a dance teacher who led class up until 8 1/2 months. She turned, she leaped, she was on the floor and back up... it was stunning. There had to be something going on for that to be possible.

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hmm-burble-blah, blah-blah-blah, take a left

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Wednesday, December 12, 2007 12:04 PM

GORRAMGROUPIE

OUCH!

I want you now
tomorrow won't do
there's a burning inside
and it's showing through.

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Wednesday, December 12, 2007 12:52 PM

SIGNYM

I believe in solving problems, not sharing them.

THERE'S NO SUCH THING AS EVOLUTION!

All of that claptrap with the bones and adaptation and everything just makes us like animals. It's all a hoax. Stop pushing that evolution stuff on us because that's what's making society go downhill, and God will get you for that!

---------------------------------
Sorry Hero!

Somebody had to say it.

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Wednesday, December 12, 2007 12:57 PM

RUE

I have a vote and I'm not afraid to use it!

student to grad student after observing his beer drinking physique: "when's it due ?"
grad student: "I don't know. I'll have to call the brewery to find out."

***************************************************************
"Global warming - it's not just a fact, it's a choice."

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Wednesday, December 12, 2007 1:04 PM

RUE

I have a vote and I'm not afraid to use it!

Oh, there was an interesting article about human evolution going faster in recent millennia. I was going to post that as well.

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It was about that process that doesn't exist. Anything that looks contrary to that fact is god's hoax on us all and a test of faith.
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But now that I think about it, with all these articles about evolution or referring to evolution, I wonder how the bible literalists take it ? What I imagine - god damn atheists ! Pushing their beliefs on us. Getting the government and the media behind it. We're in a cultural war to preserve our religion in society. We need to go on a christian jihad !

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Wednesday, December 12, 2007 4:49 PM

FREMDFIRMA

Meh, now we just need some mental and social evolution to go with it.

-F

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Thursday, December 13, 2007 2:18 AM

6IXSTRINGJACK

Quote:
Originally posted by SignyM:
THERE'S NO SUCH THING AS EVOLUTION!

All of that claptrap with the bones and adaptation and everything just makes us like animals. It's all a hoax. Stop pushing that evolution stuff on us because that's what's making society go downhill, and God will get you for that!

---------------------------------
Sorry Hero!
Somebody had to say it.

Remember now... I'm not a practicing Christian or practicing anything for that matter. If I worship anything, it's likely myself. (I doubt I'll find anyone in here who will argue me on that point either).

But I do so hope there is an afterlife, if for no other reason than to be able to look upwards from the parascope (yes, we will have a parascope in Hell that reaches all the way up to Pearly Gates) and I can see the looks on all of the Sciencefolk's faces as your stomachs drop and you exclaim "oh shit!" as St Peter presses the trap door button and you get to party with me in Hell for eternity.

Hope by then your evolution has provided you with fire resistant skin, because chances are, you're going to need it.

Down here, nobody ever needs to ask for a light.

"A government is a body of people, usually notably ungoverned." http://www.myspace.com/6ixstringjack

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Thursday, December 13, 2007 4:59 AM

SIGNYM

I believe in solving problems, not sharing them.

Come swim in the lake of magma with me.

purrrrrr.

---------------------------------
Always look upstream.

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Thursday, December 13, 2007 5:40 AM

6IXSTRINGJACK

Well... I do always take nearly scalding showers...

I suppose after years of that a dip in the magma would feel like a nice warm bubble bath in a natural spring in Iceland....

Don't mind if I do Signy

"A government is a body of people, usually notably ungoverned." http://www.myspace.com/6ixstringjack

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