Research refutes long-held theory: Mother's metabolism, not birth canal size, limits gestation

New research by a University of Rhode Island professor suggests that the length of human pregnancy is limited primarily by a mother's metabolism, not the size of the birth canal. The research, published in the Proceedings of the National Academy of Sciences the week of August 27, challenges the long-held notion of an evolutionary trade-off between childbirth and a pelvis adapted for walking upright.

Two traits that set humans apart from other primates—big brains and the ability to walk upright—could be at odds when it comes to childbirth. Big brains and the big heads that encase them are hard to push through the human , but a wider might compromise bipedal walking. Scientists have long posited that nature's solution to this problem, which is known as the "obstetric dilemma," was to shorten the duration of gestation so that babies are born before their heads get too big. As a result, are relatively helpless and seemingly underdeveloped in terms of motor and cognitive ability compared to other primates.

"All these fascinating phenomena in —bipedalism, difficult childbirth, wide female hips, big brains, relatively helpless babies—have traditionally been tied together with the obstetric dilemma," said Holly Dunsworth, an anthropologist at the University of Rhode Island and lead author of the research. "It's been taught in anthropology courses for decades, but when I looked for hard evidence that it's actually true, I struck out."

The first problem with the theory is that there is no evidence that hips wide enough to deliver a more developed baby would be a detriment to walking, Dunsworth said. Anna Warrener, a post-doctoral researcher at Harvard University and one of the paper's co-authors, has studied how hip breadth affects locomotion with women on treadmills. She found that there is no correlation between wider hips and a diminished locomotor economy.

"That throws doubt on the assumption that the size of the birth canal is limited by bipedalism," Dunsworth said. "Wide hips don't mean you can't walk efficiently."

Then Dunsworth looked for evidence that human pregnancy is shortened compared to other primates and mammals. She found well-established research to the contrary. "Controlling for mother's body size, human gestation is a bit longer than expected compared to other primates, not shorter," she said. "And babies are a bit larger than expected, not smaller. Although babies behave like it, they're not born early."

For mammals in general, including humans, gestation length and offspring size are predicted by mother's body size. Because body size is a good proxy for an animal's metabolic rate and function, Dunsworth started to wonder if metabolism might offer a better explanation for the timing of human birth than the pelvis.

To investigate that possibility, she enlisted the help of Peter Ellison of Harvard University and Herman Pontzer of Hunter College in New York, two experts in human physiology and energetics. Building on Ellison's prior work on human pregnancy and childbirth, the researchers developed a new hypothesis for the timing of called the EGG (energetics, gestation, and growth).

"Under the EGG, babies are born when they're born because mother cannot put any more energy into gestation and fetal growth," Dunsworth explains. "Mom's energy is the primary evolutionary constraint, not the hips."

Using metabolic data on pregnant women, the researchers show that women give birth just as they are about to cross into a metabolic danger zone.

"There is a limit to the number of calories our bodies can burn each day," says Pontzer. "During pregnancy, women approach that energetic ceiling and give birth right before they reach it. That suggests there is an energetic limit to human gestation length and fetal growth."

Those metabolic constraints help explain why human babies are so helpless compared to our primate kin, like chimpanzees. A chimp baby begins crawling at one month, whereas human babies don't crawl until around seven months. But for a human to give birth to a newborn at the same developmental level as chimp, it would take a 16-month gestation. That would place mothers well past their energetic limits. In fact, even one extra month of gestation would cross into the metabolic danger zone, the researchers found.

"It would be physiologically impossible, regardless of pelvic bone anatomy, to birth a more developed baby," Dunsworth said. "Our helplessness at birth is just a sign of how much more brain growth we have to achieve once we start living outside our mother."

The energetics, gestation and growth hypothesis would downplay an implication of the obstetric dilemma that Dunsworth finds odd.

"We've been doing anthropology with this warped view of the male pelvis as the ideal form, while the female pelvis is seen as less than ideal because of childbirth," she said. "The female births the babies. So if there's an ideal, it's female and it's no more compromised than anything else out there. Selection maintains its adequacy for locomotion and for childbirth.

"If it didn't, we'd have gone extinct," Dunsworth said.

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TheGhostofOtto1923
3 / 5 (24) Aug 27, 2012
"The first problem with the theory is that there is no evidence that hips wide enough to deliver a more developed baby would be a detriment to walking"

-No but this would have made doors unnaturally wide and difficult to construct.

"She found that there is no correlation between wider hips and a diminished locomotor economy."

-Wider hips within the normal range of human width may not mean that hips wide enough to accomodate mature human heads, would not have exceeded some basic structural limitation of hip bones. Or doors.

"Our helplessness at birth is just a sign of how much more brain growth we have to achieve once we start living outside our mother."

-So- the study still supports the notion that the domestic humanoid brain is far too large, energy-hungry, delicate, and defect-prone to withstand the rigours of natural selection. It is an organ pushed to grow far beyond what nature would allow. And, much as with the wienerdogs spine, the associated physiology simply cannot adapt.
PPihkala
5 / 5 (4) Aug 27, 2012

-So- the study still supports the notion that the domestic humanoid brain is far too large, energy-hungry, delicate, and defect-prone to withstand the rigours of natural selection. It is an organ pushed to grow far beyond what nature would allow. And, much as with the wienerdogs spine, the associated physiology simply cannot adapt

There are 6 billion humans on earth and you think that all those have had unnatural heads? Not very likely. I think that head size at birth is compromise between different requirements but certainly it is not too big currently. Some mother-child -combinations might be non-workable, but that is to be expected from father-mother gene fight. From mother inherited genes prefer small and father genes prefer big babies.
TheGhostofOtto1923
3.1 / 5 (23) Aug 27, 2012
all those have had unnatural heads?
Absolutely. The FACT that we have to be born premature in order to accomodate them, and the FACT that, among other things, another set of hands is necessary in order to bear them safely, and the FACT that they are the product of a distinctly ARTIFICIAL selection process, among many other things, makes them distinctly unnatural.

They are fraught with design flaws as a result, and they are unusually prone to damage and defect. No other species exhibits such a wide range of functionality as humans.

We are not the product of natural selection processes. We are primarily the product of cultural selection, which is an entirely different thing. It has more in common with husbandry than evolution. And it explains the very poor design and high rate of disfunction, of our brains. AND all the bizarre cultural practices which have appeared to compensate for this, such as the need for religion and drugs to self-medicate.
TheGhostofOtto1923
3.1 / 5 (23) Aug 27, 2012
Our brains are very poorly designed. We can design, and certainly are designing, brains from scratch which can and will function much better and much more dependably, than ours.
http://www.ncbi.n...2262116/

And we will soon be able to improve functionality and dependability in the brains we have been cursed with. We are already outsourcing data storage as just one of many encouraging examples.
Estevan57
2 / 5 (29) Aug 28, 2012
I agree with you, Otto, your brain is unnatural.

"Unfortunately, there is not much about evolutionary neuroscience. For instance, he covers a great deal of mammalian brain evolution, calling its design "unintelligent," but fails to cite recent research evidence to support his argument. Although Linden is very persuasive in his arguments, I was not very convinced about his conclusions regarding the flawed design of our brains. That could be a flawed argument because we are still experiencing an avalanche of research efforts aimed toward deciphering fine details of how the brain works. In addition, there is no connection between his argument of a flawed brain design and why there is so much interest in developing robots that try to imitate the human brain. The human brain must not be so flawed then, I would argue."

From the review in your link.

Your link apparently totally disagrees with your conclusions. Wow! Perhaps a little less frothing and a little more actual reading? Peace,
Estevan57
1.8 / 5 (29) Aug 28, 2012
"Selection maintains its adequacy for locomotion and for childbirth. "If it didn't, we'd have gone extinct," Dunsworth said."
- From the article
Next time read it, Otto. Jeesh you make a lot of shit up. What a
BS - er. With love.
TheGhostofOtto1923
3.1 / 5 (21) Aug 28, 2012
Your link apparently totally disagrees with your conclusions. Wow! Perhaps a little less frothing and a little more actual reading? Peace,
Referring to human development as 'evolution' instead of something is preferable to academics for obvious reasons yes? But it is obvious that culture has driven human change. Weapons use has made us human. I am sure academics will eventually be free to acknowledge this.
I agree with you, Otto, your brain is unnatural.
And how do we explain your compulsion to post outrageous bullshit under multiple sickpuppets? This is distinctly unnatural and indicates a condition which would have been selected out in the wild long ago.

You are the lying dimwit pirouette/Ritchieguy/russkiye/pussy/Obie/esai who has always enjoyed greasy affectionate epithets. And coyly refusing to spell out cursewords but willing to post gay porn links and get banned. More indication of some sort of schism.
Torbjorn_Larsson_OM
5 / 5 (5) Aug 28, 2012
I like how metabolism and energy constraints pop up again and again in biology.

This could be a viable theory for once. It ties in naturally with the observation that our fetuses are prematurely born re brain development.

But I wonder where that leaves the traumatic birth of humans. Maybe cultural effects early allowed for this to evolve, since the mother was socially cared for. Then again, the same would apply to say wolfs.

@ The GhostofOtto:

Your momma has a problem with doors?

"It is an organ pushed to grow far beyond what nature would allow."

The article describes how it is a result of evolution. Your distinction between natural and cultural evolution isn't relevant here, already Darwin noted how artificial selection is still evolution.
TheGhostofOtto1923
3 / 5 (22) Aug 28, 2012
"Selection maintains its adequacy for locomotion and for childbirth. "If it didn't, we'd have gone extinct," Dunsworth said."

-This is assuming that our emergence was the result of the same sort of interaction with the environment as the other animals. It wasn't. We are left with all sorts of unfortunate and life-threatening complications that one just does not find in the natural world; painful, complex, and dangerous childbirth being among the most obvious.
The article describes how it is a result of evolution. Your distinction between natural and cultural evolution isn't relevant here, already Darwin noted how artificial selection is still evolution.
The distinction is the same as between cattle and wildebeest. Current science and darwin both used the term evolution but darwin and Dawkins both have no idea how tribalism works genetically.

Science is just beginning to explore how culture affects development and change. I am sure they will catch up.
Estevan57
2 / 5 (29) Aug 28, 2012
So Otto - painful, complex, and dangerous childbirth doesn't occur in the wild as you say? Really?
Lions, Tigers, and Bears have midwives and ob-gyns? Oh My.
Cattle and wildebeasts drop calves the same way, regardless of surroundings. The cattle have a higher survival rate due to the extra help they can sometimes get at birth.
Same as with humans.
Perhaps you could send Dawkins and Darwin an E-mail explaining tribalism, and please, please, please enlighten those anthropologists who have neglected how culture (and tribalism) has affected evolutionary change. Is it possible your head is too big to fit through doors?
TheGhostofOtto1923
3.2 / 5 (20) Aug 28, 2012
Cattle and wildebeasts drop calves the same way, regardless of surroundings. The cattle have a higher survival rate due to the extra help they can sometimes get at birth. Same as with humans.
P/r/r/p/o was always SO eager to demonstrate how incredibly ignorant he/she/it is, eh?
http://www.quora....s-theory

-I can imagine your mum gave birth to you kind of like this ba-WOOSH, which would explain a LOT:
http://www.youtub...Rwd_U2FU

-which was probably something more like this:
http://www.youtub...g05IgLx8

-Purely instinctive. You see, animals and dimwits have to be born active and mobile to avoid predation and punting. You stupidass.
TheGhostofOtto1923
3.2 / 5 (20) Aug 28, 2012
Culture and its influence on human development
http://plato.stan...ultural/

-Tool (weapons) use is entirely cultural and it drove the emergence of the modern human species.

So, now that weve got estevan talking it is even more painfully obvious that he and pussycat/ritchieguy are one and the same.

"Better to remain silent and be thought a fool than to speak out and remove all doubt about being a real stupidass."
Estevan57
2 / 5 (29) Aug 28, 2012
-Purely instinctive. You see, animals and dimwits have to be born active and mobile to avoid predation and punting. You stupidass.
- Otto

Would you like a large list of animals (including humans) that are born helpless? Please to thinky before speaky. I know this doesn't apply to you of course, with you being an active and mobile dimwit.

Your elephant birth would qualify as a "painful, complex, and dangerous childbirth" would it not?

Science is just beginning to explore how culture affects development and change. I am sure they will catch up.
- Otto

Based on your Philosophy Encyclopedia link it looks like those pesky scientist are well on their way now, doesn't it? Doh.

Spirow Agnew. Spirow Agnew. Spiro Agnew.
TheGhostofOtto1923
3 / 5 (20) Aug 29, 2012
Dear pussycat_lies
Would you like a large list of animals (including humans) that are born helpless? Please to thinky before speaky. I know this doesn't apply to you of course, with you being an active and mobile dimwit.
You are trying to argue your way out of your ignorance like you did when you said that zero growth meant zero birth. And it's just as pathetic.

Physorg provided this article under 'Related Stories'
http://phys.org/n...688.html
Your elephant birth would qualify as a "painful, complex, and dangerous childbirth" would it not?
I suppose it might make you cringe since you've had 5 'miscarriages' from too much sex up against your stove, but the elephant doesn't appear too uncomfortable does she?
Estevan57
2 / 5 (28) Aug 29, 2012
Otto, you are mixing up people with posts. I suppose it's easier than arguing an invalid point.

Are you trying to show Pussycateyes my post? Can't you just respond to it instead? You are the one who stated
"You see, animals and dimwits have to be born active and mobile" etc.
Thanks for the meaningless links at least.
Dude, you've gone ADHD.
Spiro Agnew. Spiro Agnew. Spiro Agnew.
TheGhostofOtto1923
3.2 / 5 (20) Aug 29, 2012
Otto, you are mixing up people with posts. I suppose it's easier than arguing an invalid point.

Are you trying to show Pussycateyes my post? Can't you just respond to it instead? You are the one who stated
"You see, animals and dimwits have to be born active and mobile" etc.
Thanks for the meaningless links at least.
Dude, you've gone ADHD.
Spiro Agnew. Spiro Agnew. Spiro Agnew.
And it is easier for you to whine about being abused than to admit that you got yet one more thing, wrong. Animals (and your mum) can give birth on the run. Humans can not.
Estevan57
2 / 5 (28) Aug 29, 2012
Hey Otto, here is a short list of animals born helpless:

Long-eared hedgehog, Aardvark, Tenrecs, Crest-tailed mulgara, Tasmanian devil, Tiger, Platypus, Armadillos, All Bats, Badgers, Mongoose, Mink, Seals, Black Bear, Brown Bear, Cheetah, Leopard, Coatis, Coyote, Wolves, Lynx, Fossa, Giant Panda, Otter, Jaguar, Lion, Meercat, Marten, Polar Bear, Striped Skunk (your relative), Stoat, Tiger, Weasel (another relative), Wolverine, Bighorn Sheep, Warthog, Pika, Rabbit, Wallaby, almost all Marsupuals, Koala, Rhinoceros, Gibbon, Macaquaqe, Lemurs, squirrels, Mice, Marmot, Rats, Moles, and more.
More Birds, Reptiles, Amphibians, Fish, Insects, Crabs, shrimp and Krill, Arachnids,
There are many, many, many more.
www.bbc.co.uk/nat...ltricial

Altricial, meaning "requiring nourishment", refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born.

All these animals and I laugh at you.
Spiro Agnew
TheGhostofOtto1923
3.1 / 5 (21) Aug 30, 2012
Estevan/pussy/obie says
Hey Otto, here is a short list of animals born helpless
-while forgetting that the article and the discussion was about large heads and painful births. Helplessness is only one result as has been adequately elucidated.
So Otto - painful, complex, and dangerous childbirth doesn't occur in the wild as you say? Really?
You can seek out the very well-educated people who wrote the articles the links to which I posted for you and argue with them, or you could argue with these people here:
http://www.google...ch?q=why is human birth painful&ie=UTF-8&oe=UTF-8&hl=en&client=safari

-Or you could keep pretending that you know what you are talking about. So hard to choose I know.

Maybe you could use google to find articles which state that no, women don't really experience painful and difficult childbirths relative to other animals, they are just whiners like yourself. You can find just about anything on google.
TheGhostofOtto1923
3.3 / 5 (21) Aug 30, 2012
Spiro Agnew - is that a reference to spirochete which vendicar used to call you when you were pirouette? What an ass. Is he really Scott nudds? Esai?

Remember when you thought he was me? Haha that was funny. Remember when you thought Ethelred and antialias and caliban and others were me as well just because we all took issue with the crap you always post? Haha that was funny too.
TheGhostofOtto1923
2.9 / 5 (21) Aug 30, 2012
"But it hurts when I bear down!" -say human mommies. Well perhaps they should just toughen up like rhinos. This one doesn't seem too plussed:
http://www.youtub...a_player

-Bring back memories?
Estevan57
2 / 5 (28) Aug 30, 2012
I have never argued that human birth wasn't painful.
This is your statement: "Animals (and your mum) can give birth on the run."
Is it accurate? Why yes it is. Is it wrong? Why yes it is.

You still deliberatly mix me with PussyCateyes and others. This is your usual attack mode, so it is to be expected.
You have my permission to continue.
Do you know what an Anagram is?
Spiro Agnew Spiro Agnew Spiro Agnew.
TheGhostofOtto1923
2.9 / 5 (23) Aug 30, 2012
This is your statement: "Animals (and your mum) can give birth on the run." Is it accurate? Why yes it is. Is it wrong? Why yes it is.
Im sorry I dont know your mum. And the statement does not state, nor does it imply, that ALL animals can give birth on the run. That would be an absurd assumption. Some animals CANT run. Did you know this?

Only an imbecile would conclude this. Ergo more evidence that you and the pussy horde are all YOU.
Estevan57
2 / 5 (28) Aug 30, 2012
The pussy horde is in your mind Otto.

Now THAT was fun sentence to type! Another!
I am I, and the pussy horde is the pussy horde, and never the twain shall meet.
You just bring out my inner poet.

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