Early humans swapped bite for brain

[~Foo Fighter~]

[size=large]Early humans swapped bite for brain[/size]
http://www.newscientist.com/channel/being-human/human-evolution/dn4817.html

Humans owe their big brains and sophisticated culture to a single genetic mutation that weakened our jaw muscles about 2.4 million years ago, a new study suggests.

The slack muscles relaxed their hold on the human skull, giving the brain room to grow. Other primates remained stuck with mighty muscles that squeezed the skull in a vice-like grip.

The finding is "pretty amazing", says Peter Currie, an expert on skeletal muscle development at the Victor Chang Cardiac Research Institute in Darlinghurst, Australia: "Changes in muscle anatomy are well known to alter the bones to which they attach. The exciting part of this is the mutation in the gene dates to exactly when this transition occurs in the fossil record."

Over the past 2.5 million years, human brains have grown enormous compared to those of other primates. Human brains are now roughly three times the size of those of chimps or gorillas.

One possible reason is that changes in the environment forced early humans to invent tools, and those with the biggest brains had greatest manual dexterity, which led to yet more sophisticated tool use. Alternatively, selection may have favoured larger brains because they permitted more complex cultures.

But why did this process occur in humans and not in other primates? According to Hansell Stedman, an expert on muscle disorders at the University of Pennsylvania in Philadelphia, it was a simple mutation in a gene found in our jaw muscles.

Gene tracking
While studying muscular dystrophy, Stedman and his colleagues were tracking down a gene thought to play a role in muscle contraction using specimens from a macaque.

"We quickly found out this gene was expressed only in the powerful bite muscle," says Stedman. Bite muscle is the most powerful of the jaw closing muscles and completely encloses the skull in all non-human primates.

The team found that the same gene was also active in a sample of human bite muscle, but there was one crucial difference. Compared to the macaque gene, the human gene had two missing base pairs in a key region.

In follow-up work, Stedman's team studied the gene in people from all over the world, including natives of Africa, South America, Western Europe, Iceland, Japan and Russia. They also studied seven species of non-human primates, including gorillas and chimpanzees. Every human had the mutation, whereas none of the animals did.

Small fibres
To nail down the effect of the mutation, Stedman's team looked closely at the structure of the bite muscle tissue where the gene is expressed. They found that the muscle fibres in humans were far smaller than those in other primates, suggesting the mutation reduced muscle mass in people. The weaker muscles would have exerted considerably less force the skull, allowing it to grow and expand.
Detailed genetic analysis suggests the human mutation occurred approximately 2.4 million years ago. Shortly after that, the earliest known members of the genus Homo appeared - with smaller jaws, and larger brains.

Paul Pettitt, an expert on human origins at the University of Sheffield, thinks the mutation could explain the earliest appearance of brains bigger than 500 cubic centimetres in Homo habilis and Homo rudolfensis around two million years ago. Both these species had significantly smaller jaw muscles compared to their ancestors, the australopithecines.

"This is a fascinating discovery which potentially sheds light on the origins of the genus Homo," says Pettitt. "It's certainly a very plausible reason for a relatively late beginning of the rise of brain size above and beyond the ape norm."

Journal reference: Nature (vol 428, p 415)
Related Articles
· Early humans smart but forgetful
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· Oldest hominid skull shakes human family tree
· http://www.newscientist.com/article.ns?id=dn2533
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· Out of Africa migration may be a no-brainer
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Weblinks
· University of Pennsylvania
· http://www.upenn.edu/
· Peter Currie, Victor Chang Cardiac Research Institute
· http://www.victorchang.com.au/staffdir/biography.asp?
· Nature http://www.nature.com/

Printed on Thu Feb 21 16:26:31 GMT 2008

~Foo Fighter~

[Chuckleberryfinn]

"The scientist later added that anyone who believes this load of bullshit may have actually swapped brain for bite."

[~Foo Fighter~]

Originally Posted by Chuckleberryfinn

"The scientist later added that anyone who believes this load of bullshit may have actually swapped brain for bite."

Whoa there...ease up Tex. It's just an article...no requirement to believe or disbelieve.

~Foo Fighter~

[Tommy Allison]

Originally Posted by Chuckleberryfinn

"The scientist later added that anyone who believes this load of bullshit may have actually swapped brain for bite."

Damn... You beat me to it.

[~Foo Fighter~]

Originally Posted by Tommy Allison

Damn... You beat me to it.

What is the world is your beef? If you disagree with the article spit it out...what's the problem?

I'm kind of baffled why someone would immediatly jump to attacking a poster instead of commenting on the content of the post.

refer to nature

http://www.nature.com/nature/journal/v428/n6981/full/428373a.html

~Foo Fighter~

[Tommy Allison]

I didn't attack anyone.

I just got beaten to the punch. I didn't get to make a wise assed comment.

I bet if Lloyd Pye were here, he could settle all this evolutionary stuff.

[~Foo Fighter~]

Originally Posted by Tommy Allison

I didn't attack anyone.

I just got beaten to the punch. I didn't get to make a wise assed comment.

I bet if Lloyd Pye were here, he could settle all this evolutionary stuff.

Lloyd Pye??? Sheet man you are reading way too much into the post.

I shared an article that interested me...I can't say what, if anything, it argues for or against.

What do YOU think it argues for or against?

~Foo Fighter~

[Tommy Allison]

I think you've got the wrong impression.

Human evolution wasn't decided by what we ate. If that were the case, we'd have stopped evolving much sooner, as neanderthals and cro-magnon man were cooking their food long before humans invented the cheeseburger.

Evolution comes about quickly, not slowly, and the funny part about it is that you never know what the catalyst is. I read the article and found it an interesting hypothesis, however I could say that human beings gave up their psychic ability for spoken communication.

[~Foo Fighter~]

Originally Posted by Tommy Allison

I think you've got the wrong impression.

Human evolution wasn't decided by what we ate. If that were the case, we'd have stopped evolving much sooner, as neanderthals and cro-magnon man were cooking their food long before humans invented the cheeseburger.

Evolution comes about quickly, not slowly, and the funny part about it is that you never know what the catalyst is. I read the article and found it an interesting hypothesis, however I could say that human beings gave up their psychic ability for spoken communication.

Interesting...

As I said...I'm just taking it in at the moment.

But it strikes me that it might be used to argue every angle from evolution to intellegent design, to ancient astronauts.

I don't have access to the Source article in the peer reviewed journal Nature...but this article seems to at least comort with the Nature abstract.

~Foo Fighter~

[TClaeys]

Interesting indeed.

From my understanding there were several things in play at this time. A chaotic climate, introduction of many new species, primitive toolmaking, and a bigger brain. Also apparently a change of veggies to meat in hominds and many other variables that we probably won't ever know.

I think one possible line of reasoning goes something like this. A change in eating may allow other variants to pass into existence because eating meat doesn't require as much bloodflow to the digestive system as does meat. Nutrients are more readily and easily absorbed.

While this doesn't CAUSE other adaptations, it allows for other variants to pass into newer bodies than would be allowed before. This also allows blood to access other, apparently more important naturally selected areas of the body (perhaps the brain).

In other words, a change in diet could have allowed mutations or at least previously forbidden variants into the deck of cards. Before this, these variants were never selected because they would not get by in a body with them.

I don't favor any particular theory, but I've just been reading some on this subject and thought I would throw this in as well. Anyway, I don't know that I've explained this very well, but perhaps it is some more to think about.