Scientists: Humans traded weaker jaws for big brains

[JTSimon]

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LONDON, England (Reuters) -- A genetic mutation that occurred 2.4 million years ago could be the reason why modern humans have such big brains and weak jaws, scientists said on Wednesday.

They discovered that a fault in a gene called MYH16 in modern humans happened at about the same time that their skulls started to change in shape from other primates, allowing their brains to increase in size.

But the trade-off was a smaller, less powerful jaw.

"The coincidence in time...may mean that the decrease in jaw muscle size and force eliminated stress on the skull which released an evolutionary constraint on brain growth," said Nancy Minugh-Purvis, a member of the team at the University of Pennsylvania School of Medicine, that made the discovery.

All humans have the MYH16 mutation but other primates, including chimpanzees and macaques, still have the intact gene. Over the past few million years, since the genetic fault occurred, human skulls have grown three times in size and the outwardly elongated jaws have receded.

Pete Currie, of the Victor Chang Cardiac Research Institute in Sydney, believes the research published in the science journal Nature could be the first functional genetic difference between humans and apes.

"Remarkably, the timing of the appearance of this genetic alteration, or mutation, roughly coincides with the appearance of "human-like" characteristics in the hominid fossil record," Currie said in a commentary in the journal.

Minugh-Purvis along with Hansell Stedman and other experts at the university pieced together the complicated puzzle after discovering that the gene was intact in primates but mutated in all humans.

A genetic fault is often linked with some type of inherited disease but the scientists were puzzled about what type of disease was common in all humans throughout the world.

Further research revealed that MYH16 was associated with muscles involved in chewing and biting and it encoded a protein in primate jaw muscles. This led the researchers to suspect the so-called disease in humans was a weaker bite.

Stedman and his colleague said the weaker bite would have lessened the force on the skull so it could grow larger and provide more space for a bigger brain.

"We can only hope that this study represents the vanguard of a new wave of analyses that focus on the genetic basis of human evolution," Currie added.

http://www.cnn.com/2004/TECH/science/03/24/science.brains.reut/index.html

[Z the laidback Virus]

Expect soem great outburst of our theist fellow posters on your neck mate!
Anyway,nice article. Did you know human jaws and teeth are a major obstacle for theologists strictly adhering to creation and their view of humans as a physically perfect creature? See the case is that our jaws have over the millions of years over our evolution become short and juvenile due to a process of neoteny we went through.

I don't know if you know what neoteny means,but it's the name for a  process in wich young animals do not fully come to the adult state of development but get 'stuck' in a certain developmental state.
Examples a
Olms,blind grotto-living salamanders that do reach sexual maturity but never lose their gills and thus never fully pass the larval state of salamanders:


Many flightless birds provide a more complex example in that it's mainly their flight apparatus (wings and sternum) do not fully develop. This makes them retain the proportions of a newly-hatched chick of flying species. That's why their wings are so small. (Penguins are a different matter,as they still use their wings to 'fly'.....they're just too big and too aquatic to be able to fly through air)
Look at this, a kiwi skeleton. Hardly any wings but huge legs:


Well for humans,there are many neomorphic traits, wich are not seen in adult apes but are present in their infants. In 'Ever since Darwin', the late and great Stephen J. Gould mentions:
1. Bulbous skull
2. Juvenile face with small brows, straight profile, small teeth and small jaws ( In fact our jaws are often too small to give room for the last teeth to come, wich undermines the perfect design God is said to have given us,according to theists)
3. The spine attaches to the lower side of the skull,not the back.
4. Skull sutures close only very late in our development
5.The vagina is positioned to the front in stead of to the back. Apes have a vaginal canal to the front as embryos but this later moves to the back.
6. Strong unrotated,unopposable big toe. Only present in juvenile apes..disappears when maturing.

I hope this interested you or any other boarders.If not, no problem...I've given you the chance.

[7even]

good trade

[Z the laidback Virus]

'Evolution isn't something you can believe in,it's something you have to admit.'
(Me,March 26th,2004)

[7even]

'Evolution isn't something you can believe in,it's something you have to admit.'
(Me,March 26th,2004)

Lmao!

[JTSimon]

  ^Thats hard to believe.


Nice post.

[smerlus]

now if i could only trade my left testicle for a britney spears clone.....

[Z the laidback Virus]

now if i could only trade my left testicle for a britney spears clone.....

You could make money out of that,you know!