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Re: [xmca] Thoughts on this

Hi Carol,

If what these conferees are trying to explain is the relatively rapid increase in the hominin brain (which seems to be the focus of this article), I would expect that multiple factors were in play.

First, a smaller jaw requires smaller jaw muscles, which allows a change in the organization of cranial bones - I've forgotten the physiological details of this, but it's a proposal that has been made - a change which required a mutation, but was nonlethal because changed practices of food selection and preparation - the shift from nuts and berries towards meat, then cooking it - meant a large crunching jaw was no longer necessary.

Second, if a large brain means greater intellect (by no means obvious; among homo sapiens there is no such correlation, as far as I know; but perhaps a threshold brain size makes a difference) then this could be selected for by anything that calls for more creative thinking. Battling with neighbors, perhaps. Rapid climate change. Simply migrating into unfamiliar territory. More complex technology. Hunting large mammals to extinction. Larger social groups (the 'social brain' theory). 

Third, a population bottleneck, such as occurred around 10,000 years ago,  would mean that a new characteristic, such as a bigger cranium, would rapidly disperse throughout the population as it increased again.

Just some musings...

On Sep 15, 2012, at 6:37 PM, Carol Macdonald wrote:

> http://www.bbc.co.uk/news/science-environment-19598980
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> Sessional teacher: Wits School of Languages
> Honorary Research Fellow: Department of Linguistics, Unisa
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