skeptickal1{at}yahoo.com (Skeptical1) wrote 

> Did this genetic mutation lift an evolutionary 
> constraint on brain growth in early humans? [...]"

I think it's the other way around: brain growth 
lifted an evolutionary constraint on the reduction 
of jaw size:

Human brain growth (which started with Apith, 8.1 mya) 
has to do with the fact that hominids depended greatly 
on external, territorially situated, resources in order 
to survive the dry season of their monsoon habitat.  
This favored the evolution of any and all of the 
following:

1) Consciousness of value of external resources.
2) Ability to cooperate and communicate with others in 
the context of an often-times highly political social 
group in order to maintain value of collective resources.
3) Ability to understand the long-term implications of 
one's own actions as well as the actions of others in 
order to maintain the value of resources.  

Is there more to human brain growth than this?  Sure, 
but these are the basics.  

Is it possible that large jaws acted to constrain 
brain growth?  Sure, to some degree, but to me it seems 
more likely that increased human intelligence lead to 
increased tool usage (which is consistent with the 
fossil evidence of tool usage) and increased tool usage 
enabled processing of foods.  With increase in 
processed foods (including meat) there was less need 
for large jaws and large jaw muscles which previously 
had been necessary for Apiths to process the hard, 
dried-out foods associated with the dry season of their 
monsoon habitat.

Jim
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