phillip smith  wrote 

> > "By relegating a gene to the evolutionary garbage 
> > heap, we were able to lift the constraints to the
> > development of human complexity," he told The Scientist.

> With out reading the original paper it seems to me 
> they have it back to front surely the increase in 
> brain complexity allowed the mutation to be fixed


I agree.

>From reading this article on gets the feeling that 
these scientists are ignoring the most important part 
of the equation: they don't indicate an "selective 
engine" of hominid brain growth.  Instead it seems 
they have assumed that hominid brain growth would be 
inevitable once the constraints are removed.

The equation they seem to propose goes as follows:

Decrease in jaw muscles enables increase in brain growth.

The equation that I would propose goes as follows:

Social complexity is the engine of human brain growth, 
large jaw muscles (which were especially necessary for 
Apiths to process the hard, dried-out foods associated 
with the dry season of their monsoon habitat) constrain 
brain growth but don't prevent it, brain growth 
eventually enables tool usage (about 2.5 to 3.0 mya), 
tool usage leads to more processed foodstuffs including 
meat, more processed foodstuffs leads to reduction of 
size of jaw muscle, reduction of size of jaw muscles 
removes the constraint of brain growth.

Jim
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