wrote:
> I contend that due to my model, no species 'evolves'
> unless they are forced to adapt to harsh changes - thus
> As environmental adaptation increases:
>    directional and diversifying selection decreases
>    AND stabilizing selection increases.
>     (and vice versa)
> So I contend that the brain development in hominids
> was due to the harsh environmental weather at the time:
> 

I am not knowledgeable enough on hominid brain development (even my own) to
comment much, but as an interested amateur, I would take issue with your
first sentence in the use of the word "harsh" and the ubiquitous and
generalized nature of the statement.  I would suggest that species'
evolution (or alternatively, reduction or extinction) is almost assured by
harsh changes, but that many other factors may also be a catalyst for
evolution.  Chief among these would be simple advantage over other species
and ancestor of a species in question.  This could be any or all of issues
like higher reproductive rates, easier access to unexploited food sources,
improved mobility, better sensory organs and processing, and many others
items which could improve a species change to thrive, even in a relatively
stable environment (i.e. nothing externally "harsh" like weather,
predators,
and so on.)

By way of example, I might point to (my understanding of) the giraffe's
neck, tongue, etc. to permit better access to fairly poorly exploited Acacia
trees; whale ancestors (Ambulocetus natans(?) and others) developing flukes
to improve ocean mobility (What a fluke THAT was!); early light sensitive
pigments developing later to eyes (this was likely very random - especially
initially - without any change in "harshness", etc., etc.)

It could be that your version of "harsh" differs from mine, but I
understand
that many, many random changes will occur with little or no change in the
existing "harshness attributes" of the environment, and selection
occur just
because of these creatures' improved ability to adapt and thrive.  That
said, I would "agree" that due to harsh changes, especially those so harsh
as to have caused mass extinctions and opened up new niches and possibly
added radiation or toxins to the environment, evolution may well go through
a SJG-ish period of punctuation (if the word can be used to indicate the
explosion/diversification of species in the manner).  Comments?  Best
regards, Brett Aubrey.
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