On Sat, 24 May 2003 17:24:44 +0000 (UTC), Brett Aubrey
 wrote:

> 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.
>

Be careful of the examples you use for evolution!  There is evidence
that the giraffe's neck is NOT an adaptation for feeding high above
the ground, but rather is the result of sexual selection.  See
  R.E. Simmons and L. Scheepers,
  "Winning by a Neck: Sexual Selection in the 
    Evolution of the Giraffe"
  American Naturalist 148:771-786 (1996)

As for Tom Hendrick's model, I fear that, once again, he takes ideas
well established in biology and recasts or reinterprets them often not
to any advantage.  No organism was ever "forced" to evolve by any
factor.  Certainly, given a stable environment and sufficient time,
selection will result in adaptation after which there occurs a period
of stabilizing selection or stasis.  Any kind of change in the
ecosystem may mean that a species niche is greatly reduced or may mean
that the fundamental niche is greatly expanded at which time selection
can then act in a directional manner to produce change.  "Harsh"
changes have nothing to do with it, nor is weather necessarily the
only or the major factor.
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