Re: Alex's gibbon-like CA
Paul Crowley (Paul@crowleyp.demon.co.uk)
Tue, 07 Nov 95 23:12:51 GMT
In article <47l816$dfo@geraldo.cc.utexas.edu>
aduncan@mail.utexas.edu "Alex Duncan" writes:
> Paul@crowleyp.demon.co.uk writes:
>
> >I'm sure this is the "evolution forces" error. A species faced with
> >a shrinking habitat does not change its diet. It declines or dies.
>
> Well, when do taxa change their diet then? (And BTW, I didn't suggest a
> change in diet, but a change in the proportions of the dietary items
> eaten. After all, human and chimp diets aren't that different, especially
> in areas where ranges overlap.)
>. . . <various snips>
>
> As far as your thing about "shrinking habitat" (or changing habitat) and
> extinction goes -- as far as I can see you've ruled out most of the
> important evolutionary changes in the history of the earth.
>
> I think you make way too much of your cute little "evolution forces" idea.
It's basic to any serious thinking on evolution. The common failure
to grasp it is at the root of most bad ideas - like all the standard
ideas on the origin of bipedalism.
A new species arises from the cross-over of a tiny group (relative
to the whole of the originating species). That tiny group is
seizing an opportunity presented by some fortuitous circumstances.
These circumstances *could* arise from some environmental pressure
operating on the whole population, but that is *most* unlikely.
Consider the numbers: a successful species will have a population of
millions and last millions of years. An environmental change (like
the decline of forests) will, over the time involved, cause the death
of billions (of gibbon-like CA's). But if that species was to give
rise to a new one, at the most a few hundred individuals are involved.
For example, a group of g-like CA's finds some fortuitous circumstance
that makes it decide "walkabout" is great idea. The death of
billions is "forced". The cross-over of the tiny group is NOT.
We can only guess at the set of fortuitous circumstances that enabled
a very small group of protohominids to adopt true bipedalism. They
are most unlikely to have arisen from forces operating on the
population as a whole. This is where your thinking (and general PA
thought) is so bad. Does it come from the weakness of the human
brain at conceiving large numbers? The odds are billions to hundreds
- or ten million to one.
Why is this fundamental evolutionary concept so hard to grasp?
Paul.
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