Date: Fri, 26 Apr 1996 11:25:22 -0600
Subject:  Punctuated equilibria -Reply


>>> Rahul Mahajan <rahul-AT-peaches.ph.utexas.edu>  4/24/96, 07:44pm >>>
Lisa, I agree with your and Dawkins's view that the theory of
punctuated equilibria is well within the pre-existing framework of
understanding.

Lisa: Super!

RM:  What seems new to me is [snip] that our picture that gradual
change within species occurs over millions of years (in addition to
whatever more rapid change/speciation may occur) is either wrong or
much less universal than we supposed. In effect, they posit a
stability of species to small deformations and present a picture of
long periods of almost complete genetic stasis (in the adaptive
sense, of course; nonadaptive genetic drift continues at a
near-constant rate). 

Lisa:  I'm not recognizing this picture.  You seem to be
distinguishing between speciation as species-splitting, and
speciation as changes in a single line.  If so, I think I disagree
with that view.  Who posits such stability?  I'd only expect it if
the sum of [possibly counter-balancing] selective forces is about
zero.  Also drift is not expected to be continuous or constant.  It's
effects are much greater in very small populations, and negligible in
very large ones, no?

RM:  What would be especially interesting would be to look at the
persistence and prevalence of stasis broken down by complexity of
organism. We already know that the more complex an organism is, the
less potential for radical change it has (viz. the evidence of the
Burgess Shale and other post-Cambrian Explosion sites).

LR:  Tell me more.  I'm a little familiar with the Burgess, but not
aware of this implication.  How does complexity break down stasis? 
What causes stasis?

Thanks,
Lisa

Rahul




     --- from list marxism2-AT-lists.village.virginia.edu ---




     --- from list marxism2-AT-lists.village.virginia.edu ---