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From: barger@aristotle.ils.nwu.edu (Jorn Barger)
Newsgroups: sci.bio
Subject: Re: Coelocanth and evolution:x
Message-ID: <1995@anaxagoras.ils.nwu.edu>
Date: 6 Jun 91 13:07:24 GMT
References: <1991Jun4.165540.13115@psych.toronto.edu>
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christo@psych.toronto.edu (Christopher Green) writes:

> Read up on punctuated equilibrium. Niles Eldridge's _Time_Frames_ is
> a good popular account. The more technical stuff can be found in _Dynamics_
> _of_Macroevolutionary_Theory_ (or something close to that). Great stuff!
> Have fun!

I'm a bit disappointed that only one coelocanth-followup mentions this
obvious-but-still-apparently-under-disseminated viewpoint.  This is hot
stuff indeed, and theoretically revolutionary.  The argument is that the
classic pattern of evolution is not a smooth, gradual blurring from one
species to another, but an alternation of relative quiescence and relatively
rapid phenotypic transformation.

I'll take this opportunity to present again my best guess as to the mechanism
at work here:

What has to be explained is why there may be adaptive mutations present in
a genepool, _that don't spread through the entire population_.  What is
the conservative principle balancing natural selection?

I claim it is sexual selection.  If an ideal sexual stereotype is set up
early on in the evolution of a new species, as it must be, then it may
serve to reduce the sexual attractiveness of new adaptations that deviate
from that stereotype.  Perhaps a wide range of favorable adaptations can
build up at the fringes of the genepool, in marginal niches where a slight
adaptive superiority counts for more than sex-appeal, but never spread through
the rest of the population, breaking through instead only when a change in
the environment makes the niche marginal for the entire population.

(Bonus question: what B-movie title is a fitting summary of this view?)