Xref: utzoo sci.bio:5118 talk.origins:15595
Newsgroups: sci.bio,talk.origins
Path: utzoo!utgpu!lamoran
From: lamoran@gpu.utcs.utoronto.ca (L.A. Moran)
Subject: Coelacanth and Evolution
Message-ID: <1991Jun6.171806.23089@gpu.utcs.utoronto.ca>
Organization: UTCS Public Access
Date: Thu, 6 Jun 1991 17:18:06 GMT


In response to a question about whether coelocanths have evolved Christopher
Green mentioned punctuated equilibrium.

Jorn Barger then said,

     "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 think that Jorn misunderstood the previous posters (including myself) who
said that lack of phenotypic change does NOT mean that evolution has stopped.
This is the same objection that I have to Eldridge and Gould's theory. They
tend to focus on changes in morphology, as seen in the fossil record, and
equate these changes with evolution. (In fairness this is actually an error
made more often by their uninformed supporters.)

I see evolution as a continual, relatively smooth, change in the frequency of
genes in a population. Sometimes these genes affect morphology, in which case
evolution is documented in the fossil record, but most of the time other
aspects of the organism are affected.

Jorn Barger then proceeds to offer an explanation of punctuated equilibrium,

     "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."

There are several better ways of explaining why a favorable allele may not
become fixed in a population. But the main argument against sexual selection
is much more obvious.

Jorn, are you aware of the fact that punctuated equilibrium was based on the
analysis of the evolution of molluscs? The other supporting evidence relies
heavily on the evolution of other marine invertebrates and plants. I don't
think that sex-appeal or sexual attractiveness is very important in oysters,
ferns, grasses, and barnacles.

-Larry Moran