[asa] Punk EEK: was Arrogance ....

From: Keith Miller <kbmill@ksu.edu>
Date: Fri Aug 24 2007 - 12:04:17 EDT

Lawrence Johnston wrote:

> I'd like to ask a question of the Bio types on our List:
>
> What has happened to Steve Gould's "Punk EEK" revelation that the
> fossil
> record shows that when a new animal type shows up, it continues
> essentialy
> simple descent for a few million years, and then goes extinct, without
> showing Darwinian gradual change. I remember he took hits from some
> big
> time professsionals, for this revelation.

Punctuated equilibrium is a highly misunderstood concept by the public,
and by some in the scientific community as well. It was proposed by
Gould and Eldredge as a mechanism for speciation -- that is, the change
form one species to another. They saw this as a logical extension of
the allopatric model of speciation in which new species arise from
small populations geographically isolated from their parent population.
  They argued that rates of evolution would be more rapid in such small
isolated populations. Furthermore, they inferred from detailed fossil
records with samples closely spaced in time that evolutionary change
was concentrated during speciation events. PE was a theory of
speciation that predicted that evolutionary change would tend to be
concentrated during speciation events when a lineage is split.
Frequency of speciation would then be expected to correlate to rates of
evolutionary change.

I think that it is safe to say that today most paleontologists accept
PE, but do not see it as the only evolutionary pattern, or necessarily
the primary one. It is also recognized that sympatric speciation also
occurs where new species can arise within the geographic range of their
parent species. This can be the result of genetic isolating mechanisms
other than geographic isolation, such as habitat use, reproductive
time, food choices etc. Also large populations can be forced to evolve
in a particular direction in response to environmental changes from
which they cannot escape.

Keith

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Received on Fri Aug 24 12:04:28 2007

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