Re: transitional fossils

From: Cornelius Hunter <>
Date: Sat Dec 03 2005 - 13:35:16 EST

>> Dear Dr. Garrison,
>> I have always assumed that the impetus for Gould and Eldredge's
>> "punctuated
>> equilibrium" hypothesis. That is, there would be no need for such a
>> hyopothesis if there were an abundance of transitional fossils.
>> God bless,
>> Bill Green
> This is a very common misunderstanding of Gould. Punctuated equilibrium
> is a model for speciation. It argues that morphological change does not
> occur at a uniform rate, but is concentrated at speciation events. This
> was presented as an extension of the allopatric speciation model that
> proposed that evolutionary change is accentuated during times when species
> lineages are in the process of splitting due to the geographic isolation
> of small populations. There are many good theoretical reasons based on
> population genetics why this might be a common pattern.

PE's call for non uniform morphological change was in response to the non
uniform character of the fossil record. It is not based on population
genetics. If you do not presuppose evolution to begin with, then population
genetics does not particularly help. That is, population genetics does not,
itself, indicate PE.

> Transitional forms are abundant in the fossil record and cross every level
> of the taxonomic heirarchy from species to phyla.

The term "Transitional forms" is not a theory-neutral description of the
data. Those forms are "transitional" if evolution is true. The bottom line
is that the fossil record is characterized by the rapid appearance and then
stasis of new species. Species persist for eons with little or no change.
You can try to align those species in "transitional" sequences if you like.
What you will find is a wide variety of patterns, all of which evolution can
explain by one means or another (gradualism, PE, missing data, selection, no
selection, environmental shifts, saltation, co-evolution, and so forth). All
of these explanations are used today, but we still are left with rapid
appearance and then stasis of new species. Hence PE. It provides an
explanation for those dashed lines between the "transitional" species.

> Keith
Received on Sat Dec 3 13:37:42 2005

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