Re: [asa] Dawkins on the fossil record

From: Keith Miller <keithbmill@gmail.com>
Date: Wed Dec 09 2009 - 11:58:17 EST

Bill wrote:

This entire picture is for me confused. At one time I saw speciation as a
> radical shift, a kind of monster. But if changes are as incremental as it
> seems, perhaps we can't really speak of species at all. Perhaps there is no
> such thing as a "human race."
>

There are some situations in which genetic mutations or paleogeographic
events can result in new reproductively isolated species within one or a few
generations. However, in the great majority of cases species indeed do
form incrementally in evolving populations. The identification of species
is easier when the splitting of lineages is involved (cladogenesis) than
when you have a single evolving population that is tracking a changing
environment (phyletic evolution). Some argue that significant evolutionary
change occurs primarily during cladogenesis -- this is the fundamental
argument that was put forward by Steve Gould and Niles Eldridge in their
proposal of "punctuated equilibrium."

But the "species question" is a major one within both paleontology and
modern biology. Species are not at all easy to define. The biological
species definition is actually very difficult, and often impossible, to
apply in the real world. This was in fact one of the observations that
moved Darwin to reject the fixity of species and propose common descent. It
was also what attracted Asa Gray to evolutionary explanations because he
recognized the plasticity and variability of species.

Keith

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Received on Wed Dec 9 11:58:29 2009

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