RE: Punctuated Equilibrium: reviving the dead man?

Joel Duff (crinoid@midwest.net)
Tue, 20 Apr 1999 13:12:40 -0500

>> [mailto:evolution-owner@udomo3.calvin.edu]On Behalf Of Ami Chopine
>
>> I am not suggesting these mutations are suppressed. I am suggesting two
>> things: since under the pressures common to that population, that
>mutation
>> will not be selected for. Under some circumstances, given enough time, it
>> may gradually take over the entire population, much like diffusion. If
>> there is a direction, however..a stressor event, or the effective
>isolation
>> of part of the population in a slightly different enviroment then you will
>> see those mutations being selected for. What was once a slow, almost
>stand
>> still process, will become almost instantaneous in the geologic record.
>
>Mutations are constant, selection is constant, therefore evolution is
>constant. That's a simple and reasonable argument. But, supporting PE by
>appealing stressor events such as a change in the environment or part of the
>population being isolated isn't so clear. I still don't see a mechanism.
>It sounds like you're suggesting that mutations are accumulated and kept in
>reserve until needed. I believe we already addressed the argument that
>environment doesn't affect the rate of evolution, only the group of selected
>mutations, so what difference would a different environment make? A monkey
>on the way to become a human might instead, if the environment changes, be
>on the way to become a bat, but it's still going to change at the same rate.
>An isolated population might lose some of the genetic variation of the
>parent population, but it's not going to evolve faster, it's just going to
>be limited to the genetic variation of the parents of that new isolated
>population.

Mutations are constant? Why must this be so? Also, this paragraph above
seems to assume that all evolution acts upon accumulated point mutations
and sounds very much like only classical beads on a string genetics is
being considered. What about exon shuffling, gene rearrangement etc.. as
a dynamic response to environmental conditions. I would ask why can't
organisms have evolved responsive systems to boost their own
"evolvability?" ie. mutations (point mutations, release of retroviral
components of the genome etc..) may be intentionally elevated to provide a
source of new genetic material. Joel