From: BillK (bill@wkidston.freeserve.co.uk)
Date: Thu Apr 03 2003 - 09:57:08 MST
On Wed Apr 02, 2003 10:19 am Ramez Naam wrote:
> Antagonistic pleiotropy has been demonstrated many times in the lab.
>
> Several genetic mutations have been found which increase mean and
> maximum lifespan of animals but which introduce features that reduce
> survivability or fertility.
>
> Thus, the alleles that lack these mutations are examples of
> antagonistic pleiotropy - they help the animal survive or breed at an
> early age, but hasten the aging process and thus death.
>
My casual rephrasing of William R. Clark's abstract to the effect that
antagonistic pleiotropy might not actually exist caused Ramez to leap to
the defence of the concept.
Clark's full text is at:
http://www.wrclarkbooks.com/downloads/evolution.html
Clark was not denying the effect exists - as Ramez said the effect has
been noted many times.
As Robert Bradbury said
> The typical concept of "antagonistic pleiotropy" is that something
> is designed to help out early on but ultimately ends up being harmful.
What I think Clark is saying is that the senescence genes are built-in
from the start.
Selected Quotes -------
The problem for evolution was how could aging have evolved when most
animals die of accidental causes well before senescence begins to be
expressed. How could a trait not expressed by the majority of members of
a species be acted on by natural selection, and come to be fixed in the
species as a whole?
There are difficulties with that portion of the theory implying that
senescence effector genes gradually accrued in different species over
evolutionary time, in a random process not directed toward aging per se.
The problem is that the senescence-related genes described so far do not
behave that way at all. Recent genetic analyses have shown that the
fundamental mechanisms of senescence, and the genes underlying them, are
remarkably similar in virtually every eukaryotic organism studied, which
is hardly consistent with a random, independent accumulation of
late-acting harmful mutations over the evolutionary history of eukaryotes.
End Quote ----
That is why he is saying that "antagonistic pleiotropy" is not real. Not
that the effect doesn't happen, because it does, but because the
cause is built in to all species DNA.
BillK
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