From: CurtAdams@aol.com
Date: Wed Jun 28 2000 - 18:18:50 MDT
In a message dated 6/28/00 11:43:18 AM Pacific Daylight Time,
cymm@trinidad.net writes:
> Curt, you're right of course...clumsy English again! But the
> "incompatibility" is really (i) diminishing (cost/benefit) returns to
> maintaining reproductive ability when viable progeny is extant...
Sib competition as a selective force for aging is an interesting idea. But
I had in mind tradeoffs where reproducing per se shortens lifespan.
Linda Partridge has shown that is the case in D. melanogaster, at least.
>and (ii)
> the negative benefits of loading the genepool with archaic combinations in
> the face of rapid environmental change....
Man, it seems like I have this argument a lot! That's
not really a problem; if the archaic combinations are
bad, the possessors will be dead anyway. Often, the
archaic combinations will carry valuable information
which is being lost due to fluctuating selection or drift.
>Some long lived complex species: tortoises; macaws; elephants; humans seem
>to have real advantages for the coexistence in a population of several
>generations.
Memetic-genetic coevolution would certainly change the game; in macaws,
elephants, and humans there's a lot of intergenerational knowledge transfer.
That's a pretty open field theoretically and experimentally (although
multigenerational selection experiments on elephants certainly have some
technical difficulties! :-)
>But generational depth is almost nonexistent in many real populations... the
>species seem to favour short life and develop interesting mechanisms to
>foster death.
I'm not aware of mechanisms to foster death except in species that reproduce
once only, like salmon and annual plants. Even there a strong theoretical
case holds that the mechanisms don't actively foster death, there's just
no selective reason to stop them (Pletcher and Curtsinger, 1998) You
do see mechanism that increase fertility and death rates; but I'd call them
fertility mechanisms: the mortality is a unaoidable side effect.
>But then they STILL eventually age and die when captive reared in suitable
>habitats. Is ageing different then... are they coming up against cellular
>ageing constraints specific to the genetic complexities of being a metazoan?
Not being a metazoan per se - metazoans that reproduce by fission often
have no aging, just a constant death rate (Michael Rose, "Evolutionary
Biology of Aging") Rose maintains, and I agree, that aging is a
semi-necessary
consequence of non-fission reproduction. When it's an option to off the
current organism in favor of its offspring, there will usually be some
circumstances
in which that is selectively favored. The existence of many such traits forms
aging.
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