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From: sa209@utb.shv.hb.se (Claes Andersson)
Subject: Re: Reason for Short Life Spans?
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References: <Pine.HPP.3.91.941209140830.1790A-100000@alnilam.krl.caltech <3cnf1u$qlm@scratchy.reed.edu>
Date: Thu, 15 Dec 1994 16:11:43 GMT
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In article <3cnf1u$qlm@scratchy.reed.edu> jhopson@reed.edu (John Hopson) writes:

>In article
><aberenzw-1312941926440001@pierson-college-kstar-node.net.yale.edu>
>aberenzw@minerva.cis.yale.edu (_madAdam_) writes:

>> I finished Dawkin's "The Selfish Gene" a couple of weeks ago, and remember
>> his explanation for the length of an organism's lifespan, which I thought
>> sounded very logical. I'm surprised no one has mentioned it.
>> 
>> He claims that the length (or shortness) of an organism's life span is
>> caused by the accumulation of genes that 'code' for qualities that have
>> detrimental effects late in life.  He reasons that there must be plenty of
>> harmful genes that don't begin to express themselves until the organism
>> has reached a certain age.  Those that express themselves (perhaps by
>> killing the organism) early in the organims' life, before it has a chance
>> to reproduce, will be selected out.  However, there is no pressure to
>> remove harmful genes from the genepool if they don't express themselves
>> until after the organism has reproduced.
>> 
>> it makes sense to me.  i'm not sure if its the _only_ way to explain the
>> length of lifespans, but sounds feasible.

>      I don't understand the claim that there is no pressure to remove
>late-lethal genes from the population.  Why do we assume that having
>post-reproductive-stage organisms die is beneficial to the population? 
>Sure, they can't add to the population directly, but I can think of any
>number of reasons why it would be a good idea to have them hang around.
> Here's a couple off the top of my head:

 It wasn't really Dawkins who came up with these ideas, it was some one 
else.. I don't remember who. You are right in some ways, the old 
specimens that aren't fertile anymore still interact with other lifeforms 
and therefor they are naturally under some sort of selection pressure. But, 
it can be much weaker than what it used to be when it was fertile.

>       Predator bait:  Predators prefer to take down slower, less fit
>prey.  Older organisms could act to prevent the predators from taking
>more fit, reproductively active organisms, and therefore increase the
>likelihood of species survival.

Yepp, the lethal genes makes them slower and they get eaten by predators. 
That is lethal genes that aren't there by chance, they could be there as a 
result of the selection pressure you mentioned.

>       Guardians:  Older organisms could provide care for the very
>young, freeing younger, more fit adults for hunting and other
>activities that require higher fitness.

I think that's right as far as fairly intelligent species are concerned. An 
insect can't really contribute to the survival of the young ones as they don'
t have enough neural mass to learn anything.

>       Has any done a simulation that includes aging?  And if so, what
>were the efffects?

Yes, that would be interesting!

Claes Andersson. University of Bors. Sweden
