Text 471, 84 rader
Skriven 2004-10-22 21:42:00 av Maurice Barnhill (1:278/230)
Ärende: Re: decrepitude
=======================


Name And Address Supplied wrote:

> "Peter F" <fell_trapforspambot_in@ozemail.com.au> wrote in message
news:<ckjj1c$spu$1@darwin.ediacara.org>...
> 
>>"Elaine Jackson" <elainejackson7355@home.com> wrote in message
news:ckhf8a$95v$1@darwin.ediacara.org...
>>
>>>>From an evolutionary standpoint, how does one explain decrepitude?
>>>
>>
>>There exists an evolutionary pressure that require that dads (and mums) drop 
>>off before they drain the environmental resources of their descendants to 
>>such an extent that the entire dynasty dies out. 
> 
> 
> That's a strong statement, and one which I find implausible. I'd be
> interested in seeing a (closed) model which favours such adaptations.
> 
I have been staying out of this for fear of having to do some 
work before I really want to, but here goes anyway.  I have 
written a simulation of a population on a lattice reproducing 
synchronously.  Once an individual occupies a site it owns it 
until its death, and the distance its offspring can move is 
limited.  Offspring from nearby sites compete for recently 
vacated "territories" on the lattice.  The idea is that on 
average, the descendents' fitnesses will be higher than the 
parents' due to the competition for vacant locations. Thus there 
would be an advantage for an organization to die if there was a 
larger chance of one of its offspring getting its spot than there 
was of a stranger.  Thus there would be a pressure for a finite 
lifetime.  That pressure could be detected by starting with a 
long-lifetime population and seeing the average lifetime decrease 
with generation number.  This may be happening in my simulation, 
but it is very difficult to detect.  It seems clear in a 
nonsexual population, but I did that run a while ago before 
learning about some of the hazards of interpreting the runs.  The 
effect is more clearly absent if both sexes disperse than if one 
is stationary and the other disperses.  I want to explore this 
possibility further, and perhaps see if something similar happens 
in the evolution of altruism.  Obviously the model I am trying to 
implement for aging is very similar to some of the ideas about 
the evolution of altruism among kin, and I believe that the two 
problems ought to be fairly closely related.

As a check of the model I implemented antogonistic pleiotropy in 
the organisms, and the decrease of an over-long lifetime is easy 
to see.

I have not (yet) attempted to implement semi-isolated 
subpopulations like some think you need to see evolution of 
altruism, and I have not (yet) looked for selection for altruism 
itself either.  The model needs recoding and the removal of a 
couple of oversimplifications at this point and I am distracted 
by other things.  I do think it is fair to say that it is 
difficult to obtain an optimum lifetime this way.  I don't think 
that it is yet safe to say that you can't.

I am a physicist, not a biologist, so this is an amateur 
operation.  However, unlike so many of my colleagues I feel that 
biology is much more difficult than physics, and I have been 
reading a little of the literature and talking to a biologist or 
two.  I have not been actively working on the model for the last 
few months because, frankly, I was hoping for the opposite 
result. However, I keep running into questions of various sorts 
that could be asked if the program were running to my 
satisfaction, so I am about to pick it up again.

-- 
Maurice Barnhill
mvb@udel.edu  [Use ReplyTo, not From]
[bellatlantic.net is reserved for spam only]
Department of Physics and Astronomy
University of Delaware
Newark, DE 19716
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