X-Message-Number: 11843
From: Thomas Donaldson <>
Subject: about aging and evolutionary reasons for it
Date: Sat, 29 May 1999 00:59:26 +1000 (EST)

To Yvan Bozzonetti:

There is and has been for some time a good evolutionary theory to explain 
the existence of aging. I've actually discussed this several times, but
here are a few sources:

GC Williams, Pleiotropy, natural selection, and the evolution of
senescence, EVOLUTION 11(1957) 398-411

GC Williams has published a number of more popular things lately but so
far as I know he hasn't discussed aging in any popular source.

Two other researchers into evolution have looked in more detail at the
basic ideas which originated with Williams:

JM Emlen, Age specificity and ecological theory, ECOLOGY 51(4)(1970)

WD Hamilton, The moulding of senescence by natural selection, 

There have been a number of experiments looking at evolutionary factors
since then. The above are quite basic papers.

The fundamental idea that Williams pointed out was that evolution does
not act on creatures which have already died. To explain that point 
more clearly, most animal populations die in nature some time before they
would come close to becoming "old" in our terms. Even most human beings
had a similar fate until quite recently, though people in the upper
classes did live longer. This means that you become old basically because
the systems needed to keep you in top shape at high ages never had any
pressure to evolve to do so at high ages... you'd already died of other
things (diseases, accidents, etc etc). It also has a corollary: if we
maintain our current lifespans, then even without any special effort
(not that this would help us!) we would eventually evolve to live long
enough so that we would not naturally become old at, say, 100, but only
at ages most people would have died by accident. (I'm not in favor of
doing this, of course, but the frequent occurrence of old age NOW is
a sign that we're under slow evolutionary pressure to live longer).

Some people have argued that aging has some positive effects and is
supported by evolution. Hamilton and others have looked at the mathematics
of this in detail, and basically find (as with most such things) that
yes, we can make up extreme circumstances which do not fit our present
situation at all but in which there really are evolutionary reasons for
aging. Does that mean anything? Well, it means that with lots of
imagination we can come up with situations quite unlike our own.

Naturally I want advances which apply to ME, not to any putative 
descendants several generations from now. These ideas do not tell us to
sit by and let evolution take its course. What they do provide is an
answer to all those people who still think that aging and death is
somehow favorable "to the species". No, it is not at all.

Finally, I will add that even some increase is helpful, because we can
then hope to live longer and get further increases. At the same time,
as someone who has been both concerned with this problem, and reading the
science about it for decades, I strongly suspect that abolishing aging
entirely will ultimately require some redesign. Not that such redesign
is bad in any way ...what does evolution do, after all? But we'd want
to do it by taking things in hand ourselves.

			Best and long long life,

				Thomas Donaldson

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