Re: Body Temperature

From: Steve Harris sbharris_at_ROMAN9.netcom.com (sbharris_at_ix.netcom.com)
Date: 07/07/04 

Date: 7 Jul 2004 11:32:24 -0700

Tim Tyler <tim@tt1lock.org> wrote in message news:<I0H86x.v3@bath.ac.uk>...
> Steve Harris wrote or quoted:
>
> Re: Good specific metabolic rate * lifespan = constant article:
>
> > Big exceptions to the rule are primates like capuchins and humans, and
> > we both have very large brain/body wt ratios. So evidentally large
> > brains are such a good evolutionary trick against predation that it's
> > worth it for evolution to spend time repairing us, and thus we age
> > more slowly metabolically and get 3 billion heartbeats in a lifetime,
> > instead of the standard billion for mice, cats, cows, etc.
>
> There are other explanations for an effect of large brains
> on lifespan that don't mention predatiton - so the effect
> of brain power on lifespan via reduced predation is not
> all that evident.
>
> The more usual arguments about the effect of large brains on
> lifespan invoke a mixture of developmental plasticity and
> neotony to explain the effect.
>
> Large brains are there to help cope with a complex variable environment.
> Large-brained organisms are less hard-wired up at birth, and more
> programmable by environmental influcences. Environmental programming
> takes its time to occur - so brainy creatures tend to have long
> childhoods - and typically are not sufficiently competent to
> reproduce for some time after being born.
>
> The whole large-brain, long childhood thing can be produced by
> twidlling some developmental rates downwards - and this tends to
> retard both development and aging.
>
> Longer childhoods and later puberty tend to stretch out the whole
> developmental program - including its final stage: senescence.

COMMENT:

Interesting thought, but it hardly explains why humans get about the
same metabolic time as Capuchins, which mature in a far, far lower
fraction of their total life span than do humans. Capuchins are
sexually mature at 2, but may live 40 years. If humans were ready to
go out on their own and breed at 6, your theory might hold water.

It's also an overly complicated hypothesis, since it posits one reason
for delayed aging in primates (neoteny for purposes of programming),
and at least one other for mammals and birds with wings, and reptiles
with shells. But if the anti-preditor effect has an effect on aging in
winged and shelled animals, it would be difficult indeed to see why it
shouldn't have an effect for animals with brains, too, as it surely
must in humans.

SBH

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