Re: Body Temperature

From: Tim Tyler (tim_at_tt1lock.org)
Date: 07/07/04 

Date: Wed, 7 Jul 2004 10:08:57 GMT

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. 

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