X-Message-Number: 7381
From: (Steven B. Harris)
Newsgroups:
sci.life-extension,bionet.molbio.agein,alt.health,bionet.sci-resource,sci.cryonics
Subject: Re: What is the oldest lived species on the planet?
Date: 30 Dec 1996 10:00:59 GMT
Message-ID: <5a83sr$>
References: <01bbf131$d6441c20$>
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Asks:
>>One question that I have that if answered should shed some
light on the aging process is what species is the longest lived
species on the planet?-I heard that the creosote bush can live
for up to 10,000 years in the desert, and that some trees on
mountain tops live 3,000 years plus, I think California redwoods
also live a long time. What is different about these plants as
compared to their shorter lived cousins that could account
for the longevity?<<
Comment: The longest lived plants are those that grow in
colonies, like creosotes and aspens and huckleberries. They are,
for all intents and purposes, functionally immortal (they can be
killed, but don't age). In such colonies, all the trees and
bushes are just offshoots of a single organism. What makes this
different from all other plants, is obviously that with colonial
plants you can loose a lot of differentiated tissue (a tree can
rot and fall, say) without killing the entire organism. This is
characteristic of ageless creatures: they don't have brains, or
any other differentiated tissue or non-repairable structure that
they cannot afford to lose. A redwood, by contrast, can live a
long time, but "ages" as its heartwood rots. Eventually, it's
going to fall, and that's the end of it. (NB, I for one do not
believe that some fish claimed to be "ageless," really are. I
think we just haven't followed them long enough).
>>Also, I have heard that the Galapagos tortise is the oldest
living animal at 150 years maximum life span-why is this?<<
See below.
>>And finally that a study shows that in general the higher
the metabolic rate of an animal the shorter its lifespan. Now
this is true and there is a constant function across species
except for one...Birds-which have a very high metabolism yet many
can live as long as much larger land animals with slow
metabolisms-why is this?<<
First of all, it's not true across species except for "one."
There are several outstanding classes of organisms that get a lot
more metabolic time (lifespan) than they should for their size.
The standard explanation for this, is that nature will postpone
aging, and give an animal more metabolic time to reproduce, *if*
the animal is less subject to death by misadventure, or
predation (there's no point in spending the food energy to repair
an animal that is just going to get eaten-- better to divert food
energy in such animals to reproduction). Thus, animals with a
particularly good mechanism for avoiding death by misadventure or
predation, will age more slowly (all other things metabolically
being equal).
Birds age more slowly than mammals of their size, and far more
slowly than mammals of their metabolic rate. Why? Birds have
wings, a neat trick to avoid predation. This is illustrated by
the fact that among mammals, bats live as long as birds. Even
bats which don't undergo torpor, may live ten times as long as
mice in their metabolic class. That's what wings do for you.
Among the rest of the mammals, primates stand out-- presumably
because big brains are almost as good as wings for keeping you
alive. The little capuchin (organ-grinder) monkey gets almost as
much metabolic time as humans do. Being a good and fast climber
is probably almost as good as being a ground-hugger and tool
user.
Finally, reptiles live longer than mammals of their size,
because of their slow metabolic rate. Within reptiles, turtles
live the longest for their size, because of the neat trick of
having a shell. The largest turtle known thus takes the prize in
both categories, and that's the explanation for the Galapagos
tortoise. These animals (until the recent coming of man, which
evolution hasn't taken into account) also had an especially low
predation rate because of their isolated and oceanic
environment. Isolated islands are a good place to avoid big
predators, because big predators aren't often carried over vast
stretches of ocean alive.
Now, I have to confess that some of this sounds to me like a
"just so" story, and there are still a few things to explain.
Like: why don't killer whales and elephants live longer? Here's
my first thought: elephants basically die in the wild when their
last set of teeth wear out (after molars are replaced 5 times, in
sets of 4, rather than replaced once in a set of 12, as in
humans). The mammal design only allows for 24 total molars in a
life time, it seems, and perhaps there is a fundamental physical
limit as to how hard these molars can be, if constructed of the
usual materials. I dunno. As for killer whales, I'm at a loss,
but perhaps a similar tooth problem operates.
Evolution can postpone aging if there is an advantage to it,
you see, but evolution cannot totally redesign, wholesale,
systems which are already in place, for this purpose. So perhaps
some large animals with a tooth-unfriendly life style, get nailed
that way, needing the kind of upkeep that evolution simply cannot
do (it's rather amazing that evolution has done as much with
elephants' teeth as it has). In such animals, cellular aging
might in theory be capable of letting them go on for a longer
time, but their teeth aren't up to it. And of course, evolution
isn't going to repair the rest of a body of a mammal to a
standard any better than is set by the fatal wear and tear on its
teeth (that is, if the animal is one which can't adapt to losing
all of its teeth, which is the case for all animals with the
possible exception of humans). It's the same deal as with
predation: if one part of an animal is weak and can't be fixed,
why should mother nature waste the energy on repairing any of the
rest of its body to a better standard? So elephant teeth "age"
prematurely, and the rest of the elephant, in consequence, ages
just as fast (i.e., don't expect zoo elephants to exceed the
species lifespan by much, even if fed soft foods). Insectivores
and fruitivores like bats and birds might luck out in this
regard, but top herbivores that have to eat tough plants, and top
carnivores that have to bite bone for a living, perhaps have a
real problem.
Your Faithful Just-So-Storyteller
Steve Harris
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