>Subject: Re: Cornering the causes of aging (was Re: AGING: Accumulation of
>Date: Wed, 5 Jul 2000 10:40:59 EDT
>In a message dated 7/1/00 10:32:34 PM, email@example.com writes:
> >and (ii)
> >>the negative benefits of loading the genepool with archaic
> >>the face of rapid environmental change....
> >Nicely put. Wish you had been available twenty years ago to debate the
> >gurus of life extension. This was also W. Donner Denkla's position, BTW,
> >but the problem was that the prior generations couldn't think very well
> >terms of "systems." They refused to see beyond the genetic driving force
> >the individual survival. Thus, they utterly rejected out-of-hand any
> >arguments for the existence of a "death gene," or "aging clock."
>You misunderstand how biologists came to the conclusion. The effects of
>selection other than individual survival were considered carefully, and
>found to be negligible compared to individual survival.
Not the impression I got. I used to be an ALCOR member and I recall the
derisive comments I got for suggesting anything other than individual
survival could be a factor. When I brought this up to various authorities
at different conferences, I got the same response. No one ever suggested
that any kind of careful analysis had been done.
>an "aging clock" is equally disadvantageous to a group; since it entails
>direct reproductive loss (death of perfectly functional individuals)
>the group is at a serious disadvantage compered to groups that don't
>off perfectly serviceable individuals. "Archaic" gene combinations
>aren't generally bad - in the case of stabilizing selection, genetic
>drift, and fast fluctuating selection, they are better. In any case,
>old individuals with bad genes will be dead anyway; continued survival
>is an excellent demonstration of quality.
To the contrary, it is quite conceivable that a series of environmental
fluctuations could wipe out a long-lived species, while a short-lived one
would survive. This is not an either-or situation, obviously. Optimum
lifespan for the purpose of species survival is a balance.
Let's imagine a species - of bacteria, for example - that can only reproduce
within a narrow temperature range, although it can survive quite well over a
much broader range. Within this species, however, there are always a few
mutants, recessive genes, etc., for other temperature ranges scattered
If the species is subject to wide fluctuations of temperature, relative to
the reproductive range, over time spans longer than the usual time between
dividings, then if the species is not subject to aging and has a probably
lifespan due to other factors that is several times that of the typical
duration of temperature swings that take it out of the reproductive range,
then there is a good likelihood that a large enough number of the
non-reproductive species members will be around to reduce the food supplies,
etc., for the minority who may have the genes necessary to keep the species
There is always a probability that the temperature will fluctuate back to
the advantage of the original dominant genotype, in which case they will
provide a species advantage. So the relative probabilities of different
fluctuation values plays into the final optimum. However, there will be
times that an aging gene itself, or a genetic clock, would be to the species
Often factors - such as temperature extremes - may effect young,
pre-reproductive age species members more than mature, physically larger,
more experienced members. Imagine a troop of mountain gorillas, with an
alpha male who doesn't age. His hair and massive body size give him a lot
of resistance to cold relative to a baby. If this is a species that grants
virtual total breeding rights to the alpha male, then if there is a change
in climate to the colder side, so few of his babies may survive, due to lack
of cold adaptation, that eventually the troop itself will dwindle from
attrition to nothing.
In real life, the alpha male will eventually get old and feeble and be
replaced by the strongest available successor - likely one of the more
cold-adapted ones who survived babyhood. Since semi-permanent climatic
changes usually take a fair amount of time - decades to centuries for ice
ages to come on - the turnover of alpha males favors the matching of
genotype to environmental need.
I suspect that, even more so, any of our ancestors over the past million
years would have gained a major genetic advantage thru not aging. As we
have gotten smarter and stored more of our survival information in memes as
opposed to genes, the survival advantages of a longer life have increased
drastically. Even much less intelligent species show greatly improved
survival competence thru experience.
When you look at really primitive peoples that most closely resemble how we
lived for most of the past million years - the natives of the New Hebrides
being the best example I have run accross - you see that the males either
died young from disease or being murdered for ritual canibalism or they live
to be a ripe old age. Men in their 50's there still look like they just
stepped out of the Jack LaLane's power weight-lifting area. If age didn't
kill these guys, they would likely survive well over one hundred years, and
the smarter ones might last a LOT longer.
Thus, no matter how maladapted the genes - virtual total lack of resistance
to a new plague that this particular individual survived because he had
lived so long that his immune system had encountered something similar -
cowpox, e.g. - the immortal continues to pass them on, dooming the majority
of his progeny, and thus his branch of the species.
At the same time, those of his progeny who were themselves immortal - or at
least relatively long-lived, would also dominate their local gene pools,
also reducing genetic turnover and making it possible for a real disaster to
wipe out the entire gene pool, especially if there is competition from
outside - e.g., Neanderthal vs. CroMagnon.
I would argue - and have argued since the '70's that it is likely that a
genetic clock is so essential and it is so necessary to species survival,
that it must be hardwired into the deep structure of the code. It is
probably tied into other essential functions - as the telomeres are tied to
cancer resistance, so that any temporary niche advantage is more than offset
by immediate downside effects. I.e., you stop aging and shortly thereafter
die of twenty different kinds of cancer.
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