Re: Newbie Questions

On Oct 10, 3:20 pm, Rusty Sites <SpameYou...@xxxxxxxxxx> wrote:
Friar Broccoli wrote:
On Oct 9, 12:58 pm, John Harshman <jharshman.diespam...@xxxxxxxxxxx>
wrote:
Friar Broccoli wrote:
On Oct 9, 12:16 pm, John Harshman <jharshman.diespam...@xxxxxxxxxxx>
wrote:
Don Tazemebro wrote:
Just a couple evo questions I wondered about:
1. Why hasn't evolution favored significantly longer lifespans? We
live longer due to health and diet issues, but it seems like over
millions of years, lifespans of many species would be very long, as
raising young seems comparatively time consuming and risky.
Mostly because living itself is time-consuming and risky. If you're
likely to be eaten by a predator before you're two years old, there is
little expected profit in spending more on longevity than on immediate
reproduction. The life histories of organisms are tailored by selection
to their environment. Everything has a cost, and selection balances the
costs and benefits. In fact it's very hard to find any evidence in
nature of old age. Most species live long enough to die of other causes
before they show signs of senescence.
I've heard this before, but am somewhat sceptical that it is a
complete explanation. My conjecture has always been that short
life spans are a positive benefit for some species because it
creates the conditions for faster adaptation, which would be
advantageous for invading new environments and living through
periods of rapid ecological change.
Is there any reason why this explanation is not plausible?
Yes. It requires that the species be adapted to change on a scale much
longer than individual lifespans. Or it requires anticipation of future
needs. Or it requires group selection. The last is possible, but the
standard argument agiainst group selection applies, that it's very weak
by comparison with natural selection.

Lynn Caporale in: "Darwin In the Genome: Molecular Strategies
in Biological Evolution" appears to be arguing IN EFFECT that
species do adapt on a scale longer than a single lifespan,
although the selection actually takes place in individuals
living through a crisis or a (near) extinction event. That is
that all the species that make it thru drastic changes are the
ones that can throw up a lot of variation quickly.

If your idea did work, it would create the conditions for its own
disappearance, since shorter-lived individuals would cause the
population to be less able to maintain long-term adaptations for
flexibility, such as short lives. They would instead respond to
shorter-term influences, which might conflict with those long-term
adaptations.

Her argument is a bit more subtle than my summary above, and
thereby (in my view) handles this problem. She points out that
particular structures in DNA are particularly prone to mutation,
and gives lots of examples where animals have highly error prone
copying in specific areas. She goes on at some length about an
extremely venomous snail whose poisons are coded for in such an
area. (I'm at work now, but can look up the reference if you
don't already know).

So if species are going through regular screening events (near
extinctions or environment shifts) that select for the fast
adapters, I cannot see why these characteristics would not be
retained unless they impose a burden in the short term. Thus,
when genetic hot spots don't occur in mission critical areas
like cell wall structure, but do occur in areas where change is
likely to be beneficial (like say bone length/size) then I would
expect them to be retained.

Shorter life spans would amplify this ability to adapt, and
would thus be retained especially if it allowed the users to
quickly spread into new niches. In this respect viral,
bacterial and other parasites are (I think) instructive extreme
examples.

Reproducing early in life would be an advantage and allow for faster
adaptation, but dying early could only help by getting less adapted,
earlier individuals out of the way. If they are less well adapted, that
would be predicted to happen anyway. Meanwhile, the individuals that
lived longer and kept reproducing would be pushing out the quick dying
strains. I really don't see how dying early offers any advantage. It
seems as if the answer really is that aging is just not selected against
very strongly because in nature disease, predation, starvation, and
accidents claim most before aging becomes much of a factor. The "use it
or lose it" rule applies indirectly, I think. Aging is not an
advantage, but some of the random mutations the lead to more
reproductive success might allow aging to proceed more rapidly without
much penalty for doing so. If there were, to oversimplify things,
anti-aging genes, they would not be very well protected by selection.

I am gradually coming around to the point of view that selection
in favor of a short life span is a completely nutty idea. I still
have
an internal dialogue going on, but don't think it can overcome the
weight of the obvious.

Cordially;

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------

.

Relevant Pages

  • Re: Newbie Questions
    ... Why hasn't evolution favored significantly longer lifespans? ... The life histories of organisms are tailored by selection ... Most species live long enough to die of other causes ... flexibility, such as short lives. ...
    (talk.origins)
  • Re: Newbie Questions
    ... The life histories of organisms are tailored by selection ... Most species live long enough to die of other causes ... longer than individual lifespans. ... flexibility, such as short lives. ...
    (talk.origins)
  • Re: Newbie Questions
    ... Why hasn't evolution favored significantly longer lifespans? ... selection balances the costs and benefits. ... Most species live long ... in favor of a short life span is a completely nutty idea. ...
    (talk.origins)
  • Re: Newbie Questions
    ... Why hasn't evolution favored significantly longer lifespans? ... selection balances the costs and benefits. ... Most species live long ... in favor of a short life span is a completely nutty idea. ...
    (talk.origins)
  • Re: Newbie Questions
    ... Why hasn't evolution favored significantly longer lifespans? ... selection balances the costs and benefits. ... Most species live long ... in favor of a short life span is a completely nutty idea. ...
    (talk.origins)