In a message dated 11/21/99 3:41:09 PM Pacific Standard Time, firstname.lastname@example.org writes:
> Does that imply that Evolution selects for
> shorter life-spans under certain circumstances?
It never selects for shorter lifespan per se. Shorter lifespan may evolve
it comes as part of a beneficial package-deal or because longer lifespan is to hard to select for.
> I still find it difficult to
> fathom why a population that reproduces or completes its life cycle in
> the time of a competing population does not garner an advantage for itself
> that it can adapt to changing environmental conditions twice as fast.
The *population* garners an advantage (assuming the environment is changing). But, *all* alleles in the population get the same benefit. Alleles for extended survival (hypothetically with no other effect) are effectively "cheaters" and oust competing alleles for short lifespan because they also get the benefit of their carriers reproducing longer.