Re: longevity
Sun, 21 Nov 1999 19:17:07 EST

In a message dated 11/21/99 3:40:49 PM Pacific Standard Time, writes:

> Curt Adams wrote,
> >It can, it's just that any individual advantages will overwhelm the group
> >advantage.
> So, if individuals who live shorter than average lives produce more
> because of their shorter life cycle, would this tend to overwhelm an
> group tendency toward greater longevity?

No, if the extra reproduction gained early exceeds that forgone late (due to earlier
death), then the mutation is beneficial to the individual's reproductive fitness. There
is actually a benefit to faster generation times, since offspring born early start
reproducing earlier. But what counts is the benefit to the organism's reproductive
fitness. Having more offspring early *and* surviving late would be even better than
early offspring and early death, it's just often not possible.

> If reproductive frequency varies among individuals (which, as you point
out, it
> does), aside from offering an advantage in the form of increased
> mutability, doesn't faster reproduction give speedy breeders a numerical
> advantage, since their genes would increase in the group faster than the
> of slower reproducers?

Dying early, per se, does not improve your rate of reproduction. If an allele which
hastens death *also* improves net reproduction yes, it will spread through the population. Such things appear reasonably common in real life. However, any affect on increased evolutionary rate is negligeable - it's the fast reproduction
which makes the allele spread.

> Could shorter life spans, which would increase the frequency of
> such occurrences, accelerate the Evolution of the entire group? --J. R.

It could, just as mutagenesis can increase evolutionary rates in the lab. However, if the shorter lifespan is in any meaningful way detrimental to the fitness of individual organisms, it will be lost anyway.

Incidentally, according to many punctuated equilibrium models, most organisms are already pretty much adapted to their environments. Evolution then becomes a matter of selection weeding out the continual onset of deleterious new mutations. In that case a shorter generation time is no help; you're getting more mutations from the faster reproduction.