Death is eventually inevitable in all likelihood, due to predation, illness, accident, etc. So, mutations that confer short term advantages to reproductive fitness in exchange for problems in the distant future are a good deal, from a Darwinian perspective. On the other hand, a mutation that only pays off in the long run, with little effect early in life or a disadvantage in early life, are unlikely to become fixed in a population.
The collective effect of these short-sighted tradeoffs are "the aging process", or at least part of it.
This is all loose and speculative, but there is, I think, some support for this. I think. At the very least, it makes sense - I don't think you have to invent some fitness advantage for death.
I don't think there is an evolutionary advantage to aging; aging may be "genetically programmed", but only indirectly; see my first post in the thread. It's not that there are genes "for" aging, rather aging may be the side effect of genes "for" something else.
Aging isn't selected for; rather short term reproductive benefits are selected for regardless of the their cost later in life.
Better to reproduce like they vote in Chicago - early and often. Or, to paraphrase another cliche, Reproduce and be merry, for tomorrow we die of the plague, or are eaten by a lion.
I don't think this sort of explanation makes any evolutionary sense. In the phrasing of Dawkins, genes are "selfish". They're also "blind" - they can't look ahead. Either they work for the organism currently, or they don't work for the organism currently. There are no Darwinian (or other evolutionary) mechanisms that can look ahead and see that an organism's replacements will be better, thus the current individual should die off.
So, suppose an organism has an "Immortality" mutation, and survives predation, disease, accidents, and natural disasters to pass on the gene to many offspring. ASSUMING this has a large benefit (which it may not, if the species of organism in question tends to die due to one of the above causes anyway), then this should spread rapidly. One might imagine this could cause a population explosion.
So let's assume we have a situation where the immortality gene confers a large advantage, and the population gets huge. Now you have a big population, including many "Methusalah"s. Resources are scarce. Food is hard to come by, because a bajillion similar organisms are competing with each other. The older population isn't going to evolve - they have their immortality gene already. So forget about them.
What's going to happen to the youngsters born with a defective immortality gene? Is the lack of immortality going to confer any sort of reproductive advantage? On the time scale of their life, no. They'll tend to leave fewer offspring.
Even so, let's assume that some sub-group emerges without immortality, enough that the population decreases a little, and there is less competition.
This is good for the non-immortal offspring, right? Yes. Does it give them a competitive advantage? No! The immortal competition is benefitting from the reduced competition as well, PLUS they have the reproductive advantage of immortality!
I can't come up with any scenario which would select "for" aging and death. Rather, aging and death seem to be best explained as the side-products of other processes, not adaptations in and of themselves.
-Zhimbo, who suspects Syamsu will have a seizure if he reads this post.
[This message has been edited by Zhimbo, 10-25-2003]