I saw a presentation from an evolutionary biologist who may the point that we die because there is no evolutionary pressure not to die. Once we've birthed and raised out young, we are no longer relevant from an evolutionary perspective. He tested this with fruit flies by separating the young by gender for increasingly longer periods of time effectively delaying breeding so only the longer lived specimens could live to breed. By doing that over many generations, I believe he tripled the life expectancy of his test group.
Would you happen to have a link? I've been interested in toying around with this idea (just for fun) for a while, but I haven't started doing the actual research.
My instinct would be that (biological) immortality is (mostly) non-existant not only because there is no evolutionary pressure not to die, but because there is evolutionary pressure to die after begetting offspring. Very long lived progenitors would homogenize the gene pool, if not by incest then by sheer number of offspring. This would make them fragile in the face of both genetic errors and environmental shifts.
To counter this fragility, child birth might be infrequent. However, if child birth is infrequent, there is an increased probability of death before child birth.
No, that's group selection. If a progenitor could live a very long time and continue to produce offspring, it might be worse for the species, but it would be so much massively better for the individual's genes that those would be passed on.
In The Selfish Gene, Dawkins proposed that grandparents - obviously well beyond child bearing - can affect their gene propagation by caring for their grandchildren, at least indirectly.
What a true scientist; most people are content to think we dote on grandchildren as a civilized people with innate appreciation for new life. Rather, our genes will eradicate those who fail to help their offspring's offspring survive.
If you live longer you can have more offspring. Maybe constraints on your time and resources for raising offspring are really what prevent longevity from being much of an advantage?
There are plenty of examples of (admitted, simpler than humans) organisms which are effectively "immortal". The heat death of the universe will get them all, but human mortality is nevertheless a good deal more complicated than just entropy.
