An interesting paper on aging in bacteria illustrates some of the present thinking on the evolutionary roots of aging; in this case, that aging seems to be an inevitable consequence of the cellular model of life.
Aging refers to a decline in reproduction and survival with increasing age. According to evolutionary theory, aging evolves because selection late in life is weak and mutations exist whose deleterious effects manifest only late in life. Whether the assumptions behind this theory are fulfilled in all organisms, and whether all organisms age, has not been clear. We tested the generality of this theory by experimental evolution with Caulobacter crescentus, a bacterium whose asymmetric division allows mother and daughter to be distinguished.
Our results confirm that late-acting deleterious mutations do occur in bacteria and that they can invade populations when selection late in life is weak. They suggest that very few organisms - perhaps none - can avoid the accumulation of such mutations over evolutionary time, and thus that aging is probably a fundamental property of all cellular organisms.
You might recall that aging in bacteria was demonstrated back in 2005; previously it was thought that bacteria might be effectively immortal. This hypothesis of aging as an inevitable consequence of evolution in cellular life versus present studies of those forms of cellular life that might be immortal will make for good science in the decades ahead - but it is largely irrelevant as to how aging in humans proceeds from here on out. Evolution's days are all but over, and the invisible hand of the market will take over as technology enables individual humans to shape themselves rather than be shaped.
When people can choose between degenerative aging or no degenerative aging, I imagine there won't be a great deal of degenerative aging in the world - much the same as for the smallpox/no smallpox choice that became available in recent times, for example.