> it is difficult to see how natural selection could have selected for senescence, because we don’t reproduce in our elderly years and natural selection is driven by differences in reproduction rates
That's an entirely backwards way to look at the problem: selection works with living organism and the only reason an organism lives or performs a particular function is that it was evolutionary useful to do so for it's genes. Aging therefore is something natural selection can't discern on: at some point, the number of additional offspring that can be produced becomes negligible compared to the exponentially increasing probability of death from environmental causes (just like the test tube example); so organisms that quickly reproduce young are much more successful than long lived organisms.
It's easy to see then, why the long term accumulating damage, irrelevant for a young organism, can't be evolved out of. We are essentially "single use" from an evolutionary standpoint.
Therefore, advanced age (anything exceeding useful reproductive life) is something outside evolution. Anything happening at senescence time is simply a byproduct of the mechanism selected for ensuring success at young age, a system that continues to work by momentum and not design or selection, up to the inescapable moment when entropy catches up to it.
But there is no fundamental physical reason for it, and it stands to reason we could create biological machines that maintain the power to self repair indefinitely, given suficient outside energy. It's just enormously more complex than "curing aging", it means artificially redoing billions of years of evolutionary choices that were good enough for reproduction. It's a God level task.
There are second-level effects where longevity can increase gene frequency: In a social species like humans or some whale species, the presence of parents and even grandparents can have positive effects on the survival of offspring, long after the older generation has stopped producing offspring.
I don't know evolutionary biology enough to estimate how big of a selection pressure that is, though. Maybe much lower than first-order effects, maybe not so much.
> But there is no fundamental physical reason for it, and it stands to reason we could create biological machines that maintain the power to self repair indefinitely, given suficient outside energy.
I agree, I would say there is a strong second order effect for parents to see their siblings to reproductive age. As more generations stack up, any longevity effects quickly become negligible, maybe with the exception of hiper-social species with a learned culture like ourselves. Since this development is very recent, I don't think it could affect such a fundamental thing like aging.
Per Google, our closest living relatives, chimps and gorillas, very rarely display grandparenting behavior and have comparable lifespans.
That's an entirely backwards way to look at the problem: selection works with living organism and the only reason an organism lives or performs a particular function is that it was evolutionary useful to do so for it's genes. Aging therefore is something natural selection can't discern on: at some point, the number of additional offspring that can be produced becomes negligible compared to the exponentially increasing probability of death from environmental causes (just like the test tube example); so organisms that quickly reproduce young are much more successful than long lived organisms.
It's easy to see then, why the long term accumulating damage, irrelevant for a young organism, can't be evolved out of. We are essentially "single use" from an evolutionary standpoint.
Therefore, advanced age (anything exceeding useful reproductive life) is something outside evolution. Anything happening at senescence time is simply a byproduct of the mechanism selected for ensuring success at young age, a system that continues to work by momentum and not design or selection, up to the inescapable moment when entropy catches up to it.
But there is no fundamental physical reason for it, and it stands to reason we could create biological machines that maintain the power to self repair indefinitely, given suficient outside energy. It's just enormously more complex than "curing aging", it means artificially redoing billions of years of evolutionary choices that were good enough for reproduction. It's a God level task.