Selecting against immortality itself would (in my view; apparently not in everyone’s) be almost an oxymoron.
But there are other ways that shorter-lived variants might be preferred by selection. The major proposed ones have in common the idea of tradeoffs: that the genes for mortality at an old age also increase fitness at a young age more than enough to compensate. The mechanism might be e.g. investing a lot of energy into producing eggs, versus investing a lot of energy into building a durable long-lived body.
I don’t think that a durable, long-lived body (for the purposes of this discussion, call it a mammal that does not lose reproductive fitness with age) has ever existed in large enough numbers to influence the gene pool.
There is little evolutionary pressure to remain reproductive for an entire lifetime if that lifetime is not much longer than the current reproductive lifetime; likewise there is little evolutionary pressure to extend the overall lifetime far beyond the reproductive lifetime. It’s possible, but by no means certain, that the two are unrelated.
Almost all animals can reproduce as long as they’re alive. They may become less fertile with age, but not totally unfertile. The menopause of human women is not uniuque, but it is very rare.
How fertile is a 30-year old dog? I meant ‘lose reproductive fitness with age’ to be inclusive of all semi-deterministic effects of age, not just menopause.
I would expect a 30-year old dog to be as fertile as it is generally healthy. In other words, I expect fertility not to decline much sooner than the rest of the body. If it does, we recognize it as something special, like the menopause.
There’s a problem predicting purely from theory. No single component or function (whether fertility or something else) would normally age faster than the others, because evolution would select against that. But if a crucial function like fertility stopped working after a certain age and there weren’t any selectable variants that kept it working longer, then animals that lived longer but were infertile wouldn’t have a much greater fitness than those who died as soon as they became infertile, and we would see the same result—animals being fertile roughly as long as they live.
If … there weren’t any selectable variants that ….
Exactly- There have never been selectable variants that are immortal (or even nearly so). Whether that is because immortality is hard (unlikely to result from random drift) or not is irrelevant for the purposes of natural selection if it never happens.
Selecting against immortality itself would (in my view; apparently not in everyone’s) be almost an oxymoron.
But there are other ways that shorter-lived variants might be preferred by selection. The major proposed ones have in common the idea of tradeoffs: that the genes for mortality at an old age also increase fitness at a young age more than enough to compensate. The mechanism might be e.g. investing a lot of energy into producing eggs, versus investing a lot of energy into building a durable long-lived body.
I don’t think that a durable, long-lived body (for the purposes of this discussion, call it a mammal that does not lose reproductive fitness with age) has ever existed in large enough numbers to influence the gene pool.
There is little evolutionary pressure to remain reproductive for an entire lifetime if that lifetime is not much longer than the current reproductive lifetime; likewise there is little evolutionary pressure to extend the overall lifetime far beyond the reproductive lifetime. It’s possible, but by no means certain, that the two are unrelated.
Almost all animals can reproduce as long as they’re alive. They may become less fertile with age, but not totally unfertile. The menopause of human women is not uniuque, but it is very rare.
How fertile is a 30-year old dog? I meant ‘lose reproductive fitness with age’ to be inclusive of all semi-deterministic effects of age, not just menopause.
I would expect a 30-year old dog to be as fertile as it is generally healthy. In other words, I expect fertility not to decline much sooner than the rest of the body. If it does, we recognize it as something special, like the menopause.
There’s a problem predicting purely from theory. No single component or function (whether fertility or something else) would normally age faster than the others, because evolution would select against that. But if a crucial function like fertility stopped working after a certain age and there weren’t any selectable variants that kept it working longer, then animals that lived longer but were infertile wouldn’t have a much greater fitness than those who died as soon as they became infertile, and we would see the same result—animals being fertile roughly as long as they live.
Exactly- There have never been selectable variants that are immortal (or even nearly so). Whether that is because immortality is hard (unlikely to result from random drift) or not is irrelevant for the purposes of natural selection if it never happens.