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Decius comments on Does evolution select for mortality? - Less Wrong Discussion
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Evolution doesn't select against immortality in any specific case. How could it select against it in general?
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.
Parsimony. It takes chemical resources (ie food) to produce any given thing the body uses, and there's selection pressure to use as little as it takes to do the job (ie produce further generations) because on the margins those who require fewer resources should outbreed those who need more. If most members of a species die in xty years or stop reproducing in those years, this creates parsimonious selection against the different needs of either an aged creature or a regenerative one.
... Except that it strongly selects FOR organisms that have an infinite number of offspring, regardless of other pressures.
Depends on when the reproduction happens. Say the organism becomes sexually mature in 20 years, then as far as evolution is concerned the organism 40 year old self is the equivalent of two addition offspring in the first litter. And that's assuming the organism is as good at reproducing at 40 as at 20.
It's all about the death rate from things other than aging, or how much immortality extends expected lifespan. Side effects of immortality which reduce competitiveness aren't inherent with immortality.
The premise is false. (Most straightforwardly: Females eat food and have a finite number of eggs.)
Therefore females who need not eat food and produce additional eggs die?
Therefore, there are specific cases where such an individual's inclusive fitness will be higher if she dies than if she lives. On account of the reproductive offspring not being starved.
Note that this is a rejection of the argument, not necessarily the conclusion.
What would happen to the offspring of an ageless mother in that circumstance?