From the perspective of an organism trying to propagate its genes, sex is like a trade: I’ll put half of your DNA in my offspring if you put half of my DNA in yours. I still pass one copy of my genes onto the next generation per unit of investment in children, so it’s a fair deal. And it doesn’t impact the average fitness of my kids very much, since on average my partner’s genes will be about as good as mine.
Wait, you seem to be assuming that both parents invest equally in the offspring, but in most (vast majority?) of species, one sex invests more than the other. In some species the male makes virtually no investment at all, and what you say here clearly do not apply to those species.
From an evolutionary perspective, males and females presumably get an equally good deal on the margin (or else the sex ratio would shift). That need not need to look like a productive investment in order to justify this basic picture (e.g. the story would be the same if males fought for territory and protected mates against other males).
If the low-investment sex doesn’t add value of any kind then it would change this picture. E.g. if males just compete for mates and then do nothing beyond mate, then females would get an advantage by cloning themselves. Maybe plants actually fit into this picture most straightforwardly of all.
(This would actually also happen if males invested 50%, if they couldn’t track paternity and females could secretly fertilize themselves.)
In the case where you get nothing in return, it seems like you are taking a 50% fitness hit from sex by passing on half as many genes. So if differences in fitness between kids were 5%, it would take about 300 generations for sex to break even. If fertilizing yourself is a complicated adaptation, then maybe that’s enough to stick with sex (after it evolves in some more equitable species) but it’s pretty different from my claim about breaking even in 6 generations. And in the case of plants or other hermaphrodites presumably there is an easier gradient to more self-fertilization, so that’s even more puzzling and maybe this would bring me back to the more usual view where there is something more to be explained (either evolution is surprisingly forward-looking, or we need some story about why the advantage is bigger than it looks).
Interestingly, this relates to our discussion about episodic vs non-episodic learning algorithms. In this case it seems clear that evolution is not episodic and assuming very large population sizes ought to maximize long-run inclusive fitness. So the puzzle here is that if it takes 300 generations for sex to break even, then if a mutation caused some member of a sexual species to start reproducing asexually, the sexual population would crash to 0 before it could recover.
My idea for solving this (which I just thought of now so take it with a grain of salt) is, because a sexual species can maintain a genome against a much higher mutation rate than an asexual species can (see past discussion), an asexual species needs to have a much lower mutation rate (i.e., much more machinery to prevent/repair mutations) to survive. When an asexual population arises from a sexual species, it doesn’t have the extra protective machinery and therefore quickly succumbs to accumulation of harmful mutations, perhaps before the sexual population can go extinct.
Or if it does drive the sexual population extinct first before itself going extinct, if most species are sexual then a phenotypically nearby species can just come occupy the now vacated niche.
Evolution isn’t episodic. In some sense the question motivating the OP was whether many of the important phenomena can come from being episodic with an appropriate utility function (something like exp(fitness) instead of fitness).
In some sense the question motivating the OP was whether many of the important phenomena can come from being episodic with an appropriate utility function (something like exp(fitness) instead of fitness
Wait, you seem to be assuming that both parents invest equally in the offspring, but in most (vast majority?) of species, one sex invests more than the other. In some species the male makes virtually no investment at all, and what you say here clearly do not apply to those species.
From an evolutionary perspective, males and females presumably get an equally good deal on the margin (or else the sex ratio would shift). That need not need to look like a productive investment in order to justify this basic picture (e.g. the story would be the same if males fought for territory and protected mates against other males).
If the low-investment sex doesn’t add value of any kind then it would change this picture. E.g. if males just compete for mates and then do nothing beyond mate, then females would get an advantage by cloning themselves. Maybe plants actually fit into this picture most straightforwardly of all.
(This would actually also happen if males invested 50%, if they couldn’t track paternity and females could secretly fertilize themselves.)
In the case where you get nothing in return, it seems like you are taking a 50% fitness hit from sex by passing on half as many genes. So if differences in fitness between kids were 5%, it would take about 300 generations for sex to break even. If fertilizing yourself is a complicated adaptation, then maybe that’s enough to stick with sex (after it evolves in some more equitable species) but it’s pretty different from my claim about breaking even in 6 generations. And in the case of plants or other hermaphrodites presumably there is an easier gradient to more self-fertilization, so that’s even more puzzling and maybe this would bring me back to the more usual view where there is something more to be explained (either evolution is surprisingly forward-looking, or we need some story about why the advantage is bigger than it looks).
Interestingly, this relates to our discussion about episodic vs non-episodic learning algorithms. In this case it seems clear that evolution is not episodic and assuming very large population sizes ought to maximize long-run inclusive fitness. So the puzzle here is that if it takes 300 generations for sex to break even, then if a mutation caused some member of a sexual species to start reproducing asexually, the sexual population would crash to 0 before it could recover.
My idea for solving this (which I just thought of now so take it with a grain of salt) is, because a sexual species can maintain a genome against a much higher mutation rate than an asexual species can (see past discussion), an asexual species needs to have a much lower mutation rate (i.e., much more machinery to prevent/repair mutations) to survive. When an asexual population arises from a sexual species, it doesn’t have the extra protective machinery and therefore quickly succumbs to accumulation of harmful mutations, perhaps before the sexual population can go extinct.
Or if it does drive the sexual population extinct first before itself going extinct, if most species are sexual then a phenotypically nearby species can just come occupy the now vacated niche.
Evolution isn’t episodic. In some sense the question motivating the OP was whether many of the important phenomena can come from being episodic with an appropriate utility function (something like exp(fitness) instead of fitness).
I don’t understand this. Want to elaborate?