It seems odd for mitochondria to be causing the mutation problem sex is supposed to solve, when mitochondria themselves don’t reproduce sexually.
Restricting mitochondria reproduction to one mating “type” does not by itself prevent a “selfish” mitochondria from arriving. If one mitochondria develops a new mutation, it is now competing against all the other mitochondria in that same organism without the mutation (like a cancer). But in fact the restriction goes beyond merely the “type”, as all the somatic cells are dead-ends for mitochondria.
Robin Hanson has a worthwhile post on why some organisms are exclusively male rather than being hermaphrodites capable of male & female mating “types”.
I think there’s an obvious problem with the theory of runaway sexual selection: once a trait gets deleterious, there will be selection for different preferences. As Lloyd theorized, initially there would be a preference against large breasts (it would indicate not being immediately fertile), but the trait could still get going because the male who mated with such a woman anyway would turn out to be making the right move (as it no longer signalled that). And in other species of animal, large breasts would be deleterious in females. They’re possible in humans because our females no longer have much need to outrun anything while while carrying such encumbrances (but there are still limits to that, which is why fantastically large breasts of the sort some men prefer are usually the product of surgery rather than genes).
Somatic cells are generally dead ends evolutionary. Your toe cells aren’t going to do much reproducing. Also, mitochondial (or in general organellar) DNA is split between the actual mitochondria and the cells containing them. Biology is fun!
The argument for mitochondria is that they cause the cell environment to be more toxic (what with them being the cell’s powerhouse). This in turn is going to provide a lot of selection pressure. In the same way e.g. global warming is causing a lot of selection pressure.
Runaway sexual selection has limits. This is also sort of the point. If you can carry around massive breasts, tails, noses or whatever and still be very prosperous, that means you’re good. Where “prosper” can mean running away from lions if you’re an antelope, or be the top of the village pecking order if you’re a human. Like a short pro basketball player. If they’re short, but still at a pro level, that’s someone you want on your team. This is known as the handicap principle, and can be explained via signaling mechanisms.
It seems odd for mitochondria to be causing the mutation problem sex is supposed to solve, when mitochondria themselves don’t reproduce sexually.
Restricting mitochondria reproduction to one mating “type” does not by itself prevent a “selfish” mitochondria from arriving. If one mitochondria develops a new mutation, it is now competing against all the other mitochondria in that same organism without the mutation (like a cancer). But in fact the restriction goes beyond merely the “type”, as all the somatic cells are dead-ends for mitochondria.
Robin Hanson has a worthwhile post on why some organisms are exclusively male rather than being hermaphrodites capable of male & female mating “types”.
Nikolas Lloyd has an evolutionary theory on why human females have breasts instead of teats (well before they even get pregnant).
I think there’s an obvious problem with the theory of runaway sexual selection: once a trait gets deleterious, there will be selection for different preferences. As Lloyd theorized, initially there would be a preference against large breasts (it would indicate not being immediately fertile), but the trait could still get going because the male who mated with such a woman anyway would turn out to be making the right move (as it no longer signalled that). And in other species of animal, large breasts would be deleterious in females. They’re possible in humans because our females no longer have much need to outrun anything while while carrying such encumbrances (but there are still limits to that, which is why fantastically large breasts of the sort some men prefer are usually the product of surgery rather than genes).
Somatic cells are generally dead ends evolutionary. Your toe cells aren’t going to do much reproducing. Also, mitochondial (or in general organellar) DNA is split between the actual mitochondria and the cells containing them. Biology is fun!
The argument for mitochondria is that they cause the cell environment to be more toxic (what with them being the cell’s powerhouse). This in turn is going to provide a lot of selection pressure. In the same way e.g. global warming is causing a lot of selection pressure.
Runaway sexual selection has limits. This is also sort of the point. If you can carry around massive breasts, tails, noses or whatever and still be very prosperous, that means you’re good. Where “prosper” can mean running away from lions if you’re an antelope, or be the top of the village pecking order if you’re a human. Like a short pro basketball player. If they’re short, but still at a pro level, that’s someone you want on your team. This is known as the handicap principle, and can be explained via signaling mechanisms.
The distinction between “somatic” and “germ” cells only exists for sexually reproducing species.