There’s another problem with iterated embryo selection that I haven’t seen accounted for. I don’t recall the exact numbers, but some surprisingly large fraction of natural human pregnancies result in a spontaneous abortion. Exact causes of this may vary, but I think a significant fraction of those are simply not viable due to genetic mutations. Adult parents have at least proven they have the genes necessary to both survive until adulthood and find a mate. Embryonic parents haven’t proven that. Certainly we can use genetic tests to screen them for known genetic diseases, and that is kind of the point, but how do we screen them for unknown genetic diseases?
Searching around the web, it looks like most miscarriages are due to aneuploidy. That would be easy to detect and select against.
It’s hard to find good numbers for the human mutation rate. I saw numbers ranging from 42 to 200 per generation. Sperm seem to have more mutations than eggs on average. It can vary based on environmental exposure to mutagens, and older parents tend to have more mutations on average. Perhaps embryonic parents simply wouldn’t have the time to accumulate many mutations. On the other hand, one has to do unnatural things to get these embryonic cells to turn into gametes. If any of these steps are mutagenic, then the mutation rate could be even worse.
I feel confused wrt the genetic mutation hypothesis for the spontaneous abortion phenomenon. Wouldn’t genes which stop the baby from being born, quickly exit the gene pool? Similarly for gamete formation processes which allow such mutations to arise?
Wouldn’t genes which stop the baby from being born, quickly exit the gene pool?
Yes, by killing the fetus before it’s born. New mutations still happen all the time. Usually they hit junk DNA and not much happens, but what if it breaks something vital? And it’s possible to inherit deleterious recessive alleles from both parents. That why incest is still a problem, from a genetic standpoint.
Similarly for gamete formation processes which allow such mutations to arise?
And yet we still have transposons. Evolution requires some amount of mutation, which is occasionally beneficial to the species. Species that were too good at preventing mutations would be unable to adapt to changing environmental conditions, and thus die out.
Evolution requires some amount of mutation, which is occasionally beneficial to the species. Species that were too good at preventing mutations would be unable to adapt to changing environmental conditions, and thus die out.
We’re aware of many species which evolved to extinction. I guess I’m looking for why there’s no plausible “path” in genome-space between this arrangement and an arrangement which makes fatal errors happen less frequently. EG why wouldn’t it be locally beneficial to the individual genes to code for more robustness against spontaneous abortions, or an argument that this just isn’t possible for evolution to find (like wheels instead of legs, or machine guns instead of claws).
There’s another problem with iterated embryo selection that I haven’t seen accounted for. I don’t recall the exact numbers, but some surprisingly large fraction of natural human pregnancies result in a spontaneous abortion. Exact causes of this may vary, but I think a significant fraction of those are simply not viable due to genetic mutations. Adult parents have at least proven they have the genes necessary to both survive until adulthood and find a mate. Embryonic parents haven’t proven that. Certainly we can use genetic tests to screen them for known genetic diseases, and that is kind of the point, but how do we screen them for unknown genetic diseases?
Searching around the web, it looks like most miscarriages are due to aneuploidy. That would be easy to detect and select against.
It’s hard to find good numbers for the human mutation rate. I saw numbers ranging from 42 to 200 per generation. Sperm seem to have more mutations than eggs on average. It can vary based on environmental exposure to mutagens, and older parents tend to have more mutations on average. Perhaps embryonic parents simply wouldn’t have the time to accumulate many mutations. On the other hand, one has to do unnatural things to get these embryonic cells to turn into gametes. If any of these steps are mutagenic, then the mutation rate could be even worse.
I feel confused wrt the genetic mutation hypothesis for the spontaneous abortion phenomenon. Wouldn’t genes which stop the baby from being born, quickly exit the gene pool? Similarly for gamete formation processes which allow such mutations to arise?
Yes, by killing the fetus before it’s born. New mutations still happen all the time. Usually they hit junk DNA and not much happens, but what if it breaks something vital? And it’s possible to inherit deleterious recessive alleles from both parents. That why incest is still a problem, from a genetic standpoint.
And yet we still have transposons. Evolution requires some amount of mutation, which is occasionally beneficial to the species. Species that were too good at preventing mutations would be unable to adapt to changing environmental conditions, and thus die out.
We’re aware of many species which evolved to extinction. I guess I’m looking for why there’s no plausible “path” in genome-space between this arrangement and an arrangement which makes fatal errors happen less frequently. EG why wouldn’t it be locally beneficial to the individual genes to code for more robustness against spontaneous abortions, or an argument that this just isn’t possible for evolution to find (like wheels instead of legs, or machine guns instead of claws).