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This seems to be based on the idea that the only feedback mechanism for improving sperm is to have sperm fight with other sperm. That's not correct though. What

This seems to be based on the idea that the only feedback mechanism for improving sperm is to have sperm fight with other sperm. That's not correct though. Whatever trait in sperm leads to pregnancy more often will be evolutionarily selected for. There doesn't need to be any direct fight between sperm.

Dalewyn 4y ago
The basis for how "healthy" sperm is is implied to be how mobile it is, and in an environment where sperm are competing to reach the egg first, being more mobile is absolutely a trait that will be evolutionarily selected for because less mobile ("less healthy") sperm will conceive less. But in an environment where that doesn't matter anymore, it's only natural that sperm "health" will consequently deterioriate. Natural selection doesn't select for "the best", it only selects for "good enough". And if "unhealthy" sperm that can't move sufficently is "good enough", well so be it. Especially if we take factors like in-vitro and artificial insemination into account, those really remove the "health" of sperm from the equation of pregnancy.
- Thorrez 4y ago
  If health has no effect on conception success, I don't see any reason to be worried about declining health. I agree that in-vitro and artificial insemination could remove an important feedback mechanism for sperm evolution, and that would be a cause for worry.
  - Dalewyn 4y ago
    My understanding is that it is starting to (presumably anyway) have an effect on conception, because a sperm that can't move is a sperm that can't fertilize an egg, and there aren't competing superior sperm to make up for the shortfall. Which by itself is fine, really. Sperm that fails to reach an egg means the genes that made that sperm do not "deserve" to reproduce. However, if people want to make a fuss over low birth rates, and this is one factor behind it, it's going to get attention.

Dalewyn 4y ago

The basis for how "healthy" sperm is is implied to be how mobile it is, and in an environment where sperm are competing to reach the egg first, being more mobile is absolutely a trait that will be evolutionarily selected for because less mobile ("less healthy") sperm will conceive less. But in an environment where that doesn't matter anymore, it's only natural that sperm "health" will consequently deterioriate. Natural selection doesn't select for "the best", it only selects for "good enough". And if "unhealthy" sperm that can't move sufficently is "good enough", well so be it. Especially if we take factors like in-vitro and artificial insemination into account, those really remove the "health" of sperm from the equation of pregnancy.

Thorrez 4y ago
If health has no effect on conception success, I don't see any reason to be worried about declining health. I agree that in-vitro and artificial insemination could remove an important feedback mechanism for sperm evolution, and that would be a cause for worry.
- Dalewyn 4y ago
  My understanding is that it is starting to (presumably anyway) have an effect on conception, because a sperm that can't move is a sperm that can't fertilize an egg, and there aren't competing superior sperm to make up for the shortfall. Which by itself is fine, really. Sperm that fails to reach an egg means the genes that made that sperm do not "deserve" to reproduce. However, if people want to make a fuss over low birth rates, and this is one factor behind it, it's going to get attention.