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Still the mechanisms by which the male body might control the ratio of sperms with X vs. Y is astoundingly simpler than mechanisms by which an egg can somehow "

by craigyk 13y ago

Still the mechanisms by which the male body might control the ratio of sperms with X vs. Y is astoundingly simpler than mechanisms by which an egg can somehow "sense" and reject sperm. On the other hand, a mechanism by which the female body can selectively abort an embryo is way more plausible. Either way, this leads to some pretty testable predictions. You might not even need to do much direct experimentation, an outcome of the second hypothesis is that if gender selection is highly activated than more eggs/embryos are wasted, which might lead to smaller litters/ longer time between pregnancies.

dllthomas 13y ago
> mechanisms by which an egg can somehow "sense" and reject sperm. Evolution doesn't work like an engineer. If you or I were going to sit down and say, "Hmm, how do we control the sex ratio from within the female's body?" we'd come up with things like a mechanism to differentiate the sperm and then try to apply that to a mechanism to block or help one group or the other, because modularity is good and such. Evolution doesn't pay attention to the mechanism, just the result. Maybe it happens that one type of sperm is disproportionately affected by acidity levels or viscosity of cervical mucous or any of potentially hundreds of attributes of the environment the sperm will be encountering between meiosis and conception, and that's assuming any differentiation happens pre-conception. If there is such an effect, there's a good chance evolution will "spot it" and exploit it where the gain outweighs the cost; the female has (evolutionarily speaking) far more motivation to make use of it, if it involves any tradeoff with chance of conception. Note that by his hypothesis, smaller litters or longer time between pregnancies probably is what you'd see if the decision was being made in the female's body, whether pre- or post-conception.
- dllthomas 13y ago
  s/by his hypothesis/by this hypothesis/

by craigyk 13y ago

dllthomas 13y ago

> mechanisms by which an egg can somehow "sense" and reject sperm. Evolution doesn't work like an engineer. If you or I were going to sit down and say, "Hmm, how do we control the sex ratio from within the female's body?" we'd come up with things like a mechanism to differentiate the sperm and then try to apply that to a mechanism to block or help one group or the other, because modularity is good and such. Evolution doesn't pay attention to the mechanism, just the result. Maybe it happens that one type of sperm is disproportionately affected by acidity levels or viscosity of cervical mucous or any of potentially hundreds of attributes of the environment the sperm will be encountering between meiosis and conception, and that's assuming any differentiation happens pre-conception. If there is such an effect, there's a good chance evolution will "spot it" and exploit it where the gain outweighs the cost; the female has (evolutionarily speaking) far more motivation to make use of it, if it involves any tradeoff with chance of conception. Note that by his hypothesis, smaller litters or longer time between pregnancies probably is what you'd see if the decision was being made in the female's body, whether pre- or post-conception.

dllthomas 13y ago
s/by his hypothesis/by this hypothesis/