Graham Cromar/Annette Tavares-Cromar (argiope at pathcom.com) wrote:
>The time it would take for any trait to become fixed in a population would
>depend on the selection pressure.
>example, this would mean imagining a situation where all the males in the
>population were so attracted to the females that could menstruate that they
>completely refused to mate with the females that couldn't.
This sort of a scenario is adequate, but not necessary. One could
imagine a scenario where the eggs in mothers who didn't menstruate
were incapable of being fertisised and thus weren't able to propagate
their genes, and so on.
While I agree that the trait could be fixed in the population within
15,000 years, I disagree that the trait EVOLVED (and here, I mean
evolved as in "arose") in 15,000 years in the first place. In an
extreme scenario, just imagine the number of mutations it would
require to go from an organism without ANY function resembling
menstruation to one that resembles menstruation, and the probability
of that happening.
Obviously this occured gradually, but even then, I suspect a lot more
than 15,000 years was spent evolving this trait (zero to non-zero
frequency) in the first place.
But as I said, I've seen referred in more than one place that primate
females menstruate. So it's not such a recent trait.
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