The time it would take for any trait to become fixed in a population would
depend on the selection pressure. First, some individual or individuals in
the population would have to exhibit the trait (selection cannot operate in
the absence of genetic variation). Its anybody's guess when this may have
happened (or for that matter, just how many such heritable changes would be
involved in a trait like "menstruation"). If the selection pressure were
very great indeed, then a trait could become fixed (all members of the
population exibit the trait) in a single generation! Following your
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. In other words,
all subsequent children were born of menstruating mothers and inherited
that trait. Perhaps this is not so far-fetched if you consider that the
advantage to menstruating appears to be the ability to mate more
frequently. I would hazard a guess that menstruation could have taken hold
within a 15000 year time frame. I suspect it did not happen in a single
generation. These, however, are blatant guesses. I invite anyone to
propose a more solid reasoning if they think they can.
argiope at pathcom.com
B. Moosang <bmoosang at uoguelph.ca> wrote in article
<5acclh$eir at ccshst05.cs.uoguelph.ca>...
> OK, just trying to settle an argument between two non-science people -
> how long would something like menstruation take to evolve?
> 5000-15000 years, would this be enough time for this to evolve?
>> Thanks for your time,