Question re:Evolution and Menstruation

John R. Campbell campbejr at phu989.mms.sbphrd.com
Fri Jan 3 13:22:26 EST 1997

On 3 Jan 1997 05:12:18 GMT, Ram Samudrala <ram at mbisgi.umd.edu> wrote:
>B. Moosang (bmoosang at uoguelph.ca) wrote:
>>OK, just trying to settle an argument between two non-science people - 
>>how long would something like menstruation take to evolve?  The argument 
>>that I have been presented with is that woman began menstruating (rather 
>>then doing what other critters do (which I can't remember the scientific 
>>term for but is basically go into heat)) 
>I would like a reference to this.   As I understand it, this
>discharing of blood and tissue occurs in primate females also.

	Yes, but for most other mammalia (IIRC) this is a *yearly*
	process, reducing the reproductive rate (though, come to
	think of it, rabbits may destroy this general line of thought).

	The argument, as I understand it, was how would a monthly
	cycle have evolved in humans?  While a monthly fertility cycle
	would have advantages in expanding the birth rate, how would
	this have provided enough of a selection pressure to eliminate
	the yearly fertility cycle...

	Mind you, I'm not all that well educated in Biology (other
	than by observation of my wife and childbirth).

>>after people began living in more fixed shelters between - let's say
>>for arguement sake between 5000-15000 years ago.  Would this be enough
>>time for this to evolve?
>Humans have been around a bit longer than that.  Assuming a mechanism
>for transporting the egg to the uterus, for the lining of the uterus,
>and for getting rid of debris, didn't exist, it boggles my mind to
>think how long such a function would take to evolve in the first place
>(going from 0 frequency to >0 frequency), let alone be naturally
>selected for.

	He's thinking that the monthly cycle was selected for in the last
	15K years.  Beats me, though I'd think it unlikely;  I don't see
	how there's enough selection pressure to eliminate the yearlies
	around the globe;  After all, the australian aborigines were
	isolated far longer than that and the trait is consistent...

	Though, once again, I've a specific lack of knowledge in details.

 John R. Campbell, Speaker to Machines, Resident Heckler          soup at jtan.com
  "As a SysAdmin, yes, I CAN read your e-mail, but I DON'T get that bored!"-me
   Disclaimer:	I'm just a consultant at the bottom of the food chain, so,
		if you're thinking I speak for anyone but myself, you must
		have more lawyers than sense.

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