z47\doc\web\2000\12\5pct.txt
12/28/2000


>   having  a  mere  5% of males in the population would suffice to keep
>   all  the females regularly fertilized. 
> 
what experimental data is this based on???<


   Obvious enough.    Fecundability is the fraction of menstrual cycles
plus sperm that results in a baby; in humans, it's around 30%, surprisingly
low.   So, roughly speaking, if you time things just right, you need to
have sex three times (on average) with a woman to have a  baby.   If each
woman has 5 kids ( a ridiculously lagre number, considering  current
fertility rates) she'd need to have sex about 15 times in her entire life. 
  The average guy can have sex at least twice a week without running out of
sperm ( probably much more often, actually, especially in youth) and is
fertile for at least 40 years.  That'd be 4000 impregnations,    This
conservative estimate says that each man  could easily take care of > 250
females, so the necessary male fraction is in fact less than  a quarter of
1%. 


         Gregory Cochran