"John Edser"  wrote in
news:bari34$5p3$1{at}darwin.ediacara.org: 

> 
> BM:-
> ...Men and women  do have a _different_ sex drive. But monogamy is
> in general predicted by equal parental investment in the energy
> required to raise children. For most human societies over most of
> human history,  the investment has been generally equal and the result
> is monogamy. It is not imposed by society but is imposed by biology.
> 
> 
> JE:-
> No imperative exists within nature for
> "equal parental investment". In fact,
> investments of both sexes are almost always,
> unequal. All nature is concerned with is
> that the number of young raised to fertile
> adulthood is maximised. As long as this is
> the case then both sexes benefit in fitness.
> Reducing this absolute fitness count by quibbling
> over relative investment costs is just
> madness (common in man but unknown in nature).


Relative amounts of parental investment vary widely among different 
species, and as you noted are almost always unequal. What I was saying is 
that when they happen to be equal (because that results in maximizing 
reproductive success), the result is monogamy. 


 
> Spurious arguments such as: human females
> invest more in larger eggs than males invest
> in tiny sperm, are just, incorrect. One males
> ejaculate is vastly more than one
> human female egg. Males take more reproductive
> risks than females. If they were restricted to
> monogamy they could not make up for the fecundity
> deficit that they carry, because of this risk
> increase. Nature provides a way to make up
> the deficit by allowing a fast increase
> in fecundity that is not possible for females.
> When males reach the top of the status ladder,
> they become "entitled" to polygamous matings.
> Suddenly, they can make up their fecundity
> deficit (deficit in the number of infertile
> young they have fathered ).

In a number of  fish and some birds the males invest more (via parental 
care, not in egg vs. sperm production) in offspring than the females. In 
these species the males tend to be choosier than the females. In numerous 
other species the total investment on either side is just in eggs and 
sperm, and most of the courtship seems to consist in making sure that one 
is mating with the correct species. The particular behavior you describe 
above does occur, but only in a limited number of species. 


Yours,

Bill Morse
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