"The observed equality of males and females, in the face of obvious advantages for female predominance if evolution worked on groups, stands as one of our most elegant demonstrations that Darwin was right - natural selection works by the struggle of individuals to maximize their own reproductive success...let us say, for example, that fewer males than females are born.  Males now begin to leave more offspring than females since their opportunities for mating increase as they become rarer...if any genetic factor influence the relative proportion of males born to a parent (and such factors exist), then parents with a genetic inclination to produce males will gain a Darwinian advantage - they will produce more than an average number of grandchildren thanks to the superior reproductive success of their predominantly male offspring...since the same argument work in reverse to favor female births when females are rare, the sex ratio is driven by Darwinian processes to its equilibrium value of one to one."

So, next time I'm lonely I can blame Darwin, I guess.

The quote is from an essay with one of my favorite titles ever by Dr. Gould: "Death Before Birth, or a Mite's Nunc Dimittis" - which focuses on a species of mite in which the females hatch from their eggs already pregnant with the next generation, having been fertilized in their mother's womb by their (usually) lone brother, who does nothing but die hours after birth.  Since exclusive sib mating destroys the premise of the above mechanism driving the sex ratio to 1:1, these mites do tend to maximize their reproductive success by producing one male and as many females as possible.  The male, having done his part, is free to "depart in peace", hence the reference to the Canticle of Simeon.

So, if we really want to bring about the whole "two girls for every boy" fantasy, we should just start mating with our siblings exclusively.  Since I'm an only child, I'm not real big on this plan.

Wumpus