This sentence in particular interested me, for values of "interested" that include "annoyed."
One possible explanation is that after giving birth to a first son, the mother may develop maternal antibodies directed against male-specific proteins. These might then disrupt development of the younger son, says Dr Puts.
I seem to recall Peter mentioning some studies to me, a while back, that tended to indicate that there was some genetic utility in homosexuality (and I don't remember what species of animal we were specifically talking about) in that the siblings of individuals that exhibited a same-sex preference tended to produce more surviving offspring.
So, again, why do we persist in acting as if homosexuality was perforce maladaptive? Right, because it's politically convenient for some of us to do so.
(Also--as came up last night at dinner with ashacat and netcurmudgeon--nice baboons finish first. Apparently, the male baboons who pal around with the females, help out with child care, and so on, have more offspring than the alpha males that spend all their time playing status games. This all amuses me greatly; even in the animal kingdom, it's the boys that help out with the housework who get more fun.)
That must be hard on the alpha males....