Besides chance, there have been numerous theories floated about how the sex of newborns is determined. Here's the latest. If a woman rides a motorcycle, swings a sledge, and has the strength to bench press a pallet of watermelons, I understand that her elevated testosterone will produce a boy.

From TimesOnline.co.uk:

Scientists have established that eggs taken from female mammals have varying levels of testosterone and that those with the highest levels are more likely to develop into male embryos. Testosterone in women has been linked to more dominant character traits.

The discovery of the "queen bee" syndrome in mammals is the latest in a growing body of work that challenges the traditional view that a baby's sex is determined by chance.

The research comes from behavioral scientist Valerie Grant at Auckland University who found that cow eggs were predisposed to accept "male sperm" when the female cow had high levels of testosterone.

From Interested-Participant.