Testosterone and Sex Ratio

Written by Neill Abayon

The mother’s level of testosterone influences the probability of having a boy or girl.

This potent chemical hormone has important effects on human bodies. Even tiny quantities can change the physical and psychological characteristics of both men and women. It also affects the way people behave. Since testosterone influences people’s behavior in known ways, it is possible to get an idea of a person’s testosterone levels by asking them about some of their characteristics. Thus it is quite feasible that a psychological test will indicate whether a mother will have a boy or a girl.

After war, more boys are born than usual, and, today, fewer boys are being born throughout the western world.

For every 100 baby girls, there are 106 baby boys. Nobody knows why. It’s a puzzle because other animal species have half male and half female offspring, and human males produce equal numbers of x-chromosome sperms (which make girls) and y-chromosome sperms (which make boys).

Women have only one tenth the amount of testosterone that men do. In both humans and animals, testosterone has been shown to be related to dominance. There is evidence to suggest that testosterone in women rises during periods of chronic stress — the sort of situation that arises in time of war, famine or disease. There are several documented examples of more boys being born in such circumstances.

Although the sex ratio averages out everywhere to 106 boys for every 100 girls, researchers have found that men in some occupational groups, such as airline pilots, astronauts, timber workers and deep sea divers, have a tendency to have more girls.

Dominant female deer have more male offspring than non-dominant deer; far more than would be expected by chance. A famous study describing this phenomenon was published in the top science journal Nature in 1984. Since then there have been more than forty animal studies published in reputable scientific journals documenting unusual sex ratios. For most animals living in the wild — different kinds of monkeys, wild horses and even whales — dominant mothers have more male offspring. When the animals were kept in captivity, however, the sex ratios sometimes ran in the opposite direction and the dominant females had more female offspring. Caging is likely to have an effect on both social hierarchies and hormones.