A new study shows that sex hormones are important for developing gender role behaviours in boys, such as active play.
In laboratory animals, sex differences in behaviour arise from different hormone levels produced by males and females influence patterns of gene expression in the developing brain. However, the origins of sex differences in human behaviour are not as well understood.
“In the lab, you can do experiments on how these hormones affect animal brains and perform other experimental manipulations. We can’t do those things to people, so we looked to a natural experiment,” explained study leader David Puts, associate professor of anthropology.
Prof Puts and his collaborators made use of a natural experiment called isolated GnRH deficiency (IGD), a rare endocrine disorder. Individuals with IGD lack sex hormones from the second trimester of development right through until they begin hormone replacement therapy to induce puberty. However, as the external genitals develop earlier, during the first trimester, people with IGD are clearly male or female at birth, and are raised according to their sex.
IGD therefore presents the chance to study the behaviour of those raised as boys but exposed to low testicular hormones, or raised as girls but exposed to low ovarian hormones.
The researchers compared 97 individuals with IGD (a small number due to its rarity) to 1665 individuals with typical hormonal development. Differences in behaviour were investigated; boys being encouraged toward active play, girls pushed to more passive pursuits. The researchers asked subjects to recall behaviours they had as children.
“We asked them, ‘When you read a book, were you the male or female in the story?’, ‘Where your friends boys or girls?’, ‘Did you play with dolls or trucks?’,” said Talia N Shirazi, doctoral recipient in anthropology now working in the reproductive health industry.
These childhood gender role behaviours are among the largest differences in behaviour between sexes, Prof Puts said. Typically, males will say they were the male character, played with other boys and preferred trucks, while females will say they were the female character, played with other girls and preferred dolls.
However, males with IGD reported more gender non-conforming in this regard. The researchers found in that men with IGD recalled a higher level of childhood gender non-conformity than typical men, while women with IGD did not differ from typical women in childhood gender conformity.
‘”We don’t see this effect in the women with IGD,” said Shirazi, indicating that low levels of ovarian hormones does not significantly impact childhood gender role behaviours.
“Our results suggest that in humans, androgens, such as testosterone produced by the testes, influence male brain development directly as they do in other mammals, rather than only indirectly by influencing external appearance and consequently gender socialisation,” said Prof Puts. “Both the direct influence of androgens on the developing brain and gender socialisation probably play important roles in producing sex differences in childhood behaviour.”
Prof Puts and Shirazi agree that despite their modest sample of participants with IGD, they are encouraged that the results were very similar in subjects who came from a clinical setting and those recruited from support groups.
“It would be nice to be able to identify people with IGD when they are younger, before they reach what should be puberty,” said Shirazi. “We need to focus on recruitment for our studies because there is a lot that can be learned about the cause of gender behaviours.”
Source: Penn State
