Higher maternal testosterone levels in pregnant women correlate with tomboy behavior in young femal children:

"Because hormones influence basic processes of brain development, they also exert permanent influences on behavior," says lead author Melissa Hines, Ph.D., of City University in London "In both rats and rhesus monkeys, genetic female animals treated with testosterone during critical periods of prenatal or early postnatal life show increased levels of … male-typical play behavior as juveniles."

Hines and her co-authors note that girls with congenital adrenal hyperplasia (CAH), a genetic disorder involving prenatal exposure to high levels of male hormones, tend to prefer masculine-typical toys and activities.

The study results appear in the November-December issue of Child Development.

Participants were part of the Avon Longitudinal Study of Parents and Children, a long-term study of biological, environmental and social factors associated with pregnancy outcomes and child health. A total of 13,998 pregnant women -- who represented 90 percent of all pregnancies occurring in the Avon, England, area during an 18-month period in the early 1990s -- enrolled in the study. Data from 679 offspring of the 14,138 children born during the study were analyzed.

The researchers obtained blood samples from the pregnant women during routine prenatal medical care; 55 percent of the women had blood taken between weeks 8 and 24 of the pregnancy; a quarter of the women had the samples taken between weeks 5 and 7, and the remainder after week 25. The samples were analyzed for levels of testosterone and a hormone that limits the ability of testosterone to act, called sex hormone binding globulin.

Once each child reached age 3 1/2, a primary caregiver completed the Pre-School Activities Inventory (PSAI), which assesses the child's engagement in various sex-typed behaviors, such as play with certain toys, games and activities. Higher scores indicate more masculine-typical behavior. The questionnaire was completed again when the child was 3 1/2.

The authors found a link between testosterone level in mothers and girls' scores on the PSAI, with high testosterone levels related to high "masculine" scores. No relationship was found between testosterone levels and boys' gender-role behavior, however.

In case it seems odd that I post alot on research about neurobiology and behavior on a blog dedicated to the future I'd like to explain why I do this. These studies demonstrate jut how much of human nature is determined by genes and by hormones and other biochemical factors that regulate genetic expression. In the future we are going to be able to make choices about the genetic sequences of genes for our offspring and we therefore will be able to change the mental aspects of human nature. It is important to appreciate just how many ways biological variations can cause variations human minds and human behavior because all of those variations and many more will be manipulated intentionally. When we acquire the ability to control gene that determine personality characteristics in offspring this it will simultaneously provide a great benefit and pose a great threat. It is important that we start thinking about this topic now.