According to a study published in Psychoneuroendocrinology, researchers at the University of Montreal have found that environmental factors determine testosterone levels in infancy and not genetics.

Lead author of the study, Dr. Richard E. Tremblay, of the university’s Research Unit on Children’s Psychosocial Maladjustment, explained:

“Testosterone is a key hormone for the development of male reproductive organs, and it is also associated with behavioral traits, such as sexual behavior and aggression.

Our study is the largest to be undertaken with newborns, and our results contrast with the findings gained by scientists working with adolescents and adults, indicating that testosterone levels are inherited.”

The team examined 314 pairs of twins and took saliva samples in order to measure levels of testosterone. Testosterone levels were then compared between identical and fraternal twins in order to determine whether genetics or environmental factors contribute more to the levels.

According to the researchers the results showed that differences in testosterone levels were primarily due to environmental factors.

Tremblay said:

“The study was not designed to specifically identify these environmental factors, which could include a variety of environmental conditions, such as maternal diet, maternal smoking, breastfeeding and parent-child interactions.

Because our study suggests that testosterone levels in infants are determined by the circumstances in which the child develops before and after birth, further studies will be needed to find out exactly what these influencing factors are and to what extent they change from birth to puberty.”

Written by Grace Rattue