Researchers have found that hormone's levels are governed by environmental factors and not by genes. They have concluded after comparing testosterone levels of five-month-old pairs of twins, both identical and non-identical.
"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," said Richard E. Tremblay of Canada's Montreal University's research unit on children's psycho-social maladjustment, who led the study.
"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 journal Psychoneuroendocrinology reports.
Researchers took saliva samples from 314 pairs of twins and measured the levels of testosterone. They then compared the similarity in testosterone levels between identical and fraternal twins to determine the contribution of genetic and environmental factors, according to a Montreal statement.
Identical twins arise from a single fertilized egg that for some reason splits itself in two. Identical twins have exactly the same genetic make-up. Fraternal twins arise from two separate eggs.
Results indicated that differences in levels of testosterone were due mainly to environmental factors.
"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," Tremblay said.
"Because our study suggests the testosterone level in an infant is 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," Tremblay said.