Biology and Behavior: Human Male Testosterone Responds to Changes in Social Environments

An important new study has just been published by PNAS, "Longitudinal evidence that fatherhood decreases testosterone in human males'" by Gettler et al. In the research reported, the authors discuss a study in which they followed a large sample of originally young (about 21) single, non-fathers until they were about 26 years of age. Testosterone levels were sampled, and the participants provided behavioral data -- in this particular case about their subsequent relationships and whether they became a father.

This PNAS study had three primary, and important, findings:

1. The young, single, nonparent men who had higher levels of testosterone initially were more likely to be in a relationship with children later.
2. These men who had later entered into a relationship, and who during the period of the study had fathered children, had substantially lower testosterone levels relative to other men in the study who had not fathered children.
3. Among those who fathered children during the study, those who were closely involved in taking care of their children had lower testosterone levels than fathers who were not closely involved in taking care of their children.

These are quite interesting results to come from this longitudinal study, and they have some potentially important implications for the growing research interest in the social, behavioral and neurosciences on the interconnections between human biology and our social environments.

As I've written before, there is an accumulating body of research that shows that our biology influences our political behavior and who we interact with. What's most interesting about this study is that it also provides solid evidence in support for a bidirectional relationship between biology and social interactions. On the one hand, the first result shows that our biology influences our social interactions. On the other hand, the results indicate that the social situations that we place ourselves in then in turn influence our biology. It's this second pathway that I find most interesting, as it hasn't been tested using longitudinal data like this in other types of social and in particular political or economic settings, but I suspect that along with Gettler's study we will likely see similar research in other social contexts.

This is a rich study, opening a number of new doors for subsequent inquiry. I'm looking forward to reading this paper more closely, reflecting more on the results and its implications.