From Science news 5/23/02. I think TC had an atomic dog along these lines a while back, but didn’t realize there was scientific evidence for literal truth. "In male birds from monogamous species, their level of testosterone seems to be a reliable indicator on whether they’ll stay and tend to their own nest, or fly off and look for some extra-curricular action in someone else’s. Anthropologist Peter Gray and a team from Harvard University decided to see whether the same happens in men, and their results were very interesting. In order to gather their data, they began by separating the 58 men in their study into three different groups: single, married with no children, and married with kids. By studying the hormone levels in each group over time, they were able to identify some definite trends in testosterone levels that seem to correlate with that found in the male monogamous birds. All of the men experienced a surge in testosterone in the morning and then a lower level as the day went on. The amount of the decrease was greatest in the married men with children-by a dramatic margin. Married men with no children showed the next greatest decline in testosterone as the day went on, followed by the bachelors.
Scientists aren’t sure exactly why this is so, but it makes sense that the lower levels would encourage the men to stay in their family unit and nurture/propagate their species, rather than seeking out new mates. The lower levels of testosterone may be influenced by spending large amounts of time around their family, in addition to making them less likely to fly the coop. This would create kind of a feedback loop, where one behavior reinforces the other, which in turn reinforces the first. Other activities such as winning or loosing at a sporting event have been measured to raise or lower testosterone levels, so it’s quite possible that being around their family has a similar affect on men as well. Dr. Gray is planning another study in which they’ll gather data on the effects of marriage vs. the effects of parenting by studying the testosterone levels of men who have separated from their wives but who have joint custody of their children.
Source: New Scientist; Reuters