A study found that men’s testosterone levels fell by around a
third in the days and months after their partner gave birth
By Stephen Adams, Medical Correspondent
The more caring side of a man’s character emerged as levels of the hormones fell, said scientists, who believe that the process is nature’s way of trying to ensure that fathers stay for the long haul of child-rearing.
They found that men with higher testosterone levels – associated with dominant and aggressive behaviour – were both more likely to secure a partner and father children. But after the birth itself testosterone levels in these men dropped.
“Humans are unusual among mammals in that our offspring are dependent upon older individuals for feeding and protection for more than a decade,” said Christopher Kuzawa, a faculty fellow at the Institute for Policy Research at Northwestern University in Chicago, and a coauthor of the study, published in the journal Proceedings of the National Academy of Sciences. “Raising human offspring is such an effort that it is cooperative by necessity, and our study shows that human fathers are biologically wired to help with the job.”
Lee Gettler, an anthropology doctoral student who also worked on the study, added: “It’s not the case that men with lower testosterone are simply more likely to become fathers.
“On the contrary, the men who started with high testosterone were more likely to become fathers, but once they did, their testosterone went down substantially.”
It was the act of child care that seemed to reduce testosterone, he explained.
“Our findings suggest that this is especially true for fathers who become the most involved with child care.”
The biggest effect appears to be temporary, in the period immediately after bringing home the baby, with levels rising slowly after that, although not returning to pre-fatherhood levels.
The team studied 624 men in their twenties in the Philippines and followed them for four-and-a-half years. Dr Allan Pacey, a male sexual health expert at Sheffield University, commented: “To see dramatic changes in response to family life is intriguing. The observations could make some evolutionary sense if we accept the idea that men with lower testosterone levels are more likely to be monogamous with their partner and care for children.
“However, it would be important to check that link between testosterone levels and behaviour to be certain.”
The study found that testosterone levels fell on average by 34 per cent when men became fathers, with the biggest falls in those most involved in childcare.
Dr Pacey added that, as high levels of testosterone were also associated with a strong sex drive, lower levels could reduce the chances of a man “straying”.
However, he cautioned that the paper did not prove that. He added: “Testosterone is the key hormone that defines male physiology. We know that levels correlate with a man’s sex drive, his risk-taking behaviour and social dominance. It has also been suggested that it may increase his attractiveness to women and help him find a mate.”
Stephen Adams / telegraph.co.uk
© Telegraph Media Group Limited 2011