Let's face it - throughout most of human history, stereotypes have dictated that women are more adept caregivers for children than men. Child-rearing is assumed to be in the female domain, while providing is considered inherently male. A large study of testosterone levels in men is turning that assumption on its head, suggesting that fatherhood actually lowers levels of the hormone once men become fathers, re-wiring them to be more nurturing.

"This suggests that a lot of stereotypes about men and child-rearing, maybe we need to rethink them a little bit," said Chris Kuzawa, associate professor of anthropology at Northwestern University, and co-author of the study. "It seems like it's part of our biological make-up to shift into the role of caregiver once it's required of us."

That shift occurs as a man becomes a father, according to the study, just published in the journal, Proceedings of the National Academy of Science. Several hundred Filipino men participating in the Cebu Longitudinal Health and Nutrition Survey had their testosterone levels measured in their early twenties, when they were single and at their most virile. Their testosterone was measured again about five years later, once they had married and had children.

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