The study, to be published Monday, found testosterone levels in men sharply decline when they become fathers, the Chicago Sun-Times reported.
The reduction of testosterone can steer males away from competing for a mate and towards spending more time on the responsibilities of fatherhood, the study says.
"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," said Christopher Kuzawa, who co-authored the study with Ph.D. student Lee Gettler.
The study followed 624 childless men in the Philippines in their early 20s into fatherhood.
Gettler said he and Kuzawa found "the men who started with high testosterone were more likely to become fathers." Then, after their children were born, "their testosterone went down substantially."
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