Testosterone levels drop in men after they become fathers allowing them to aid in care giving for their children, according to a new research published Monday.

The greatest declines occurred in fathers of newborns, one month old or younger, suggesting that men evolved to take fatherly roles and help nurture their children, according to the research published in the Proceeding 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," said Christopher Kuzawa of Northwestern University in Illinois who co-authored the research, according to AFP.

Researchers studied 600 men from the Philippines before they married and then again after marriage and fatherhood.

Men who were partnered fathers experienced large declines in Testosterone from 26 to 34 percent which were significantly greater than declines in single non-fathers.

Also, fathers reporting 3 hours or more of daily childcare had lower Testosterone levels compared with fathers not involved in care.

Testosterone is a hormone that affects sexual features, boosts male sexuality, aggression and physical robustness, and is typically highest in young, single men with no children, according to the research.

The research also found that men who started with high testosterone were more likely to become fathers but once they did, their testosterone went down substantially, reports AFP.