What's the price of fatherhood? Time, money, and testosterone.S

Becoming a parent means making a lot of sacrifices in your life, from giving up sleep to giving up your paycheck. But new research shows that if you're becoming a dad, you should also be prepared to give up some testosterone — but don't worry, it's all so you can better provide for your child.

Across numerous species, the sex hormone testosterone proves really useful to males when they're in the process of looking for a mate; libido, the drive and ability to compete with other males, even risk taking during financial decisions — all of these are directly affected by testosterone levels.

But once a male has found a mate, raising a child requires much less male-to-male competition, and much more partner-to-partner cooperation — not to mention other responsibilities that can conflict with the courting-and-mating-related activities driven by testosterone. This is a conclusion drawn by past research which shows that fathers, as a group, tend to have lower testosterone levels than non-fathers.

What past research hasn't shown is whether fatherhood actually causes a decrease in testosterone levels, or if men with lower testosterone are simply more likely to become fathers. Now, by examining the hormones of 624 men over a period of 4.5 years, a team of researchers led by anthropologist Christopher W. Kuzawa has put both of these mysteries to rest.

The researchers' study, which is published in today's Proceedings of the National Academy of Sciences not only shows that men with higher testosterone levels are actually more likely to become fathers, it also reveals that once they do, they experience a dramatic drop in testosterone levels. How dramatic you ask? The researchers explain:

Men who became partnered fathers...experienced large declines in waking (median: −26%) and evening (median: −34%) T, which were significantly greater than declines in single nonfathers.

That is to say: very dramatic.

"Humans are unusual among mammals in that our offspring are dependent upon older individuals for feeding and protection for more than a decade," said Kuzawa. "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."

Northwestern's Lee Gettler, who co-authored the study, expands upon Kuzawa's explanation:

Fatherhood and the demands of having a newborn baby require many emotional, psychological and physical adjustments...Our study indicates that a man's biology can change substantially to help meet those demands.

Via Proceedings of the National Academy of Sciences
(A direct link to the article will be made available when the paper goes live)
Thanks to Lee Gettler and Christopher Kuzawa for the advance copy of their paper

Top image via Enigma Photos's photostream