Fatherhood Plummets Testosterone... Maybe.

It's so easy to tie things to hormones. We usually think of it as a woman's thing. Fat after a baby? It's her hormones. Cranky when she's hitting her late 40s? It's her hormones.

But what about men? In the July issue of Hormones and Behavior, scientists link a man's sinking testosterone levels during his partner's pregnancy to an increased investment in fatherhood. The study tracked 27 heterosexual couples, measuring everyone's testosterone (men and women) three to four times during the pregnancy. Then they all filled out a survey about their investment, commitment, and satisfaction when the baby turned 3-and-a-half months.

The study confirms earlier research suggesting that men with lower levels of testosterone are better nurturers than higher-testosterone men who are thinking more about making babies than taking care of them. This kind of thinking meshes with the old fashioned notion that links all things manly and macho with testosterone and all things cuddly with estrogen. It's a notion that some doctors have been fighting against every since testosterone was named testosterone.

In 1927, when the University of Chicago's Dr. Fred Koch eked out .0007th of a gram of active ingredient from 44 pounds of bulls' testicles, he refused to give the newfound hormone a name. "It is our feeling that until more is known about the chemical nature of the hormone no name should be given," he wrote in a scientific article, "The Testicular Hormone." Eight years later, University of Amsterdam's Ernst Laqueur purified the substance and called it testosterone. There was griping about the name. The problem was testosterone implied that it's from the testicles and only from the testicles, which it isn't. And that implies it's just a man's hormone, which it isn't. The adrenal glands make testosterone. So do ovaries -- in tinier amounts. Dr. A. S. Parkes, a British endocrinologist, loathed the name: "The idea of maleness and femaleness as clearly defined endocrine states was finally shattered by the early work on the steroid hormones," he said in lecture to the Zoological Society of London. But it wasn't.

Hormones do impact behavior. And maybe they are onto something. Women know all too well about monthly mood swings with our hormones going this way and that. But still, I'm not convinced about the testosterone-parenting thing. Along with the strengths of their study (repeated sampling of testosterone and tracking parents throughout pregnancy), they admit to a few weaknesses. For one, it was small. More importantly, they didn't compare parenting attitudes between fathers with plummeting testosterone to fathers without a decline.

So where does that leave us? Well, its nice to see that at least 27 of these new fathers, according to this study, are enjoying their newborns and finding satisfaction with the diaper changing. I'm just not persuaded that the lower testosterone is the main cause of their new parental urges. Maybe the guys in this study just like being new dads.