Humans classify as a biparental species, since both parents are expected to take part in childcare. But more often than not, mothers tend to devote much more time to the kids than fathers. Whether dads are employed or not, in fact, average American moms still clock more hours cleaning, feeding, clothing and transporting children. Specifically, according to the 2008 National Survey of Families and Households out of the University of Wisconsin, the wife-to-husband ratio of childcare is five to one, and in general, dads don't spend more than two or three hours per week with their kids [source: Belkin].
However, that paternal contact, albeit less time-intensive than mothers' interactions, not only correlates to improved child development outcomes down the road, but is also linked to better long-term health in men [source: World Health Organization Europe]. Engaged fathers, for instance, tend to live longer and enjoy better mental health than their childless and single counterparts. And those paternity rewards may be the direct result of fatherhood diminishing testosterone production.
In September 2011, Northwestern University anthropologist and human biologist Lee T. Gettler published a study finding that sparked countless sensational headlines. Examining the testosterone levels of Filipino men across a five-year period revealed a drop in the stereotypical He-Man hormone after a particular shared milestone: fatherhood. Although separate studies had identified a testosterone-fatherhood correlation in other species, this was the first to document longitudinally the hormone drop in human dads [source: Gettler et al]. Compared to the men who remained single throughout the study term, those who got hitched and had babies had much less testosterone in their saliva [source: Gettler et al]. Not only that, the men who went on to become fathers often had higher than average amounts of testosterone at the start of the study, when they were single. So what gives?
Evolutionary biology maintains that males with more testosterone tend to be more sexually desirable, since the hormone selects for certain come-hither traits, such as facial symmetry and bulked-up musculature. Therefore, as potentially fitter mate prospects, it makes sense that those testosterone-rich fellows settled down [source: Lende]. Meanwhile, the fatherhood-prompted dip in testosterone production may represent an evolved mechanism for preening hunter-gatherer males into caregivers. In other words, by tamping down on the aggression-sparking and sex drive-revving chemical that is testosterone, the male body essentially settles itself down to help raise the kids, with heightened protective and care-giving instincts [source: Lende].
Furthermore, a 2002 study examining the hormonal changes associated with marriage and parenting also revealed that husbands with lower testosterone spend more time with their wives [source: Gettler et al]. On the flip side of these family-oriented fellows, a 2002 study from the University of Toronto found that male participants with higher baseline testosterone levels were less sympathetic and responsive toward the sound of crying babies [source: Gettler et al].
However, just like the mouse dads that sprouted brain cells in response to offspring interaction, lowered testosterone isn't a standalone turnkey for paternal care-giving. In these cases, behavior seems to presuppose biology, first requiring quality interaction with offspring to signal the male body to dial down testosterone production. Single dads who didn't see their children experienced little hormonal change in the Northwestern University study, for instance [source: Gettler et al]. So, while it might seem like less testosterone makes a new father into less of a man, it does the exact opposite. It quite possibly primes that man to become more of a dad.