Moms' bodies aren't the only ones that change after childbirth: Testosterone dips in fathers who sleep next to their children, say researchers who want us to reconsider dutiful dads as deeply ancestral – and masculine.
We didn't realize they weren't masculine?
University of Notre Dame researchers looked at a longitudinal study that followed men in the Phillipine province of Cebu since 1983 when they were just a year old. In 2009, scientists had measured the testosterone levels in 362 of these men, who were now new fathers. They found that fathers who co-slept with their kids showed significantly lower levels of the hormone than dads who slept in separate bedrooms. But this was only the case before bedtime: After they woke up in the morning, those testosterone levels rose up again.
The findings, published in the journal PLoS ONE, echo a 2011 study conducted on the same respondents, which found testosterone took a 30 per cent dip in fathers of fresh newborns.
The declines may help men go from competing riskily against other dudes for a woman and into "daddy mode." Or as Doug Barry at Jezebel puts it, from "supreme bloodsport champion and mastodon hunter to the calmer, gentler role of nurturer."
The findings suggest "that active fatherhood has a deep history in the human species and our ancestors," study researcher and anthropologist Lee Gettler told LiveScience. "If many human/hominin fathers have been actively taking care of their offspring for hundreds of thousands or millions of years, doesn't that suggest that such behaviors should be considered a part of 'what it means to be a man' or manliness or masculinity?"
He continued: "For some people, the social idea that taking care of your kids is a key component of masculinity and manliness may not be new, but we see increasing biological evidence suggesting that males have long embraced this role."
Some caveats: The Filipino fathers slept on mats, blankets, beds or mattresses on the floor. Some 92 per cent said they shared a "sleeping surface" with their children; just 17 of the 362 fathers slept away from their kids. Although the dads reported normal sleep, any co-sleeping mother, let alone anyone with a newborn in the house, can tell you about "transient sleep."
Add to that University of Chicago research that found testosterone dropped in men who slept few hours, and you have a new question: Is dad's competitive, Neanderthal side mellowing with baby in tow, or is he just really tired?