New research suggests dads who sleep near their children experience a drop in testosterone.

The researchers believe this phenomenon could make men more responsive to their children's needs and help them meet the demands of fatherhood, the University of Notre Dame reported.

A team of researchers sampled 362 fathers between the ages of 25 and 26 and divided them by the proximity to which they slept to their child. They measured the participants' testosterone levels by looking at saliva samples taken upon waking and just before sleep. They found fathers who slept in a separate room as their children, the same room, or on the same surface as their children had similar waking testosterone levels, but the evening testosterone levels were lowest in those that slept in the same bed as their kids.

"Human fathers' physiology has the capacity to respond to children," Gettler says. "Our prior research has shown that when men become fathers, their testosterone decreases, sometimes dramatically, and that those who spend the most time in hands-on care -- playing with their children, feeding them or reading to them -- had lower testosterone. These new results complement the original research by taking it one step further, showing that nighttime closeness or proximity between fathers and their kids has effects on men's biology, and it appears to be independent of what they are doing during the day."

In other species, testosterone has been found to enhance the effort males put into mating, and it may operate in a similar way with humans. Higher testosterone levels could make men less efficient parents by boosting risk taking and sensation seeking behaviors. Past research has shown men with lower testosterone levels reported feeling more sympathy when they heard an infant cry compared to men with higher testosterone.

"Testosterone is a hormone that frequently is a part of public discourse, but the false idea that 'manliness' is exclusively driven by testosterone often dominates the conversation. There is growing evidence that men's physiology can respond to involved parenthood -- something that was long thought to be limited to women. This suggests to us that active fatherhood has a deep history in the human species and our ancestors. 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," Gettler said.

The findings were published in a recent edition of the journal PLOS One.