Mascaro and her colleagues at Emory University and the University of Arizona took apart each exchange and coded them to see whether there were any patterns based on the children's genders.
The differences were startling.
With their boys, the dads tended to engage in more rough-and-tumble play. They also favored language related to achievement, such as “proud,” “win” and “top.” Fathers of daughters sang more and used more emotional words, especially as related to sadness, and more analytical words, such as “all,” “below” and “much.”
“Historically, this is a thorny thing to study,” Mascaro explained in an interview. “It isn't something that's very amenable to asking people, so we've never really had a good handle on how the gender of a child influences the behavior of a parent.”
Until recently, little research has looked at the role of fathers in parenting. Part of that was because of the history of gender roles in the United States and other Western societies; not until this generation did fathers begin to spend significant time with their children. One study, presented at a social research conference in 2014, found that today's working fathers spend an average of 35 minutes a day focused on their offspring. That's a huge increase — seven times more than the five minutes their predecessors were spending in 1974 — but still only about half the full hour mothers spend with their children daily.
The analysis of the recordings by Mascaro and her colleagues, published in Behavioral Neuroscience, a journal of the American Psychological Association, is one component of a larger study about paternal relationships. Although the study is small and limited to fathers who live with their partners, it captures what is considered to be a key stage in a child's development. At age 1, breast-feeding is typically over and children are starting to walk, and that's often when a father's relationship with his child really begins to blossom.
The Behavioral Neuroscience paper also revealed the results of a second experiment in which those same dads were shown pictures of their child with happy, sad and neutral expressions while MRI images were taken of the men's brains. These results, too, were striking.
Based on the finding that fathers tend to attend to and talk about emotions more with girls, Mascaro said she predicted fathers would respond more to daughters. That turned out to be true, with greater neural responses in the regions for reward and processing emotions when the men were shown the happy pictures. Their reaction to the boy pictures were slightly less expected, she said, as they tended to respond more robustly to neutral facial expressions.
Mascaro is not sure how to explain this, but the researchers noticed one “potential clue,” she said: that a dad's strong reaction to a boy's neutral facial expression appeared to be correlated with the amount of their more physical play.
All social mammals do this play when they are young, and scientists have theorized that it may be important training for social competence.
“Rough and tumble is this special situation where this kind of movement is okay, but you really have to attend to your partner's emotions: Are they still having fun? I think it's really intriguing to think that attending to more ambiguous facial expressions might be important,” she said.
Mascaro, an assistant professor in family and preventive medicine at the Emory School of Medicine, said there isn't nearly enough information yet to draw conclusions about children's future outcomes from the study. Nor is there evidence to figure out much about the origins of the fathers' brain responses, such as whether they were caused by some genetic component or a matter of conforming to societal norms about gender.
“Findings like this shouldn’t necessarily be taken as ill-intent or negative on the part of the fathers,” she said. “It really could indicate fathers trying to do the best they can to prepare their children for the world.”