The ratio of boys to girls born in the United States is 51 percent to 49 percent. Since 1940, an average of 91,685 more male babies have been born each year than females, a total of 5,776,130 over that 63-year period.

An early review notes that in the United States, parents — especially fathers have shown a strong preference for sons. Couples with sons are more likely to marry and are less likely to divorce if married. Fathers also tend to spend more time with sons than with daughters.

Yet when it comes to fathers and their interactions with their daughters, there is something very different if not special about girls. Research indicates that fathers often treat boys and girls differently in ways that impact child outcomes.

Although studies and statistics have shown just how important fathers are to all children, fathers are especially important to girls. From the early years to beyond the teens, fathers have a dynamic influence on their daughters.

Fathers may have more impact than mothers on their daughters' academic and career success especially in math and science dealing with authority figures, developing self-confidence and self-reliance, willingness to accept challenges, maintaining good mental health and expressing anger constructively. Fathers may also be more open about their emotions with their daughters, possibly because they are more accepting of girls' feelings than boys' feelings.

According to a recent study, this is because fathers' brains may respond differently to daughters than to sons.

In this study, led by Jennifer Mascaro, Ph.D., an assistant professor in family and preventative medicine at Emory University School of Medicine, researchers compared fathers of daughters and fathers of sons in terms of naturalistically observed everyday care-giving behavior and neural responses to child picture stimuli.

Because participants are often influenced in lab settings, the researchers took this study into the real world. They used data from 52 fathers of toddlers (30 girls, 22 boys) in the Atlanta area. The fathers clipped small handheld computers onto their belts and wore them for one weekday and one weekend day. The computers randomly turned on for 50 seconds every nine minutes, recording any sounds during the 48-hour period.

Compared with fathers of sons, fathers of daughters were more attentively engaged with their daughters, sang more to their daughters, used more analytical language and language related to sadness and the body with their daughters. They also had a stronger neural response to their daughters' happy facial expressions in areas of the brain important for reward and emotion regulation (medial and lateral orbitofrontal cortex [OFC]).

In contrast, fathers of sons engaged in more rough-and-tumble play (RTP), used more achievement language with their sons and had a stronger neural response to their sons' neutral facial expressions in the medial OFC (mOFC). Whereas the mOFC response to happy faces was negatively related to RTP, the mOFC response to neutral faces was positively related to RTP, specifically for fathers of boys.

These results indicate that real-world paternal behavior and brain function differ as a function of child gender. According to Mascaro, most dads try to do the best they can to help their kids succeed in life, but understanding how their interactions with their children might be partly biased based on gender is important to recognize.