Previous research has found that children raised in homes without a biological father have sex earlier than children raised in traditional nuclear families. Now a new study that used a novel and complex design to investigate why this is so challenges a popular explanation of the reasons.

Among prior explanations of why children who live in homes without fathers have sex earlier are that early childhood stress accelerates children's physical development, that children who see their parents dating may start dating earlier, and that it's harder for a single parent to monitor and supervise children's activities and peers. All of these are environmental explanations.

"Our study found that the association between fathers' absence and children's sexuality is best explained by genetic influences, rather than by environmental theories alone," according to Jane Mendle, assistant professor of psychology at the University of Oregon, who led the study.

Conducted by researchers at the University of Oregon, the University of Virginia, the University of Chicago, the University of Indiana, Columbia University, and the University of Oklahoma, the study appears in the September/October 2009 issue of the journal Child Development.

Mendle and her colleagues looked at more than 1,000 cousins ages 14 and older from the National Longitudinal Survey of Youth. The study design tested for genetic influences as well as factors such as poverty, educational opportunities, and religion. It compared children who were related in different ways to each other, and who differed in whether they'd lived with their fathers. The more genes the children shared, the more similar their ages of first intercourse—regardless of whether or not the children personally had an absent father. This finding, the researchers say, suggests that environmental theories don't fully explain the puzzle. Instead, genetic influence can help us understand the tie between fathers' absence and early sex.

"While there's clearly no such thing as a 'father absence gene,' there are genetic contributions to traits in both moms and dads that increase the likelihood of earlier sexual behavior in their children," notes Mendle. "These include impulsivity, substance use and abuse, argumentativeness, and sensation seeking.

"These traits get passed down from parents to children, resulting in a situation known as 'passive gene-environment correlation,' because the same genetic factors that influence when children first have intercourse also affect the likelihood of their growing up in a home without a dad."

Note: If no author is given, the source is cited instead.

• Children's Health
• Infant's Health
• Attention Deficit Disorder

• Child Psychology
• Child Development
• ADD and ADHD

• Child
• Cyber-bullying
• Sex education
• Heritability
• Language acquisition
• Bone age