Girls who grew up without fathers at home tend to be early bloomers in the sex department compared with those whose fathers lived with them. Researchers have been trying to figure out the reason for this for years. Is it because there’s no watchful eye looking over them and keeping them in line? Is it a natural response that happens even in the animal world (that when a strange male, i.e., a stepfather or stepbrother, is around, girls grow up more quickly)?
Now, new analysis of data from the American National Longitudinal Survey of Youth offers another suggestion. Jane Mendle of the University of Oregon looked at NLSY surveys, which asked mothers a variety of questions, including whether the father of their children lived with them. The children of these women were asked questions starting at age 14, and, among other things, they were asked whether they’d engaged in sexual intercourse yet. Mendle and her colleagues compared cousins’ ages of first sexual intercourse—some of whom had their father living in their home and others who did not—to see whether early sexual activity could be genetic.
Mendle and her colleagues found that closely related cousins (those whose mothers were identical twins) were closer in age at first sexual experience than others. This was true of both the girls and boys surveyed, regardless of whether or not the father had been around or not, leading the researchers to believe that there might be a gene influencing both when a child has intercourse for the first time and the likelihood that they would grow up without their father living at home. Or, people who are genetically disposed to have sex earlier might get pregnant at a younger age with a partner they didn’t intend to settle down with, resulting in the father leaving the home. Whatever the reason, it’s fascinating to think that the age at which we first had sex could be a result of our genes. [The Economist]