Walk into any middle school classroom and it’s obvious that puberty hits some kids earlier than others. Some students daydream about kissing while others are still planning their latest LEGO creation. Now a new study suggests that the genes that drive puberty also influence some of the next stages of sexuality: age at first intercourse and—for women—age at first birth.
Of course, genes are not the only factor. Parenting, religion, social mores, peers and many other factors come into play. But researchers at the University of Cambridge estimate that genetics can explain about a quarter of the difference in the likelihood that an individual will have sex relatively early or wait to start. By comparison, about 80 percent of height is genetically determined and 30 to 50 percent of many common diseases are driven by genetics.
A person’s age at the onset of sexual behavior matters, because early sexuality and becoming a parent at a young age are linked to many measures of health and economic success. “If you look in [scientific] literature, relatively early ages at first sex and first birth have been associated with lower educational achievement, poorer physical health, poorer mental health—a complex web of negative stuff,” says John Perry, a geneticist at Cambridge who led the research, published Monday in Nature Genetics. Perry says he was particularly intrigued by the idea that something people think of as purely a matter of free choice would have a large contribution from genetics. (Scientific American is part of Springer Nature.)