Missing Link

Ah, the loss of virginity. For some young people, when they lose their virginity is based on how promiscuous or prudish they are, how much "game" they have or how long they're willing to wait for the right person.

But a new study suggests that the age we lose our virginity might be determined by our genes – and that's not the denim kind.

The study, lead by Nancy Segal, a psychologist at California State University in Fullerton, looked at 48 pairs of twins raised in separate households and 23 individual twins.

The twins were administered a sexual life history interview, which included a sexual meaning survey, a sexual history timeline and a sexual behavior questionnaire.

Interviews found that, on average, the age of first intercourse among the participants was 18.8 years. Identical twins raised apart were recorded at an average of 18.9 years and fraternal at 18.6 years.

"We're not looking at any specific gene. What we're looking at is a genetic component to behavior. The way we can [make sure] that's the case is that, when we compare the similarities in the identical and the fraternal twins, we should find considerable more similarity in the identicals than the fraternals," Segal says, adding that the results were almost exactly the same.

"The reason that lets you conclude there is a genetic component is the identical twins share all of their genes, but fraternals only share half on average."

Studies in the past have examined the relationship between twins and first intercourse before, but Segal was the first to use twins that were raised separately to control for "nurture" factors like social and sexual mores. Another scientific team at University of North Carolina at Chapel Hill has attributed the gene DRD4, which encodes a receptor for dopamine, to risk-taking behavior like excessive alcohol, drug use and first intercourse.

Other "nurture" factors could play a role in when first intercourse occurs, which the CSU study examined in females specifically.

"Those [females] who were less happy than their friends, and so less fulfilled in their rearing home, had intercourse earlier as opposed to later," Segal says. "So that shows you that some peer influences, as well as home influences, can play a role."

But this doesn't necessarily mean that there is a biological timeline that determines when people lose their virginity for a fact. That is, there is no predetermined date. "Nature" factors, like heritable traits shared among families, are likely the factors that determine the "genetic link" to first intercourse. Impulsivity, self-control and risk-taking can be indicators, for example.

An article in New Scientist, a leading international science magazine, said of the study "as genetic determinism goes, the new findings are modest."