• By Dartington SRU
  • Posted on Wednesday 05th October, 2011

Why don’t smart teens have sex?

There are consequences for all those who engage in unprotected sex. However, teenagers are particularly at risk, mostly because they use effective contraception less consistently than adults. No surprises, then, that the reduction or delay of sexual involvement among young people has become a major priority for policy-makers motivated by concerns about sexually transmitted infection and unintended pregnancy. In order to understand how best to get teens to delay having sex, researchers have looked at factors that might influence sexual timing. The evidence lends support to an old stereotype: geeks really don’t get laid. Studies consistently report that young people with higher scores on measures of intelligence and academic performance are significantly more likely to delay the age at which they first have sex. The problem is that to do anything useful with this knowledge, program developers and policy-makers need to know why intelligence and academic performance influence the age at which young people first have sex. It could be that each factor influences sexual behavior directly, but an alternative theory is that the link can be explained by the same family background factors that contribute to both cognitive and sexual outcomes.The link between intelligence, academic performance, and sexIt may be that some “background” factor links intelligence, academic performance, and sexual activity, suggest US researchers writing in Child Development. They say, “The existing findings on age at first sex, intelligence, and academic achievement have likely been muddied by ‘background’ variables that may have not been adequately accounted for in the literature to date.”In other words, environmental and genetic characteristics that “run in families” might simultaneously influence intelligence, academic performance and sexual timing. Kathryn P. Harden, of the University of Texas at Austin, and Jane Mendle, of the University of Oregon, tested this idea out in a study involving over 500 same-sex monozygotic twins (that is, twins who share 100% of their genes) who were recruited from a larger project known as the National Longitudinal Study of Adolescent Health (NLSAH). NLSAH was designed to collect information on health and risk-taking behavior in a nationally representative sample of adolescents. Intelligence was measured via the Peabody Picture Vocabulary Test (PPVT; a measure of verbal intelligence) and academic achievement measured via grade point average. Age at first sex was obtained from teenagers’ own self-reports. Harden and Mendle argue that intelligence and academic achievement are related to sexual timing via different processes. Intelligence, they say, is linked to age at first sex by environmental differences between families. “Families who, on average, have higher intelligence also delay, on average, initiating sexual activity, but twins raised in the same family who differ in their intellectual capacities do not differ in their age at first sex.“Thus, it is not intelligence, per se, that results in delayed sexual activity; rather, intelligence represents a proxy variable for socioenvironmental differences between families that are associated with both higher average levels of intelligence in family members and later average ages at first sex.”By contrast, the authors find that the association between academic achievement and age at first sex is fully accounted for by common underlying genes - independent of genes related to intelligence. This leads to the startling conclusion that the genes that influence academic achievement also influence age at first sex.Next steps: opening the “black box”But there is still more work to do. The specific environmental and genetic variables operating in the link between intelligence, academic performance and sexual timing remain a “black box.” Twin studies may be able to identify whether an influence is broadly genetic or environmental, but this research design can’t pinpoint specific genetic or environmental factors. It is important to note that neither intelligence nor academic performance “causes” sexual activity – or the lack of sexual activity. Improving academic attainment or somehow increasing intelligence will not necessarily discourage a teenager from engaging in sexual intercourse. More research is required on causal mechanisms before developers can create prevention programs to delay adolescents’ first experiences of sexual behavior. One thing Harden and Mendle know for sure is that environmental influence is more than can be captured in economic status, race or ethnicity - none of which could fully explain the relationship between intelligence and sexual behavior in this study. Possible additional factors might include levels of parental supervision and monitoring. That is, parents involved in their children’s education may actively monitor and gate their children’s opportunities for romance and sex. Extra-familial influences may also be important. Twins may share other environments; they probably attend the same school and have similar friendship groups. School-wide norms about the acceptability of sexual behavior may therefore also have a role to play. Where genetics are concerned, one potential avenue of further exploration is the extent to which genes influence the timing of pubertal maturation. Harden and Mendle say, “When children mature physically is one of the strongest predictors of when they report sexual desire, first date, behaviors such as kissing and petting, and first sexual intercourse.” At the same time, early pubertal timing is also correlated with lower achievement, truancy and a range of poor academic outcomes. Reference:Harden, K.P., & Mendle, J. (2011). Why don’t smart teens have sex? A behavioral genetic approach. Child Development, 82(4), 1327-1344.

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