Genetic influence and human responsibility

Via FuturePundit, an interesting look at the influence of genetic factors on human behavior. New Scientist reports a new study of twins that suggests genetic factors affect the age of first intercourse.

“It’s not like there’s a gene for having a sex at a certain date,” says Nancy Segal, a psychologist at California State University in Fullerton who led the new study. Instead, heritable behavioural traits such as impulsivity could help determine when people first have sex, she says.

As genetic determinism goes, the new findings are modest. Segal’s team found that genes explain a third of the differences in participants’ age at first intercourse – which was, on average, a little over 19 years old. By comparison, roughly 80% of variations in height across a population can be explained by genes alone.

The study nicely illustrates a larger point about the relationship between our genetic makeup and our behavior. Contrary to what some Christians have argued (particularly in regards to homosexuality), our genes indisputably shape our personalities and lives in powerful ways. However, this does not mean, as others argue, that we are simply the sum of our genetic predispositions.

Rather, our genetic makeup provides us with traits, tendencies, and predispositions that influence but do not determine our behavior. As Dr. Segal explains in the quote above, personality traits such as impulsivity are genetically-linked, and such traits certainly affect the likelihood that one will lose one’s virginity at an earlier age. If we picture an axis ranging from Strong Self Control on one end to Significant Impulsivity on the other, our genetic makeup contributes to where we fall on that axis; and where we fall on the axis is certainly relevant to the question of how easily sexual temptations will be resisted.

However, genetic predisposition does not equal necessity, a point that the study also makes. “On the other hand, conservative social mores might delay a teen’s first sexual experience… Indeed, Segal’s team noticed a less pronounced genetic effect among twins born before 1948, compared with those who came of age in the 1960s or later.” As FuturePundit’s Randall Parker explains, “This supports an argument I’ve made here previously: the breakdown of old cultural constraints on behavior frees up people to follow genetically driven desires and impulses. We become more genetically driven as external constraints weaken.” Or, looking at the flip side, the stronger our internalized moral code, the more likely it is to overcome genetic predispositions towards illicit behavior.

Our genetic makeup matters. It creates the set of traits, tendencies, and predispositions – the “raw material” – that we have to work with, and different people have different raw material. What we make of what we are, though, is ultimately up to us.