Nature vs. Nurture

For most of the late twentieth century, political scientists embraced blank-slate theories in which people soaked up the ideology of their parents or the TV programs they watched. Some political scientists even said that most people were so confused about political issues that they had no real ideology at all.11 But then came the studies of twins.

In the 1980s, when scientists began analyzing large databases that allowed them to compare identical twins (who share all of their genes, plus, usually, their prenatal and childhood environments) to same-sex fraternal twins (who share half of their genes, plus their prenatal and childhood environments), they found that the identical twins were more similar on just about everything.

And what’s more, identical twins reared in separate households (because of adoption) usually turn out to be very similar, whereas unrelated children reared together (because of adoption) rarely turn out similar to each other, or to their adoptive parents; they tend to be more similar to their genetic parents. Genes contribute, somehow, to just about every aspect of our personalities.

We’re not just talking about IQ, mental illness, and basic personality traits such as shyness. We’re talking about the degree to which you like jazz, spicy foods, and abstract art; your likelihood of getting a divorce or dying in a car crash; your degree of religiosity, and your political orientation as an adult. Whether you end up on the right or the left of the political spectrum turns out to be just as heritable as most other traits: genetics explains between a third and a half of the variability among people on their political attitudes. Being raised in a liberal or conservative household accounts for much less.