Individuals homozygous for the G allele (carrying two copies of the G version of the gene) of the oxytocin receptor tend to be more "prosocial," defined by researchers as the ability to behave in a way that benefits another person. In contrast, the carriers of the A version of the gene (AG or AA genotypes) tend to have a higher risk of autism, as well as self-reported lower levels of positive emotions, empathy and parental sensitivity.
Not Exactly Rocket Science notes that the sample size for the study is very small, so it's too early to say "this gene causes this trait." But imagine we reach that point. Imagine further, we reach a point where we find a set of genes that influences not only sociability and altruism, but tribalism - the ability to be extremely caring and altruistic towards your own kind, but dehumanize the outgroup.
Regardless of how we think about it in this country, in the world's dictatorships, genetic engineering will easily make the leap from "forbidden" to "mandatory." The Chinese state, says Mr. Derbyshire elsewhere, already encourages strong tribalism through propaganda. If their state doesn't liberalize before cheap genetic engineering comes along, what's their likely use of the technology? How about the world's Islamic dictatorships, which employ tribal instincts in a different form? (And given the inborn nature of religious instincts...with those?)
Mr. Derbyshire paraphrases Trotsky: "You may not be interested in this stuff, but it's interested in you."