Genes and social networks in monkeys and people

My latest Mind and Matter column in the Wall Street Journal:

Not only is the capacity for forming large social networks in monkeys partly genetic, but some of the genes that affect this ability may now be known. So suggests a new study of an isolated population of free-living macaques on an island off Puerto Rico.

Lauren Brent of Duke University and her colleagues collected information on the social networks of about 100 monkeys, measuring how much time they spent grooming each other and how close together they sat. The researchers recorded not only how many "friends" each had but how many "friends of friends." The latter measure, in both social animals and human beings, has proved valuable in determining rank and well-being.

Because the family tree of this isolated population of monkeys is well known, Dr. Brent and her colleagues could tease apart the influences of nature and nurture. They found that, correcting for things such as sex and age, a monkey's "tendency to interact frequently in an affiliative manner with partners who themselves interact affiliatively at high rates with others" could be at least partly predicted from its genetic parentage.

Moreover, based on which version the monkeys had of the genes SLC6A4 and TPH2, the researchers were able to predict which individuals spent a lot of time grooming partners who themselves spend a lot of time grooming their own partners. The statistical significance of this finding remains tentative, but it looks as if having the rare version of both genes made monkeys less social, while either mutation alone had no effect.

The mutations making monkeys less social have been tied to anxiety and a tendency to avoid risks. This may explain why they persist. Although well-connected monkeys generally have more offspring, anxious monkeys may be more vigilant to threats.

It's a measure of the way the intellectual world has evolved that 50 years ago such a study would have shocked the scientific world and brought down a storm of protest.

When the great California Institute of Technology geneticist Seymour Benzer set out in the mid-1960s to find mutations in fruit flies that affected behavior, rather than mere anatomy, he was ridiculed for challenging the consensus that all behavior must be learned.

Benzer told the geneticist Max Delbrück about the plan to find behavioral mutants; Delbrück said it was impossible. To which Benzer replied: "But, Max, we found the gene, we've already done it!" (Benzer's mother was more succinct: "From this, you can make a living?") He was soon able to identify mutations related to hyperexcitability, learning, homosexuality and unusual circadian rhythms, like his own: Benzer was almost wholly nocturnal.

Since then, thanks to studies of human twins and a rash of genetic investigations in animals, it has become routinely accepted that most things, including personality, sexual orientation and intelligence, are to some degree affected by genes. The University of Virginia's Eric Turkheimer has declared what he calls the "first law of behavior genetics": that all human behavioral traits are heritable.

In 2009 a study of human twins by James Fowler of the University of California at San Diego and colleagues found evidence of genetic heritability of social networks similar to that now reported in monkeys. Frankly, there's nothing surprising here. We all know people who are intrinsically less sociable than others, because of their personalities not their circumstances.

As always in such nature-nurture debates, the red herring to avoid is "determinism." A discovery that genes affect behavior is no more or less deterministic than a discovery that family or education does so. Whether you are antisocial because your mother was unemotional-a fashionable theory in the 1960s-or because of a mutation tells you nothing about whether your condition can be remedied by some intervention.