Humans tend to have either two long (L/L) or two short (S/S) versions of the serotonin transporter gene, which is known to regulate emotion. Previous research has shown that people who instead have one short and one long (S/L) version -- which is more common in people of Asian descent -- tend to exhibit more social anxiety and similar behaviors. Rhesus macaque monkeys are the only other primates with the genetic trait.

Duke University researchers, in a series of experiments discussed in the Jan. 13 online issue of PLoS One, found monkeys with the S/L versions spent less time looking other monkeys in the face and eyes, were less likely to take risks, and less likely to want to look at a picture of a high-status male monkey than those with the L/L versions.

"For both human and non-human primates, faces and eyes are a rich source of social information, and it's well-established that both humans and macaques tend to direct visual attention to faces, especially the eye region," Michael Platt, an associate professor of neurobiology at Duke University Medical Center and an expert in neuroeconomics, said in a news release issued by the school. "Rhesus monkeys live in highly despotic societies and convey social rank information by making threats and showing dominant and submissive behaviors."

The findings could give researchers a new model to help in studying autism, social anxiety and schizophrenia.

"Altogether, our data show that genetic variation in serotonin function does contribute to social reward and punishment in macaques, and thus shapes social behavior in both humans and rhesus macaques," lead author Karli Watson, of the Duke Department of Neurobiology, said in the same news release. "This study confirms rhesus monkeys can serve as a model of what goes on in our brains, even in the case of social behavior."

More information

The U.S. National Institute of Mental Health has more about social anxiety disorder.