Previous studies have already linked the hormones oxytocin and vasopressin to displays of niceness or "prosocial behavior", both in the lab and in close relationships. For example, we know that oxytocin promotes maternal behavior, and that in the lab, volunteers exposed to the hormone show greater sociability.
Now psychologists from the University at Buffalo and the University of California, Irvine, say that people's niceness may also depend on genes: namely the genes that control the receptors that bind to these two hormones.
Plus, they say, the genes' influence also depends on whether people's perception of the world is that it is generally a good place where people are basically good, or whether it is a bad place, where people are generally bad.
Hormones interact with cells by binding with receptors on their surface (rather like specialized docking stations, each tailored to receive a particular hormone). Once the hormone is attached, it can send signals into the cell that influence the cell's function.
There are several genes that control the function of oxytocin and vasopressin receptors.
Principal author Dr Michel Poulin is assistant professor of psychology at University at Buffalo. He told the media:
"We aren't saying we've found the niceness gene."
"But we have found a gene that makes a contribution. What I find so interesting is the fact that it only makes a contribution in the presence of certain feelings people have about the world around them," he adds.
For their study, Poulin and colleagues looked at the results of a nationally representative survey that asked people about their attitudes toward civic duty (eg whether people have a duty to report a crime or pay taxes); other people and the world in general (eg are people basically good, is the world more good than bad); and about their charitable activities (eg giving blood, going to PTA meetings, doing charity work).
711 of those surveyed also gave a sample of saliva for DNA analysis. This allowed the researchers to find out which variants of the oxytocin and vasopressin receptor genes they had.
Poulin said they found that the genes "combined with people's perceptions of the world as a more or less threatening place to predict generosity".
"Specifically, study participants who found the world threatening were less likely to help others - unless they had versions of the receptor genes that are generally associated with niceness," he explained.
Poulin said the "nicer" variants of the genes allow people to "overcome feelings of the world being threatening and help other people in spite of those fears".
Poulin said we should not be surprised that the genes predicted behavior only in combination with experiences and feelings about the world, because "most connections between DNA and social behavior are complex".
"So if one of your neighbors seems really generous, caring, civic-minded kind of person, while another seems more selfish, tight-fisted and not as interested in pitching in, their DNA may help explain why one of them is nicer than the other," he added.
Written by Catharine Paddock PhD