“Purity” may not be something you think about much, but research shows it is the moral foundation of human relationships. In a new study published in the Journal of Experimental Psychology: General, researchers from the University of Southern California suggest conflicting values of purity are responsible for driving people apart, and shared values of purity bring them together.

"We already knew that people were socially divided," said co-author Jesse Graham, who developed Moral Foundations Theory with NYU’s Jonathan Haidt. "We were trying to figure out which factors divide us."

The researchers tested how social distance between people would be affected by five groups of basic moral concerns: Care and harm; fairness and cheating; loyalty and betrayal; authority and subversion; and purity and degradation.

“The moral concern of purity, out of all the moral values, was the best predictor of distance between two people,” said Morteza Dehghani, lead author of the paper.

Through a unique experiment design, the study arrived at these results by combining traditional behavior experiments with big data from social media. It is one of the first investigations to do so.

"We started by observing relationships on Twitter, and by looking at distance between people — who they follow on Twitter and the type of rhetoric that they use," Dehghani said.

The study analyzed 731,000 tweets about the 2013 government shutdown, which were posted between October 1 and 24, almost one week after the shutdown. From those tweets, the researchers were able to map the social networks of 188,467 users and analyze the social distance between those users. They then used computational text analysis to measure those users’ moral concerns.

The results showed the degree to which Twitter users expressed moral purity, over all other moral concerns, could accurately predict how close their social interactions were.

"Concerns about purity could have to do with physical purity, like disgust or cleansing, but also a kind of spiritual purity — things like treating the body like a temple instead of a playground, resisting our lower carnal desires in favor of a higher, divine nature," Graham said. "It has a spiritual-moral dimension to it, but it's not necessarily explicitly religious."

Additionally, purity did not simply divide the liberals from the conservatives, as one may think. When the researchers separated the Twitter users into two distinct political groups, purity still predicted social distance within each of those groups.

"This could have potential implications for understanding political migrations, both in online social networks and in real life," Dehghani said.

The results from the Twitter study were replicated in two traditional behavioral experiments as well. In each of those experiments, participants were asked to rate how moral or immoral they thought different scenarios were, such as kicking a dog. Then, depending on the experiment and which group they were placed in, participants were given varying feedback on how well their scores matched with another person’s.

When people believed they matched highly on purity, they wished to be physically and socially closer to that person, and vice versa. Again, purity, above all other moral domains, had the most influence.

Source: Dehgani M, et al. Purity Homophily in Social Networks. Journal of Experimental Psychology: General. 2016.