Oxytocin is known as the “love hormone” because it encourages trust, cooperation and social bonding. But these effects may exist only for members of your own clan, according to a study published in January in the Proceedings of the National Academy of Sciences USA. Psychologists at the University of Amsterdam found that Dutch men who inhaled oxytocin were more likely to associate positive words, such as joy and laughter, and complex positive emotions, such as hope and admiration, with Dutch people than with Germans or Arabs.

Next, subjects had to choose whether to stop a trolley from running into five people by hitting a switch that would divert it to another track, where it would kill only one person—a commonly studied moral dilemma. Under the influence of oxytocin, Dutch men were less likely to sacrifice a Dutch male than a German or Arab. Because the drug enhances bias against people belonging to other groups, it may contribute to bigotry just as much as harmony.