B

Oxytocin’s role in human behaviour first emerged in 2005. In a groundbreaking experiments, Markus Heinrichs and his colleagues at the University of Freiburg, Germany, asked volunteers to do an activity in which they could invest money with an anonymous person who was not guaranteed to be honest. The team found the participants who had sniffed oxytocin via a nasal spray beforehand invested more money than those who received a placebo instead. The study was the start of research into the effects of oxytocin on human interactions. ‘For eight years, it was quite a lonesome field,’ Heinrichs recalls. ‘Now, everyone is interested.’ These follow-up studies have shown that after a sniff of the hormone, people become more charitable, better at reading emotions on others’ faces and at communicating constructively in arguments. Together, the results fuelled the view that oxytocin universally enhanced the positive aspects of our social nature.

C

Then, after a few years, contrasting findings began to emerge. Simone Shamay-Tsoory at the at the University of Haifa, Israel, found that when volunteers played a competitive game, those who inhaled the hormone showed more pleasure when they beat other players, and felt more envy when others won. What’s more, administering oxytocin also has sharply contrasting outcomes depending on a person’s disposition. Jennifer Bartz from Mount Sinai School of Medicine, New York, found that it improves people’s ability to read emotions, but only if they are not very socially adept to begin with. Her research also shows that oxytocin in fact reduces cooperation in subjects who are particularly anxious or sensitive to rejection.