Armies train by marching in step. Religions around the world incorporate many forms of singing and chanting into their rituals. Citizens sing the National Anthem before sporting events. Why do we participate in these various synchronized activities? A new study, published in the journal Psychological Science, suggests that when people engage in synchronous activity together, they become more likely to cooperate with other group members.

Stanford University psychologists Scott S. Wiltermuth and Chip Heath conducted a series of experiments to see how synchronous movement affects group interactions. In the first experiment, two groups of volunteers walked around campus - one group was told to walk normally and the other group was told to walk in-step. Following the walks, the volunteers participated in an economics game that measures expectations of cooperation- the more the volunteers cooperate, the larger the payoff they would receive at the end of the experiment.

. In the second experiment, volunteers listened to music via headphones and had to move cups back and forth in time to the music. The volunteers were divided into different groups, so that some of the groups listened to the same music and thus moved their cups in a synchronous manner. In the other groups, the volunteers listened to music at different tempos, so their movements were not synchronized. This was again followed by an economics game where more cooperation would result in larger payoff. This final game was designed so that players could put tokens in a public account, or keep the tokens for themselves. The general economic strategy in this game is to behave selfishly keeping one's tokens in a private account while at the same time taking advantage of others' contributions to the public account.

The results showed that synchrony fosters cooperation- even when all of the volunteers had financial incentives to cooperate, the volunteers from the synchronized groups tended to be more cooperative during the games (and ended up earning more money) than volunteers from groups who had moved asynchronously. And even more interesting, in the last economics game, participants from the synchronized groups were more willing to contribute tokens to the public account, sacrificing their own money to help their group. In addition, volunteers from the synchronous groups reported greater feelings of being on the same team. Thus, the synchronous participants cooperated during the games in part because they felt as though they were part of a team.

Societies rely on cooperation among their members to thrive and be successful. These findings suggest that cultural practices which involve synchrony (such as dancing, singing or marching) may enable groups to produce members who are cooperative and willing to make personal sacrifices, for the benefit of the group. The authors conclude that "synchrony rituals may have therefore endowed some cultural groups with an advantage in societal evolution, leading some groups to survive where others have failed."