02/27/2013 10:19 am ET Updated Apr 29, 2013

Clap Clap Boom Boom Slam

The Washington Post, my local newspaper, ran a fascinating and unusual front page story this morning. The article focused on a recent phenomenon at Alice Deal Middle School called "Cups." "Cups" is a clapping game, in which children -- mostly girls -- beat out a rhythm on upturned cups, then turn them over and slam then on the table, over and over. The interesting thing about "Cups" is that nobody seems to know where it originated. It just appeared and spread through the student body in a week's time, taking over the playground and cafeteria.

The Post reporter, Robert Samuels, did an admirable job of trying to track down the source of "Cups" -- though in the end it remains somewhat of a mystery. It's apparently akin to other rhythmic games -- "Miss Mary Mack" and "Slide" -- enduring products of an oral culture based on clapping and chanting, which today spread from child to child, playground to playground, town to town, state to state.

There is actually some intriguing psychological science that illuminates "Cups" and other rhythmic traditions. They have the same basic appeal as military formations, high school marching bands, church choirs, and synchronized swimming. Anthropologists and cultural historians have offered up a variety of theories about synchrony over the years, mostly having to do with group coherence. One theory, for example, holds that various communities benefit from the actual physical synchrony -- or "muscular bonding" -- which builds group cohesiveness. Another idea is that synchronous activities lead to "collective effervescence" -- positive emotions that break down the boundaries between self and group.

But neither of these theories has been proven, and what's more, neither is complete. Muscle bonding may explain the coherence of the 14th Infantry Regiment, but those guys don't seem very effervescent -- not in the way that, say, carnival revelers are. And gross motor coordination doesn't explain the almost motionless chanting of Tibetan monks. Psychologists have been looking for a unifying theory for the appeal of synchrony.

One idea, put forth by psychological scientists Scott Wiltermuth and Chip Heath of Stanford University a couple years ago, is that all synchrony -- movement and sound and both together -- is an ancient ritual that evolved for the economic benefit of the group. The primary goal of rhythmic dancing and marching and chanting is to solve the problem of the freeloader -- the community member who hurts the collective good by taking but not contributing. Muscular bonding and collective joy are mere byproducts of this more fundamental economic ritual.

Wiltermuth and Heath ran a series of lab experiments to test this idea. In the simplest version, the researchers simply took groups of Stanford students on walks around campus; some walked in step -- marching basically -- while others just strolled the way students usually stroll. Later, after the students thought the experiment was over, the psychologists gave them all what's called the "Weak Link" test. In this test, each volunteer chooses to act either self-interestedly or cooperatively, depending on what he anticipates others will do. The test basically measures the expectation that others will value the group over themselves.

The marchers acted more cooperatively than the strollers. They also said that they felt more "connected" than did the strollers. Notably, they did not report feeling any happier, suggesting that positive emotions were not necessary for the achieving the boost in group cohesiveness.

The scientists wanted to do a more fine-grained test of their idea. It's well known that a sense of common identity and shared fate boosts group cohesiveness, but the researchers wanted to see if synchrony contributes to group cohesiveness above and beyond this. They did a rather elaborate test to sort this out. They had students perform tasks -- moving plastic cups -- that required differing degrees of coordination with others. While doing this, they listened to "O Canada" through headphones. Remember that these were Stanford students, so the Canadian national anthem presumably had no emotional resonance for them; it was merely a synchronous act.

So some of the students sang and moved the cups in rhythm, while others just sang in unison and others merely read the lyrics silently. Still others sang and moved to different tempos -- sort of like a really bad dancer moving at odds with the music. Then they did the same "Weak Link" test on all of them, only this time there was real money involved. As before, those who had experienced synchrony were more economically cooperative than those who had not. The bad dancers were bad citizens, but the physical movement otherwise made no difference; choral singers were selfless with or without the swaying, suggesting that muscle bonding is (like joy) unnecessary to get the desired group coherence. The swaying may be enjoyable, but the group singing was sufficient.

The choral singers also said they felt more part of the team. They felt they had more in common with the others, and they trusted them somewhat more. Interestingly, as they reported a couple years ago in the journal Psychological Science, they also made more money in the end, because they shared in the group bounty.

Synchrony rituals are powerful -- so powerful that they may have endowed certain groups with a competitive advantage over the eons, perhaps even causing some cultures to flourish while others perished. It's no wonder then that such potent impulses remain entrenched in today's churches and armies -- and even in middle school cafeterias.

Wray Herbert's blogs--"We're Only Human" and "Full Frontal Psychology"--appear regularly in The Huffington Post.