To save any of his marching bandmates, Steve Marx says, he would run into onrushing traffic with no hesitation. It's the kind of language often heard from former army buddies, not musicians, but Marx brings up the scenario to show the strength of his feelings about this group. The marching band director at Gettysburg College in Pennsylvania has been participating in musical ensembles for more than 20 years, since he was in high school, and says that “the sort of bonding that you form is extremely strong. It's like a family.” Everyone is in matching uniforms, musical instruments in hands, marching forward in perfect harmony, left leg, right leg, movements and sounds so synchronized that individuals blur into the greater group. The allure is not even that much about music, he admits. Marching, for him, is mostly about the sense of kinship.

Many group activities boost our sense of belonging, but research shows that doing things synchronously can build even stronger social ties and create a greater sense of well-being. Crew rowing, line dancing, choir singing or simply tapping fingers in sync increases generosity, trust and tolerance toward others, often beyond effects seen in more disorderly doings. It can even increase people's threshold for pain. Why simultaneous, coordinated movement delivers this extra dose of affinity is just now becoming understood, according to Laura Cirelli, a psychologist and synchrony researcher at the University of Toronto. The phenomenon's powerful effects on us result from a combination of neurohormonal, cognitive and perceptual factors. “It's a complicated interplay,” she says. There is also evidence that we have a propensity for synchrony that may have been selected during the course of human evolution, in part because it allows us to bond with large numbers of people at once, offering a survival advantage.

People are not unique in their capability to synchronize activities—certain animals do it as well. Bottlenose dolphins arc through the water in unison, for instance, and males of some firefly species harmonize their flashes. Animal behaviorists theorize that, as with humans, these coordinated behaviors promote various positive social benefits, like attracting a mate. What sets us apart is that our synchrony happens across such a wide variety of behaviors. Some are organized—think of group prayers, chorale singing, military parades and flash mobs. Some are spontaneous—think of concertgoers clapping in time to a song or of a couple strolling through a park, their feet hitting the path at the exact same time. If two people sit in rocking chairs beside each other, studies have shown, they will impulsively start moving back and forth in parallel.

Marx credits synchrony for his devotion to his bandmates, and psychological experiments have shown this kind of coordination does improve group feelings. In one study, researchers at the University of Oxford split young schoolchildren into two groups. One wore orange vests and the other green vests. Such costuming can incite divisions among kids. The experimenters, however, asked the children to spend time dancing together synchronously. Afterward the greens and the oranges bonded more and played closer to each other than similarly divided children who danced in an uncoordinated way.

Performers move as a group for ingoma, a traditional Zulu dance in South Africa. Credit: Rajesh Jantilal Getty Images

Improved affinity

It's not just child's play. A series of experiments in Hungary, published in 2019, suggests that walking in sync with a person from an ethnic minority can reduce prejudice. Negative stereotyping of Roma people is prevalent in Hungary. When researchers asked non-Roma to assign positive or negative words to pictures of traditionally dressed Roma people, they used more negative words. When the same group looked at pictures of traditionally dressed Hungarian people, they used more positive words. Then the investigators asked the non-Roma to walk laps around a large room either in sync or out of sync with someone who was introduced as Roma. When later the researchers asked about the volunteers' feelings toward the Roma, those who engaged in synchrony expressed a greater sense of closeness and indicated more desire to see their partners again.

The scientists do not know how long such effects might last, so coordination may not be a permanent remedy for antagonism. Still, it does appear to minimize bias in some situations, and one possible reason may be because it simply makes us like one another more. In a study published in 2009 in Social Cognition, participants tapped their fingers in rhythm with a metronome and in some instances were joined by an experimenter who drummed either to the same beat or to a different one. Results showed that volunteers who were coordinated with the experimenter were later more inclined to say that they found him likable.

These feelings of affinity translate into more positive behavior toward others. Synchronous finger tapping, for example, can prompt people to be more generous when donating money. In a series of experiments published in 2017 in Basic and Applied Social Psychology, researchers divided volunteers into groups of six, which were then further split into subgroups of three. After members briefly worked together on a group activity, they were given various scenarios for splitting money among themselves and asked to whom they would give. If they then spent time tapping fingers in synchrony with their little trio only, they were more willing to donate money to those people. But if two of these trios tapped in sync—forming a group of six for a few minutes—the members were more likely to donate to all six. Asynchronous tapping, meanwhile, did nothing to boost generosity. A 2017 meta-analysis of 42 studies confirmed that synchronous activities, from running in sync to rocking in chairs at the same pace, prompt people to behave prosocially.

Psychologists and neuroscientists explain the way synchrony draws people together with a dry term: self-other blurring. “It's a weakening of boundaries between self and other. As we become attuned to other people's actions, whether we do it consciously or not, we integrate them with our own,” says Ivana Konvalinka, a cognitive neuroscientist at the Technical University of Denmark.

Even very small children tend to be more helpful after engaging in synchrony. Babies cannot be told to act in sync, of course, so researchers have come up with creative ways to examine the effect. In one experiment published in 2017 in Music Perception, a person had a 14-month-old infant strapped to his or her chest in a baby carrier and another person standing in front of them. Both adults began to bounce, sometimes in perfect synchrony, sometimes not. This made the babies bounce, too. Psychologists conducted a series of experiments using this design. After the in-unison bouncing session, if the second adult dropped a ball or other object, the babies were quite eager to pick it up and hand it back. But those infants who were not bounced in sync were not as helpful. The fact that the effects of synchrony are apparent in such small children suggests this behavior is important to the species, says cognitive anthropologist Emma Cohen of the University of Oxford. “If something is emerging really early in life, then it's likely fairly automatic and really salient for us as humans,” she says. It may even have played an important role in our evolution.

Evolving in unison

Psychologist Robin Dunbar of Oxford believes that by facilitating prosocial behaviors and cooperation, synchrony could have encouraged bonding in groups of early humans as their populations grew. He has been researching synchrony for years, a fascination that started at a conference on the archaeology of music. One of the evening sessions was unusual. A musician from South Africa invited Dunbar and other attendants to participate in something resembling a traditional Zulu dance. He told them to stand in a circle, handed them plastic pipes cut to different lengths and instructed them to blow across the top of the pipes, making random noise, and to start walking around the circle. At first, Dunbar says, the noise was horrible, but after a few minutes the sounds and movements changed without particular effort, the scientists became synchronized, playing music in a consistent tune with one another. “Everybody felt this sense of belonging, being part of the group. I realized this was an amazing effect,” he says.

Dunbar now theorizes that in human evolution synchrony might have enhanced grooming as an important bonding mechanism. Nonhuman primates groom one another to remove fleas and other parasites, and the time spent doing this promotes group cohesion. The activity does take a lot of time and effort as the number of groomed individuals increases, and Dunbar argues that sets an upper limit on the size of a close-knit group. When he plotted the time that various primate species spend grooming one another against their typical group size, it appeared that the two were directly correlated. The upper limit corresponded to a group size of 50 primates. No monkey or ape species forms groups that are, on average, larger, but humans do. Dunbar calculated that a natural community for us stands at about 150 people. He worked out this number based on the size of the human neocortex compared with those of other primates, as well as the populations of villages in small-scale societies and the number of friends and family that people in larger-scale societies tend to have. That figure is borne out in early historical records, too: it was the average village size in England in A.D. 1086 when William the Conqueror surveyed his new kingdom. (Not everyone agrees 150 is a solid number; some scientists have argued it is based on overly selective data.)

One reason early humans may have been able to sustain a group size that is triple that of the average ape, Dunbar suggests, is they came up with a way to “groom” several people at once—using voices or body movements instead of picking parasites with fingers. The larger size offered groups protection against raids by other humans, increasing their ability to survive and reproduce, which in turn allowed for the natural selection of a propensity for synchrony in future generations, Dunbar contends.

The adoption of such behavior often has biological underpinnings. In nonhuman primates grooming triggers the release of neurochemicals called endorphins, which seems to enhance good feelings, Dunbar says. And research suggests that endorphins, which the body produces to reinforce pleasure and relieve pain, might be among the mechanisms that allowed singing and dancing to replace classic grooming in human bonding. Some researchers have called them the “neurochemical glue” of human relationships.

Rowers who train in synchrony have higher levels of endorphins, brain chemicals that blunt pain. Credit: Harald Sund Getty Images

Brains and movement

An endorphin-infused sense of bonding and commitment has been apparent in several experiments, some of them coming from Dunbar's laboratory. One of the early studies showed not only that synchronous behaviors likely trigger the endorphin systems but also that they do so beyond the effects produced by the physical activity itself (the famed “runner's high”). In one of Dunbar's studies, male athletes from the University of Oxford Boat Club were invited to train on rowing machines independently and then work out in synchrony. After the exercise, researchers measured how much pain each of the rowers could take by inflating blood pressure cuffs on their arms until they could no longer take the discomfort. (Measuring endorphin levels directly is difficult, so brief pain perception is commonly used as a proxy.) Dunbar and his colleagues learned that athletes who exercised in sync with others were much more resistant to pain afterwards, and the scientists calculated their endorphin output basically doubled.

A similar series of experiments showed that when it comes to dancing, synchrony boosts endorphin effects far more than do dissonant moves around the floor. Volunteers were first taught some basic dance moves such as “driving” (one hand is extended as if resting on top of a steering wheel, crossing from left to right and back, while the other hand hangs relaxed along the body) or “swimming” (knees bending rhythmically, arms alternating from side to side as if doing the front crawl). Afterward, the participants were divided into groups of four and went onto the dance floor, where everyone was handed headphones through which music would flow. The trick, though, was that in some groups all four volunteers heard exactly the same music and were instructed to do the same movement routine, causing synchrony. But in other foursomes, the members heard different tunes or were instructed to do different routines—causing a weird, discordant silent disco. After the dancing was over, the blood pressure cuffs came out, and the measurements began. Once again, those who engaged in synchrony proved more resistant to pain, confirming that the effects are not merely caused by dancing with others but by dancing with others in synchrony. The scientists behind the experiments, which were published in 2016 in Evolution and Human Behavior, also checked how well the participants bonded. As in other studies of emotional reactions, those who boogied in sync said they felt closer to the other participants than did those who danced separately.

Although endorphins offer a neurochemical explanation for synchrony's powerful effects, other biological mechanisms may be at play, too. When it comes to activity patterns within the brain, synchrony seems to prompt different effects than does humming or shimmying without harmony. A 2020 study using functional near-infrared spectroscopy—a noninvasive technique that measures how much oxygen a particular brain region is using, which indicates how hard it is working—showed that while nonsynchronous movements mostly activate just the left hemisphere of the brain, synchrony involves activation of both the left and right hemispheres. This suggests that synchrony is a far more complex behavior than simpler movements.

Coordinated Rewards

Other research suggests that the brain's reward system, including the neural structures involved in desire and motivation, also plays a role in the power of synchrony by creating a positive feedback loop. Using functional magnetic resonance imaging—another way to gauge brain activity—a series of experiments revealed that for those who find drumming easy, doing it in sync hikes activity in the right caudate, a reward-related area, which in turn makes people more likely to help the person they drummed with. “We believe that during synchronized drumming, the caudate activity reflects the rewarding nature of the experience,” says Christian Keysers, a neuroscientist at the Netherlands Institute for Neuroscience and the study's lead author. “Participants will then be more likely to engage in joint actions with that person in the future.” People synchronize, our reward areas of the brain activate, and that pushes us to do more to help our partners.

Although not everyone experiences the effects of synchrony with equal force, the experience of moving in rhythm with others or of harmonizing voices appears to play an important role in human societies. That is likely why we see synchrony all over, in large symphony concerts, in dance parties and in village ceremonial performances. When we are in sync, our hormones and our brain activity help to smooth societal wrinkles, keeping us together. Joining a marching band may not be the path to world peace, but behavior like it may help make us more tolerant and better able to see the greater good in wider communities.