Published: May 2, 2011
For as long as anyone in the tiny Spanish village of San Pedro Manrique can remember, people there have been walking on fire.
They do it every June 23, at midnight, celebrating the summer solstice by crossing a 23-foot-long carpet of oak embers that have burned for hours before sizzling down to a glowing red. The event is full of pageantry and symbolism: processions with religious statues, trumpets sounding before each fire-walk, and three virgins (or, these days, three women who are unmarried).
So when scientists wanted to measure the physiological effects of fire-walking to see if there were biological underpinnings of communal rituals, they encountered a few hurdles.
“We talked about measuring blood pressure, cortisol levels, pain tolerance,” said Ivana Konvalinka, a bioengineering doctoral student at Aarhus University in Denmark who helped lead the team. “We even talked about oxytocin,” a hormone involved in pleasure.
But with such readings difficult to obtain, they settled on heart rate, strapping monitors on fire-walkers and spectators to see whether the rates of spectators increased like those of people actually walking barefoot on hot coals.
Still, even persuading people to wear heart monitors was no easy feat. Before arriving, the research team of anthropologists, psychologists and religion experts had received permission from San Pedro Manrique’s mayor, but later he demurred, Ms. Konvalinka said.
“He said to us, if we are able to recruit people, then fine,” she said, “but he didn’t approve, and he told people not to participate.”
Some people dropped out or refused, including the people the fire-walkers carry on their backs, a group researchers considered monitoring. But others approached researchers at the last minute. Ultimately, they monitored 12 fire-walkers, 9 spectators related to fire-walkers, and 17 unrelated spectators who were just visiting. The mayor also required monitors to be concealed so they were invisible to the crowd, which filled the town’s special fire-walking amphitheater, built for 3,000 spectators, five times the number of villagers.
The researchers wanted to investigate what draws people to communal rituals like fire-walking.
“There’s the idea about rituals that they enhance group cohesion, but what creates this group?” Ms. Konvalinka said. “We figured there was some kind of autonomic nervous system measure that could capture the emotional effects of the ritual.”
The results surprised them. The heart rates of relatives and friends of the fire-walkers followed an almost identical pattern to the fire-walkers’ rates, spiking and dropping almost in synchrony. The heart rates of visiting spectators did not. The relatives’ rates synchronized throughout the event, which lasted 30 minutes, with 28 fire-walkers each making five-second walks. So relatives or friends’ heart rates matched a fire-walker’s rate before, during and after his walk. Even people related to other fire-walkers showed similar patterns.
Experts not involved in the study said despite the small number of participants, the results were intriguing. They build on research showing heart rates of fans of team sports surge when their teams score, and on studies demonstrating that people rocking in rocking chairs or tapping their fingers eventually synchronize their movements.
“It’s one study, but it’s a great study,” said Michael Richardson, an assistant professor ofpsychology at the University of Cincinnati. “It shows that being connected to someone is not just in the mind. There are these fundamental physiological behavioral moments that are occurring continuously with other people that we’re not aware of. There is a solid grounding of laboratory research which is completely consistent with their findings. It’s always hard to do these studies in the real world. This is the first study that has kind of done it on a big scale in a natural situation.”
Richard Sosis, an associate professor of anthropology at the University of Connecticut, said the study was “quite exciting,” contradicting the “assumption that rituals produce cohesion and solidarity only if there are shared movements, shared vocalizations or shared rhythms,” activities like singing, dancing or marching together. With fire-walking, spectators simply watched, without sharing activity or rhythm with the walkers. And different types of spectators had different results, with villagers in sync but out-of-towners not.
Dr. Sosis, co-editor of a new journal, Religion, Brain and Behavior, said there could be parallels with more common rituals, like weddings, baptisms or bar mitzvahs. He cited an experiment in which Paul Zak, a neuroeconomist, attended a wedding and measured oxytocin levels of the bride, groom and some relatives and friends, finding that several experienced surges in oxytocin as if bonding with the couple.
David Willey, a physicist at University of Pittsburgh at Johnstown, fire-walks himself and has reasoned that it does not normally burn because the embers do not transmit enough heat in their brief contact with feet. Heart-rate synchronization makes sense, he said, based on his fire-walking parties, where “there is very much a group feeling.”
Researchers might find similar heart-rate synchronization in other high-arousal rituals like “bending rebar with your throat, walking on broken glass, bungee jumping,” he said. “They can come to my backyard if they want.”
Ms. Konvalinka said the team plans another fire-walking study, this time in Mauritius. But they may also return to San Pedro Manrique. “At the end,” she said, “I think the mayor was O.K. with us being there.“