The names may vary — medicine man, witch doctor, holy man, prophet — but the notion of the shaman, someone who uses trance to commune with the supernatural and effect real-world change, is one that crosses virtually all cultural boundaries.

The question of why is among the central puzzles of anthropology.

At least part of the answer lies with the way humans — from hunter-gatherer tribes in the rainforest to people living in a modern city — are wired to think about the world and other humans, contends Manvir Singh, a graduate student in the Department of Human Evolutionary Biology in the Graduate School of Arts and Sciences, whose paper was published in Behavioral and Brain Sciences.

Singh’s paper, along with more than two dozen commentaries from researchers in a host of fields, argues that shamanism develops as specialists compete to provide magical services to their community. The outcome is a set of traditions that hacks people’s psychological biases to convince them that they can control the uncertain.

“The theory is that there are important things we really want to have control over — calling rain, summoning animals, healing illness,” he said. “All around the world, people believe that these important, uncertain outcomes are influenced by invisible forces — gods, witches, their ancestors, fairies, and more. But a shaman says, ‘I can control that. I can talk to fairies. I can see signs of witches. I can be possessed by a god or speak to them.’”

To understand how shamanism emerges, Singh first had to address a nagging question in anthropology — what exactly is a shaman?

“It’s a hugely debated and contested idea,” he said. “But in the most general terms, a shaman is a person in a group who enters a type of trance — a very foreign behavioral and psychological state — to provide services to the community.”

Those services, Singh said, could range from healing disease to exorcising evil spirits to telling fortunes, or even changing the weather.