“If the authors are right, or even in the vicinity of being right, it couldn’t be bigger,” says Stephen Stich, a philosopher and cognitive scientist at Rutgers University in New Brunswick, New Jersey, who wasn’t involved in the work. “What they are offering to explain is the emergence of democratic institutions, of individualism in the West.”

In what may come as a surprise to freethinkers and nonconformists happily defying social conventions these days in New York City, Paris, Sydney and other centers of Western culture, Dr. Henrich and collegaues' study traces the origins of...