Today's most successful religions have one thing in common: moralizing gods that care about how people treat one another and will punish those who are selfish and cruel. But for most of human history, these "big gods" were the exception. If today's hunter-gatherers are any guide, for thousands of years our ancestors conceived of deities as utterly indifferent to the human realm, and to whether we behaved well or badly. Now, to crack the mystery of why and how people around the world came to believe in moralizing gods, researchers are using a novel tool in religious studies: the scientific method. By combining laboratory experiments, cross-cultural fieldwork, and analysis of the historical record, an interdisciplinary team has proposed that belief in judgmental deities was key to the cooperation needed to build and sustain large, complex societies. And once big gods and big societies existed, their moralizing deities helped religions as dissimilar as Islam and Mormonism to spread by making groups of the faithful more cooperative and therefore more successful. Critics say the big gods team is projecting modern values onto ancient cultures, and that belief in moralizing deities is a byproduct of other social changes. To settle the debate, researchers are looking for quantitative data in novel places, including the historical record.

To read the full story, see the 28 August issue of Science.