Researchers have found why we are surprisingly fair and trusting with unfamiliar individuals.
This pro-social behaviour results from a change in social norms that allowed us to trust strangers, according to the new study.
The change is likely linked to a rise in markets where goods are exchanged for money, as well as increased participation in major world religions.
The finding challenges a previously suggested theory- the idea that we treat strangers fairly because we mistakenly transferred our feelings of kinship to unrelated individuals as societies grew.
The results, based on more than 2,000 participants from 15 societies across the globe, show that "fair" behaviour during a bargaining game increases the more a society has incorporated market exchange and world religions.
"Measures of fairness toward anonymous others, in terms of motivations and beliefs, vary dramatically across human societies. And we can explain most of the variation between groups by the degree of market incorporation and the presence of a world religion," Live Science quoted study author Joseph Henrich, an anthropologist at the University of British Columbia, Canada, as saying.
According to researchers, in order for market exchange to really take off, societies had to evolve new norms for interacting with strangers.
Similarly, major world religions, with their beliefs about fairness and punishment, could have also influenced changes norms and allowed societies to grow.
Religions in small-scale societies tend to lack such moralizing gods that are concerned with generosity toward strangers, said Henrich.
"One of the things that might have occurred through cultural evolution to help build these larger groups, is the evolution of religious systems with supernatural agents that were in some sense police, concerned about those elements of behavior that would facilitate exchange and trade and harmonious groups, allowing groups to get larger and larger," he said.
To test out these ideas, the researchers studied participants from small-scale communities in Africa, North and South America, Oceania, New Guinea, and Asia.
The subjects played three bargaining games.
Very small communities with almost no market integration and less involvement in world religions generally made lower, or less fair, offers during the games, and were less willing to punish unfair offers.
On the flip side, the largest societies with the most market integration and world religion participation made higher offers, and were more willing to penalize those who made unfair offers.
"This is consistent with the idea that the expansion of human societies was driven by the evolution of these norms that allowed people to interact with strangers," said Henrich.
The results will be published in the journal Science.