Generosity and cooperation found to be contagious

A new study has demonstrated that generosity and cooperation are contagious. The research was focused on hunter-gatherers in Tanzania – individuals who are far removed from the modern world – over the course of six years.

The research team found that the Hadza are generally willing to share, but this does not mean that they always do so. The willingness to share depended less on an individual and more on the group that they happened to live with at the time.

“We found that year after year, willingness to share with others clustered within residence groups or what we call ‘camps,’” said study lead author Coren Apicella of the University of Pennsylvania. “People were living with other people who were similar to them in levels of generosity.”

Study first author Kristopher Smith added, “We also found individual willingness to share changed from year to year to match their current campmates and found no evidence that people preferred living with more cooperative people.”

Significantly, the researchers observed that these trends persisted even as the Hadza people changed campmates every couple of months.

The study demonstrated that it is not simply that people who like to share choose to live with others who also like to share. Instead, people adjust their behavior to match that of their cohabitants.

The researchers were interested in investigating cooperation among the Hadza, particularly due to their hunter-gatherer lifestyles.

“The Hadza are one of the last populations left on the planet who live a similar lifestyle to how our ancestors lived for millions of years,” said study co-author Ibrahim Mabulla. “They offer insight into how cooperation evolved.”

“Food is unreliable and people often worry about there being enough food to feed themselves and their families,” said Apicella. “To counteract this, the Hadza share their food with their campmates. High levels of cooperation help to ensure survival in this unpredictable setting.”

To investigate what drives cooperative behavior among the Hadza, the researchers visited 56 camps in Tanzania over six years. Nearly 400 Hadza adults of all ages were asked to play an economic game in which participants were asked to consider sharing their favorite food, straws of honey.

The individuals started the game with four honey straws, which could be contributed to the group depending on each player’s decision. When the participants chose to share their honey straws with the group, the number of straws was tripled.

The experiment revealed that Hadza individuals living in certain camps were consistently more generous than others. The individuals were also found to modify their behavior over time to match the norms of the camp they were currently living in.

“You have some camps in which everyone is contributing and some where people are contributing very little,” said Smith. “In a random population, you’d expect all the camps to contribute similar amounts.”

“We were surprised to find that people do not have a stable tendency to cooperate and are instead influenced by those around them,” said Apicella. “Our results show that there is no such thing as good guys and bad guys.”

The researchers explained that the study findings highlight the flexible nature of human cooperation. Overall, the research also shows that generosity can be contagious.

“If you find yourself surrounded by selfish people, you don’t necessarily have to find a new crowd, but by being generous yourself, you can get others to be generous as well,” said Smith.

The study is published in the journal Current Biology.

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By Chrissy Sexton, Earth.com Staff Writer