While we have always heard that sharing is caring, a new study has shown that an individual's tendency to be generous depends on how much people around him or her are sharing.
In other words, sharing, being contagious, is driven by local group norms and behaviour and not individual generosity.
"We were surprised to find that people do not have a stable tendency to cooperate and are instead influenced by those around them," said Coren Apicella from the University of Pennsylvania.
"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," added Kristopher Smith, from the University of Pennsylvania.
The study, published in Current Biology, is based on Hadza hunter-gatherer people in Tanzania -- also one of the last populations left on the planet.
During the study, the team visited 56 camps in Tanzania over six years. They asked nearly 400 Hadza adults to play public goods game where, instead of money, they were asked to consider sharing straws of honey, their favourite food.
Each person started with four straws, which they could put toward the whole group or not. The honey straws contributed to the group got tripled.
The results revealed that Hadza individuals living in certain camps were consistently more generous than others were.
Moreover, individuals behaved differently over time, modifying their behaviour to match the norms of the camp they were currently living in.
"We found that year after year, willingness to share with others clustered within residence groups or what we call 'camps,'" Apicella said.
"People were living with other people who were similar to them in levels of generosity," Apicella noted.