Super-additive cooperation. (https://pubmed.ncbi.nlm.nih.gov/38383778/)

These scientists wanted to understand why people help each other, even when they don't expect anything in return. Some scientists thought that cooperation evolved over time because people interacted with each other many times and learned to trust each other. Other scientists believed that competition between groups of people led to cooperation within those groups.

To test these ideas, the scientists created models and conducted an experiment where people played a game to see if they would cooperate with each other. They found that neither repeated interactions nor group competition alone could explain why people cooperate.

They discovered that a type of strategy called ambiguous reciprocity, which is often ignored in models of cooperation, actually made it harder for people to cooperate over time. However, when they combined repeated interactions with group competition, they found that cooperation was more likely to happen.

The scientists also studied people in Papua New Guinea and found that their behavior matched the idea of cooperating with people within their own group but not with those outside their group. This suggests that cooperation evolved as a result of both repeated interactions and group competition working together.

In conclusion, the scientists found that cooperation in humans is influenced by a combination of factors, including interacting with the same people over time and competing with other groups.

Efferson C., Bernhard H., Fischbacher U., Fehr E. Super-additive cooperation. Nature. 2024 Feb 21. doi: 10.1038/s41586-024-07077-w.