A study by Arizona State University researchers looks at how culture may have fueled our capacity to cooperate with strangers. The idea is that culturally different groups compete, causing the spread of traits that give groups a competitive edge.

It may not always seem so, but scientists are convinced that humans are unusually cooperative. Unlike other animals, we cooperate not just with kith and kin, but also with genetically unrelated strangers. Consider how often we rely on the good behavior of acquaintances and strangers -- from the life-saving services of firefighters and nurses, to mundane activities like our morning commute and queueing at the airport check-in counter. Of course, we encounter people who cheat, disregard the welfare of others, and engage in cronyism and nepotism. But we tend to perceive these behaviors as deviant, whereas in most animal societies these behaviors are the gold standard.

The hotly contested issue is why we are the famed cooperators of the animal kingdom. The answer is thought to be some characteristic that is exaggerated in humans compared to other animals: language, intelligence, culture, large-game hunting, or our very needy children. Teasing apart how these traits influenced the evolution of cooperation has been challenging and has led to a proliferation of theories -- and acrimonious debates -- that emphasize one or other of these characteristics.

Carla Handley, Sarah Mathew. Human large-scale cooperation as a product of competition between cultural groupsNature Communications, 2020; 11 (1)

DOI: 10.1038/s41467-020-14416-8

A fundamental puzzle of human evolution is how we evolved to cooperate with genetically unrelated strangers in transient interactions. Group-level selection on culturally differentiated populations is one proposed explanation. We evaluate a central untested prediction of Cultural Group Selection theory, by assessing whether readiness to cooperate between individuals from different groups corresponds to the degree of cultural similarity between those groups. We documented the normative beliefs and cooperative dispositions of 759 individuals spanning nine clans nested within four pastoral ethnic groups of Kenya—the Turkana, Samburu, Rendille and Borana. We find that cooperation between groups is predicted by how culturally similar they are, suggesting that norms of cooperation in these societies have evolved under the influence of group-level selection on cultural variation. Such selection acting over human evolutionary history may explain why we cooperate readily with unrelated and unfamiliar individuals, and why humans’ unprecedented cooperative flexibility is nevertheless culturally parochial.