It doesn't seem like it if you watch political news but humans are unusually cooperative. We are unique in that we often cooperate with genetically unrelated strangers.

Nurses, firefighters, helping someone who dropped a package, standing in line, there is no natural selection benefit to that. In a natural selection-dominated world, the cheats, nepotists, and cronies would always win but unlike most of the animal kingdom, those behaviors are considered deviant.

Why do we cooperate? Language, intelligence, religion, the desire to hunt large game, there is no shortage of speculation about why we became Apex Cooperators. 

A new paper posits that culture fueled our capacity to cooperate with strangers. The researchers empirically tested and confirmed predictions of controversial "Cultural Group Selection Theory", theory being used in the proper name sense, like String Theory, rather than the science sense.

The idea behind "cultural group selection theory" is that culturally different groups compete, causing the spread of traits that give groups a competitive edge. Cooperation is exactly such a trait--costly for individuals, but advantageous for groups. 

This is in defiance of biology, where the idea that selection could act on groups was debunked decades ago. The reason is because groups are not different enough from each other for selection to act on. Individuals migrate, so over time migration makes the composition of groups similar.

Group-beneficial behaviors like cooperation lose out? 

Proponents of group selection believe that behaviors that are culturally, rather than genetically, transmitted, can influence selection. When people migrate, social learning allows groups to culturally acquire the behaviors that are popular in their new surrounding. If cultural groups can remain different, even if people move a lot, then "selection" can act on groups, and group-beneficial behaviors like cooperation can flourish. 

To test their belief, the scholars examined cultural variation and cooperation among Kenyan pastoralists. They sampled 759 individuals from nine clans spanning four ethnic groups--the Borana, Rendille, Samburu and Turkana--all of who practice semi-nomadic subsistence pastoralism in the arid savanna of northern Kenya. These groups compete intensively among each other for pasture, dry-season water wells and livestock, including through lethal cattle raids. The researchers found that, as predicted, cultural practices and beliefs were substantially variable between populations. Ten to 20 percent of the observed cultural variation was between competing groups. In contrast, typically less one percent of genetic variation is between groups. This indicated that there is potential for cultural group selection to occur.

Carla Handley meeting with Turkana children and adults. Credit: Carla Handley

Next, they examined who people cooperate with and found that cooperation is indeed directed towards cultural in-group members. People feel obliged to cooperate with strangers, as long as they share their cultural values, beliefs and norms with those people. Such culturally parochial cooperation is to be expected if competition between cultural groups influenced the evolution of cooperation. 

There are challenges to this. Although humans are hyper cooperative, our evolved cooperative dispositions are still limited in their scale, thus proving challenging for solving global-scale problems and therefore being a function of true selection.