Cooperation is Very Hard

Few animals engage in productive cooperation outside family kin groups.

It might be hard to imagine in our current political climate, but cooperation is the core trait of modern humans- the ability to form groups, make rules, exchange favors, and get big things done. We even cooperate for fleeting efforts with people we will never meet again. But theories explaining cooperation have been hard-won and so far quite limited in evolutionary biology. Kin selection is perhaps the only serious theory of this type, making cooperation a strict function of shared genes, which in turn sees its role rapidly diminishing in larger groups of organisms, with the exception of peculiar families like the social insects. 

Two other explanations for cooperative behavior have been developed- repeated interaction, and group selection. In the first, assuming that humans evolved in small groups, everyone knew everything about everyone, so reputation is everything, and thus cooperation within a group is the default state. In the second, different groups with different levels of in-group cooperation would fight it out in some form, perhaps militarily, leading to the success of better-cooperating groups. A recent paper (with review) used improved modeling to suggest that neither of these two explanations holds much water on its own, but in particular ways could be combined into something they call "super-additive cooperation". I.e. human society.

The key modeling advance here was to use graded rather than binary functions for interaction rewards. Likewise, they also allowed other forms of cooperation to compete with reciprocal cooperation. This allowed subjects and modeled entities to do what people always do- get away with giving a little less in return, which sends the whole game sliding into oblivion. That is, unless you are known to others in your own group, in which case, getting and giving positive rewards becomes a virtuous cycle with ever-increasing payoffs, thus the term super-additive. The combination of in-group membership and repeated interactions provides the magic. 

Detailed modeling of cooperation (termed "escalation" of cooperation) under some key conditions. Top is repeated interactions without group selection. Next is group competition without repeated in-group interactions. Third is the joint combination. The legend at top right ranges from generous cooperation at top to selfishness at the bottom. This is modeled as money transfers between participants, which are tallied in the leftmost graphs, and fall to minimal levels over time in the top two scenarios.

But does this amount to group selection? These authors suggest that, as typically understood, group selection is not very strong and not strong enough to support the evolution of cooperation. Among humans, conflicting groups are genetically different to only infinitesimal degrees. Migration and intermarriage (forced and otherwise) are so frequent that it would be practically impossible to build selectable differences over the needed time scales. On the other hand, human societies exhibit cultural variation as well, and this kind of variation is more extensive and much more rapidly developing than genetic variation, creating differences between groups that can withstand moderate levels of migration and remain distinctive and selective. As cultural group selection, this is not the same as group selection in classic evolutionary theory, and indeed, it may be hard to relate this to evolutionary theory at all. But it certainly leads to differential survival and reproduction, whatever the genetic background to the cooperative, group feeling, and other traits that feed into the culture.

"We also show that combining the two mechanisms generates strong positive interactions. Positive interactions occur because intergroup competitions can stabilize ingroup cooperation against ambiguous reciprocity, and intergroup competitions often do this even when they do not support cooperation on their own. When the mechanisms interact, the result is the evolution of cooperative reciprocity with ingroup members, which amplifies cooperation within groups, and uncooperative reciprocity with outgroup members, which erodes cooperation between groups."

...

"Group competition can change the balance of forces by adding a mechanism that favours relatively cooperative groups. The higher payoffs associated with escalation can now dominate the fragility of escalation, with the final outcome a cooperative escalating equilibrium. When group competition shifts the balance in this way, the cooperative outcome does not require large differences between groups."

Humans and their culture are extremely complex, and this is hardly the last word on mechanisms of cooperation, which include surveillance, punishment, and much else. But at least this study can dispose of the simpler evolutionary explanations, that are accessible to uncultured organisms and explain why free cooperation among unrelated individuals is limited out in nature, to behaviors with immediate paybacks like schooling, herding, flocking, and nutrient exchanges.

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