An international team of researchers has developed a new model to explain how human cooperation is possible within the wider context of evolution. The scientists contend that a combination of direct reciprocity and population structure has allowed the human trait of cooperation to evolve.
At first glance, the notion of cooperation does not sit comfortably with the tenets of evolutionary theory. Natural selection seems to favour the survival of genes that help themselves over those responsible for more selfless behaviours. However, it is clear to see that cooperative actions are common within our daily lives.
Scientists from the Max Planck Institute of Evolutionary Biology in Plön, Harvard University and the University of Amsterdam have developed a new model to explain how it is that evolution could have produced human beings willing to work together, despite the fact that acting selfishly could result in greater individual gains.
The team began its research by considering the prisoner’s dilemma from game theory. This dilemma allows for two different types of prisoner; cooperators and defectors. Whilst cooperators are willing to pay a personal cost to help their peers, defectors avoid paying this cost and reap personal benefits at the expense of other prisoners. In general terms, prisoners would be better off if every one of their number cooperated. However, from the perspective of an individual, defection is most beneficial. One would therefore expect natural selection to favour defectors, yet cooperative individuals have undeniably evolved.
In order to reconcile this apparent paradox, the scientists invoked the concepts of direct reciprocity and population structure. Although these approaches have previously been regarded as separate entities, Dr Julián García and his colleagues from Max Planck’s Group for Evolutionary Biology used computer simulations and mathematical models to create a system in which both of these concepts are accounted for. In structured populations, cooperators and defectors are more likely to interact with likeminded individuals than with their opposite numbers. At the same time, direct reciprocity, which entails repetition of interaction, is based on previous experiences of events involving cooperation.
The team found that direct reciprocity on its own would not have been sufficient for cooperation to have evolved. Population structure was therefore a necessary ingredient in the creation of high levels of cooperation. Because likeminded individuals tend to interact with one another, when some reciprocity exists, the average level of cooperation increases. The researchers discovered that cooperation occurs if the two different types of individuals are highly clustered, and if repetition is present. Surprisingly, the results suggested that too much repetition can actually harm
cooperation in instances where the population structures make cooperation very likely. This is because reciprocity has the potential to protect defectors from other
defectors in addition to protecting cooperators from defectors.
"Without population structure, cooperation based on repetition is unstable," explained Dr García. "Therefore, the recipe for human cooperation might be: a bit of structure and a lot of repetition."