Does cooperation require both reciprocity and alike neighbours?

Max Planck scientists develop new theoretical model on the evolution of cooperation 

June 08, 2012

Evolution by definition is cold and merciless: it selects for success and weeds out failure. It seems only natural to expect that such a process would simply favour genes that help themselves and not others. Yet cooperative behaviour can be observed in many areas, and humans helping each other are a common phenomenon. Thus, one of the major questions in science today is how cooperative behaviour could evolve. Scientists from the Max Planck Institute of Evolutionary Biology in Plön, Harvard University, and the University of Amsterdam have now developed a new model combining two possible explanations - direct reciprocity and population structure - and found that both repetition and structured population are essential for the evolution of cooperation. The researchers conclude that human societies can best achieve high levels of cooperative behaviour if their individuals interact repeatedly, and if populations exhibit at least a minor degree of structure. 

The scientists addressed the question how cooperative behaviour could evolve using a game called the prisoner’s dilemma, which considers two types of players: co-operators who pay a cost to help others; and defectors who avoid paying the cost, while reaping benefits from the co-operators they interact with. In general, everyone would be better off if they had engaged in cooperation, but from the point of view of the individual, defection is more beneficial. Selection will therefore always favour the defectors, and not cooperation. Researchers have used population structure and direct reciprocity to explain why cooperation has nevertheless evolved. In structured populations, co-operators are more likely to interact with other co-operators and defectors with defectors. Direct reciprocity involves the repetition of interaction and is therefore based on experiences gained from prior events involving cooperation. In the past, both approaches have been regarded separately.