In the fascinating world of evolution and human cooperation, the concept of direct reciprocity in structured populations has emerged as a central focus of research. Reciprocity in repeated games has long been touted as a powerful mechanism in the evolution of cooperation among humans. It is generally believed that direct reciprocity can lead to high levels of cooperation in society.
Researchers have delved into an open-ended, infinite strategy space to explore how every strategy can be encoded into a finite state automaton, making it possible for mutants to arise. Surprisingly, it has been found that direct reciprocity alone does not necessarily result in high levels of cooperation. Instead, there are perpetual oscillations between cooperation and defection, with defection being more common than cooperation.
The reason for this is that indirect invasions can disrupt equilibrium strategies. In other words, every strategy has neutral mutants that can be invaded by other strategies, leading to a breakdown in cooperation. This challenges the conventional view that direct reciprocity is the key to promoting cooperation among individuals.
Another interesting mechanism that has gained attention in the evolution of cooperation is the assortment of population structure. Researchers have developed a theory that allows for the study of the synergistic interaction between direct reciprocity and assortment. This framework is particularly useful in understanding human interactions, which are often repeated and occur within relatively fluid and unstructured populations.
When repeated games are combined with a small amount of assortment, natural selection tends to favor behaviors that are typically observed among humans: high levels of cooperation that are implemented using conditional strategies. The Prisoners Dilemma is a classic example that captures the complexity of cooperation in its simplest and most challenging form.
In the game of Prisoners Dilemma, two individuals must decide whether to cooperate or defect. If both cooperate, they receive a greater payoff than if both defect. However, if one defects while the other cooperates, the defector receives the highest payoff while the cooperator gets the lowest. In a one-shot Prisoners Dilemma, it is in each person’s individual interest to defect, even though both would be better off if they had cooperated.
This game highlights the tension between private and common interests, making cooperation a complex and dynamic phenomenon to study. As researchers continue to explore the intricate mechanisms underlying human cooperation, from direct reciprocity in structured populations to the assortment of population structures, new insights are being uncovered that shed light on the evolution of cooperation in society.
