Heterogeneous networks do not promote cooperation when humans play a Prisoner’s Dilemma

Abstract

It is not fully understood why we cooperate with strangers on a daily basis. In an increasingly global world, where interaction networks and relationships between individuals are becoming more complex, different hypotheses have been put forward to explain the foundations of human cooperation on a large scale and to account for the true motivations that are behind this phenomenon. In this context, population structure has been suggested to foster cooperation in social dilemmas, but theoretical studies of this mechanism have yielded contradictory results so far; additionally, the issue lacks a proper experimental test in large systems. We have performed the largest experiments to date with humans playing a spatial Prisoner's Dilemma on a lattice and a scale-free network (1,229 subjects). We observed that the level of cooperation reached in both networks is the same, comparable with the level of cooperation of smaller networks or unstructured populations. We have also found that subjects respond to the cooperation that they observe in a reciprocal manner, being more likely to cooperate if, in the previous round, many of their neighbors and themselves did so, which implies that humans do not consider neighbors' payoffs when making their decisions in this dilemma but only their actions. Our results, which are in agreement with recent theoretical predictions based on this behavioral rule, suggest that population structure has little relevance as a cooperation promoter or inhibitor among humans.evolutionary game dynamics | network reciprocity | conditional cooperation

Evolution of cooperation under social pressure in multiplex networks

“…In the last years, the analytical results of the theory are faced against experimental studies with humans facing game theoretical dilemmas [7][8][9][10]. Interestingly enough, these experiments have challenged the way we understand human cooperation, and more work on the consequences of these experiments have to follow.…”

Multiplicative noise enhances spatial reciprocity

“…To interpret the survival of cooperation, a theoretical framework that has shed light onto this long-standing issue is the evolutionary game theory [3,4,5,6]. In particular, a simple, paradigmatic model, the prisoners dilemma (PD) game, has attracted much attention, both theoretical and experimental [7,8,9,10,11,12,13]. In its basic version, two players simultaneously decide to adopt one of two strategies: cooperation (C) and defection (D).…”

Role-separating ordering in social dilemmas controlled by topological frustration

“…This means that the logit rule is an innovative dynamic, since new strategies can spontaneously appear. Recently, the logit rule has been the focus of many works [38,[67][68][69]74,79,80,[83][84][85] as it leads to very different results compared to imitation models. As we see, this rule is closely related to rational analysis of a situation, instead of the reproduction of the "fittest" behavior.…”

“…As we see, this rule is closely related to rational analysis of a situation, instead of the reproduction of the "fittest" behavior. Although evolutionary game theory has its bases rooted in biological populations dynamics, recent works shows that the modeling of humans playing games can have more in common with innovative dynamics [67][68][69]79,89]. The imitation rule, or imitation dynamics, is one of the most common update rules in iterated evolutionary game theory [6,38] and is based on the concept of the fittest strategy reproducing to neighboring sites.…”

“…In the light of recent human experiments [38,[67][68][69][70][71][72], we here consider not only the generally used imitation dynamics, but also the so-called logit rule (also known as myopic dynamics) [73][74][75]. The latter can be considered as more innovative, allowing players to choose strategies that are not within their neighborhood if they provide a good response to the strategies of their neighbors.…”