Cooperative behaviour is widespread in nature , but explaining how cooperation evolves constitutes a major scientific challenge. Computer simulations have shown that social network structure plays a key role for the viability of cooperation. However, not much is known about the importance of correlations between cooperative strategy and network position for the evolution of cooperation. Here, we investigate how cooperation is affected by correlations between cooperative strategy and individual connectedness in different networks, by means of simulation models. We find that placing cooperators on well-connected (high-degree) nodes can - as expected - enhance cooperation, but will only do so under certain conditions. The effect depends nontrivially on the combination of the social network structure (degree distribution and assortativity), the type of social dilemma, and the presence of Trojan horses , i.e. defectors placed within clusters of cooperators. Interestingly, the largest enhancement is observed in Poisson networks with increased degree assortativity, where cooperation does better than under scale-free degree distribution. The study provides new knowledge about the conditions under which cooperation may evolve and persist . The results are furthermore important to consider in regard to cooperation experiments, as they imply that stochastic initial correlations between cooperativeness and network position can affect the results of such experiments.
Cooperative behaviour constitutes a key aspect of both human society and non-human animal systems , but explaining how cooperation evolves represents a major scientific challenge. It is now well established that social network structure plays a central role for the viability of cooperation. However, not much is known about the importance of the positions of cooperators in the networks for the evolution of cooperation. Here, we investigate how cooperation is affected by correlations between cooperativeness and individual social connectedness. Using simulation models, we find that the effect of correlation between cooperativeness and connectedness (degree) depends on the social network structure , with positive effect in standard scale-free networks and no effect in standard Poisson networks. Furthermore, when degree assortativity is increased such that individuals cluster with others of similar social connectedness, we find that bridge areas between social clusters can act as barriers to the spread of defection, leading to strong enhancement of cooperation in particular in Poisson networks. But this effect is sensitive to the presence of Trojan horses ( defectors placed within cooperator clusters). The study provides new knowledge about the conditions under which cooperation may evolve and persist , and the results are also relevant to consider in regard to human cooperation experiments.
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