André F. d’Almeida
Evolutionary Game Theory (EGT) has given several accounts on how cooperation is maintained by a population’s network structure (Ohtsuki, H., et al., 2006). These studies are based on several assumptions, namely that individuals only take into account benefits and costs and that they decide to update their strategy by comparing pay-offs with random members of the population (Roca, C.P. et al., 2009). Up until now, experimental game theory had only been able to study interactions in small networks, a world away from the thousands of nodes networks used in theoretical research. This proved difficult to accurately test theoretical models experimentally. Recently, a study where 1229 subjects play a Prisoner’s Dilemma (PD) game simultaneously (Gracia-Lázaro, C., et al., 2012) demonstrated that there are no differences in cooperation levels in homogeneous vs. heterogeneous networks. Unlike what was suggested in a Public Goods Game context (Santos, F.C. et al., 2008), where network diversity increased cooperation. Furthermore, individuals did not compare pay-offs with their neighbours but only accounted for their actions in order to make decisions, meaning that they acted reciprocally.Does this mean theoretical studies are not saying the right things? Yes and no. Yes, because theoretical studies make plenty assumptions regarding human behaviour, over-simplifying it to the level of particles with only two choices and strict rules on how individuals update strategies. No, because theoretical research only provides guidelines on the evolution of cooperation, of ultimate causation alternatives of a behaviour. It is the experimenters who must test which alternatives are proximally exhibited by real individuals, both human and non-human and provide guidelines for better theoretical models, mainly how people decide and react to social dilemmas.
Ohtsuki, H., et al. (2006) A simple rule for the evolution of cooperation on graphs and social networks. Nature, 441, 7092: 502-505.
Roca, C.P., J.A. Cuesta, and A. Sánchez (2009) Evolutionary game theory: Temporal and spatialeffects beyond replicator dynamics. Physics of Life Reviews; 6,4: 208-249.
Gracia-Lázaro, C., et al. (2012) Heterogeneous networks do not promote cooperation when humans play a Prisoner‚Äôs Dilemma. Proceedings of the National Academy of Sciences; 109, 32: 12922-12926.
Santos, F.C., M.D. Santos, and J.M. Pacheco (2008) Social diversity promotes the emergence of cooperation in public goods games. Nature; 454, 7201: 213-216.