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. 2014 Jul 23;8:248. doi: 10.3389/fnbeh.2014.00248

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Copyright © 2014 Chen and Perc.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Time evolution of the mean payoff difference between cooperators and defectors (A–D) and the fraction of cooperators (E–H) as a function of degree k for three typical values of α. Institutional punishment and absolute payoffs apply. The insets of (A,B) show the mean payoff difference between cooperators and defectors for low-degree and middle-degree nodes during the early stages of evolution. During the evolutionary process, if the enhancement factor is small, cooperators always have a higher mean payoff than defectors at an intermediate value of δ. Parameter values are r = 1 and δ = 0.5.