Li Kun, Cong Rui, Wu Te, Wang Long
Center for Systems and Control, State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, Beijing 100871, China.
School of Mechano-Electronic Engineering, Xidian University, Xi'an 710071, China.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Apr;91(4):042810. doi: 10.1103/PhysRevE.91.042810. Epub 2015 Apr 27.
Social exclusion, keeping free riders from benefit sharing, plays an important role in sustaining cooperation in our world. Here we propose two different exclusion regimes, namely, peer exclusion and pool exclusion, to investigate the evolution of social exclusion in finite populations. In the peer exclusion regime, each excluder expels all the defectors independently, and thus bears the total cost on his own, while in the pool exclusion regime, excluders spontaneously form an institution to carry out rejection of the free riders, and each excluder shares the cost equally. In a public goods game containing only excluders and defectors, it is found that peer excluders outperform pool excluders if the exclusion costs are small, and the situation is converse once the exclusion costs exceed some critical points, which holds true for all the selection intensities and different update rules. Moreover, excluders can dominate the whole population under a suitable parameters range in the presence of second-order free riders (cooperators), showing that exclusion has prominent advantages over common costly punishment. More importantly, our finding indicates that the group exclusion mechanism helps the cooperative union to survive under unfavorable conditions. Our results may give some insights into better understanding the prevalence of such a strategy in the real world and its significance in sustaining cooperation.
社会排斥，即阻止搭便车者分享利益，在维持现实世界中的合作方面发挥着重要作用。在此，我们提出两种不同的排斥机制，即同伴排斥和群体排斥，以研究有限群体中社会排斥的演变。在同伴排斥机制中，每个排斥者独立地驱逐所有背叛者，因此独自承担全部成本，而在群体排斥机制中，排斥者自发形成一个机构来排斥搭便车者，每个排斥者平均分担成本。在一个仅包含排斥者和背叛者的公共物品博弈中，我们发现，如果排斥成本较小，同伴排斥者的表现优于群体排斥者，而一旦排斥成本超过某些临界点，情况则相反，这对于所有选择强度和不同更新规则均成立。此外，在存在二阶搭便车者（合作者）的情况下，排斥者在合适的参数范围内可以主导整个群体，这表明排斥相对于普通的代价高昂的惩罚具有显著优势。更重要的是，我们的研究结果表明，群体排斥机制有助于合作联盟在不利条件下生存。我们的结果可能有助于更深入地理解这种策略在现实世界中的普遍性及其在维持合作方面的意义。
