Leaving is usually an option for individuals if they cannot tolerate their defective partners. In a two-player game, when a player chooses to leave, both she and her opponent become single players. However, in a multi-player game, the same decision may have different consequences depending on whether group cohesion exists. Players who choose not to leave would still be united together rather than be separated into singletons if there is cohesion among them. Considering this difference, we study two leaving mechanisms in public goods games. In the first mechanism, every player would be single once any of the group members leaves. In the second, we assume group cohesion exists that members who don't leave form a union. In our model, each player adopts a trigger strategy characterized by a threshold: she leaves if the number of defectors in her group exceeds the threshold. We find that under both mechanisms, when the expected lifespan of individuals is long enough, cooperators with zero tolerance toward defection succeed in the evolution. Moreover, when cohesion exists in groups, cooperation is better promoted because the cooperators have a higher chance to play together. That is, group cohesion facilitates positive assortment and therefore promotes cooperation.

中文翻译：

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有条件分离下群体凝聚力如何促进公共物品博弈合作的兴起

如果个人不能容忍其有缺陷的伴侣，则通常选择离开。在两人游戏中，当一个玩家选择离开时，她和她的对手都成为单人游戏。但是，在多人游戏中，取决于是否存在团队凝聚力，相同的决定可能会产生不同的结果。如果选择离开的话，如果他们之间有凝聚力，他们仍然会团结在一起，而不是被分成单身。考虑到这种差异，我们研究了公益游戏中的两种离开机制。在第一种机制中，每个小组成员离开后，每个参与者将是单身。在第二个例子中，我们假设存在群体凝聚力，即那些不离开的成员组成一个联盟。在我们的模型中，每个参与者都采用以阈值为特征的触发策略：如果小组中的叛逃者人数超过阈值，她就离开。我们发现，在两种机制下，当个体的预期寿命足够长时，对叛变零容忍的合作者都会成功进化。而且，当团队中存在凝聚力时，由于合作者有更大的机会共同参与，因此可以更好地促进合作。即，群体凝聚力促进了积极的分类并因此促进了合作。