Graser Christopher, Fujiwara-Greve Takako, García Julián, van Veelen Matthijs
Dana-Farber Cancer Institute, Harvard University, Boston, Massecheusetts, United States of America.
Department of Economics, Keio University, Tokyo, Japan.
PLoS Comput Biol. 2025 Feb 4;21(2):e1012810. doi: 10.1371/journal.pcbi.1012810. eCollection 2025 Feb.
Repetition is a classic mechanism for the evolution of cooperation. The standard way to study repeated games is to assume that there is an exogenous probability with which every interaction is repeated. If it is sufficiently likely that interactions are repeated, then reciprocity and cooperation can evolve together in repeated prisoner's dilemmas. Who individuals interact with can however also be under their control, or at least to some degree. If we change the standard model so that it allows for individuals to terminate the interaction with their current partner, and find someone else to play their prisoner's dilemmas with, then this limits the effectiveness of disciplining each other within the partnership, as one can always leave to escape punishment. The option to leave can however also be used to get away from someone who is not cooperating, which also has a disciplining effect. We find that the net effect of introducing the option to leave on cooperation is positive; with the option to leave, the average amount of cooperation that evolves in simulations is substantially higher than without. One of the reasons for this increase in cooperation is that partner choice creates endogenous phenotypic assortment. Compared to the standard models for the co-evolution of reciprocity and cooperation, and models of kin selection, our model thereby produces a better match with many forms of human cooperation in repeated settings. Individuals in our model end up interacting, not with random others that they cannot separate from, once matched, or with others that they are genetically related to, but with partners that they choose to stay with, and that are similarly dependable not to play defect as they are themselves.
重复是合作进化的一种经典机制。研究重复博弈的标准方法是假设每次互动都有一个外生的重复概率。如果互动很有可能重复，那么互惠和合作就能在重复的囚徒困境中共同进化。然而，个体与谁互动也可能受其控制，或者至少在一定程度上受其控制。如果我们改变标准模型，使其允许个体终止与当前伙伴的互动，并找其他人来进行囚徒困境博弈，那么这就限制了伙伴关系中相互约束的有效性，因为一个人总能离开以逃避惩罚。然而，离开的选择也可用于摆脱不合作的人，这也具有约束作用。我们发现，引入离开选项对合作的净效应是积极的；有了离开选项，模拟中进化出的合作平均量显著高于没有该选项的情况。合作增加的一个原因是伙伴选择创造了内生的表型分类。与互惠和合作共同进化的标准模型以及亲缘选择模型相比，我们的模型因此能更好地匹配重复情境中多种形式的人类合作。在我们的模型中，个体最终进行互动时，不是与一旦配对就无法分开的随机他人，也不是与有基因关联的他人，而是与他们选择与之相处且同样可靠不会背叛的伙伴。
