What is it about?

Evolution of moral norms of cooperation “Do not steal”, “Do not cheat”, “Help others”, probably are among the first examples which come to mind when someone thinks about moral norms. All these examples suggest moral norms are inherently good and are there to promote "good". But what about what to wear, what to eat, and how to have a conversation. These examples hint towards the other face of morality, which seems hardly reconcilable with the notion that moral norms are inherently good. The two faces of morality hint at two completely separate functions of morality. One is curbing individuals’ selfishness to motivate individuals in societies to help others. To live in groups, humans have to devise ways to limit their selfishness and forego personal benefits for the sake of others. Morality can be an evolutionary response to this demand. However, the other face of morality seems hardly reconcilable with such a function. They do not require individuals to sacrifice their selfishness. Rather, provide a set of behavioral norms that humans use to coordinate their activities in societies. Such as turn-taking rules in a conversation, norms prescribing how loud to speak in a library, cafeteria, or street, or how to dress in different places, where to smoke, and where not to eat. But how these two faces of morality came together? How does morality come into existence in the first place? A key to the answer to this question can be the observation that while necessary, curbing their selfishness is not sufficient for humans to form stable societies: they also need to coordinate their activities and form agreements as to what is considered acceptable or not, "good" or "bad". To examine how this may have been possible in the course of evolution, the article asks what evolutionary outcomes are in a situation where individuals need to make strategic decisions of different natures? Using the prisoner's dilemma as a metaphor for a social dilemma, where the success of the group requires individuals to forego personal benefit, evolutionary game theory has argued morality may evolve as a device to curb individuals' selfishness (the so-called indirect reciprocity theory). To see if these simple approximations can be extended to describe more realistic contexts, this article, considers a context where individuals play two games in parallel or consecutively, a social dilemma followed by a second game that exemplifies a typical problem individuals in groups often face, such as coordination, conflict resolution, or leader choice. At the beginning of evolutionary simulations, individuals behave independently in the two-game, which paints the disastrous picture where individuals fail to solve the social dilemma and are unable to coordinate their activities. However, in the course of evolution, individuals learn to take the information of what happens in a social dilemma in their strategic decisions in the non-social dilemma task into account, and do this in a particular way: those who behave selflessly in the social dilemma, and thus pay a cost for others to benefit, get to receive a higher status, a higher share in the coordination task. This ushers the evolution of a set of moral norms which hints at the two faces of morality: a set of behavioral norms which facilitate the coordination of activities and also promote self-sacrificing behavior. Interestingly, the positive role of moral norms in solving coordination problems is exactly what makes moral norms evolvable: Individuals embrace moral norms because they provide a mechanism to coordinate, which, in contrast to the selfless behavior which benefits the group but not the individual, is beneficial both for the individuals and for the group. In a sense, humans are trigged into accepting norms that curb their selfishness: "a moral system behaves like a Trojan horse: Once established out of the individuals' self-interest to promote order and organization, it also brings self-sacrificing cooperation". A surprising finding of the article is that the conditions for the evolution of moral norms depend only on the cost of cooperation and are independent of their benefit, which implies that "moral norms can be harmful and incur a pure collective cost, yet they are just as effective in promoting order and organization." This hints at a less studied aspect of moral norms: harmful social norms, such as severe punishment, ritual or honor killing, and some pious religious practices. According to the article, the same mechanism reconciling the two faces of morality and gives rise to its birth can lead to a less spoken of and dark side of morality and reminds us how evolution can lead to unexpected outcomes.

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Why is it important?

Evolutionary game theory has extensively studied the evolution of behavior in a simple strategic setting where individuals need to solve a strategic problem, such as a social dilemma. In contrast, individuals often simultaneously face strategic problems of diverse nature. However, not much is known about individuals' behavior in that context. The article shows such strategically complex settings, such as when individuals need to solve simultaneously solve a collective action and a coordination or anti-coordination problem, can provide important insights into the important problems of the evolution of moral norms and cooperation.


Studying what phenomena arise from the interaction between simple games can provide essential insights into the evolution of individuals' behavior.

Mohammad Salahshour
Max-Planck-Gesellschaft zur Forderung der Wissenschaften

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This page is a summary of: Interaction between games give rise to the evolution of moral norms of cooperation, PLoS Computational Biology, September 2022, PLOS,
DOI: 10.1371/journal.pcbi.1010429.
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