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Score-Mediated Mutual Consent and Indirect Reciprocity

journal contribution
posted on 2024-01-29, 00:17 authored by Marcus FreanMarcus Frean, Stephen MarslandStephen Marsland
Helping strangers at a cost to oneself is a hallmark of many human interactions, but difficult to justify from the viewpoint of natural selection, particularly in anonymous one-shot interactions. Reputational scoring can provide the necessary motivation via “indirect reciprocity, ” but maintaining reliable scores requires close oversight to prevent cheating. We show that in the absence of such supervision, it is possible that scores might be managed by mutual consent between the agents themselves instead of by third parties. The space of possible strategies for such “consented” score changes is very large but, using a simple cooperation game, we search it, asking what kinds of agreement can i) invade a population from rare and ii) resist invasion once common. We prove mathematically and demonstrate computationally that score mediation by mutual consent does enable cooperation without oversight. Moreover, the most invasive and stable strategies belong to one family and ground the concept of value by incrementing one score at the cost of the other, thus closely resembling the token exchange that underlies money in everyday human transactions. The most successful strategy has the flavor of money except that agents without money can generate new score if they meet. This strategy is evolutionarily stable, and has higher fitness, but is not physically realizable in a decentralized way; when conservation of score is enforced more money-like strategies dominate. The equilibrium distribution of scores under any of this family of strategies is geometric, meaning that agents with score 0 are inherent to money-like strategies.

History

Preferred citation

Frean, M. & Marsland, S. (2023). Score-Mediated Mutual Consent and Indirect Reciprocity. Proceedings of the National Academy of Sciences of USA, 120(23), e2302107120-. https://doi.org/10.1073/pnas.2302107120

Journal title

Proceedings of the National Academy of Sciences of USA

Volume

120

Issue

23

Publication date

2023-06-01

Pagination

e2302107120

Publisher

National Academy of Sciences

Publication status

Accepted

Contribution type

Article

Online publication date

2023-05-30

ISSN

0027-8424

eISSN

1091-6490

Article number

ARTN e2302107120

Language

en