Why cooperation is not running away

Abstract

A growing number of experimental and theoretical studies show the importance of partner choice as a mechanism to promote the evolution of cooperation, especially in humans. In this paper, we focus on the question of the precise quantitative level of cooperation that should evolve under this mechanism. When individuals compete to be chosen by others, their level of investment in cooperation evolves towards higher values, a process called competitive altruism, or runaway cooperation. Using a classic adaptive dynamics model, we first show that when the cost of changing partner is low, this runaway process can lead to a profitless escalation of cooperation. In the extreme, when partner choice is entirely frictionless, cooperation even increases up to a level where its cost entirely cancels out its benefit. That is, at evolutionary equilibrium, individuals gain the same payoff than if they had not cooperated at all. Second, importing models from matching theory in economics we, however, show that when individuals can plastically modulate their choosiness in function of their own cooperation level, partner choice stops being a runaway competition to outbid others and becomes a competition to form the most optimal partnerships. In this case, when the cost of changing partner tends towards zero, partner choice leads to the evolution of the socially optimum level of cooperation. This last result could explain the observation that human cooperation seems to be often constrained by considerations of social efficiency.

An evolutionary contractualist theory of morality

“…This approach has played an important role in shifting the community's focus from an exclusive emphasis on reciprocity to other mechanisms, and has strongly influenced our early theorizing and models. Historically, this line of research was focusing on the effect of competition among individuals to be chosen as a social partner, so-called competitive helping (Aktipis, 2004(Aktipis, , 2011Barclay, 2011;Ecoffet et al, 2021;Geoffroy et al, 2019;McNamara et al, 2008). More recently, the actors in this field have undertaken a broader view, encompassing the role of reputation and signaling in the evolution of cooperation .…”

“…Competitive helping models are all built around a radical hypothesis with regard to the conditional capacities of individuals. They assume that individuals express a constitutive level of cooperation, and are only able to respond to the level of cooperation expressed by their partners in two simple ways: staying with them and keeping on cooperating at the same level, or leaving them altogether (see e.g., Aktipis, 2004Aktipis, , 2011Barclay, 2011;McNamara et al, 2008, and also two of our own models Ecoffet et al, 2021;Geoffroy et al, 2019). This hypothesis is sometimes called the "walk away" rule.…”

“…Even in the more complex models where reciprocity is not direct, what individuals must do to have a good reputation and attract cooperation from others is simple and stereotyped. Typically, they must cooperate rather than defect (Leimar and Hammerstein, 2001;Nowak and Sigmund, 1998;Ohtsuki and Iwasa, 2006), or cooperate beyond a certain quantitative level (Geoffroy et al, 2019;McNamara et al, 2008). From a proximate point of view, therefore, the implementation of these strategies is relatively simple.…”

“…That is, competitive helping is the only force able to favor cooperation. Typically, this occurs through assortative matching (Geoffroy et al, 2019;McNamara et al, 2008): the most cooperative individuals tend to interact with other cooperative individuals, and this selects for individuals who cooperate at a Pareto optimal level (which also corresponds to the idea put forward by Weibull, 2013, 2016, see below). Note that the same principle is also at work in the "cooperation on graphs" literature, where the co-evolution between individual strategies and the structure of social networks leads to the evolution of cooperation through assortment (Cong et al, 2012;Fehl et al, 2011;Fu et al, 2008;Pacheco et al, 2006;Van Segbroeck et al, 2008;Wu et al, 2010.…”

Trinidadian guppies use a social heuristic that can support cooperation among non-kin

“…That is, with a 'walk away' strategy, individuals do not need to be able to exhibit plasticity in their own cooperative behaviour, further contributing to its simplicity and, importantly, possible traits under selection (e.g. [40][41][42][43]).…”