We applaud the conceptual clarity that Baumard et al. bring to the subject of cooperation, and endorse their focus on mutualism – as opposed to both true altruism and reciprocity – as a form of cooperation likely favored under a wide range of evolutionary scenarios. Moreover, the authors' model of a market for mutualistic cooperators driven by partner choice provides a plausible account of the evolution of mental mechanisms that generate, and act on, concepts of fairness. However, they do not carry the premises of their market model to their logical conclusions. Baumard et al. endorse and build on prior positions that hold that selection has favored a moral compass that leads individuals to “do the right thing” in a relatively invariant fashion. Such invariance was ostensibly selected for because an inflexible moral compass is thought to preclude both erroneously trading the larger long-term gains of mutualism for the smaller short-term gains of defection, and erroneously underestimating the likelihood of getting caught in the act. Baumard et al. bolster prior arguments to this effect by stating that people are fairly accurate when inferring others' intentions in situations involving such temptations, and hence that the odds are stacked against cost-free defection. While we share with Baumard et al. a market model of mutualism, we challenge the notion of an invariant moral compass on both empirical and theoretical grounds.
Empirically, we submit that, with the exception of the (infrequent) types occupying the respective tails of the moral distribution (psychopaths and saints, respectively), most people appear somewhat flexible in their moral behavior in general, and in their mutualistic behavior in particular. True, many people behave in what is locally construed as a moral manner much of the time, but this is not the same as being invariantly moral or invariantly fair. Moreover, it is not simply the case that people engage in some fixed level of moral behavior most of the time, and occasionally fall below this level, as might be expected if an evolved moral compass were merely imperfect due to constraints on optimality. Rather, most people are plastic in both directions. Inspired by others' virtuous acts, people episodically rise above their baseline levels of prosociality (Haidt Reference Haidt2000; Reference Haidt, Keyes and Haidt2003; Schnall et al. Reference Schnall, Roper and Fessler2010). Likewise, rendered cynical by others' self-interested behavior, people episodically fall below their baseline levels of prosociality (see Keizer et al. Reference Keizer, Lindenberg and Steg2008; Raihani & Hart Reference Raihani and Hart2010).
From a theoretical perspective, the situational plasticity of individual moral behavior is not surprising – indeed, we contend that it is exactly what is predicted by market models of partner choice for mutualism. As Baumard et al.'s own analogies with biological markets indicate, the behavior of individual actors in a market reflects the effects of supply and demand on pricing. Consider first the simplest case, in which all mutualism is dyadic, and cooperativeness is a binary trait. Here, market dynamics do not operate, as all (or virtually all) prospective cooperators eventually find partners. However, if prospective partners vary in quality, then market dynamics arise: Vying to pair with the best partners, prospective cooperators will escalate their prosociality in order to compete with their rivals for limited slots. This situation is exacerbated if some or all of the most profitable mutualisms involve groups of actors rather than dyads, as this means that large numbers of unattached actors can accumulate (rather than simply pairing off, as occurs under dyadic scenarios). When the supply of prospective cooperators is greater than the number of open slots in cooperative ventures, the prospective cooperators can be expected to advertise that they have lowered their expected wages by displaying a willingness to engage in more costly prosocial behavior. Conversely, when the supply of prospective cooperators is lower than the number of open slots in cooperative ventures, the prospective cooperators can be expected to display a reduced willingness to engage in costly prosociality. Following Fessler and Haley (Reference Fessler, Haley and Hammerstein2003), we argue that such facultative adjustment of prosocial inclinations is mediated by genuine moral emotions, themselves the products of adaptations that evolved to regulate behavior in exactly this market context. When individuals are surrounded by prosocial actors, they are genuinely motivated to “match others' bids,” while the converse is true when they find themselves surrounded by self-interested others. The result is that there are multiple stable equilibria with regard to prevailing levels of cooperation, a pattern evident even on relatively small geographical scales (e.g., Wilson et al. Reference Wilson, O'Brien and Sesma2009). While some such heterogeneity is undoubtedly due to self-selection of the type described by Baumard et al. in their discussion of mobility in small-scale societies, we argue that much of this heterogeneity reflects the fundamental plasticity of people's moral inclinations – the same actor will feel and behave differently in different social contexts.
In keeping with the above perspective, we also take issue with Baumard et al.'s position that there has been little selection for psychological mechanisms that motivate altruistic punishment aimed at deterrence. Because it is impossible to forecast others' behavior with complete accuracy, and because the moral compass is not invariant, cooperative groups benefit from policing both in the short term and over the long term as deterrent effects accrue. As punishment constitutes a public good for such groups, advertising one's willingness to punish norm violators makes the actor more attractive as a prospective partner (Fessler & Haley Reference Fessler, Haley and Hammerstein2003). As in the case of escalating feedback loops of prosociality motivated by genuine emotions, this can lead to bid-matching behavior wherein one actor expresses moral outrage at a norm violation, leading other actors to express similar – or higher – levels of outrage.
In sum, market models of morality are indeed powerful – more powerful even than Baumard et al. recognize, for such models can not only explain the evolution of mutualistic cooperation and the emotions that support it, but, importantly, they can also explain the vicissitudes of morality both within and between individuals, groups, and societies.
We applaud the conceptual clarity that Baumard et al. bring to the subject of cooperation, and endorse their focus on mutualism – as opposed to both true altruism and reciprocity – as a form of cooperation likely favored under a wide range of evolutionary scenarios. Moreover, the authors' model of a market for mutualistic cooperators driven by partner choice provides a plausible account of the evolution of mental mechanisms that generate, and act on, concepts of fairness. However, they do not carry the premises of their market model to their logical conclusions. Baumard et al. endorse and build on prior positions that hold that selection has favored a moral compass that leads individuals to “do the right thing” in a relatively invariant fashion. Such invariance was ostensibly selected for because an inflexible moral compass is thought to preclude both erroneously trading the larger long-term gains of mutualism for the smaller short-term gains of defection, and erroneously underestimating the likelihood of getting caught in the act. Baumard et al. bolster prior arguments to this effect by stating that people are fairly accurate when inferring others' intentions in situations involving such temptations, and hence that the odds are stacked against cost-free defection. While we share with Baumard et al. a market model of mutualism, we challenge the notion of an invariant moral compass on both empirical and theoretical grounds.
Empirically, we submit that, with the exception of the (infrequent) types occupying the respective tails of the moral distribution (psychopaths and saints, respectively), most people appear somewhat flexible in their moral behavior in general, and in their mutualistic behavior in particular. True, many people behave in what is locally construed as a moral manner much of the time, but this is not the same as being invariantly moral or invariantly fair. Moreover, it is not simply the case that people engage in some fixed level of moral behavior most of the time, and occasionally fall below this level, as might be expected if an evolved moral compass were merely imperfect due to constraints on optimality. Rather, most people are plastic in both directions. Inspired by others' virtuous acts, people episodically rise above their baseline levels of prosociality (Haidt Reference Haidt2000; Reference Haidt, Keyes and Haidt2003; Schnall et al. Reference Schnall, Roper and Fessler2010). Likewise, rendered cynical by others' self-interested behavior, people episodically fall below their baseline levels of prosociality (see Keizer et al. Reference Keizer, Lindenberg and Steg2008; Raihani & Hart Reference Raihani and Hart2010).
From a theoretical perspective, the situational plasticity of individual moral behavior is not surprising – indeed, we contend that it is exactly what is predicted by market models of partner choice for mutualism. As Baumard et al.'s own analogies with biological markets indicate, the behavior of individual actors in a market reflects the effects of supply and demand on pricing. Consider first the simplest case, in which all mutualism is dyadic, and cooperativeness is a binary trait. Here, market dynamics do not operate, as all (or virtually all) prospective cooperators eventually find partners. However, if prospective partners vary in quality, then market dynamics arise: Vying to pair with the best partners, prospective cooperators will escalate their prosociality in order to compete with their rivals for limited slots. This situation is exacerbated if some or all of the most profitable mutualisms involve groups of actors rather than dyads, as this means that large numbers of unattached actors can accumulate (rather than simply pairing off, as occurs under dyadic scenarios). When the supply of prospective cooperators is greater than the number of open slots in cooperative ventures, the prospective cooperators can be expected to advertise that they have lowered their expected wages by displaying a willingness to engage in more costly prosocial behavior. Conversely, when the supply of prospective cooperators is lower than the number of open slots in cooperative ventures, the prospective cooperators can be expected to display a reduced willingness to engage in costly prosociality. Following Fessler and Haley (Reference Fessler, Haley and Hammerstein2003), we argue that such facultative adjustment of prosocial inclinations is mediated by genuine moral emotions, themselves the products of adaptations that evolved to regulate behavior in exactly this market context. When individuals are surrounded by prosocial actors, they are genuinely motivated to “match others' bids,” while the converse is true when they find themselves surrounded by self-interested others. The result is that there are multiple stable equilibria with regard to prevailing levels of cooperation, a pattern evident even on relatively small geographical scales (e.g., Wilson et al. Reference Wilson, O'Brien and Sesma2009). While some such heterogeneity is undoubtedly due to self-selection of the type described by Baumard et al. in their discussion of mobility in small-scale societies, we argue that much of this heterogeneity reflects the fundamental plasticity of people's moral inclinations – the same actor will feel and behave differently in different social contexts.
In keeping with the above perspective, we also take issue with Baumard et al.'s position that there has been little selection for psychological mechanisms that motivate altruistic punishment aimed at deterrence. Because it is impossible to forecast others' behavior with complete accuracy, and because the moral compass is not invariant, cooperative groups benefit from policing both in the short term and over the long term as deterrent effects accrue. As punishment constitutes a public good for such groups, advertising one's willingness to punish norm violators makes the actor more attractive as a prospective partner (Fessler & Haley Reference Fessler, Haley and Hammerstein2003). As in the case of escalating feedback loops of prosociality motivated by genuine emotions, this can lead to bid-matching behavior wherein one actor expresses moral outrage at a norm violation, leading other actors to express similar – or higher – levels of outrage.
In sum, market models of morality are indeed powerful – more powerful even than Baumard et al. recognize, for such models can not only explain the evolution of mutualistic cooperation and the emotions that support it, but, importantly, they can also explain the vicissitudes of morality both within and between individuals, groups, and societies.