The message of this commentary is that self-regulation plays a decisive role in social cooperation. Baumard et al. have proposed that cooperation and other moral behavior reflect an evolved disposition toward fairness. They elaborate that humans cooperate when the benefits of doing so outweigh the costs – as they often do, because the benefits include social acceptance. Humans depend on belonging to social groups in order to survive and reproduce, so natural selection favored traits such as a disposition toward fairness that facilitate groups.

We agree, but with some reservations. Selfishness is natural in the animal kingdom, and humans have presumably not shed these selfish impulses. Therefore, fairness impulses must compete in the psyche against selfish impulses. Self-regulation is the executive capacity to adjudicate among competing motivations, especially in favor of socially and culturally valued ones (e.g., Baumeister & Vohs Reference Baumeister and Vohs2007). Self-regulation may often be needed in order that the relatively new and fragile impulse toward fairness can prevail over hunger, greed, lust, anger, and other uncooperative impulses.

The cost–benefit calculation described by Baumard et al. is further complicated by the fact that the costs of cooperation are often immediate, whereas the benefits are anticipated in the future. Most animals live in the present (Roberts Reference Roberts2002), and so the capacity to forego immediate gains for the sake of possible future benefits probably depends on the evolutionarily recent expansion of self-regulatory powers. Indeed, much of today's work on self-regulation is descended from Mischel's (e.g., Reference Mischel and Berkowitz1974) studies on the capacity to delay gratification.

Empirical findings confirm the role of self-regulation in ensuring fairness and cooperation. This work has proceeded by exploiting the finding that the capacity for self-regulation functions like a limited energy resource akin to the folk notion of willpower: After self-regulating, performance suffers on other, seemingly unrelated self-regulation tasks, suggesting that some energy has been depleted (e.g., Baumeister & Tierney Reference Baumeister and Tierney2011). The state of diminished self-regulatory capacity is called ego depletion.

Recent work has shown that fairness and helpfulness diminish when people have depleted their willpower. Banker et al. (in preparation) show that ego depletion causes people to become less fair in allocating rewards between self and others. Specifically, after exerting self-control in one context and then going to a different situation, people selfishly keep a larger portion of the cash stake for themselves instead of sharing it fairly. Outright dishonest behavior has also been shown to occur among ego-depleted participants. Mead et al. (Reference Mead, Baumeister, Gino, Schweitzer and Ariely2009) let participants grade their own tests and claim cash rewards based on their scores. Participants who had exerted self-control earlier claimed implausibly more correct answers and took home more cash than those who had not depleted their self-regulatory strength.

Moreover, many prosocial tendencies diminish when self-regulation has been compromised. Willingness to help others is lower during ego depletion than at other times (DeWall et al. Reference DeWall, Baumeister, Gailliot and Maner2008). The only exception is willingness to help kin, and that is unaffected by depletion, which suggests that the impulse to treat kin favorably may have a different and stronger biological root than any impulse to be kind to non-relatives. Although moral judgments seem largely unaffected by ego depletion, moral behavior is highly sensitive to self-regulatory powers. Self-control has been called the “moral muscle” (Baumeister & Exline Reference Baumeister and Exline1999) because it constitutes the capacity to override selfish impulses and to do what is morally right instead. Sexual and aggressive misbehavior likewise increases when self-regulatory powers have been weakened (DeWall et al. Reference DeWall, Baumeister, Stillman and Gailliot2007; Gailliot & Baumeister Reference Gailliot and Baumeister2007). Conversely, a highly influential theory of criminal behavior treats poor or low self-control as the central, decisive trait in criminality (Gottfredson & Hirschi Reference Gottfredson and Hirschi1990).

We find much to admire in the work by Baumard et al. reflected in the target article. It is highly conducive to our general view of human nature, which is that the distinctively human traits were mostly selected by nature to facilitate culture, which is understood as a new form of social life and the means by which humans survive and reproduce (Baumeister Reference Baumeister2005). Fairness in social relationships and economic trade offers great advantages to human cultural systems. Our commentary simply adds the point that an impulse toward fairness could not by itself be enough to prevail widely over selfish and other motivated impulses. The human capacity for self-regulation has been vital toward enabling human culture to flourish, and one of its key uses is enabling fairness to prevail as often as it does. When self-regulation fails, fairness and cooperation diminish sharply.