Tomasello offers a compelling account of the evolutionary and ontogenetic emergence of the uniquely human sense of obligation. The target article alludes to some affective experiences in these “feelings of obligation” but does not directly address the role of emotions. Further, to the extent that Tomasello does consider the role of affect, he describes obligations as having a fundamentally coercive (negative) quality. In this commentary, we propose (1) a more central role of affect in the development of a sense of obligation, and (2) that positive emotions such as gratitude represent an evolutionary solution to the fundamentally negative quality of obligations.

First, Tomasello emphasizes the development of obligation through the me–you equivalence established first through collaborative activities and then in cultural groups. This account is certainly persuasive, but we think that it is not sufficient. Research shows that from the very start, children's collaborative interactions are also heavily affect-laden, and this affect is vital for establishing their sense of obligation. According to the affect-as-information theory (Storbeck & Clore Reference Storbeck and Clore2008), affective signals provide children with cues about what is safe and important in the environment. For example, visual cliff experiments show that even 1-year-olds take their parent's nonverbal signals into account and use their emotional expressions to make decisions about their future behaviors (e.g., whether or not to crawl across the cliff; Sorce et al. Reference Sorce, Emde, Campos and Klinnert1985).

More pertinently, caregivers use affect to convey vital information about obligations to infants and young children. For instance, parents use distinct affect when communicating with infants about norm violations compared to pragmatic violations (Dahl & Tran Reference Dahl and Tran2016). Parents even use distinct affect when communicating about moral versus other kinds of norm violations: They use angry vocalizations when their infant violates a moral norm (e.g., hits another person) but use fearful vocalizations when their infant violates a prudential norm (e.g., harming themselves; Dahl et al. Reference Dahl, Sherlock, Campos and Theunissen2014). This affective information guides children's attention to important distinctions between various types of social norms and the obligations that accompany those norms (Arsenio & Ford Reference Arsenio and Ford1985). This in turn helps children to successfully navigate their obligations and avoid breaking commitments. Affect-laden testimonies, for example, moralize novel rule violations and elicit moral judgments from children (Rottman & Kelemen Reference Rottman and Kelemen2012; Rottman et al. Reference Rottman, Young and Kelemen2017). Similarly, among young children as well as adults, witnessing violations of moral norms induces higher physiological arousal than witnessing violations of conventional norms (Yucel et al., Reference Yucel, Hepach and Vaishin press). As mentioned by Tomasello, as children begin to differentiate these social norms from one another, they begin to understand who is obligated to adhere to particular norms and when an individual is obligated to do so. Affect-laden communication and children's own affective experiences thus aid children in developing a sense of obligation and help children work out the nuances of the particular system of obligation in which they must function.

Second, Tomasello argues that obligation makes us do things we do not want to do but feel we must do. He emphasizes the negative emotions associated with obligation (guilt, blame, and resentment) and argues that positive emotions (such as gratitude) cannot account for a sense of obligation. We propose, however, that positive emotions such as gratitude, which motivate us to reciprocate favors to our benefactors, may have evolved precisely to counter the fundamentally negative quality of obligation: to turn actions such as reciprocity into something we want to do, not only because it is right but also because it feels good. On its face, this goes against Tomasello's argument that obligation cannot involve things we want to do. Yet perhaps the ultimate and proximate stories diverge on this point: In our evolutionary history, we needed psychological mechanisms to make us put aside our selfish interests and invest in our cooperative, interdependent relationships (as Tomasello himself has elegantly argued: e.g., Tomasello Reference Tomasello2016a). Emotions are just such psychological mechanisms (Krebs Reference Krebs2008; Nesse & Ellsworth Reference Nesse and Ellsworth2009). It is highly likely, then, that some emotions have evolved to help us fulfill our obligations to others. Some of these emotions are negative (resentment, guilt), but some are also positive (gratitude). At the proximate (ontogenetic) level, these positive emotions do not seem to carry the fundamentally coercive quality of obligations. However, we submit that positive emotions are precisely the evolutionary trick that allows us to happily carry out many of our social obligations. Positive emotions are part of the toolbox that allows us to meet our obligations, and to do so without resenting them.

Taken together, we seek to highlight the important functions that affect serves in the emergence of the human sense of obligation. We presented evidence from the affect literature and argued that affect plays an important role in how obligations are socialized and maintained during development. Moreover, we suggested that positive emotions may have evolved to counteract the negativity associated with the sense of obligation one feels to one's collaborative partners and cultural group. Thus, we argue that a full account of the evolutionary and ontogenetic emergence of humans’ sense of obligation must include the vital role of affect in the creation, enforcement, and maintenance of these obligations.