Humans are more helpful, generous, and informative than any other ape (Tomasello Reference Tomasello2009). We share information with people who are neither kith nor kin, and we cooperate with people we have never met and will never meet again. Stanford argues that human ultrasociality is possible because we treat moral obligations as part of an externally imposed moral order, which applies equally to all; because the experience of moral motivation feels objective, it automatically generates the demand that others be similarly motivated, and in populations of like-minded individuals, this yields correlated interactions that are less likely to be exploited (target article, sect. 5, para. 7). We are skeptical of Stanford's psychologically oriented approach to human morality. People do take others to be governed by the same moral norms as they are, and to be motivated to do so by something more than desires, preferences, or conventional assumptions (target article, sect 2). But if morality is understood as a kind of complex cooperative disposition, objectification becomes unnecessary, as correlated patterns of interactions that require conformity with open-ended and cooperative norms can be sustained by a sophisticated form of homophily (Ohtsuki et al. Reference Ohtsuki, Hauert, Lieberman and Nowak2006; Rand et al. Reference Rand, Arbesman and Christakis2011). Therefore, we maintain that a plausible understanding of the evolution of objective morality must look beyond human psychology, to the objective features of the world that govern cooperative human ways of life (henceforth “lifeways”).

Stanford appeals to an objectification mechanism to explain why we disaffiliate from those who act differently. But this downplays the role of affiliative tendencies in producing automatically coupled values and preferences. We adjust our normative expectations to track prevalent forms of social behavior; we treat conformity as rewarding, and deviation from social norms as aversive (Bicchieri Reference Bicchieri2016; Klucharev et al. Reference Klucharev, Hytönen, Rijpkema, Smidts and Fernández2009; Reference Klucharev, Munneke, Smidts and Fernández2011; Milgram & Sabini Reference Milgram and Sabini1978; Montague Reference Montague2006); and within a shared normative framework, feelings of social fluency will promote affiliation among those with similar normative views (Reber & Norenzayan, Reference Reber, Norenzayan, Proust and Fortierin press). If such forces are sufficient to drive complex, open-ended, and cooperative forms of behavior – as we believe they are – then objectification will be unnecessary to explain why people who engage in contra-normative behavior are judged to be “less attractive potential partners in social interaction” (target article, sect. 5, para. 7).

On their own, such facts will not explain why we treat moral obligations as objective. But as Stanford rightly notes, humans are obligate cooperators, who must rely upon one another to survive (target article, sect 5). Although forms of social tolerance and differential affiliation are present across the ape clade, these tendencies are greatly enhanced in humans, and this opens up lifeways that place social learning and cooperation at center stage (Hare Reference Hare2017; Henrich Reference Henrich2016). Like other domesticates, we have become more docile and less reactive (Wilkins et al. Reference Wilkins, Wrangham and Fitch2014); development is also slowed, allowing more time for juveniles to engage in social learning and to learn how to trust others (Hrdy Reference Hrdy2009). Just as importantly, we have lost the adaptations that would allow us to survive and flourish on our own: We lack sharp teeth for defense and hunting (Henrich Reference Henrich2016), we cannot extract nutrients from uncooked food (Isler & Van Schaick Reference Isler and Van Schaik2012; Wrangham Reference Wrangham2009), and without cultural scaffolding, we rapidly lose access to tools and technologies that allow us to overcome these limitations (Henrich Reference Henrich2004; Reference Henrich2016). In acknowledging the critical changes that have emerged over the course of human evolution, it becomes clearer that our reasons for treating moral obligations as external has little to do with feelings of objectivity. Cooperation, coordination, and trust are objective features of our social lifeway. If successful attempts to contravene the cooperative structure of society were widespread, they would trigger population collapse. No less dramatically, defectors would be unable to survive without networks of cultural scaffolding. Consequently, the felt objectivity of the norms governing correlated interactions is not just a fact about motivation; obligations emerge as a consequence of our relationship to the social order, and our moral motivations are determined by our (often tacit) recognition of this relationship.

Stanford's focus on psychological factors obscures the significance of one of the most distinctive features of human evolution: the emergence of complex and adaptive social networks, which are structured by rich patterns of social interaction (Apicella et al. Reference Apicella, Marlowe, Fowler and Christakis2012; Fehl et al. Reference Fehl, van der Post and Semmann2011; Hill et al. Reference Hill, Walker, Božičević, Eder, Headland, Hewlett, Hurtado, Marlowe, Wiessner and Wood2011). We do not just rely on culture-sustaining social processes to survive and flourish, we also constitute these processes. For culture-sustaining social processes to persist, people must be motivated to preserve the network structures they constitute. This requires a robust sensitivity to the structural constraints that govern the organization and dynamics of our social lifeway, as significant deviations from these constraints will prevent these networks from playing their constitutive role in sustaining culturally acquired knowledge (Barkoczi & Galesic Reference Barkoczi and Galesic2016; Derex & Boyd Reference Derex and Boyd2016; Muthukrishna et al. Reference Muthukrishna, Shulman, Vasilescu and Henrich2014; Reia et al. Reference Reia, Herrmann and Fontanari2017; Sterelny Reference Sterelny2012; cf. Hooker Reference Hooker2013). This yields a motivation to preserve the non-optional features of the social order we depend upon and constitute. But this is not just a fact about human motivation, human preferences, or some other feature of human psychology. The structural and dynamic constraints that characterize culturally robust social phenomena are determined by the emergent patterns of compatibility and incompatibility that obtain between various social practices and routines.

We contend that our moral psychology is grounded in our ability to track and respond to the structural features of our social environment. Likewise, our moral obligations are grounded in the relationship between individuals and the stability of their social groups – a relationship that is largely independent of individual attitudes (Jebari, Reference Jebariin preparation). Of course, we can converge on locally stable, but otherwise optional norms, and where this occurs, such norms will feel objective. Here too, the experience of objectivity and the motivation to preserve such norms will be grounded in the relationship between individuals and the adaptive networks they constitute. Because moving away from stability is dangerous, different groups may converge on different norms, and more generally, this will make threats to local stability feel dangerous. Consequently, moral progress will typically require finding points of higher-order stability. But that is another story for another day.