We commend Moffett's effort to generate a definition of “society” that can fuel comparative study across not only human groups but also those of other species. In doing so, Moffett lays out two broad classes of societies that differ principally in how its members determine who belongs: Individual recognition societies, like those of most animals, wherein members “keep track of every other member as a unique individual,” and anonymous societies, like those of humans and some eusocial insects, in which members “employ markers of identity, such as specific gestures, rituals, and modes of dress, to establish who belongs.” There is, however, limited discussion of the psychological mechanisms that could support a species' ability to identify its members, in each type of society. Characterizing such mechanisms is critical to elucidating the nature and evolution of different kinds of societies, since these mechanisms constrain possible evolutionary transitions (based on phylogenetic inertia) and may also yield qualitatively and phylogenetically distinct sub-types of each kind of society. It is not hard to imagine, for example, that the anonymous societies of ants and humans are likely supported by rather different mechanisms. Our goal here is, first, to enrich this classification of societies by outlining hypotheses about the multiple psychological mechanisms that would allow members of each type of society to represent their groups and identify who belongs. Second, we consider how uniquely human forms of anonymous society could emerge from the individual recognition societies and social cognitive foundations we share with other apes.

On the lean end, basic physiological mechanisms may trigger tolerant responses to individuals perceived to be familiar or remembered (in the case of many individual recognition societies) or who broadcast perceptual markers of the group (as is likely the case for the simpler anonymous societies of insects) (Peso & Richards, Reference Peso and Richards2010; Tsutsui, Reference Tsutsui2004; Tibbetts & Dale, Reference Tibbetts and Dale2007). In some species, these mechanisms also activate intolerant responses toward others. Individual or group markers can include faces, vocalizations, or chemical odor cues (Carlson, Kelly, & Couzin, Reference Carlson, Kelly and Couzin2020). Thus, fundamental physiological mechanisms, plus some social memory in the case of individual recognition, could subserve social recognition in societies of both types. Critically, however, this way of recognizing who belongs only requires animals to distinguish individuals as belonging or not; it does not require animals to group these individuals in their mind, or generate a conceptual representation of an “identity group” that would allow them to classify or mentally represent the members of their society as belonging to a group. Yet, determining who belongs in human societies depends fundamentally on such conceptual representations of the identity group. These representations are powerful because they license novel predictions. For example, as soon as someone is identified as a member of a group, we already expect them to abide by a set of social norms, even if we have never observed them previously engaging in those norms. Where present, conceptual representations could also shape individual recognition societies – potentially allowing mental representation of group boundaries or identity but even more fundamentally classification of individuals, as dominant, as allies, as mothers, and so on. Such conceptual representations would again license novel predictions that help animals to navigate the complexities of their societies. Thus, individual recognition and anonymous societies can each be further subdivided by their underlying psychology: Whether members distinguish one another via basic physiological responses only as familiar versus unfamiliar, ingroup versus outgroup, or whether they also represent a group concept.

We think these distinctions can help explain how uniquely human anonymous societies could evolve from the individual recognition societies of the ancestors we share with chimpanzees and bonobos. Although humans share apes' capacities for individual recognition, human anonymous societies additionally require abilities to: (A) Hold in mind a conception of one's identity group, (B) bind abstract physical and behavioral identity markers to that conception, and (C) use those markers to distinguish one's group from others. Research is needed into each of these capacities in nonhuman animals.

Although apes live in bounded societies (Samuni, Langergraber, & Surbeck, Reference Samuni, Langergraber and Surbeck2022) and clearly distinguish familiar from unfamiliar conspecifics (Keenan et al., Reference Keenan, Mathevon, Stevens, Guéry, Zuberbühler and Levréro2016; Lewis et al., Reference Lewis, Wessling, Kano, Stevens, Call and Krupenye2023), we do not yet know whether they mentally represent their groups as social units. That said, there is evidence hinting that primates may have the requisite cognitive machinery: A capacity for conceptual representation of social categories, like dominance, that enables generalization and licenses novel predictions. Touchscreen tasks in rhesus macaques show that subjects can categorize unfamiliar conspecifics in videos as dominant or subordinate, and spontaneously generalize these categories to untrained dominance contexts (Bovet & Washburn, Reference Bovet and Washburn2003; Paxton et al., Reference Paxton, Basile, Adachi, Suzuki, Wilson and Hampton2010). However, follow-up studies eliminating perceptual explanations for generalization (e.g., Penn, Holyoak, & Povinelli, Reference Penn, Holyoak and Povinelli2008) are needed to definitively show that primates succeed based on predictively powerful conceptual representations of social categories like dominance. An important further follow-up question is whether primates apply that conceptual lens to representing their groups. Although we suspect that apes do have cognitive machinery that could be harnessed for a basic group concept, language and more elaborate theory of mind may also be necessary for the socially constructed identity concepts we see in humans.

With regard to markers of identity, apes exhibit socially learned traditions (e.g., tool use) that differ between groups (e.g., Whiten et al., Reference Whiten, Goodall, McGrew, Nishida, Reynolds, Sugiyama and Boesch1999) and there is a growing call for research into the possibility that some behaviors could constitute social norms (e.g., Westra et al., Reference Westra, Fitzpatrick, Brosnan, Gruber, Hobaiter, Hopper and Andrews2024). Critically, however, although apes can predict others' behavior (e.g., Krupenye, Kano, Hirata, Call, & Tomasello, Reference Krupenye, Kano, Hirata, Call and Tomasello2016) likely in part by identifying social regularities, we do not yet know whether they expect groupmates to adhere to norms, or whether they use norms as abstract markers of identity to distinguish members of groups.

Additional research is needed to test these intermediate accounts. This work may reveal that, despite their individual recognition societies, apes already possess several key cognitive precursors of a human-like anonymous society (social concepts and perhaps normative expectations). Even with this latent cognition, intergroup competition and group sizes exceeding capacities for individual recognition were likely necessary conditions to motivate humans' use of markers, like norms, to distinguish groups.