Moffett's definition of “society” implicitly describes societies as a species-level phenomenon. Here we test whether individuals from different species could also qualify as a society on this account.

Mixed-species animal groups range from oceanic cetaceans, fresh and saltwater fish shoals, social mammals such as ungulates and primates, and flocks of birds (Goodale et al., Reference Goodale, Sridhar, Sieving, Bangal, Colorado, Farine and Shanker2020) which can be stable over decades, occupy fixed home ranges, defend common territory (Martínez & Gomez, Reference Martínez and Gomez2013), and which enjoy higher survival rates than single-species bird flocks (Srinivasan, Reference Srinivasan2019). Some mixed-species groups include humans, as when humans and free-ranging animals such as dolphins, honeyguide birds, wolves, and orcas hunt and gather food together (Cram et al., Reference Cram, van der Wal, Uomini, Cantor, Afan, Attwood and Spottiswoode2022; Fogg, Howe, & Pierotti, Reference Fogg, Howe and Pierotti2015). Dog–human groups are perhaps most obvious when we think of pets, but they include street dogs who share spaces with humans, defending their territory from unknown individuals, and relying on social cues (Nagasawa, Kikusui, Onaka, & Ohta, Reference Nagasawa, Kikusui, Onaka and Ohta2009). Dog–human communities can also include additional species, such as livestock herders living in association with sheep or goats. These working dogs recognize their flocks and defend them from wolves, other humans, and other dogs (Gompper, Reference Gompper2014). Mixed-species animal groups have mainly been studied from the perspectives of community ecology, anthropology, and ethnoprimatology as communities (Cormier, Reference Cormier2003; Fuentes, Reference Fuentes2012; Govindrajan, Reference Govindrajan2018; Shell, Reference Shell2019). Can they also qualify as societies?

Applying Moffett's criteria A–H, we find that the first three aspects are clearly met. Mixed-species animal groups are groups (A) that extend beyond an immediate family (B) and are capable of perpetuating the population for generations (C).

The other criteria require a bit more attention. There is little research on whether multi-species members perceive one another as belonging together (D). But as Moffett points out, many non-human species recognize in-group and out-group members of their own species. We hypothesize that capacity exists in multi-species groups as well. An implication of this hypothesis is that social relations and societies might not emerge only from biological or evolutionary sources, but might also be discovered in interaction, through learning. A core commitment of theoretical social science is that societies can be self-reflective, or can observe themselves (Luhmann, Reference Luhmann1995), providing a basis for asking how new interactions emerge among multiple species.

Preliminary evidence for our hypothesis may be found in a recent study of the different human cultures working with honeyguide birds who lead humans to bee nests; humans crack open and extract the honey, leaving the wax for the birds to eat. The Hadza–honeyguide and the Yao–honeyguide societies have different communicative signals, and the birds respond to their local signal at a significantly higher rate – providing evidence that these capacities are learned (Spottiswoode & Wood, Reference Spottiswoode and Wood2023).

Whether multi-species groups are set apart from other groups (E) raises the largest questions. Moffett may be underestimating, even in humans, the degree to which multiple membership is possible beyond dual citizenship. Human code-switching, originally a linguistic term, also now refers to the ability to navigate norms and forms of cultural life in different societies, often occupying the same territory (Morton, Reference Morton2014). Network structure in social science has long emphasized the role of “weak ties” across groupings, suggesting forms of social belonging that help societies scale (Granovetter, Reference Granovetter1973). It is conceivable that street dogs and humans may form one society, while the same dogs may interact with one another or smaller mammals in the same spaces, at other times. These cases cannot be explained by the mutually agreeable (F) or initially forced (G) transfer between societies that Moffett allows. It raises interesting questions about the temporal structure of belonging in a society (from moment to moment as well as over a longer period of time). We hypothesize that the key element when identifying spatially overlapping societies will be the social norms that govern the interactions in these different groups (Andrews, Fitzpatrick, & Westra, Reference Andrews, Fitzpatrick and Westra2024; Westra et al., Reference Westra, Fitzpatrick, Brosnan, Gruber, Hobaiter, Hopper and Andrews2024).

We take the criterion that societies regulate access to space they control (H) to be closely related to the criterion that members perceive one another as belonging together (D). When we see a dog behave aggressively toward a newcomer dog, we gain evidence that the dog perceives the newcomer as not belonging with them because the dog is regulating the newcomer's access to the space. Dogs also do this on behalf of the humans they associate with. Thus, insofar as multi-species groups take up space together, and regulate proximity to group members, they are regulating access to space it controls, even if that space is just the personal spaces of the society's members. This reasoning may also help with the geladas case Moffett raised as a possible outlier to (H).

In sum, we think that Moffett's account can accommodate multi-species groups, but their existence raises two key points. First, societies rest on shared rules – social norms that allow group members to recognize who belongs together and which regulate access to group members. Second, it is common to be a part of multiple societies, and we propose that membership in multiple societies and having to coordinate between societies is an evolutionarily ancient phenomenon (Hussain, Weiss, & Kellberg Nielsen, Reference Hussain, Weiss and Kellberg Nielsen2022). An implication of these points is that the distinction between what is social and what is biological is poorly drawn, resting too much on species-level definitions, and not enough on shared forms of interaction, relating, recognition, and norms. While species membership is clearly relevant for reproduction, it is less relevant for social organization in a world of overlapping societies and the code-switching that entails.

Moffett's proposal is oriented to “deep questions about the human condition.” However, a more just society of the future ought to address deep questions of our shared condition, not only that of the human. Future forms of social justice would include a wider range of interests, organized in the name of mutual flourishing. An over-valued human exceptionalism has been the source of much injustice in the world; it might also be the source of some intellectual confusion among humans themselves.