Dunbar’s original (Reference Dunbar1993, p. 693) solution to this conundrum was that the “ability to categorise individuals into types clearly makes it possible to create very much larger groups than is possible by direct interaction.” Apparently, he no longer thinks so, as he makes no mention of “types” (social specialization) in the current article. His focus has turned to the hypothesis that animals tailor their capacities to bond with allies to generate “stable social groups,” including, in humans, exceptionally populous ones.

I quote Dunbar’s above question in section 5 of my 2025 article for this journal, where I reach a different conclusion. The groups of interest to Dunbar (designated in Moffett [Reference Moffett2025a] by the moniker “societies,” of which modern states represent an extreme) are products not of often malleable social relations but the constituent members’ recognition of who belongs, and as such are ingroups, per social psychologists – in this instance, ones of an enduring sort.

Briefly: While societies foster social bonds, they aren’t necessarily reducible to social networks even if you include their weak or indirect ties – and certainly not for many primates, humans among them (consider your foreign friend; or the misanthropic hermit who is still identifiably American): “Since societal borders needn’t conform to the aggregated contacts between all its members… accurately describing a society requires going outside the logical universe of networks; similarly, portraying how networks relate to a society requires independently assessing who belongs where” (Moffett, Reference Moffett2025a). Nor are individuals necessarily aware of being part of a social network in the way society members perceive themselves as belonging together. For such reasons, the social connectedness (e.g., by grooming: Dunbar & Shultz, Reference Dunbar and Shultz2010) of individuals doesn’t serve to effectively define, and distinguish, their memberships (which for humans include strangers who share an identity but lack even indirect ties). As Seyfarth & Cheney (Reference Seyfarth and Cheney2017, p. 83) conclude, “In the mind of a baboon…social categories exist independent of their members.”

A category shift is required for an outsider to become integrated into a society. Upon joining a troop, a male vervet alters his call signaling he is an outsider to one indicating his initially low social rank (Seyfarth & Cheney, Reference Seyfarth and Cheney1984). Robert Seyfarth (personal communication) tells me it’s likely the troop members similarly adjust the calls they direct at the new arrival, even while some may continue their attacks on him.

I don’t deny that social relations factor into group stability; we can expect that animals will evolve to categorize one another into groups of sizes and configurations that function effectively, perhaps including, e.g., Dunbar’s “upper” and “lower grade” primate species (though his assertion in section 3.2 that there exist “distinct clusters,” i.e., “grades,” with “a natural breakpoint” between them, is baffling given the distribution of mean group sizes shown in Figure S2; note that internal cross-cutting groups could be a stabilizing factor for very large societies: Moffett, Reference Moffett2019, p. 134). Dunbar has insights regarding the social deterioration that can spread as a population grows, but I would argue that the resultant stresses lead to a category shift in who primates perceive as belonging to their group (Moffett, Reference Moffett2025b). In one carefully documented macaque troop, for example, the conflicts that led to a permanent severing shifted from fights between individual members of two recognizable factions to confrontations between the factions as a whole, as though the monkeys had ceased viewing one another as individuals and begun acting as collectives (“the two groups were becoming autonomous”: Prud’Homme (Reference Prud’Homme1991, p. 14)). Goodall (Reference Goodall2010, p. 239) wrote of the Kahama and Kasekela chimpanzee communities that had split off from each other at Gombe:

While, as in other primate societies (e.g., Langergraber et al., (Reference Langergraber, Rowney, Schubert, Crockford, Hobaiter, Wittig, Wrangham, Zuberbühler and Vigilant2014) for chimpanzee communities), breakdowns that result in permanent divisions appear to be inevitable in the long term, Moffett (Reference Moffett2019, pp. 248-50) proposed that shared traits “marking” our ancestors’ identities would help keep societies intact at sizes exceeding those of other primates despite the stressors that Dunbar describes. These generate such emotional connections that, as Brewer (Reference Brewer1991, p. 475) states, “People die for the sake of group distinctions” – a preadaptation to the emergence of the nations which Dunbar puzzled over in the headlining quote, a topic with far-reaching implications (Moffett Reference Moffett2019, Reference Moffett2025a).

Other details: Dunbar brings up “a natural tendency for animals who are foraging together to drift apart as their activity schedules become desynchronized,” but neglects how individual recognition keeps groups together. Many society-dwelling species stay connected at a distance via voice recognition and give a “lost call” to reconnect when out of contact (e.g., Todt et al., Reference Todt, Goedeking and Symmes2012). He sees the need to rest as taking time away from social grooming, which he claims is exhausting, even though the cited study (Giorgi et al., Reference Giorgi, Arlettaz, Christe and Vogel2001) concerns bats stricken with tenacious mites. Might it be that all but the most sick or worn-out animal is free to groom (by what Dunbar calls “soft touch”) or be groomed even as they thermoregulate or digest a meal (which ruminants absolutely can do while tending their allies: Daryl Codron, personal communication) The fact that Rose (Reference Rose1977) found that olive baboons spend thrice the time at rest that they do grooming one another argues against primates maximizing their efforts at building relationships.