Dunbar persuasively argues that a central problem that mammals confront is how to manage the challenges that arise from living in large, stable groups. Some of the stresses identified can be succinctly summarized as having to do with two kinds of problems that permeate group-living – problems of cooperation, and problems of coordination (De Dreu, Gross, & Romano, Reference De Dreu, Gross and Romano2024). While Dunbar mainly refers to the latter in terms of staying together despite different needs, cooperation and coordination extends far beyond group cohesion and is important for many species in terms of territory defense, food acquisition and rearing of offspring. The problem of cooperation is that when paying some cost resulting in safety and prosperity individuals can hardly achieve alone, individuals are better off when others cooperate and they themselves do not. Cooperation is exploitable by free-riding, and this requires the individual to spend effort on detecting whom to cooperate with, and whom to avoid. The problem of coordination is that collective action requires individuals to adapt their actions to those of others, with failure to do so leading to costly outcomes for individuals and their group. The problem of coordination requires individuals to spend effort in detecting what others do or will do, and to adjust oneself accordingly.

Often, group-living requires dealing simultaneously with problems of cooperation and coordination. Cooperative hunting, for example, requires individuals to take personal risks and to contribute effort to align their actions within the coalition. Dunbar’s analysis suggests that primates successively exploited different kinds of strategies to solve these intricate problems of group-living, including enhanced cognitive capacities involving energetically costly forms of executive functions and mentalising.

While capacities for executive function are critical for solving problems of cooperation and coordination, Dunbar’s analysis overlooks that evolved capacities for enhanced cognitive skills are necessarily in-group bounded and ‘parochial.’ There is good evidence that humans solve problems of cooperation and coordination first and foremost in terms of what could be termed “group-mindedness” – a tendency to perceive and treat ‘in-group’ members more favourably than strangers and ‘out-group’ members (Brewer, Reference Brewer1999; Brooks & Yamamoto, Reference Brooks and Yamamoto2022; Romano et al., Reference Romano, Sutter, Liu, Yamagishi and Balliet2021). Group-mindedness, and related concepts such as social identification (Brewer, Reference Brewer1999) and group entitativity (Lickel et al., Reference Lickel, Hamilton, Wieczorkowska, Lewis, Sherman and Uhles2000), involves a sense of belonging to the in-group, which can explain the increased willingness to work together towards common objectives (Brooks & Yamamoto, Reference Brooks and Yamamoto2022; Ellemers, Spears, & Doosje, Reference Ellemers, Spears and Doosje1997; Tomasello et al., Reference Tomasello, Melis, Tennie, Wyman and Herrmann2012), to aggressively defend the in-group against outside enemies, and to join coalitionary raids on neighbouring groups and communities (De Dreu & Triki, Reference De Dreu and Triki2022; De Dreu et al., Reference De Dreu, Gross, Méder, Giffin, Prochazkova, Krikeb and Columbus2016; Lemoine et al., Reference Lemoine, Samuni, Crockford and Wittig2022).

Unlike the cognitive solutions postulated by Dunbar, group-mindedness is organized at the group level and not reliant on tracking dyadic interactions. Furthermore, whereas the cognitive solutions offered in Dunbar’s analysis reside in the primate’s neocortex, group-mindedness likely involves the evolutionary ancient and structurally and functionally preserved social decision-making network in the vertebrate brain (O’Connell & Hoffman, Reference O’Connell and Hofmann2011; Rilling & Young, Reference Rilling and Young2014). This network includes various brain nuclei known for their crucial roles in regulating social recognition, affiliation and parental behaviour, responses to social stressors, and aggression (Goodson, Reference Goodson2005; Rilling & Young, Reference Rilling and Young2014; De Moura Oliveira et al., Reference de Moura Oliveira, Lukas, Wolf, Durante, Lorenz, Mayer, Bludau, Bosch, Grinevich and Egger2021) and is critically dependent on neurohormonal modulations in the oxytocinergic circuitry (De Dreu & Kret, Reference De Dreu and Kret2016; Samuni et al., Reference Samuni, Mundry, Deschner, Crockford and Wittig2017; Triki, Daughters, & De Dreu, Reference Triki, Daughters and De Dreu2022). Group-mindedness involves neural structures and functions seen across a range of species. It may have evolved as well in other animal species than anthropoid primates.

As an explanatory mechanism, group-mindedness has several advantages compared to the analysis offered by Dunbar. First, Dunbar’s analysis largely rests on the anatomical volume of the primate’s neocortex, but brain size is a rather removed proxy of the number and interconnectivity of cortical neurons that make up brain functionality (Roth & Dicke, Reference Roth and Dicke2005). Group-mindedness as an explanatory mechanism more directly relies on the functionality of the vertebrate’s social decision network, that can be independent of anatomical volume and structure. Second, group-mindedness as a solution to the problems of group-living can extend beyond primate species to social vertebrates more general. Indeed, not only primates but various other mammalian species live in stable groups, breed cooperatively, hunt together (Ausband & Mitchel, Reference Ausband and Mitchell2021; MacNulty et al., Reference MacNulty, Tallian, Stahler and Smith2014; Range & Marschall-Pescini, Reference Range and Marshall-Pescini2022) and engage in intergroup contest and conflicts (Cassidy et al., Reference Cassidy, MacNulty, Stahler, Smith and Mech2015; De Dreu & Triki, Reference De Dreu and Triki2022; Smith et al., Reference Smith, Swanson, Reed and Holekamp2012). Third, group-mindedness provides the animal a simple heuristic to quickly decide whether, how much and when to cooperate with others, and whether and how to adapt behavioral actions to those of others, independent of dyadic interaction histories. This makes group-mindedness cognitively less effortful and expensive than cognitive processes involved in perspective taking and inhibition. Fourth, group-mindedness can explain cooperation and coordination beyond the dyadic level, which is important for many species engaging in territory defense or cooperative hunting where success depends on numbers (Lemoine et al., Reference Lemoine, Boesch, Preis, Samuni, Crockford and Wittig2020). Finally, and in contrast to executive function principles, group-mindedness captures that most if not all group-living species are inherently in-group bounded and parochial, with cognitive and behavioural investments spend on those the individual relies on for survival and reproduction – those that are familiar rather than not, physically close rather than distant, and phenotypically similar rather than dissimilar.

Evidence for group mindedness in group-living animals other than humans is presently indirect, and research is needed to specify whether and how group-mindedness evolved for group-living. As a mechanism, however, group mindedness might better explain how social vertebrates – primates included – solve recurrent problems of cooperation and coordination through in-group bounded and parochial integration (e.g., cohesiveness, conformity) and synchrony (e.g., coordinated movement, mimicry, neural coupling) than metabolically expensive forms of cognitive skills. In anthropoid primates, including humans, capacities for enhanced cognitive abilities may be built atop more foundational capacities for group-mindedness that may have evolved in other group-forming species as well. Whether capacities for complex cognition are at all needed to deal with the recurrent stresses of group-living remains an open issue to be addressed.