I first summarise the argument in the target article so as to make the main points clear. I then address a number of major misunderstandings (mainly in relation to the social brain hypothesis), consider some specific issues that require clarification, and finally identify points that would merit more detailed consideration. I conclude with a list of possible future projects.

Grooming and cognition support primate group cohesion but are insufficient for maintaining stability in large groups. We propose tolerance, the capacity to accommodate social stress, as an additional mechanism. Tolerance fosters flexible social skills and cooperation beyond small cliques. Shaped by hormonal adaptation and development, tolerance plays a foundational role in overcoming group size limits by sustaining complex social networks.

The current manuscript rightly points out that non-human primates evolved complex social cognitive skills to maintain weaker social ties. However, these capacities are likely more expansive than currently proposed: research shows that apes behave more socially to those with whom they experience similar things, suggesting that they possess some precursor of humans’ capacity to bond through shared experiences.

Facial expression has evolved as a solution to the primate group living problem. A growing body of empirical evidence suggests that the evolution of facial expression has been driven by the need to bond. Dunbar’s theories of group cohesion are therefore key to understanding primate (including human) facial expression.

Dunbar proposes strategies to solve the fragmentation problem experienced by group-living animals. We highlight that bondedness not only mitigates stress but also provides structural scaffolding for group stability. Furthermore, we posit tolerance as a complementary mechanism smoothing social interactions and argue that variation in cohesion-promoting traits reflects context-dependent socio-ecological pressures, challenging static models linking sociality to cognition. Finally, we propose two further mechanisms—cultural transmission and dominance dynamics—that can enhance social cohesion by aligning behaviour and reducing uncertainty.

As the third solution to group dispersion, Dunbar proposes primates use several higher order cognitive skills to especially manage ‘weak ties’ in a nuanced and fast-tracked way, therewith avoiding unnecessary conflicts. We here argue that subconscious, automatic processes including attention allocation and behavioral or neurophysiological state matching can serve a similar function in maintaining group cohesion.

Life history strategies adaptively calibrated to levels of environmental harshness and unpredictability shape not only the fundamental issue of fertility but also whether and to what extent people engage in the structural, behavioral, and cognitive solutions proposed by Dunbar. Considering behavioral ecology can, therefore, add nuance to Dunbar’s novel and important theory.

Dunbar explains primates group cohesion through cognitive and structural mechanisms like grooming and social cognition. We extend this by highlighting collective social niche construction, where emergent social properties arise from feedback loops, selection pressures, and self-organisation. Adaptive social networks evolve through multilevel selection, cultural transmission, and ontogenetic changes, shaping survival, cognition, and collective intelligence across species.

The Social Brain Hypothesis (SBH) connects primate brain size to social complexity but faces empirical limitations. We propose expanding the SBH by incorporating hippocampal functions across species, demonstrating how cognition emerges from both social and ecological pressures. This extended framework moves beyond cortical-centric models, providing a comprehensive understanding of brain evolution and the origins of human cognitive abilities, including language.

Specialised forms of social cognition enable primates to manage the stresses of group living by allowing for flexible and intentional communication. This is used to increase the predictability of conspecifics’ behaviour for both signallers and receivers. Intentional communication helps to overcome the stimulus-driven processing that may occur due to stress, enhancing attention allocation in receivers.

We propose that the emergence of relationship-based social expectations and their evolution into fairness expectations played a key role in the size and cohesion of hominin societies. One of the central challenges of group living is the need to create and sustain stable and mutually beneficial patterns of cooperation. By regulating collaborative interactions, social expectations make group living less stressful.

Dunbar suggests that social stressors set “glass ceilings” on the evolution of mammalian group size and cohesion. We argue that this glass ceiling narrative conceals three contentious anthropocentric assumptions. First, large stable groups would always be beneficial. Second, grooming is an indicator for maintaining group cohesion. Third, group size is primarily limited by cognitive or behavioral incapacity. We challenge all three assumptions.

While grooming and other forms of physical bonding are crucial for stress management, social play and laughter deserve equal recognition as tools for both stress relief and the reinforcement of social relationships. They play a pivotal role in the development of motor and social skills and serves as a foundational behavior in species that rely on cooperation and alliance-building.

Dunbar suggests structural, behavioral, and cognitive mechanisms to mitigate the costs of living in large groups. While we generally concur with the notion of group size effects on female productivity, we call for a more explicit treatment of how functional support alleviates social costs and disagree with the outright dismissal of ecological drivers and phylogenetic inertia.

Dunbar exclusively sees groups as arising through the aggregate relationships between individuals and thereby makes the serious omission of not considering the capacity of those individuals to categorize one another as ingroup versus outgroup members.

Meta-cognition enhances the social bonding hypothesis for musicality, integrating imagination, episodic simulation, causal inference, and inhibition. Music fosters group cohesion by engaging the endogenous opioid system, supporting intergroup understanding through vivid mental imagery, and facilitating socio-affective fiction. Additionally, causal inference enables contextual interpretation of music, while inhibition refines musical coordination and executive function, reinforcing cognitive flexibility for cooperative social behavior.

Dunbar presents an intriguing analysis of variance in primate group sizes, and social glue’s (grooming) relationship to cognitive evolution. This focus on primates with consistent and stable grouping excludes perspectives on the evolution of grouping beyond predation and competition. The analysis raises important questions about variation, dynamic sizes, and the conservation implications of variance for primate population extinction vulnerabilities.