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.

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.

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.

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.

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.

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.

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.

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.

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.

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.