Updating social knowledge under stress: communicative complexity and the evolution of primate social bonding

The integration and updating of social knowledge is central to the formation and maintenance of social bonds in primates. Social knowledge enables individuals to predict others' behaviour, with expectations revised in response to incoming sensory input. Yet the socio-ecological environment presents continuous challenges that engage neurophysiological stress responses, shaping how knowledge is processed. Stress can be defined as the reaction of an organism to a detected stimulus ('stressor'), with psychology and neuroscience distinguishing between acute stress-short-term, with clear onset and offset-and chronic stress-persistent, with limited recovery phases. Ecological stressors, such as predator threat, typically elicit acute stress responses, whereas social stressors, including uncertainty and instability, are key drivers of chronic stress. Both types of stress disrupt the integration and updating of social knowledge, thereby undermining social cohesion. I argue that communicative complexity in primates evolved as an adaptive mechanism to mitigate these constraints. Rather than viewing intentional communication as mere transfer of meaning encoded in signals, I propose that it constitutes a diverse set of behaviours-including subtle attentional cues such as gaze or response waiting, as well as culturally transmitted features such as dialects-that function to heighten conscious awareness, regulate affect, and motivate receivers to update social knowledge even when cognition is constrained by stress-induced, stimulus-driven processing. From this perspective, 'meaning' lies not in the signal itself but in its conscious construction through the integration of social knowledge and affective experience. This paper develops this account by considering communicative complexity as an adaptation enabling primates to sustain social bonding under ecological and social stress.