Evolution of primate vocal repertoires: vocal systems as embodied capital for mediating within-group conflict

Life history traits constrain investments in costly neural and somatic embodied capital, potentially shaping the evolution of primate vocal communication systems. This study integrates life history theory with the social complexity hypothesis to test a sequential pathway from longevity to social dynamics to vocal repertoire size, using updated vocal repertoire data for McComb & Semple's (2005) set of 42 non-human primate species, alongside measures of group size and within-group conflict. We compiled data on vocal repertoire size, within-group conflict, group size, endocranial volume, and maximum longevity, analysing these via Phylogenetic Sequential Canonical Cascade Model and ancestral character reconstructions. Within-group conflict directly predicts vocal repertoire size, with earlier cascade steps-maximum longevity → endocranial volume → group size → within-group conflict-providing mechanistic support for this relationship. These findings suggest that embodied capital investments in neural and somatic traits enable conflict management across primate societies, with within-group conflict-itself scaled positively with group size-emerging as the proximal driver of vocal repertoire size, clarifying the coevolution of vocal systems and sociality across primates. This framework elucidates macroevolutionary patterns in nonhuman primates with relevance to hominin vocal complexity and language emergence.