How body size and habitat shape the vocal repertoires of primates
Biologists, zoologists and psychologists have been trying to trace the origins of human language for centuries. One well-known theory, known as the social brain hypothesis, suggests that increasingly complex social lives prompted primates to evolve increasingly larger brains, which in turn led to increasingly advanced communication skills.
A recent study published in Biology Letters challenges the conventional theory that larger primates with bigger brains have richer vocal repertoires. Instead, researchers suggest that body size and habitat play a more significant role in shaping the evolution of primates' communication strategies.
Biologists and psychologists have long been intrigued by the origins of human language, with one well-known theory being the social brain hypothesis. This hypothesis posits that as primates evolved increasingly complex social lives, they developed larger brains and more advanced communication skills. However, this study aimed to reassess the role of sociality in the context of a larger, more recent dataset while controlling for physical and ecological factors.
To conduct their analysis, researchers examined the vocal repertoires of 77 different primate species. They compared the size of these species' vocal repertoires (i.e., the number of distinct vocal signals or calls they can produce) with their average body and brain sizes, typical social group sizes, and habitats. The research team accounted for the phylogenetic distance between species and analyzed how body size and habitat interact to influence vocal repertoire size.
Surprisingly, the study found that a primate's average brain size and social group size did not predict the richness of its vocal calls. This finding contradicts the social brain hypothesis, which suggests that having a larger brain and being more social should lead to a larger vocal repertoire. Instead, the researchers discovered that each species' vocal repertoire could be explained by the interaction between its body size and habitat (arboreal or terrestrial).
The findings indicate that the evolution of more sophisticated communication strategies was not solely driven by more complex social lives. Instead, the benefits of group size may plateau, and larger social groups could become a burden on communication. Moreover, body size appears to have a substantial impact on vocal repertoire size, with a doubling of body size potentially increasing a primate's vocal repertoire by 28%.
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