Guenon vocalizations and human language: parallels and contrasts
Résumé
Human language is too complex to have emerged without any evolutionary precursors. Our research on the vocal behaviour of forest guenons (Cercopithecus spp) has revealed a number of possible precursors that may have been important as building blocks in human language evolution. First, despite a rigid species-specific vocal repertoire, there is considerable acoustic plasticity in some calls of Campbell’s monkeys, which is related to the social function of the calls. For example, contact call variants of females are more similar between preferred than not preferred partners, suggesting a process of vocal sharing. Second, contact calls also take part in conversation-like vocal exchanges that are socially controlled. Third, several guenon species produce acoustically distinct calls to specific external events. For example, Campbell’s monkeys produce acoustically different alarm calls to the same predator. Calls are meaningful within and between species. Female Campbell’s monkeys possess a complex alarm call repertoire, although there are interesting differences between captive and wild individuals. Males produce six call types that differ in frequency contour and in whether they have an acoustically invariable suffix. Suffixed calls carry a broader meaning than unsuffixed ones. Fourth, the six calls are concatenated into context-specific sequences, following basic combinatorial principles. Sequence composition, order, and rhythm enable males to inform about type and degree of danger, predator class, as well as some environmental and social events. Data suggest that a strong dichotomy between human language and nonhuman primate vocal communication is no longer tenable.