Exploring the form and functions of chimpanzee pant-hoots from basic evolutionary principles.

Abstract

Researchers have studied chimpanzee vocal communication extensively, focusing on evidence of parallels with human language. This approach has been effective in encouraging vocal communication research and providing some insights about the evolution of language. However, it has obscured our understanding of non-human animal communication by motivating researchers to adopt a problematic conceptual framework that uses complex linguistic phenomena as models for simpler primate vocal communication mechanisms. An approach focusing on basic evolutionary principles involves studying the intimate connection between form and function to obtain insights about the biological and evolutionary origins and mechanisms of traits. Such an approach, when employed for studying chimpanzee vocalizations, may be more fruitful in revealing fundamental factors that may shape their vocalizations. This dissertation extends our knowledge of the forms and functions of chimpanzee vocal communication. I first explored different acoustical and statistical analysis methods for describing the form of vocalizations. Next, I studied connection of the form of chimpanzee vocalization, the pant-hoot, to its possible functions. Using audio recordings and behavioral data from two chimpanzee communities in Gombe National Park, Tanzania, and one chimpanzee community in Kibale National Park, Uganda, I tested if the variation in chimpanzee calls is explained primarily by (i) community membership, or (ii) by individual traits such as age, rank, and health, and (iii) if any of these acoustic cues predicted male mating success. Individual traits better explained the acoustic variation in pant-hoots than community membership. Acoustic variation also reflected male mating success. These findings suggest that sexual selection is a key evolutionary force shaping chimpanzee vocalizations.