Orangutan call communication and the puzzle of speech evolution

Abstract

Speech is a human hallmark. However, its evolution is little understood. It remains largely unknown which features of the call communication of our closest relatives – great apes – may have constituted speech evolutionary feedstock. In this study, I investigate the extent to which speech building blocks can be found in orangutan call communication. Orangutans represent the oldest great ape lineage but early and recent studies indicate they represent a promising model species in this endeavor. I investigate orangutan call communication in natural(istic) conditions recognizing the calls individuals actually produce. Instead of seeking (to teach) human words, I identify speech features potentially present in orangutan call communication in the absence of full-blown speech. Moreover, I borrow terminology from linguistics and semiotics (social sciences dedicated to the study of human speech and signs, respectively) in order to establish a direct comparative approach based on structural and behavioral homology between great apes and humans. Accordingly, I examine speech building blocks traditional presumed to be uniquely human, since any valid hypothesis for speech evolution must suitable explain the emergence of these features. Multiple speech building blocks are present in orangutan call communication, challenging traditional assumptions that great apes do not represen a suitable model for the study of speech evolution.