The evolution of laughter in great apes and humans

Abstract

It has long been claimed that human emotional expressions, such as laughter, have evolved from nonhuman displays. The aim of the current study was to test this prediction by conducting acoustic and phylogenetic analyses based on the acoustics of tickle-induced vocalizations of orangutans, gorillas, chimpanzees, bonobos, and humans. Results revealed both important similarities and differences among the various species’ vocalizations, with the phylogenetic tree reconstructed based on these acoustic data matching the well-established genetic relationships of great apes and humans. These outcomes provide evidence of a common phylogenetic origin of tickle-induced vocalizations in these taxa, which can therefore be termed “laughter” across all five species. Results are consistent with the claims of phylogenetic continuity of emotional expressions. Together with observations made on the use of laughter in great apes and humans, findings of this study further indicate that there were two main periods of selection-driven evolutionary change in laughter within the Hominidae, to a smaller degree, among the great apes and, most distinctively, after the separation of hominins from the last common ancestor with chimpanzees and bonobos.

Acknowledgements

Thanks go to Hugh Spencer (Cape Tribulation Tropical Research Station) for providing the video material. The study was funded by the University of Veterinary Medicine Hannover and the Center for Systems Neuroscience Hannover. Acoustic analysis was partly supported by the Center for Behavioral Neuroscience under the STC Program of the National Science Foundation under Agreement No. IBN-9876754 and by the Brains & Behavior Initiative and Neuroscience Institute at Georgia State University. Travel costs were funded by Forschungszentrum Jülich and Freundeskreis der Tierärztlichen Hochschule Hannover.

Figures and Tables

Figure 1 Representative spectrograms (40-ms Hanning window) of tickle-induced vocalizations from four great ape species and humans. Recordings had a 22,050-Hz sampling rate. This illustration first appeared as Figure 1 in Davila Ross et al.20

Figure 2 Model of the evolution of laughter and other vocalizations of tickling and play in great apes and humans. Two main periods of acoustic and function-related changes in laughter were likely to have occurred within the past ten to sixteen million years while other tickle- and play-induced vocalizations evolved. It remains unknown whether laughter and squeaks emerged prior to or in the common ancestor of great apes and humans. Notably, lesser apes produce tickle-induced vocalizations that acoustically resemble orangutan laughter (e.g., Symphalangus syndactylus: Davila Ross et al.20; Hylobates lar: Zimmermann pers. obs.) and squeak-like calls during play (Nomascus spp.: Thomas Geissmann, pers. comm.). The figure is adapted from Davila Ross et al.20 Figure 4.

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