A multifactorial investigation of captive gorillas’ intraspecific gestural laterality

ABSTRACT

Multifactorial investigations of intraspecific laterality of primates’ gestural communication aim to shed light on factors that underlie the evolutionary origins of human handedness and language. This study assesses gorillas’ intraspecific gestural laterality considering the effect of various factors related to gestural characteristics, interactional context and sociodemographic characteristics of signaller and recipient. Our question was: which factors influence gorillas’ gestural laterality? We studied laterality in three captive groups of gorillas (N = 35) focusing on their most frequent gesture types (N = 16). We show that signallers used predominantly their hand ipsilateral to the recipient for tactile and visual gestures, whatever the emotional context, gesture duration, recipient’s sex or the kin relationship between both interactants, and whether or not a communication tool was used. Signallers’ contralateral hand was not preferentially used in any situation. Signallers’ right-hand use was more pronounced in negative contexts, in short gestures, when signallers were females and its use increased with age. Our findings showed that gorillas’ gestural laterality could be influenced by different types of social pressures thus supporting the theory of the evolution of laterality at the population level. Our study also evidenced that some particular gesture categories are better markers than others of the left-hemisphere language specialization.

KEYWORDS:

• Social laterality
• intraspecific communication
• manual gestures
• primates
• brain lateralization

Acknowledgements

We are very grateful to all the keepers and collaborators of the zoo of La Vallée des Singes (France), the zoo of Apenheul and the Burgers’ zoo (Netherlands) and particularly Jean-Pascal Guéry, Frank Rietkerk, and Wineke Schoo for allowing us to study their gorillas groups as well as for their friendliness and helpfulness. We are also indebted to Amandine Chapelain for her advice about the design of the observation protocol, to Caroline Coste for entering a part of the data, and to Russell Lenth and Maxime Hervé for their statistical advice for the use of “lme4” and “lsmeans” packages as well as to Ann Cloarec for correcting the English.

Disclosure statement

All authors declare that they have no conflict of interest.

Notes

1 The visual field used refers to the spatial extent (from 0 to 180°) in which the recipient is located (i.e. on the left or on the right visual field of the signaller). It is termed “enlarged field” by Baraud et al. (2009).

Additional information

Funding

This study was part of a PhD funded by the French Ministry of Research and Technology with additional financial support of Rennes Metropole and the VAS Doctoral School. In addition, it was supported by a Sofja-Kovalevskaja Award of the Humboldt Foundation to S. P.