Great apes have an aversion to a restricted range of core pathogen sources that they share with humans; this extends beyond distaste to resemble a muted form of disgust, long thought to be unique to humans

The Animal Origins of Disgust Reports of Basic Disgust in Nonhuman Great Apes. April 2019. Trevor I. Case, Richard J Stevenson, Richard W Byrne, Catherine Hobaiter. Pre-print, DOI: 10.1037/ebs0000175

Abstract: Intrinsic to an evolved disease avoidance account of disgust is Darwin’s assumption of continuity between the emotional lives of humans and animals. However, beyond the case of avoiding stimuli that taste bad, there has been little exploration of the existence of basic disgust elicitors in animals. Moreover, one influential perspective holds that disgust is unique to humans-a preadaptation of distaste that expands through culture to include a wide range of elicitors (e.g., Rozin, 2015). The present study represents a broad-scope investigation into disgust-like responses that might be present in nonhuman great ape species. A survey of aversions, contamination reactions, and signs of disgust in nonhuman great apes (principally chimpanzees) was collected from 74 great ape researchers, fieldworkers, and keepers. Overall, the results suggest that nonhuman great apes share with humans an aversion to a restricted range of core pathogen sources, which extends beyond distaste to resemble human disgust. However, in nonhuman great apes, this aversion is muted. Candidates for this difference between humans and other great apes are considered, including frequent exposure to basic disgust elicitors in nonhuman great apes and increased dependence on meat-eating in hominin ancestry. We suggest that differences in disgust–like behavior between humans and nonhuman great apes reflect the specific ecological standpoint of the animal and that rather than being unique to humans, disgust is a continuation of the armoury of disease avoidance behavior ubiquitous in animals.

Public significance statement: A systematic survey of great ape experts suggests that nonhuman great apes have an aversion to a restricted range of core pathogen sources that they share with humans. This extends beyond distaste to resemble a muted form of disgust. Long thought to be unique to humans, disgust is likely a continuation of the armoury of disease avoidance behavior ubiquitous in animals.

Keywords:  Pathogen, Primate, Disease avoidance, Evolution, Aversions