Disgust in Other Species

Studies of disgust in nonhumans are starting to emerge. In the last few years, they’ve been conducted on chimpanzees, great tits (Parus major), rats, and flies. This would be quite a development, since evolutionary psychologists are convinced disgust is a “new” emotion, due to its apparent absences in other primates. So far though, this smattering of findings is still framed mostly around understanding humans. Rats, though unable to vomit, can be subject to induced nausea, which may serve as a useful model for thinking about this still poorly understood sensation in humans. Chimpanzees, experimentally, demonstrate avoidance behavior in relation to contaminated food, which may “hint at the origins of disgust in humans.” This suggestion at least leads in a favorable direction: “further comparative research is now needed.” But at the risk of reducing disgust to an instinctual physiological reactions, missing its important social dimension. Starting with the fact that social learning plays a role in the formation of this sensation or sentiment; continuing with the fact that disgust plays a crucial role in developing, enforcing and reproducing social boundaries. Notably, the socially learned aspect of disgust is evident in an intriguing recent study of great tits. Experimenters modeled “social transmission” by showing birds a video of other tits selecting their prey; when the “model predator” was repulsed by an insect, the observer learned to avoid that creature, too. Researchers frame this finding as indicative of how “learning by observing others occurs throughout the animal kingdom. Species ranging from fruit flies to trout can learn about food using social transmission.” Because this study is as much about how prey species might escape predation and flourish through this exchange, their broader point is that “social information may have evolutionary consequences right across ecological communities.” But in terms of the learned aspects of disgust, this study highlight the importance of “social signaling” understanding this dynamic.

Even psychologists—who are prone to regarding disgust as an instinctual evolutionary adaptation—are beginning to recognize its function as social signaling. That is, much like nonhuman rituals, it is communicative and in some sense performative. Kupfer and Ginger-Sorolla posit the role of disgust “in signaling social motivation to others”; that “disgust is not just an expression of an inner reaction to impurity but a signal that advertises a moral position” (2017:632). Transposing this assessment, we can then ask of its appearance in nonhumans whether this similarly indicates, first, the kind of performance of self entailed by conveying motivation or, second, a moral sensibility, and a socially informed one at that.

The moral capacity and sensibilities of nonhumans is a sprawling subject, much broader than this limited discussion of disgust. The basic consideration, as Kupfer and Ginger-Sorolla stress, is that disgust is triggered (and facially expressed) as much over a perceived unfairness as by encountering an impurity. The perception of unfairness is both moral and social, involving a sense of a collective order within which the subject is located. Taken in concert, their framing of disgust posits it as much more than a mechanistic reaction to an instinctual impulse; this is what moves it into the “social” register, rather than just being a biological matter. If chimpanzees can express disgust, perhaps they, like us, are doing so with the intent of affirming or asserting social perceptions and sensibility. This question falls outside of the experimental design developed by Sarabian et al (2017). But their opening speculative frame for the paper does lead in a useful direction for thinking more broadly about disgust in nonhumans. Their article begins, “Many major infectious diseases (e.g. infectious intestinal diseases, herpes, hepatitis) are transmitted via contact or ingestion of particles of bodily products such as faeces, blood, semen and saliva.” With humans, such secretions are policed with copious taboos and intense moral charges, as captured by the cultural concept of pollution. Two points follow. One is that pollution is a social means by which boundaries are established, not just between subjects and offending materials but in walling off threatening “others” from an in-group. The second is more complicated and it involves disease.

The biologistic view of all this—as conveyed in the above quote—is that disgust is an evolved means of protecting an individual from life-threatening diseases. But disease entails social dimensions as well, and here we get to the matter of distance. Social species contend with heightened forms of contagion due to intensive proximity. Basically, the vast majority of animals avoid each other. Social ones, obviously, do not. So there’s a fundamental question, evolutionarily, over how such species overcame such avoidance; then, too, what is the ‘mechanism’ by which they manage social proximity? The latter is a subject I have been addressing in terms of the “social gaze,” but disgust, because it concerns contaminants or pollution, leads us to hygiene. This activity is something of a fulcrum for analytics that teeter between biological and social interpretations. Hygienic activities can be construed as largely instinctual, but they also are a foundational aspect of social relations for many species. Allogrooming, where one conspecific cares for or tends to another, is a medium by which alliances are asserted or reproduced, challenged or rejected. It also exactly brings these two creatures into contact with some of the bodily substances listed above that may well engender disgust. So hygiene, in its social forms, suggests that such substances are not inherently noxious; they can, in fact, be managed by others through relational behaviors. And they are managed through activities that close what might otherwise be an insurmountable distance between conspecifics. This is how it’s worth following disgust in nonhumans—like ritual (particularly forms like allogrooming), it may well feature social conventions that are mediums of expression and performance.

A recent review of research on social immunity in insect colonies suggests an interesting direction for further consideration. “Social immunity” characterizes colony-level disease protection achieved through collective defenses of colony members. This phenomenon is also intriguing because it seems to parallel immune responses of individual organisms—yet another aspect of how the “superorganism”-status of such insects appears uncannily to mirror our brains and bodies. The review by Cremer et al (2018) keys in on “how social immunity emerges from its components to provide colony-level protection by avoidance, resistance, or tolerance.” The matter of avoidance, of course, involves distance and its social mediation. Such forms of mediation help generate social immunity; these measures “involve nest hygiene and sanitary care behaviors that prevent or reduce the disease risk of colony members.” But these forms of care can shift quickly, characterized by a “care–kill dichotomy, depending on whether the individual can be cured or is a threat to the fitness of a colony.” Allogrooming, in these colonies, varies to some extent, so it’s quite possible such practices are both learned and reflective of “local” or cultural character. Underscoring this is the finding that “ants also show increased grooming levels with pathogen experience.” That is, they develop grooming practices through what we might equate with local history. As observational methods and techniques with colony insects become more fine-grained, it is possible to imagine they will reveal something very much like “pollution” being socially learned and enacted. If so, then we can wonder at the role disgust might play in eusocial dynamics—how it is cultivated and what it is used to socially signal. At the very least, “targeted sanitary care of contaminated insects, such as cleaning the body surface by allogrooming and prohibiting pathogen germination or growth by disinfection,” appears to be a complex social behavior; one that may well reflect distinct colony cultures—a more interesting matter than the idea of “colony personality,” which behavioral variation a matter of psychology.