Tybur et al (2012) offer an evolutionary theory of disgust’s origins, nature, and expansion. Their theory has much in common with our older theory of disgust (Rozin & Fallon, 1987; Rozin, Haidt & McCauley, 1993; 2008). Both theories presume a food-related origin, although Tybur et al., by invoking a pathogen origin, are open to non-oral (e.g. airborne) original disgusts. Both invoke the process of preadaptation to explain the expansion of disgust (although Tybur et al. use the term “co-opted”). Preadaptation (related to the later idea of exaptation) (Mayr, 1960) refers to the fact that in biological (and cultural) evolution, something already present–usually something that evolved for another purpose–can be recruited to a new function. Both theories recognize a role for disgust in response to certain other humans and certain types of moral violations. That is a lot of similarity.
Our main differences arise in two areas: 1) what are the domains into which disgust expanded? and 2) is biological evolution for pathogen avoidance sufficient for explaining disgust and its expansion, or does cultural evolution play a crucial role? Tybur et al (2012) subsume what we call “animal reminder” disgust into their central category of pathogen disgust. Animal reminder disgust as we use the term refers to the disgust response to corpses, blood, gore, amputations, piercings, and other violations of the normal, culturally-agreed-upon outer “envelope” of the human body. Tybur et al. note that many of these elicitors – such as blood and corpses – are vectors for pathogens, and that is certainly true (and more important than we acknowledged in our early papers).
But many of these “creepy” items have little to do with pathogens, e.g., seeing a man with a glass eye remove the eye from its socket, or seeing someone who is morbidly obese. Items such as these repeatedly factored together in our early work. That is, when we examined hundreds of candidate items for our Disgust Scale , animal reminder items were rather highly correlated with one another, and less highly correlated with what we called core disgust items, like rotting food (Haidt, McCauley & Rozin, 1994).
In trying to make sense of this cluster, we drew on anthropological work, and on the writings of Ernest Becker (1973). We suggested that many cultures have come to use disgust to reinforce their own norms about the ideal human body (an ideal that varies across cultures). Part of the motivation for guarding this ideal was the motivation to believe that human beings and human bodies are special; we are not like other animals, and things that remind us that we are in fact animals tend to recruit disgust. In particular, one animal property–death–is particularly threatening to the only species that consciously appreciates its own mortality. A significant motivating force in human history and cultural evolution, at least over the last 10,000 years, has been coping with death. And a major function of many religions is to relieve death anxiety. Tybur et al. (2012) have raised some good objections to our explanation of the animal reminder items (e.g., animals breathe, yet breathing is not disgusting). But they include only one item of the animal-reminder type on their Three Domains of Disgust (3DD) scale (Tybur et al., 2009). The single item is touching a person’s bloody cut – but because the item includes touching blood, it is clearly a pathogen threat. We think they may have ignored these disgust elicitors, and hence an important component of disgust, because it didn’t fit their theory.
Our biggest area of disagreement with Tybur et al. is over the nature of moral disgust. We carved out a well-defined subset of moral violations and showed that they were linked more closely to disgust than to anger (Rozin et al., 1999). These were violations of what Shweder et al. (1997) called the “ethics of divinity.” Many cultures create sacred objects and values; many treat the body as a temple; many have notions of purity, pollution, desecration and degradation. These cultural values and practices are heavily moralized, and they involve elements of contagion, yet they cannot be interpreted as efforts to guard against actual pathogens. We did not include such items on our disgust scale because we found, early on, that they did not seem to correlate well with the other disgust subscales—just as the moral component of Tybur et al’s 3DD scale correlates rather weakly with their sexual and pathogen components. We think that part of the problem with moral disgust is that, in English, the word disgust is used in the specific sense we and Tybur et al. propose, but also to generally mean “bad”, either morally or otherwise (Nabi, 2002). It is a fact of interest that people will say that a wide range of moral violations are “disgusting” and show the disgust face. Perhaps in the most recent stage of its history, “disgust” began to be loosely used to signal general moral rejection.
The 3DD has a subscale for moral disgust, but it consists exclusively of questions about violations of fairness, for which we know that the dominant emotion is anger, not disgust. For example, the 3DD asks subjects to rate how disgusting is the concept of “shoplifting a candy bar,” or the concept of “a student cheating to get good grades.” People do indeed vary in their willingness to use disgust to describe these acts, but we don’t believe this variation tells us anything about disgust sensitivity, or about moral disgust. Olatunji et al. (2012) have reported evidence that the moral items on the Tybur et al. disgust scale are more associated with anger than disgust, and we have unpublished evidence showing the same.
Clearly there is much more work to be done on disgust, particularly on moral disgust. Tybur et al., in our view, have oversimplified the moral domain in their quest for parsimony. Human beings are cultural creatures who have woven disgust into their religious, political, and moral practices. We think that the expansion of disgust beyond its probable original role as an “oral defense” system is more complex. Preadaptation in biological and cultural evolution may be the processes through which this has occurred, but how and when the expansions happened, the changes in function that occurred, and the interactions between biology and culture are yet to be described. Unlike Tybur et al., we think that cultural psychology, as well as evolutionary psychology, is necessary to tell the whole story.
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