The Evolutionary Biology of Disgust, Part I

How can a rational emotion be hijacked for political purposes? The answer holds the key to much human misery . . .

In a forthcoming book, Martha Nussbaum describes the Politics of Disgust that has frequently dominated American discourse over homosexuality. She reminds us that its roots run deep in human history, providing historical depictions of Jews and Untouchables in India as filthy, disease-ridden, and necrotic. She has no problem finding current examples in American politics to support the notion that anti-gay sentiment (but not anti-lesbian sentiment) is driven by the same strategy of rendering homosexual acts, real and imagined, as disgusting and unnatural. For practical reasons, however, she cannot spend too much time examining the rational basis for disgust as an emotion and its stunning amenability to being hijacked.

Evolutionary biology would suggest that disgust should be a rational emotion. The vast majority of humans probably feel disgust at the thought of incest or eating feces or handling a rotting corpse. How come? Quite probably because of natural selection. Cave people with an aversion to incest developed a stronger and more diverse gene pool; those who stayed away from feces and rotting corpses probably lived longer and therefore had more children. This is disgust as an emotion in the service of humanity. Critically, it explains why we don’t automatically reject disgust as an illegitimate emotion when we feel it. In fact, we are probably more likely to accept it in ourselves than anger, which we suspect usually evidences a problematic loss of self-control. We curse ourselves for losing our tempers, but we seldom say, “I shouldn’t have been disgusted by that.”

This evolutionary salience creates tremendous opportunities for exploitation. A crude political strategy therefore is to accuse someone of routinely doing something disgusting. Our disgust at the act gets transferred to the person or group with predictably horrific results. Nussbaum describes pamphlets accusing gay men of drinking blood and eating feces. This story is far too simple, however. First of all, it does not explain the motivation of the original accuser. Why conceive of the discriminatory strategy in the first place—from whence comes the original disgust? Second, it doesn’t explain why people who don’t read or believe the lurid pamphlets seem nonetheless disgusted by homosexuality.

I’ll reject one possible theory immediately: disgust with homosexuality itself is evolutionary, e.g. our primitive ancestors who avoided certain sex acts thrived as compared to those who did not. First, natural selection does a poor job of explaining the significant percentage of the current population who are gay or lesbian. Shouldn’t disgust have helped select out the trait? Second, as Martha points out in her book, present feelings of disgust aimed at homosexuals are quite a-historical. There’s no evidence that mankind has felt this way over the millennia . . . can we work out a more complex story?

Comments

[Martha Nussbaum]

Paul gives a nice summary of this important issue (which, actually, I discuss at much greater length in my 2004 book HIDING FROM HUMANITY: DISGUST, SHAME, AND THE LAW). But he doesn't mention the large amount of first-rate experimental work on disgust that has been done by psychologist Paul Rozin of the University of Pennsylvania and his colleagues, so let me describe what it shows. First of all, disgust is not just an animal instinct: it has a definite cognitive content, having to do with the rejection of a contaminant. The way the subject sees the object is crucial, even when we're dealing with the "primary objects" of disgust, such as feces, spoiled food, corpses, and other bodily products such as semen, sweat, and blood. Subjects who are told that what they are sniffing is cheese usually like the smell; if they're told that the vial contains feces, they are usually disgusted -- even if it's the very same smell. So disgust is different from mere sensory distaste: the conception of the object matters. On the other side, disgust is also different from an aversion to danger. Some dangerous objects are not disgusting. But some objects continue to disgust long after the danger has been removed. (For example, subjects refuse to eat detoxified cockroaches. In one experiment, the cockroach was sealed in a plastic capsule that would emerge intact in the subjects' feces, and they still refused to eat it.) Rozin concludes that disgust is a way of policing the borders of the body against things thought to be contaminating. These things, he then finds in further experiments, all have in common that they are reminders of our bodily mortality and animality. So even disgust at primary objects is more complicated than it seems. In evolutionary terms, it did supply a rough heuristic against danger, but it also did something more, reassuring humans about the boundaries between humanity and animality, and policing these boundaries.
It's no surprise, then, that disgust easily gets extended to objects and people who are thought similar in some way to the primary objects. Thus, subjects refuse to eat soup stirred with a sterile fly swatter, or to drink juice from a sterile bedpan. Most pernicious of all, as Heald indicates, is the projection of disgust onto people and groups, always subordinate groups, who come to symbolize (mere) animality. In all societies, some groups are widely thought to be physically disgusting: smelly, linked to uncleanness, etc. The function of what I call "projective disgust" is probably to shore up even further the boundaries between humanity and animality by creating a class of sub-human humans who stand between the "transcendent" humans and their own mere bodily humanity. They are thought to contaminate the dominant group. (Of course it is something about themselves that they are hating and fearing.) Women have often played this role. German sex-theorist Otto Weininger held that the woman is the body of the man, which he must repudiate and hate on the way to being pure and transcendent. While he was at it, he said that Jews were really women, since they had (he fantasized) all the loathsome characteristics of women, such as being soft, sticky, and smelly. (Weininger was a self-hating Jew and homosexual who committed suicide shortly after writing this highly influential book.) When we study the excellent research on disgust, we have good reason not to go along with theorists such as Lord Devlin and our U of Chicago colleague Leon Kass, who hold that disgust is a good basis for lawmaking.

[Fazal Khan]

I concur with Heald that the emotion of disgust can be seen as a highly adaptive trait. It is easy to conceive that those who innately retch at the smell of bacteria in feces or rotting carcasses, or are instinctively perturbed by the notion of mating with close kin, would be more evolutionarily fit. Further, I share Heald’s reluctance in identifying disgust as a maladaptive emotion per se in contrast to anger. For instance, immediately after 9/11 (and unfortunately even now) there were many acts of violence directed at the American Muslim community that appeared to be motivated not by disgust, but by anger. In fact, mainstream pundits spilled much ink “defending anger” as a rational response, seemingly giving a wink-wink, nudge-nudge to such acts. Which begs the question, are acts of violence or discrimination against the “other” more acceptable if committed from a state of anger rather than disgust? If there is no morally justifiable basis for such action (e.g., true self-defense), the answer cannot be “yes.” A separate inquiry is whether discrimination stemming from anger, as opposed to disgust, is less worrisome. Here the answer might be yes, because anger tends to subside, much like pain, as time and distance increases from the inciting event. However, disgust, once learned, seems to be a more durable emotion that is imprinted upon us and thus less likely to subside.

Most people do not have to be taught to be disgusted by spoilt milk, on one’s initial exposure most would recoil at the smell or taste of it, and then hold on to this aversion. However, people do have to be taught that they should be disgusted by homosexuals, untouchables, Tutsis, Muslims, Jews, etc., and perceive them akin to parasites or filthy animals. Heald is correct in rejecting as ahistorical the notion that somehow disgust of any particular group, including homosexuals, is an innate or universal human trait. One need only look at ancient and contemporary societies where this is no such “innate” response. This brings up the important question which Heald asks, “from whence comes the original disgust?”

The notion of singling out an easily identifiable “other” as the explanation for various social and political ills, and therefore an object of disgust, is an old and recurring story. Hence Jews become the scapegoat for the malaise of modern Europe; hence Balkan Muslims are the “traitorous seed” (in the words of Nobel laureate Ivo Andric) holding back the ambitions of a proud Slavic nation; and hence homosexuals are to blame for hurricanes and terrorist attacks in the U.S. according to right-wing preachers and political operatives.

To summarize, as Heald points out, disgust as an emotional reflex can be very beneficial in its unlearned, instinctual form. However, I am sympathetic to the notion that this powerful emotional reflex can be hijacked and be socially maladaptive when directed at the other. The answer to Heald’s question might then be that this form of disgust, displaced on the socially vulnerable other, comes from a sublimated self-loathing and disgust of one’s own failings and ills, much like the biblical scapegoat.

[Frank M. Cook]

Carl Sagan wrote in one of his books, sorry I forget which one, that ideas like genes are subject to evolutionary forces. Perhaps that is the point you are making but I understood your references to evolutionary biology to suggest a possible genetic component to disgust. Sagan suggests a parallel but separate survival of the fittest ideas. Notions like disgust need not be hardwired in our DNA to be passed on from parents to children. Sometimes, in the words of South Pacific, the ideas "have to be carefully taught." Yet, even if taught, the ideas that spread over time are the ones that promote survival because the "bad" ideas died out with the cultures that believed in them. All of which leads to a very different way to think about the origins of "natural law."

[Resveratrol]

Most people do not have to be taught to be disgusted by spoilt milk, on one’s initial exposure most would recoil at the smell or taste of it, and then hold on to this aversion. However, people do have to be taught that they should be disgusted by homosexuals, untouchables, Tutsis, Muslims, Jews, etc., and perceive them akin to parasites or filthy animals. Heald is correct in rejecting as ahistorical the notion that somehow disgust of any particular group, including homosexuals, is an innate or universal human trait. One need only look at ancient and contemporary societies where this is no such “innate” response. This brings up the important question which Heald asks, “from whence comes the original disgust?”