From Physical to Moral Disgust

Does physical disgust spill over into moral disgust?

I’ve been thinking a lot lately about the emotion of disgust and the role that it can play in a social and moral context. For anyone new to psychology, disgust can be described as a strong feeling of rejection or repulsion and is one of Paul Eckman’s seven universal emotions experienced across hundreds of cultures.

The seven universal emotions (source: APA)

Disgust has evolutionary significance as it is believed to have evolved as a response to foods that could harm us. For example, many harmful bacteria give off an odor that we find disgusting which encourages us to not eat spoiled foods. Disgust could also be a mechanism to counter self-harm and promote hygiene as evidenced by the fact that many people find blood, guts, urine, and feces disgusting.

The above examples are all what I would call “physical disgust” or repulsion of physical objects in our environment in an effort to keep us safe from harm. But there is another domain, in humans in particular, in which disgust likely plays a role: our social and moral lives.

From Physical to Moral Disgust

While feelings of physical disgust have been observed in other animals on the evolutionary tree, humans are uniquely complex, social beings. It therefore shouldn’t be surprising that there is a large body of evidence that human disgust likely plays a role in our social and moral judgements.

However, there is an interesting question in here that is worth asking: to what extend does physical disgust “spill-over” (i.e., have overlapping neural mechanisms) into social and moral disgust, and what should we do about it?

First, let’s look at the case in favor of this spill-over effect

In 2008, Andrew Jones and Julie Fitness coined the term “moral hypervigilance” to describe the phenomenon in which people who are more prone to physical disgust are also more prone to moral disgust. Colloquially, this link can be seen in two ways:

1. We often describe particularly immoral criminals as “disgusting” or as “scum” and criminal activity as “fishy.” I don’t know about you but I have often utilized the word “disgusting” has a way of conveying strong moral outrage.

2. People avert their eyes to visual depictions of morally disgusting acts such as incest or murder in the same way that they do for physically disgusting depictions such as an oozing open wound.

Similarly, Schaich and colleagues looked at the brains of individuals viewing violations of both pathogen-related disgust and moral disgust and found many common brain activations—thus claiming that our moral judgements may have underlying disgust-related causes.

However, there isn’t consensus around the connection between physical and moral disgust

Oaten and colleagues asked an important question in response to the above evidence: are studies that find a connection between physical and moral disgust confounded by the fact they they often use the same or similar disgust elicitors? For example, “killing your sister” is likely seen as morally disgusting but could also bring up images of blood and guts which are “physically disgusting.”

Oaten attempted to better distinguish between physical and moral disgust by looking at the residual disgust leftover after any kind of physical disgust has been accounted for. They found that any increase in disgust from a physical elicitor (e.g., blood) to a moral elicitor (i.e., murder) was more consistent with “moral anger” than disgust per se. This sheds doubt on the view that our physical and moral disgust are actually connected.

What do we do about the possible connection between physical and moral disgust?

In a toward and quest of understanding, I outlined evidence of the emotional underpinning of our moral judgements. One of the goals from that piece was to highlight how our moral judgements can be shaped by subconscious, less-than-rational aspects of our nature.

Here, we zoomed in on one emotion, disgust, and asked whether our feelings of physical disgust could spill-over into moral disgust. If this is true, there is at least one domain in which this spill-over effect could have negative consequences: our view of marginalized people.

At first glance, it can be difficult to reconcile some of the most morally horrifying acts in human history (e.g., 20th century holocaust) with our strong evolutionary nature to protect members of our own species. That is, until one considers the effect of dehumanization. If we cease to consider a being human, our moral rules can suddenly change, and there is a lot of evidence that this is exactly what happened in the holocaust.

If our goal is to live a moral life to the best of our ability, then we should be on the lookout for dehumanizing tendencies.

It turns out that disgust could play a role in dehumanization. One study subjected people to images of widely stigmatized groups of people such as the homeless or drug addicts and found that these images did not activate the medial prefrontal cortex as much as images of non-stigmatized groups. Given that the medial prefrontal cortex is most often activated when viewing humans vs objects, and is associated with mentalizing, these data provide evidence that people are disinclined to attribute mental states to the homeless and drug addicts—a classic sign of dehumanization.

Here, it’s easy to see the connection between physical and moral disgust. The homeless, for example, are often associated with poor hygiene which tends to illicit physical disgust that could “spill-over” into moral disgust. It is these kinds of biases that we should be vigilant against in our effort to live moral lives.

Thanks for reading.

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