What are you disgusted by? For me, it’s cockroaches. Not them physically, but their extremely sporadic and unpredictable pattern of movements. It doesn’t help that roaches are one of those dastardly creatures that – when threatened – scuttle towards you at breakneck speeds, leaving you little time to realize that the tiny schmuck couldn’t cause any real harm to your human-sized self, anyway.

Despite cockroaches not being biological vectors of disease (although they could transmit pathogens mechanically), human beings share an innate, biological disgust for them – as we do for maggots, excreta, or pus. This experience of visceral disgust is shared between human beings and animals, and is different from moral disgust, which is a distinctly human characteristic. Moral disgust could be any behaviour by others deemed unsocial or that contradicts our ingrained moral principles. So think of your best friend’s partner who cheated on her with another of her friends, and you might feel moral disgust.

The intensity with which we feel either type of disgust has implications for our behaviour. For instance, how many of us would be comfortable eating out of a fresh-out-of-the-factory bed pan? It’s never been used, so it’s as clean as a plate, but knowing the object’s purpose is collecting human waste means that most of us would rather go hungry. Disgust is also distinct from tangential negative emotions like anger. As cited by Jones, a 2008 study by Jonathan Haidt and his colleagues provided physiological evidence that the body reacts differently for disgust (in which the heart rate drops) than for anger (heart rate rises). Participants were responding to representations of neo-Nazis, and those whose heart rates dropped reported feeling morally disgusted. So our vehement protest of “that’s disgusting!” for something we’re pissed off about is only a colloquial use for the term, and actual disgust – whether visceral or moral – is operationalised differently.

But can visceral disgust have any implications for how we process social and moral disgust? Research suggests so. Schnall et.al (2008) conducted a series of experiments in which visceral disgust was induced for participants through exposure to pungent smells, a disgusting desk and room strewn with waste tissues stained with suspicious fluids, or an activity that required them to remember an instance that made them physically ill from disgust. Turns out visceral disgust significantly influenced moral judgments in comparison to a control group for which these somatic markers for disgust were absent. Subsequently collected physiological evidence has supported these findings.

How does disgust sensitivity affect our interactions with other people?

Some scholars say that disgust sensitivity in humans evolved as a mechanism to avoid disease by altering our behaviour in ways that minimized risk. This explains why we may avoid strangers who are from a community outside of ours, yet we might feel more comfortable with strangers from within our own community – even though we may not know them personally and they could just as easily be a carrier of pathogens as well. To explain this from an evolutionary psychology perspective, it is likely we will have developed antibodies to diseases we have already been exposed to by our in-group community, than diseases spread through out-group members which are novel to us and, hence, potentially life threatening.

While such theories might seem far-fetched, recent studies show that when perceived disease vulnerability is induced through disgust, participants show an increase in ethnocentric attitudes. That is, people are more likely to favour members of their own community and exhibit negativity towards other communities when they are primed for exposure to diseases… very much like the COVID-19.

In light of the Coronavirus pandemic, writing from around the world has documented an increase in xenophobic attacks against those deemed visibly “foreign”. American-Chinese children residing in the U.S were not spared. In India, students from north-east Indian states have spoken out against racist harassment, demanding to be treated humanely in these universally distressing times. Heightened fear of infection and distrust against ‘outsiders’ have reinforced xenophobic anti-immigration narratives, and not simply curbing travel to and from high risk locations, showing that justifications for these policies have little to do with disease transmission.

The insidious transmission of COVID-19 – manifesting asymptomatically for a period, particularly in the young – makes an in-group member (those situated in your close proximity to you geographically, workmates, or high density co-travelers) statistically more likely to infect you, by virtue of more contact. The evolutionary perspective of producing relevant antibodies would not protect against the COVID-19 considering the novelty of the virus for the global population.

Such considerations make it even more pressing to practice social-distancing and self-quarantining, maintaining hygiene, and sanitizing high-touch surfaces frequently to slow the spread, till such time as vaccines and treatments can be developed. It also means we must follow evidence-based precautions by sanctioned authorities, and curb the other pandemic – that of misinformation. To be sure, understanding the psychology behind xenophobia does not excuse xenophobic behaviour. Academic explorations of xenophobia and perspectives from evolutionary psychology shed light on phenomena as they are, not as they should be. Scientific research should not be used as an endorsement or justification of psychological phenomena. The onus is on us to demonstrate our tolerance for different ethnicities, and use the anxieties that a pandemic understandably births to caution and protect those most vulnerable amongst us.

And then, maybe, science will tell the ever progressing story of our evolution as a species.