A study published in Social Psychological and Personality Science proposed that when people judge someone or something as ugly, it activates their behavioral immune system, which alerts them to the presence of potentially harmful diseases.
Before the days of modern medicine, humans had very few ways of assessing the threat of disease. It’s believed that humans developed the ability to detect cues associated with infectious disease by relying on appearance as a source of relevant heuristics (e.g. presence of bodily fluids, lesions, etc.).
If an individual was approached by someone containing these cues, they would likely react with disgust, which then would have motivated them to avoid the person in question. Although it may seem cruel to avoid someone based on their appearance, research suggests that this mechanism helped humans avoid the threat of disease in our evolutionary history.
Although we now have more effective ways to detect diseases, this process – which comprises the behavioral immune system, or BIS – may still be a driver of human behavior today. Thus, the researchers hypothesized that people may judge others as ugly when they detect the potential for disease, which motivates them to avoid that person in order to remain safe.
To explore their hypothesis, the researchers first investigated whether ugly stimuli would elicit disgust. Participants were presented with six unattractive faces, six average-looking faces and six attractive faces. The participants were shown an equal number of White, Black and Asian faces.
Participants were also asked the amount of pleasure they experienced while viewing the images to assess any negative emotions they were feeling (i.e. disgust, fear and sadness). In addition, they were also asked whether they felt motivated to approach or avoid the person in the image.
The results of this study showed that participants experienced greater disgust in response to the unattractive faces. However, experiences of sadness or fear were not significant to the results.
The researchers also found that participants reported being more motivated to avoid the unattractive faces and approach both the attractive and average-looking faces.
In the following experiment, the researchers were curious whether unattractive nonhuman entities would elicit a similar disgust response from people.
Participants were presented with seven images of animals high in ugliness and seven images of animals low in ugliness. Each pair of images displayed animals from the same species (e.g. an attractive lizard paired with an unattractive lizard). This was to ensure equivalence matching in the stimuli, so that the only thing differing between the two was the level of attraction versus ugliness.
Similarly, participants were also presented with seven buildings high in ugliness and seven buildings low in ugliness. Participants were also asked to report any negative feelings they experienced while looking at the image.
The results of this experiment supported the researcher’s hypothesis. The images displaying animals and buildings high in ugliness elicited greater disgust from the participants, compared to the images low in ugliness.
In the next experiment, the researchers investigated whether objects that appear disease-ridden would be perceived as uglier, compared to objects lacking disease cues.
Half the participants were assigned to the disease condition and were presented with seven disease-ridden images (e.g. a busy subway train). The remaining participants were placed in the control condition and shown seven images that didn’t suggest the presence of disease (e.g. an empty subway train). Each participant was asked to rate each image on the extent to which they found the images disgusting, ugly, etc.
The researchers found that the images in the disease condition were rated as more ugly, impure, unhealthy, distressing, and frightening than the images in the control condition. Thus, perceiving something as ugly may be a response to the potential presence of disease.
To recap, the researchers found that ugly faces, animals and building elicited disgust (but not fear or sadness). They also found that images depicting the presence of disease were rated higher in ugliness and other negative factors.
This suggests that perceiving someone or something as ugly may be a response to the potential for disease. As part of the behavioral immune system, ugliness may be an aesthetic judgement that alerts to the potential threat of disease.