In discussing the topic on behavioral immunity, I suggested that other people’s bodily wastes provoke a lively sense of disgust, and that this reduces our contact with contagious bacteria and viruses. There’s a plausible adaptiveness that could have supported the evolution of disgust.
Why should we feel the same disgust about some of our own waste? We might guess that disgust, like fear, doesn’t discriminate; what we fear in one context we fear in all. But that’s clearly not the case. Many Americans don’t think twice about blowing their noses at the dinner table, and Koreans who can’t stand mucus at dinner may talk with their mouths full of food. In a dozen countries people defecate openly, though not at the table. Our gorge does not rise at the same opportunities, though every culture eventually has its limits. Disgust may be universal, but the manners it inspires are learned.
This leaves us immersed in perplexity: if disgust has evolved biologically and manners are a cultural custom, how do they fit together?
BIO: The easiest biological resolution of the dilemma is to cite biological preparedness.
For a long time people thought that traits must be either inherited or acquired, developed through nature or nurture.
Modern genetic research has made it clear that behavior always reflects an interaction between genes and the environment. No behavior is learned without a hereditary component, just as no behavior is inherited without some influence of the environment.
When John Garcia published his research on conditioned taste aversions* we learned that we are biologically prepared to learn some things but not others. We easily remember the taste of food we ate before getting sick but not the sights and sounds that preceded the nausea.
In other words, we can inherit a predisposition to learn without inheriting the results of the learning. We inherit a capacity for learning language better than other species, but no one inherits a specific language.
In the case of manners as well as language we have to recognize cultural evolution as well. It is different from biological evolution because it (often) operates on a much shorter timescale and does not arise from gene mutations but from environmental changes.
Disgust often feels like fear, yet the two emotions are associated with quite different neural mechanisms: disgust with parasympathetic activation and fear with sympathetic arousal. Parasympathetic activation has been labeled the “rest and digest” function, while sympathetic arousal comprises the “fight or flight” function. These two divisions of the autonomic nervous system are often studied separately, but of course they operate in coordination, often in tandem, to maintain homeostasis.
* Garcia’s research is discussed in greater detail here.
PSYCHO: The biological preparedness concept discussed for the BIO approach helps us to understand why we learn some connections between a stimulus and a response more easily and faster than we learn others, which in turn may explain why we develop disgust for some body wastes but not others, like tears.
And in private we tend to accept what our bodies—and our mate’s and children’s bodies—produce. In fact, body wastes are not as threatening as we might hear from others. Poop, urine, saliva and mucus are better than we usually imagine, although the benign view can be taken too far. Urine is not sterile.
We tend to be repelled by wastes, seen* or unseen, that carry contagious diseases or are injurious. There is evidence of linkage between disgust and the perception of risk. However, the inferences of folk microbiology will not account for all of the many threats we perceive. The principal sources of our culture-specific disgust reactions will have to be discussed using the SOCIAL approach, below.
* Though bodily wastes are sometimes regarded as better unseen, they show an endearing variety. Colors, for example, tend to be brown, but are often yellow or a surprising green. They can be as surprising in composition and volume as in color. In contrast, toilet paper is almost always white and conformable to one overriding rule.
SOCIAL: People tell us what to abhor to avoid giving offense. Our parents enforce toilet training (which is nearly ignored in some countries) and at school, friends warn others of the dangers of catching cooties.
The consequences of giving offense by a lack of hygiene include not only stigmatization and avoidance by others but a punishing moral disgust. Social opprobrium overwhelms some people to the extent of making it impossible for them to relieve themselves in public. Thus we have developed the Western bathroom. Our custom of hiding in sexually restricted chambers to perform universal functions should not be regarded as a universal norm, or even normal, but as a historical monument to anxiety and a poor accommodation to nature.