Why do we feel that some things are more gross than the others? Can you imagine eating feces? Just the sheer thought could trigger massive disgust and EWW in you. The strange poop-eating behavior is called coprophagia. A majority of people would not do that but individuals with schizophrenia often suffer from coprophagia. Most of us probably would eat poop in the future. (Fun fact, but serious: One Japanese scientist is tackling global food crisis by making poop burger from the sewage because it is rich with protein due to the bacteria living in the sewage mud.) Despite being processed safely, the poop meat still needs to be colored red. So people wouldn’t feel so disgusted.

It is not just feces per se, we feel disgusted toward “bad” food, diseases, blood, saliva, sneezing, coughing, etc. In short, the function of the disgust is to avoid infectious pathogens.

However, there could are times when we do not feel disgusted at a cooked hamburger that houses serious harmful bacteria or at fudge that looks like feces. So how do people avoid pathogens? One article by (Tybur and Lieberman, 2016) in the current opinion in psychology explains the mechanism of pathogen avoidance in humans. http://ac.els-cdn.com/S2352250X15001670/1-s2.0-S2352250X15001670-main.pdf?_tid=7a6f2994-df64-11e5-b6b9-00000aab0f02&acdnat=1456806014_cb30ded4118e9906fa1127c8229ad98f

The “HOW” model is primarily based on information processing of our brain. Our perceptual systems such as vision, olfaction first monitor the pathogen estimates in the environment, generating the internal representation of pathogen presence. Then our perceptual system incorporates the cues of other contextual information such as kinship benefits, overall nutrition, sexual benefits, etc. Then the system generates net output value, leading us to whether we should avoid or contact. And the process does not have to be a conscious calculation.

You would say that the best way to avoid pathogens is to avoid them completely. However, completely avoidance would also lead to greater losses. Therefore there are times we would contact things that have higher probability of pathogens. So think about the saliva, which is loaded with high pathogen content. Although we usually feel yuck towards someone’s saliva, kissing with romantic partners could lead to sexual contact and possible reproduction. Romantic kissing can be used as a mate assessment (No no for bad kisser. Or the romantic mouth loaded with pathogens, Eew! Here is the article on the blog I wrote awhile ago, https://allaboutevolutionarypsychology.wordpress.com/2015/08/27/what-does-evolutionary-psychology-say-about-our-kissing-behaviors/ ) Reproduction is an important feature of evolution; successful mating can confer higher evolutionary benefits to a person, who is at risk for pathogen contacts. In the eyes of evolution, survival is not important per se. What is important is the survival long enough for the species to reproduce and pass on the genes.

Another example would be the environment in which nutritious food is rare, Foods that could potentially have high pathology contents, but have higher nutritional contents could still be a valuable source for energy. People would still approach foods. In extreme cases, some people in Heidi would even eat dirt cookies (yes, cookies made with dirt, some butter and salts) that have little nutritional value. But the cookies have some survival values because the cookies are rich in Vitamins and minerals. Sometimes the children die from these cookies though. It’s really sad and depressing.  Watch the video here: https://www.youtube.com/watch?v=s3337cj4sJQ

In America though, I was greatly disapproved by my friends at AppleBee’s. No double dipping!

The article I read also suggested that our prejudicial attitudes toward elderly could be tested using evolutionarily informed hypotheses. It could be the case that elderly’s physical features such as wrinkles, body scent, etc. could be incorporated with other contextual dependent cues (poor hygiene, hospitalization, etc.). Elderly then would be perceived as infectious. Or it could be the case could be that sexual or cooperative contacts would yield fewer evolutionarily significant benefits; hence, contact with elderly is mostly avoided. Pretty amazing, isn’t it? Are you now thinking about your pathogen approach/avoidant behaviors?




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