It’s True, Your Shit Doesn’t Stink, And You Can Thank Evolution For It

Fine, your shit probably does objectively stink, but because you know you’re less likely to catch an unfamiliar disease from it, it disgusts you less. Here’s the abstract from a forthcoming paper by Ming Peng, Lei Chang, and Renlai Zhou that supports an evolutionary explanation for the “source effect.”

Known as the source effect, feelings of disgust have been found to differ depending on the source of the disgusting material, with that emanating from oneself and familiar others eliciting less disgust than that of strangers. We tested the source effect on self-report of disgust feelings (Study 1), physiological response in heart rate (Study 2), and behavioral response in terms of approach–avoidance movement (Study 3). The results showed significantly higher levels of disgust feelings, more reduced heart rates, and faster avoidance behavior when processing disgusting material associated with strangers compared to that of familiar persons. Together these findings support the evolutionary view that disgust, as part of the human behavioral immune system to drive avoidance from disease-carrying agents, will likely be activated more intensely and quickly in response to unfamiliar as compared to familiar conspecifics who carry common germs more defendable by our shared physical immunity.

Now you’ll think twice next time you want to make fun of a dog for sniffing another dog’s poop.


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