Sewage water, it seems, is thought of as contaminated even once every last contaminant has been removed. As the psychologist Carol Nemeroff told NPR: “It is quite difficult to get the cognitive sewage out of the water, even after the real sewage is gone.”
In his highly readable book On Second Thought: Outsmarting Your Mind's Hard-Wired Habits, Wray Herbert classifies contagion as part of the “cooties heuristic”, named after the imaginary disease that US schoolchildren believe they'll get from kissing members of the opposite sex. As adults, we're barely more rational. Deep down, we seem to think in binary terms of purity and defilement, especially when it comes to what we eat. Studies on “processed” versus “natural” foods show we're far more bothered by the sheer fact of anything being added to something “natural”, no matter what's added, or how much. To certain commentators, that's reason enough to dismiss as nonsense all objections to modern food production, or genetic modification. (I'm looking at you, Sense About Science!) That's silly: avoiding processed food is still an excellent strategy for healthy eating, since you'll avoid most of the worst stuff that way. But not because “processing”, per se, is a problem.
Such biases make sense in evolutionary terms – avoiding impurities would have favoured survival, after all – and it's probably foolish to imagine we'll ever uproot them completely, but it's worth remaining conscious of them, given how deeply they influence us. A recent study on “emotional residue” is a case in point: if people learn that a depressed person has been sitting in a room all day, they'll feel deflated on entering, even if that person has since left. It's as if some residue of sadness hangs in the air. The cooties heuristic causes needless extra gloom. After all, the room itself isn't sad. Just like Hitler's sweater isn't evil.
On Second Thought: Outsmarting Your Mind's Hard-Wired Habits looks like an interesting read.
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