If someone is interested in the truth, it’d be a blessing to them to learn exactly what falsehoods they believe. An ideal truth-seeker would love to be wrong, because it would give them the chance to improve their ideas. This is the basis of scientific thinking, but it’s not a very good description of how people actually behave. Most people (especially those with little training) react defensively to criticisms of their ideas and show a strong preference of comfortably holding familiar ideas rather than putting them to the test. Why is this?

Some of this bias can be explained by a desire for familiarity (“if democrats are wrong than my whole world-view would fall apart”) and an attachment of self-esteem to being right (“only bad people are wrong”), but I think I’ve stumbled across another, more biological, explanation.

Imagine some ancestral hominids try two kinds of fruit: one kind that is delicious, and one kind that is poisonous. Those who eat the poisonous fruit spend all night in terrible pain, but eventually recover and learn to eat the good fruit. Twenty years later, some of the same hominids return to the grove with the two fruit. It’s been a while, so maybe they’ve forgotten about the good fruit, but they certainly haven’t forgotten about the poisonous one. The reason for this is that brain weights memories surrounding unpleasant events more heavily than pleasant ones. In short: it’s more important to remember what could’ve killed you or your family than just about anything else.

This mnemonic weighting is present in rats and other animals only distantly related to humans, so it’s sensible to conclude that it developed in a very primitive animal, far before logical reasoning, language and culture. When it became possible to reason about the world, humans were stuck with their old equipment for remembering. It was still more important to remember mistakes (even if they were mistakes of reasoning), but rather than build an emotionality-neutral way to add weight to such fallacies, evolution took the shortcut of adding unpleasant feelings to logical errors. By making it annoying and embarrassing to be wrong, evolution ensured we’d learn our lesson. Many years later, when scientific thought has become important, we’re left with the reality that, by default, people tend to avoid criticism.

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