From Edge:
Last July, opening the Edge Seminar, “The New Science of Morality”, Jonathan Haidt digressed to talk about two recently-published papers in Behavioral and Brain Sciences which he believed were “so important that the abstracts from them should be posted in psychology departments all over the country.” One of the papers “Why Do Humans Reason? Arguments for an Argumentative Theory,” published by Behavioral and Brain Sciences, was by Hugo Mercier and Dan Sperber. “The article,” Haidt said, “is a review of a puzzle that has bedeviled researchers in cognitive psychology and social cognition for a long time. The puzzle is, why are humans so amazingly bad at reasoning in some contexts, and so amazingly good in others?”
“Reasoning was not designed to pursue the truth. Reasoning was designed by evolution to help us win arguments. That's why they call it The Argumentative Theory of Reasoning. So, as they put it, “The evidence reviewed here shows not only that reasoning falls quite short of reliably delivering rational beliefs and rational decisions. It may even be, in a variety of cases, detrimental to rationality. Reasoning can lead to poor outcomes, not because humans are bad at it, but because they systematically strive for arguments that justify their beliefs or their actions. This explains the confirmation bias, motivated reasoning, and reason-based choice, among other things.”
More here.