Mercier and Sperber prefer the term "myside bias." Humans, they point out, aren't randomly credulous. Presented with someone else's argument, we're quite adept at spotting the weaknesses. Almost invariably, the positions we're blind about are our own.
[...]
This lopsidedness, according to Mercier and Sperber, reflects the task that reason evolved to perform, which is to prevent us from getting screwed by the other members of our group. Living in small bands of hunter-gatherers, our ancestors were primarily concerned with their social standing, and with making sure that they weren't the ones risking their lives on the hunt while others loafed around in the cave. There was little advantage in reasoning clearly, while much was to be gained from winning arguments.
