The vertebrate retina is a kludge, but we don't have a percentage of the population with octopus-style retinas, so there's no selectable variance to favor the genes that that produce octopus-type retinas. Similarly, we can't evolve a proper set of long back bones because there's no variance in the human population to use to select against our ludicrous stacked vertebrae arrangement.
But the degree to which people favor certainty does vary, and accordingly it is vulnerable to selection pressure. There accordingly must be a why as to the continued existence of certainty bias.
Perhaps all variation in certainty favouring is simply due to environmental factors. Remember that all complex adaptions must be universal so there must be a simple difference, something like single gene present or absent, which controls how much someone desires certainty for any of the variance to be genetic.
Even if some is genetic, I would guess that the primary difference is in which side of the system1 vs system 2 dichotomy is more likely to win. This affects lots of things other than certainty bias, and so may have been kept where it is by many other ...
Today's post, Zut Allais! was originally published on 20 January 2008. A summary (taken from the LW wiki):
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