The reason we reason - To win arguments, not for the pursuit of truth.

  We are social animals all the way down.

Presumably now (and for quite some years, though how far back this extends I wouldn't personally be able to say) winning arguments is something that we're meant to do. It helps get your way in life, whether it's when negotiating the price of a car or part of your job. And 2000 years ago I'm sure there were plenty of other reasons for being able to win an argument, even if they weren't buying cars.

Maybe it's too recent in history to be classified as evolution, but certainly socially we can evolve that quickly, and presumably something like this does fall under the classification of things that can be influenced by how you are raised and the society around you?

(I'm absolutely no expert on evolution, or how social changes have influenced our developements, or on pretty much anything I just wrote about. But from a non-scientific point of view it seems to make sense to me, and I can say with absolutely confidence than confirmation bias probably didn't influence my thoughts.)

So if you are stranded on an island with no one else, reason is pointless? I don't think so.... I think the so called confirmation "bias" comes from the fact that the primary mode of reasoning is induction not deduction. The implicit goal of the confirmation bias is to identify the causal connections that will convert a probable conclusion to a certain conclusion. For the Humean skeptics in the audience, yes, the sun will rise tomorrow and we know it. The authors of this study should learn a little epistemology before spouting epistemological theories.