By my informal count, about 60% of the news articles forwarded to social media sites are prefaced with an exclamation like, “Finally, the truth!” As I understand it, the phrase means something like this: “ignorant people and biased media sites have been getting this story all wrong, but here is the argument-ending set of facts that proves that what I have always believed about it is, in fact true.”

Once we have this final truth, we can cling to it and reject other versions of the truth, as lies and propaganda.

I have been seeing this a lot over the last few weeks as my (fairly politically diverse) Facebook feed has tried to come to terms with the events in Ferguson, Missouri. “Finally the truth,” wrote one of my liberal friends, forwarding an article saying that the police officer who shot Michael Brown did not, in fact, suffer a broken eye socket. “Finally, the truth,” wrote a more conservative friend, passing on another article alleging that  he actually did.

And so on.

This is one of those times when the combination of 1) an unlimited supply of information combines with 2) unlimited access to social media to exacerbate something about human nature that cognitive scientists have known for some time: we are really good at being certain, but really bad at finding the right things to be certain about.

Blame it on evolution. Nothing is worse for one’s evolutionary fitness than the inaction born of inductiveness. Natural selection rewards decisive action. It does not necessarily reward action on correct information, and it certainly does not reward organisms who spend too much time gathering information and too little time fighting, fleeing, mating, and eating, which, really, are the only things that matter much where evolutionary fitness is concerned.

What this means for us is that our cognitive mechanisms for arriving at certainty are much more effective than our cognitive mechanisms for arriving at truth, a dynamic that Robert Burton explores in his wonderful 2008 book, On Being Certain. “The feeling of knowing,” he explains, “is a primary mental state not dependent on any underlying state of knowledge” (41).

And we are hard wired to crave the certainty of conviction—which gives us the grounding that we need to take decisive action—even when we have only the vaguest notion of what we are certain about. Uncertainty is a greater evolutionary sin than error.

But it gets worse. Human beings have the biggest brains around. We are capable of cognitive calculations many orders of magnitudes beyond those of any other species. But none of this big-brain computing power actually evolved to help us discover the truth. Rather, it developed to help us defend truths that we have already arrived at for irrational reasons.

We are good at believing whatever we need to be true. And by this I mean that we are good at convincing ourselves that we are speaking truth when we are actually engaged in much more evolutionary meaningful pursuits--such as defending our turf, showing off for potential mates, humiliating social rivals, and making ourselves look scary in front of those who might someday challenge our position.

If you want to see what I mean, just skip down to the comments section of this or any other opinion piece, hold your nose, and start reading.