Evolution does not work quickly. It takes many generations for our genetic code to adapt to changing environments and circumstances. What this means is that our 21st century human genome is still basically the genome of a caveman.
Our genome was well-adapted to the environment of our hunter-gatherer ancestors, because that environment lasted for hundreds of thousands of years. Unfortunately, the 21st century world we live in bears little resemblance to the prehistoric world. Most of the change has occurred in the past few centuries, and ongoing change is only accelerating.
The prehistoric world was a “small-data” world. It was in this world that the human propensity toward confirmation bias first developed. Confirmation bias is the tendency to favor information that confirms our preconceived beliefs — and to ignore data that contradicts those beliefs.
When a caveman walked in the woods and heard a rustling noise behind him, he had very little data on whether it was a leopard or a squirrel making that sound. Cavemen had to infer danger or opportunity from limited data inputs. When they heard a growl or a squeak, it would reinforce a hunch, and they would act accordingly. But our ancestors were mostly inferring things and acting on hunches based on locally accessible information. The small data set they relied on was a product of their five senses and their limited personal experience of the small world in which they wandered.