I don't have the patience to express this clearly. But here's what I am driving at:
Everybody is doing the best they can.
Realizing that the other tribe is full of people doing the best they can is maladaptive.
Daniel Dennett's new book on the evolution of human consciousness raises an important point:
Our genes were selected because the humans who inherited them tended to survive. Our conscious brain evolved because the humans who inherited it tended to survive. The elements of our cultured evolved because the groups that practiced them tended to survive.
There is only one criterion: survival.
People generally sort of know this in the positive sense of survival of the fittest. The critical insight is negative: everything else in NOT a reason why we evolved this way.
Being correct is not the criterion. Natural selection cares not one whit whether we are insightful or confused, perceptive or blind. Survival is the only criterion.
"Ah ha," people think, "but being correct helps people survive. Being correct about bear behavior, for example, is an adaptive trait that allows people to avoid bear attacks and thus pass on their genes."
But what about the areas of understanding that are maladaptive? This might seem to form a problem of infinite regress: if we have evolved to be wrong about something, wouldn't that imply that we've evolved not to notice that we are wrong?
In reality, it's generally a matter of perspective. Individuals can step outside our big picture general human behavior and discover our wrongness.
This has resulted in the growing list of cognitive biases. Specific ways evolution has given us brains and cultures that consistently produce wrong answers. We did not evolve this way because it produces humans who correctly understand our fellow humans and the way they organize themselves into societies and cultures. In fact, to the extent that a correct understanding would hurt our survival chances, then we have evolved to be wrong, not right.