Airstreams aside, I think there must be an inborn sense of truth. Things we just know, not things that we are taught. For example, human beings are such malleable creatures, able to adapt to almost any conditions. Yet when little girls are repeatedly raped by their fathers, only the bastards tell them it's a loving act, there's something about that particular thing that the little girls never get used to, never decide is all right, and are permanently scarred by it. What is it that tells those innocent little souls that this is not okay, despite the fact that the person they love and trust and know to be the source of their taught information is telling them otherwise?
I agree that truth evolves; knowledge certainly does. But there's another truth, a human truth that seems to underlie our personalities.