That's an interesting point, McGraw. Gave me some good pondering time. I can accept that racism would be greatly exacerbated by imperialism. I'm not sure that I can accept that differences in appearance would be irrelevant to our most base instinct of tribalism. Perhaps we will never know, because it never happened? Stories of white children raised by native americans come to mind, but I only know that from Hollywood. There's the genetic impulse to socialization in ever larger(?) groupings. What kept native american tribes separated? Genetic impulses (couple with competition for resources)? Cultural xenophobia (however mild)?

Were white Europeans many centuries ago more predisposed to develop racism due to circumstances? Were native americans really blind to any differences in appearance between tribes?

You may be right on that point (ethnic strife may be prehistoric, but racial is recent), and I am just babbling. Back to pondering. Apologies for this brief interruption. . .