Reasonable segregation is the reasonable norm of civilization. We are all mentally segregated and coexist on a borderland. With minimal diffusion. At the same time, each community preserves itself. That's why the Golden Billion has become what it is, not merging with the less organized communities and evolving creatively from antiquity to the present day. Within it, the achievements of some of its communities were smoothly transferred to others. And its overall level was rising and becoming more complex.