I think they mean that people in large groups segregate themselves into smaller ones, by whatever characteristics available. If they had the same religion they’

I think they mean that people in large groups segregate themselves into smaller ones, by whatever characteristics available. If they had the same religion they’d be separated into orthodox and progressive versions of it, or people who had come off well out of the last great flood vs people who got screwed by it. And then they’d create a religion as explanation for the flood and why it was from god/the devil.