You always find interesting articles. Thsnks for linking to them.
I suppose human nature has been shaped by evolution to support "the tribe", for want of a better word. Gang culture, unswerving allegiance to a political party, irrespective of the situation, old school tie networks, instinctive dislike of someone perceived as "posh" by those who are biased, football club fans, the list is endless ......
If you study the behaviour of Chimpanzees or baboons, these same traits appear strongly, right down to inter-tribal competition and warfare although surprisingly, the bonobo is far more relaxed about it. However, even fish exhibit tribalism in the form of shoals. It's an effective technique to ensure survival of that species.