The thing is that races are a little bit different from each other. Our abilites, behaviors, and appearances differ slightly or greatly dependent on your point of view. These differences naturally drive us apart but human behavior can change and often does for the sake of lasting cultural peace. That road to peace can't always be peaceful because with any compromise, you give something up you value for something else. Change is painful and sometimes it is necessary and sometimes it is not.
I think racist feelings explains tribalism and the fact that throughout the majority of history most countries have been racially homogenous. The one thing we do have to watch out for is that when we artificially lift up one race above another (affirmative action) or constantly degrade and blame a race for other races' problems(like how the press constantly attacks whites).
As someone said above, a lot of it is “classism” or better said culturalism.
I recall a vivid example of this in college, when I lived in an on-campus house, divided into apartments.
In the single 2 bedroom apartment below mine, an African (that is from Africa) family lived. They spoke with a delightful accent, and even with their slightly bratty small boy, were always very kind and nice—and were literate and well educated—the husband after all was attending college. Later however when they moved (they were forced out, because apparently they didn’t pay their rent...) they left the apartment utterly trashed.
Soiled disposable diapers were piled in the closets, the kitchen was totally dirty with spilled food, etc., etc. I knew one of the maintenance guys who cleaned the place, and he said he’d never (ever) seen an apartment left like such a total pig sty as that place. Knowing them, this shocked me.
When reflecting on it I realized though, these folks likely had parents or grandparents who lived in huts—without proper clothing, education or hygene, in an African tribal environment. In other words, despite their literacy and education, these were people whose culture was not far removed in time and habits from the stone age.
If I were the good British doctor, I wouldn’t want some YOB types with 6 guys in the house, playing Gothic Rock all the time...as these are similarly uncouth people culturally than the ones he mentions. But it’s culture (or the lack thereof), not color which is key.