I believe it'd be "...identical pressure for all cultural groups" where cultural groups tend to contain (or become?) predominantly one race. I'd argue it's lear

I believe it'd be "...identical pressure for all cultural groups" where cultural groups tend to contain (or become?) predominantly one race. I'd argue it's learned behavior because centuries ago, trusting outsiders was risky and what better way to identify "outsiders" than "they don't look like us."?