I don't see these two ideas as mutually exclusive. While putting aside our tribal nature seems unlikely, it seems realistic to think we could do something that would let most people stop considering race when deciding which "tribe" someone may belong to. You see this difference as well, which is why you based your example of reasonable tribal behavior on someone's actions/experiences rather than their skin color. It make sense to have tribal affiliations with other people that speak the same language as you do, it doesn't make sense to exclude someone from your tribe just because their skin is a different color.