Pride is an old human frailty. We look to some reason to justify putting ourselves before others. One typical way is an association with a group, eg. family/ancestry, but could also be other organization types, like fraternities or a country club membership. "I am better than you because..." "I deserve special consideration because..." fill in the blanks.
I also think we're taught to think that way through socialization. That's why the Lord tells us to be humble and teachable like a child. Children typically don't see these kinds of dividing lines.