First of all "tend to be" and also they are not that old believes for the most part. You have to keep in mind that for most of human history we have been hunter gatherers and they did not practise slavery for the most part. They would also understand that black people, as human beings are animals, but that women are humans. Jews are pretty new anyway. Gays would have been mostly seen as natural(it actually has a lot of history of being seen that way)