There is a story related to Eden where actually those of the higher races were not supposed to mix until their own race had populated sufficiently. Those were to be of the Adamic Ascension. But evolutionary creatures crept in and they mixed anyways and what we have now is a sort of amalgamated mixture of both. The story of God being upset because the Sons of God in Genesis (Genesis 6:1-2
When people began being numerous on earth, and daughters had been born to them, the sons of God, looking at the women, saw how beautiful they were...)
Anyways, as the story goes, here we are, an admix of many races.
From only the Biblical aspect with no other source of information it is pretty hard to figure all this out. There have been a few other books on the subject, one I say in the bookstore the other day and I've already forgotten the title, talks about a find in or around the middle east that can only leave one with a different more awakened and sensible feeling that there is lots more to it than what is alone given in the Bible.