Actually I think we are on that path and you do have history right. Mine was a simplistic form. There are more mixed race babies being born everyday, taking traits from each race, call it a new race or the combining of races that someday will lead to basically, in concept anyway one basic race. I see more and more mixed couples everyday and they are growing. I am sure you will have pockets where one race or another survive much longer than on the whole.
I just have to look around where I live today. My neighbor on one side is Black, married to a Korean with two beautiful children. Myself, married to a Thai with 3 children, my oldest daughter married to a Laotian with 4 kids and on one of my grandkids by her married a black guy, 2 kids. The neighbor on the other side is pure a pure white family, but the next place down has a white guy and black woman married with one kid.
I go to the PX and see many, many mixed race couples with kids. Go down to Walmarts or the Mall, the same, but a lot of them are these young college kids. We live in a very small world today, it is getting smaller with each passing day. At least come the future race will have less and less meaning as more and more people will come from mix race couples and they too will have kids.
This is if man doesn't destroy himself first.