Science will tell you that what determines a species is whether or not the creatures can interbreed and have viable offspring. That view has more to do with political corectness than fact. I will tell you what actually constitutes a separate species. Scientists, take note.
A long time ago, a species of bird somehow managed to make it all the way to the Galapagos Islands. Obviously, once they were there, they weren't isolated from each other. Yet over time, this species of bird diverged into separate species of bird, physically suited to exploiting different ecological niches.
Near the beginning of this process, there were obviously fewer differences between these birds than there are, for example, between Whites and negroes. But they still managed to diverge. Obviously, at the beginning of this divergence, what constituted a separate species must have been little more than a state of mind. Or to put it differently, what was to lead to a different species had to be little more than a state of mind.
What does this mean in human terms? To me, there is little difference between ecological nich, culture or customs. Another thing is that humans were apparently able to interbreed with Neanderthals. And they were quite different.
All of this politically correct race mixing bullshit goes against nature. Species diverge to exploit different ecological niches for a reason. Which is that it helps some survive in a major cataclysm. Also, the world is full of similar but different creatures that inhabit the same areas. But for the most part, they stick to their own kind and don't interbreed. What some people call "racism" is natural and absolutely necessary. Even babies have been shown to be "bigoted." There are a lot of politically correct people out there who I wish had the sense of a baby.