I'm old enough to remember this 1960s Lay's Potato Chips commercial. (Hell, I'm almost old enough to remember when plays were in black and white!) In the commercial a man (Bert Lahr, the cowardly lion in The Wizard of Oz) faces a challenge from the devil, who has a bag of Lay's: "Bet you can't eat one." "That's absolutely absurd," Lahr says; of course he can eat one. After enjoying the chip he says, "I'll have another," to which the devil says, "Oh no. I said just one. Ha-ha-ha-ha-ha...."
Admittedly, this is a long and winding road to my point: there can't be only one race. Most people believe that human beings come in different genetic models: black, white, Asian, and a couple more. (Of course one can believe this without hating anyone.) But biologists and geneticists know better. There are no significantly distinct genetic groups of human beings that correspond to skin tone, hair texture, or other such visible features. Individuals within one grouping of superficially similar persons can have more genetic variation among themselves than they do with individuals in other superficial groupings. (We all are of African ancestry, though for some it's more recent than for others.) As Barbara and Karen Fields discuss in Racecraft: The Soul of Inequality in American Life, the idea of race grows out of the discriminatory practice of racism, not the other way around. In other words, the double standard people used in the treatment of others itself generated the justificatory concept of race. It's like witchcraft.
Does it follow from this that, as humane people like to say, there's only one race, the human race? I don't think so. In this case 1 = 0. Leaving aside the biologists' technical genetic concept of race (which has nothing to do with appearance), a concept of race would be useful only for making distinctions. But if there is only one race, then by definition, there are no distinctions to make. Therefore, one equals none.
We already have a perfectly good biological category for distinguishing human beings from other animals: species. So we have no need for the category of the human race. "Race" is worse than superfluous. It's dangerously divisive.