>that is typically used to separate us into racial and ethnic categories is a very small subset (imagine some genetic 'knobs' for hair color, skin color, statur

>that is typically used to separate us into racial and ethnic categories is a very small subset (imagine some genetic 'knobs' for hair color, skin color, stature, morphology, etc). What they're saying is that they're no genetic components that do this at all. There's no "black dna" or "Asian dna" or genetic component that is present in all peoples of a particular "race" that separates them from other "races".