A biologist can correct me if I'm wrong, but I understand "race" in humans to be little different than, say, hair-color. Perhaps there's data showing that brunettes are smarter than blondes?
EDIT: Never mind, user krapp's comment is what I was reaching for, "Race isn't biological, it's a social and political construct."
It's not completely correct, though- "race" as we currently classify it has a strong correlate to genetic background and self-identified race is often used as a proxy for genetic background.