I don't think I'm confusing anything (although it's always possible!).

Nobody believes that all Africans, or all "blacks" form a perfectly homogenous group. Of course there are distinctive subgroups, or "populations" if you like, within the greater whole. But you rather give the game away when you say the Igbo suffer sickle-cell anemia "in greater numbers". By that, I take it you mean in greater numbers than the other African populations (who have it in lesser numbers).

But hold on, non-blacks don't suffer from sickle-cell anemia at all. So, it would seem that for sickle-cell anemia, "black race" is a pretty good predictor of having that gene in the gene pool, though sometimes in greater and sometimes in lesser numbers.

Isn't this discussion just another version of the age-old "lumpers vs splitters" argument? Acknowledging the existence of sky-blue, light blue, blue-grey and aquamarine doesn't mean that I have to give up the concept of "blue". Acknowledging your "populations" doesn't mean there's no such thing as "race".

So, I am quite willing to take you at your word that the Igbo and Meru are not the same, but I would hazard they are more similar to each other than to the Han Chinese or the Celts. And Japanese and Chinese are, I would guess, more similar to each other than to the Igbo.