[buildingsramen]

Just a couple thoughts on this.

No, it's not impossible.

The position of the American Anthropological Association is that there is far, far greater variation within races (however that concept is defined) than between races. I think this is a sensible position to take, and one supported by evidence, even though it does not directly answer your question.

For me, the real question is: Do we really want to pursue this research goal? As psychology is very far from a complete science there's a lot of room for ambiguity and interpretation in the cutting edge of the evidence. Given human history, and up to and including the present state of our politics, I really do not trust our society to see the nuance and contingency in emerging data. The risk of studying such a topic would be gargantuan, and for what practical benefits? There are certainly many other worthy topics which deserve our scientific attention without carrying all the risk of this one.

On top of that: defining and measuring a concept as nebulous as "intelligence" is a nightmare. To reduce it to a 1-dimensional scale I think is your first sign that things are not quite right.