> there are africans and europeans who share more dna than with others of their own ancestry

You're probably referring to the "greater variation within than between races" argument. But it's only true when looking at single genes, not collections of genes - that is how genetic tests can accurately determine race. And most traits are polygenic, so it does not even make sense to compare using only individual genes.

That's the reason Asian couples don't spontaneously give birth to European-looking children, and vice versa. And genes not expressed in superficial appearance were exposed to selection pressure just as much.

Whenever you see a theory so obviously contradict the evidence of your eyes, you should be at least skeptical of it (though not dismissive - e.g. quantum mechanics are true, however counterintuitive)