The biologists concluded that the human species had a single origin, and that the so-called races of mankind were statistically distinguishable groups only. Physical differences were not correlated with behavioral or psychological differences. Ethnicity refers to the social elaboration of collective identities whereby individuals see themselves as one among others like themselves.
Ethnicity is about social classifications emerging within relationships.
Particularly through language, ancestry and culture. The notion that racial difference could account for many other differences was replaced by the observation that historical circumstance and cultural difference accounted for these differences much more satisfactorily. There are differences within populations in the world, and what we should consider are not those differences, but the meanings attributed by society to those differences.