The visible characteristics of race -- the ones that were used as justification to enslave people of African ancestry -- are the product of biology.
I've already explained how that is not the case.
Yet again: Italians were "black," until they weren't.
Yet again: Irish were a separate "race" from Anglos, until they weren't.
Asians aren't a "race." Han, Uighurs, Pakistanis, Ainu, Filipinos, Kazhaks, Nepalis, Afghanis don't have a common skin color or eye shape. Needless to say, there is quite a bit of genetic diversity to the human inhabitants of Asia.
Indian castes are hereditary. That doesn't prove that "caste is a biological concept."
Yet again: The so-called "Aryan race" wasn't actually a race, and had the same skin color as other Europeans and "Semites." Many claims about the lineage of the "Aryan race" were based on linguistics, not biology.
Jews are not a "race." They're an ethnic and religious group. Biologically, they're nearly identical to neighboring communities. And yet, plenty of people insist that there is a "Jewish race."
Yet again: Many proclaim that "black" or "African" is a race, but in fact Africa has the greatest degree of genetic diversity of any continent.
The reality is that people create "racial" divisions based not on biological facts, but on whatever is culturally convenient at the time.
The "visible characteristics of race" are superficial features, that tell us nothing about the individual's biology,
except for those "visible characteristics of race."
There are all sorts of ways that the concept of "race" does not match any biological facts at all. This is because... wait for it...
race is a social construct, which is not actually based in any real biological categories.
Even before genetics were understood the concept of ancestry was used to determine who was eligible to be a slave and who was not.
...except that those "visible signs of race" weren't and aren't reliable indicators of ancestry -- which is, again, why some people could pass as members of another race, or why the concept of "race" keeps changing.