system
Given the following post, respond as if you're commenting on Reddit:
human
If sociologists do not believe in race how do they define different social and cultural groups in society?

Since race is not real how do we define groups? Where does one cultural group start and another end? 

Also, why is genetics the only thing able to define race?
gpt
Race is a cultural construct loosely based on surface phenotypic differences. Just because it's a cultural construct does not mean it's not "real." Genetics do not define race, people define race, though there are some genetic correlates, categories of race varies strongly by time and culture. 

Many of us also operate on the Thomas theorem, that if people believe something to be real, it is real in its consequences. Doesn't mean it's "natural" or inevitable.