I think most people associate race with biology and ethnicity with culture. It's important to stress the culture and language part of it. Ethnicity isn't just a question of affiliation; it's also a question of choice. It's also a question of group membership. And it's usually associated with a geographic region. It's also often confused or conflated with nationality, but that's not the same thing. Today people identify with ethnicity positively because they see themselves as being part of that group. People can't just simply say, "Well, I want to become a member of that race." You either are or are not a member of that race. Whereas, if you wanted to look at ethnicity based on culture, you could learn a language, you can learn customs - there are things that you can learn so that you could belong to that group.