Now I REALLY Don't Know How to Fill Out Those Forms

I'm referring to the forms that ask you to list your ethnicity. I usually put "Other," just to push us one nanometer closer to a post-racial society. And now I read in The Rest Is Noise, by Alex Ross, a confusing description of the music scene in New York during the 1920s and 30s, when "Jewish, African-American, and even Caucasian composers were working shoulder to shoulder, trading ideas, borrowing themes, plundering the past, and feeding off the present." Did I miss something?