Jonathan Zimmerman teaches history at New York University. E-mail him at Jlzimm@aol.com.

So it turns out that Massachusetts Senate candidate Elizabeth Warren listed herself as a Native American when she taught at the University of Pennsylvania law school. And now GOP incumbent Scott Walker has called on Warren to authorize the release of her university personnel records to see whether she used her ethnicity to get the Penn job or her current post at Harvard.

Should we care? Yes, but not for the reasons Brown assumes. Despite his suggestion that Warren was working some kind of affirmative-action scam, there’s simply no evidence that her avowed Native American heritage affected her professional trajectory.

But this story is important, nevertheless, for what it tells us about contemporary America. Like Warren, more of us are choosing new racial identities or — more commonly — mixed ones. That’s good news, because it reminds us that “race” itself is a fiction. It exists, of course, but only in our minds....