Erin Aubry Kaplan is a contributing writer to The Times' Opinion pages and the author of Black Talk, Blue Thoughts, and Walking the Color Line.

There's a new twist in the ongoing story line of our post-historical racial age allegedly represented by Barack Obama.

Last week, genealogists at Ancestry.com announced the strong likelihood that Obama is a descendant — the 11th great-grandson, to be exact — of John Punch, who in 1640 became the first black person to be legally defined as a slave. This lineage comes not through Obama's African father but through his white mother, Stanley Ann Dunham, who is apparently descended from children Punch had with a white woman.

The researcher's conclusions are not ironclad. But even if Obama turns out not to be related to Punch — which is highly unlikely — researchers have established beyond doubt that Dunham's family has black ancestry that almost certainly can be traced back to American slaves. Which means that Obama is more black than we imagined. A familiar kind of black...