EVERYTHING I HAVE LEARNED ABOUT my one known ancestor from Maryland comes from a pair of Census reports, and the clarity they fail to offer is a lesson in itself. Some years ago, I began to look at them every so often; one is from 1870, the other from 1880. I’m always hoping to discover something I missed—about myself, about my past. Every gaze is a moment of wonder and frustration. There she is, twice. In 1870, she is Easter Lowe. Born in Maryland in 1769, 101 years old, Black. In 1880, she is Esther Watkins, born in Georgia in 1789, 91 years old, widowed, Black. Both improbable and extraordinary. In rare, lighter moments, it makes me think of Mark Twain’s humorous story about George Washington’s mammy, Joice Heth, who…