Norman Rockwell’s 1959 painting “Family Tree” offers viewers an entertaining and instructive look at ancestry and pedigree. A pirate who weds a Spanish beauty, a Confederate and a Union soldier, a Native American woman, a mountain man and cowboy, a starchy New England clergyman—all these progenitors lead to a modern-day couple and their smiling son. At the beginning of “Look Homeward, Angel,” Thomas Wolfe, like Rockwell, reminds us of our exhaustive heritage: “Each of us is all the sums he has not counted: subtract us into nakedness and night again, and you shall see begin in Crete four thousand years ago the love that ended yesterday in Texas.” We humans are living links between the past and the future. The blood of our deceased grandparents runs in our veins even as we tenderly repair a granddaughter’s knee cut in a fall while running on the sidewalk. In the gray eyes …