It seems talent runs in the family for actor Michael Douglas. During a recent episode of the PBS show “Finding Your Roots,” which examines celebrities’ ancestral backgrounds, Douglas learned, much to his astonishment, that he’s related to another famous actor. After the program produced all that it could via “paper trail,” it turned to genetics and compared Douglas’ DNA with other guests who had previously appeared on the show. Host and educator Henry Louis Gates Jr. had Douglas flip a page of a book to reveal the identity of his relative. He was astounded to find a photograph of Scarlett...