Know Thyself takes up the search for the guests’ ancestries where the historical record leaves off and links their distinctive family histories to the broader history of “the family of man.” Combining the documented stories of some of the guests’ last known ancestors with DNA evidence, the series travel backward through time to reveal both distant relatives and surprising shared ancestral connections. Elizabeth Alexander learns that she is a direct descendent of Charlemagne, and that her paternal roots are not only European, but Jewish. Meryl Streep and Mike Nichols discover that they are distant cousins, as do Yo-Yo Ma and Eva Longoria. Interwoven with these stories and others is the journey of the host, Henry Louis Gates, Jr. as he and his father and brother undertake an historic project to have their entire genomes mapped, and thereby to learn everything they possibly can about their own family. This episode offers a compelling and thought-provoking meditation on the importance of ancestry, the meaning of family and the role of both in creating identity.