A.J. Jacobs has received some strange emails over the years, but this note was perhaps the strangest: “You don’t know me, but I’m your eighth cousin. And we have over 80,000 relatives of yours in our database.” Who are these people, he wondered, and how do I find them? So began A.J.’s three-year adventure to help build the biggest family tree in history. His journey would take him to all seven continents. He drank beer with a US president, found himself singing with the Mormon Tabernacle Choir, and unearthed genetic links to Hollywood actresses and real-life scoundrels. After all, we can choose our friends, but not our family.