In this extended May 2020 interview (part one, part two) Libby Copeland and Dani Shapiro, author of the bestselling memoir “Inheritance,” discuss the age of DNA revelations, how people process the trauma of such discoveries (and why they’re so often glad to know the truth, even when it’s painful), and what it means to come to a profoundly different understanding of the past and one’s own personal history through the secrets revealed by our saliva.