This episode is a conversation based on two of Nancy Segal's books The Twin Children of the Holocaust: Stolen Childhood and the Will to Survive and Gay Fathers, Twin Sons: the Citzenship Case that Captured the World.

Shermer and Segal discuss: her historical interest in twins research and behavior genetics • the many different types of twins and family arrangements • twins separated accidentally • twins separated intentionally • twins reunited • a brief history of twins research • Josef Mengele • Minnesota Study of Twins Reared Apart • the gay fathers and twin sons story • immigration and naturalization law related to IVF, twins, gay couples, etc. • abortion • eugenics and the Nobel Prize sperm bank • the meaning of "heritability" • the relative role of nature and nurture in how lives turn out • the "nonshared environment."

Nancy Segal is a Psychology Professor, and Director and Founder of the Twin Studies Center at California State University, Fullerton. She has authored over 300 scholarly articles and eight books. Her 2012 book, Born Together-Reared Apart: The Landmark Minnesota Twin Study, won the American Psychological Association's William James Book Award. Her recent work, Deliberately Divided: Inside the Controversial Study of Twins and Triplets Adopted Apart, was the focus of a July 2022 BBC-TV documentary. She's a member of the editorial board of Skeptic magazine.