This is a conversation with Nancy Segal. She is a prof of psychology at California state university and Director of the Twin studies Center which she founded in 1991. She has written seven great books focusing on Twin studies. Her recent book is 'deliberately divided: Inside the controversial study of twin and triplets adopted apart. In this discussion we talk about nature-nurture debate why study twins?, lessons from twin studies, A study related to Louise wise adoption agency, what factors shape our behavior, and major questions today for the understanding of nature-nurture.