Episode 09, available on Spotify, Apple Podcasts, and YouTube

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“Every pair of twins, whether identical or fraternal, is a unique twist on human nature, and can really get you thinking in all kinds of novel ways about why we are the way that we are.”

To gain insight into human nature, psychologist Nancy Segal has spent her entire career studying twins. She's interviewed thousands of them, identical and fraternal, comparing those reared together to those raised apart. A key question in her research has been: how do our genes shape our lives?

Nancy joins Dan on this episode of Keep Talking to share her learnings from a four-decade-long career. She explains the striking similarities in identical twins, suggesting that genetic determinants play a major role in shaping our behavior and personality. Her knowledge and expertise may help all of us better understand how to more accurately view ourselves, our own natures, and what it means to be human.

About Nancy Segal (quotes from Wikipedia):

"Nancy L. Segal is an American evolutionary psychologist and behavioral geneticist, specializing in the study of twins. She is the Professor of Developmental Psychology and Director of the Twin Studies Center, at California State University (CSU), Fullerton, and was recognized as CSU Fullerton's 2004-5 Outstanding Professor of the Year, as well as the 2004-5 Distinguished Professor in Humanities and Social Sciences. Segal also received the 2005 James Shields Award for Lifetime Contributions to Twin Research from the Behavior Genetics Association and International Society for Twin Studies. Her research focuses on human behavior and includes cooperation and competition, altruism, personal bonds, and bereavement. She studies twins to understand social relationships in the general population, hoping to derive implications for what makes people get along."

Time Stamps:

[00:59] Nancy shares her background and what got her interested in twin studies
[02:04] The state of research around twins when Nancy started her career
[03:40]  Nancy’s initial intuition about fraternal twins and identical twins and what that looked like once the research was actually fleshed out
[06:04] About identical twins, how they're created, and their biological similarities
[07:51] The story of two pairs of identical Columbian twins who were raised as two pairs of fraternal twins
[13:48] The University of Virginia’s study on identical and fraternal twins
[17:43] The role of epigenetics in the development of any human being
[21:12] A peek into Nancy’s upcoming book, Deliberately Divided: Inside the Controversial Study of Twins and Triplets Adopted Apart
[26:01] Nancy talks about the Louis Wise Agency
[34:23] What is the moral and reasonable way to try to raise the next generation of kids?
[41:20] Misunderstandings or corrections that Nancy clarifies about twins through her research and expertise
[43:26] The most interesting information Nancy has received about her discipline, both research-based and anecdote-based
[50:03] Do our genes predispose us in a particular direction when making decisions?
[56:25] Nancy talks about virtual twins, their traits, and about Canadian photographer, Francois Brunelle who has taken pictures of look-alikes (not biological twins)
[59:03] Questions on twins beyond the realm of scientific inquiry
[01:07:42] What are the pushbacks to academic research on twin studies? What can we, as citizens, do to help protect researchers?


“We go to certain places, we go to certain people, we go to certain events because we like them, we enjoy them, we find them fulfilling. And so we believe that most identical twins raised apart, do the same thing.”

“Epigenetics, as you say, refers to turning on or turning off of genes, whether a certain gene is expressed or whether it isn't.”

“It [Epigenetics] may have to do with the distribution of how certain genes and certain cells occur prenatally, but these are fascinating processes. But epigenetics is a turning on or turning off of genes that may affect expression. It's not a change in DNA.”

“The conventional wisdom was that they, the twins, were being separated anyway, so why not study them. But having talked to a lot of people, and having given us a great deal of thought, I'm not so sure which one came first, it could have been the idea of studying them that fueled the agency's separation and policy.”

“I think that in some ways children bring up parents, not the other way around. Children will let you know, in their own way, what's best for them. So I think that parental responsibility really lies in being sensitive to the talents and interests of your child, nurturing those, discovering the weaknesses, and perhaps trying to get the child over those types of things.”

“I think that parents have to just kind of let the child's talents unfold. And this is what I mean by children bringing up parents. I think that's really the way things work.”

“Every pair of twins, whether identical or fraternal, is a unique twist on human nature, and can really get you thinking in all kinds of novel ways about why we are the way that we are.”

“I think the fear that people have is, they're stuck, the genes stick them at a certain place and they can't change.”

Relevant Links:

Documentaries mentioned:

Books Mentioned:

People mentioned (quotes from Wikipedia):

  • Peter B. Neubauer - “A(n) Austrian-born American child psychiatrist and psychoanalyst.”
  • Dr. Viola Barnard - “Psychiatric consultant to Louise wise agency.”
  • Joshua Rothman - Archive Editor at The New Yorker.
  • Francois Brunelle - Canadian photographer who takes pictures of biologically unrelated look-alikes.
  • John Money - “(A) New Zealand psychologist, sexologist and author known for his research into sexual identity and biology of gender and his conduct towards vulnerable patients.”

Connect with Nancy:

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