What Twins Separated At Birth Teach Us About Human Genetics - Nancy Segal

1. 0:00 – 4:51

   How Evolutionary Psychology Explains Twins

   1. CWChris Williamson0:00

      How would you describe what you work on when somebody asks?

   2. NSNancy Segal0:04

      Well, I tell them that I'm a developmental psychologist, but my interests also cover behavior genetics and evolutionary psychology. And I'm passionate about twins because twin studies are a simple and very elegant way of combining all three, developmental psychology, behavior genetics, and evolutionary psychology, different levels of analysis and application. But also, I'm a twin myself, and so I really think that when you're personally invested in something, you have greater, um, interest and passion for the topic. And so my whole career, I liken to a candy store. I've just had a wonderful ride, and the ride is continuing.

   3. CWChris Williamson0:46

      That's how I feel when I get to speak to anyone from the EP world or the behavioral genetics world or the sex research world. It's, uh, yeah, it's, it, it's the absolute most fun. Uh, William Costello, the guy that's doing all of this stuff on incels at the moment, famously keeps on reminding me that research is me-search. It's a little bit different for him doing it on incels and you doing it on twins. Given that you're a twin, I don't know what it says about William, given that that's what he's studying. Um, what is the evolutionary psychology angle of, uh, twin research? I c- I can see how behavioral genetics comes in. You know, we're, we're splitting apart genetically and environmentally what the contributing factors are. Uh, but I- I'm less sure about, about the others.

   4. NSNancy Segal1:26

      Right. So one of the, you know, very provocative theories that was launched was kinship genetic theory by William Hamilton, who asserted that we feel greater cooperation, altruism, investment in people with whom we share higher degrees of genetic relatedness. We don't consciously do the calculations in our head, but we behave as though we do. And so I've always known for years that identical twins are more cooperative, m- m- closer socially than fraternal twins are on average. And so I felt that this was another level of analysis that I could bring to twin studies because many people say, "Well, they're, they're closer 'cause they look alike or people encourage it," but I- I don't believe that's the case because behavior is not built on appearance. Behavior is built on the brain. And so I always felt that there was some deeper level to this. And so I've been able to use twins, I've been able to use unrelated lookalikes, I've been able to use virtual twins, many, many types of relationships that vary in genetics and in environmental connectedness. And the findings are, are beautiful 'cause they really converge on the same thing. You know, I remember when I was doing my doctoral dissertation, my first major study, and I used seven to 11-year-old children, twins, and what I did was I put them into a puzzle completion situation, a kind of semi-naturalistic study where they all completed the same puzzle under the exact same circumstances with the exact same instructions. And without a word from me, and I kept their mothers out of there, the identical twins just did this orchestrated dance, beautifully coordinated. There was little rough play. Everybody was very cooperative, and they were very successful at puzzle completion. But the fraternal twins, on the other hand, tended to grab different pieces of the puzzle to their side of the table and work on it independently, and the whole thing looked like a mess, and there were lots of elbow jabs and snatching of pieces. And so that really told me that twins can tell us so much just by being themselves.

   5. CWChris Williamson3:35

      What is your explanation for why identical twins and fraternal twins had that difference? For the people that don't understand, am I right in saying that fraternal twins are essentially just simultaneously born brothers and sisters?

   6. NSNancy Segal3:49

      That's correct. Identical twins result when a single fertilized egg divides between the first and fourteenth day of conception, whereas fraternal twins result when a mother releases two eggs at the same time, separately fertilized by two sperm, and so the kids share 50% of their genes on average by descent, which is exactly the same as ordinary siblings. So I think that what is going on here, Chris, is that identical twins who have the same genes are responding to the world the same way. They have similar temperaments. They process information the same way. And so all those ingredients allow them to work more cooperatively in a joint situation, whereas fraternal twins bring very different interests and understanding and abilities to a particular task. I can tell you that I have a fraternal twin sister, and in a puzzle completion task as kids, we'd be at each other's throats. We had very different understandings and ways of doing things, and we still do. We're close sisters. I think a lot of siblings get closer as they age, but nevertheless, as children, we would have been definitely on the competitive side.

   7. CWChris Williamson4:50

      I wonder

2. 4:51 – 8:22

   Unique Connections Between Identical Twins

   1. CWChris Williamson4:51

      whether teams... I- i- it would very much depend on what the activity is that you're doing, but I can imagine some activities in which you want someone that's very similar to you, but in other activities, you might actually want someone who has a different skill set. You want to be the analytical one, you want them to be the creative one. You want to be the slightly more risk-averse one, you want them to be the slightly more adventurous one. Uh, so I imagine that depending on what the task is at hand, you could have scenarios in which being identical twins would be an advantage or sometimes a disadvantage.

   2. NSNancy Segal5:20

      Yes, I think that's right. For example, if you are very skilled, say, at coming up with great ideas, but you don't know how to put them into play, you might want somebody who's more analytical, more statistical-minded to really complement you. And so to that degree, somebody a little different would be helpful. But identical twins would probably just pick a topic or pick an area where they both excelled and they do very well at it. One area I'm really fascinated in is twins in sports, and it is amazing to see these matched levels of elite athletes. You know, it's extraordinary when one person wins an Olympic event, but even more extraordinary when the other one comes in second. How is this possible?... part of it is because of the way their bodies are built, there's similar motivations, there's similar interests, and the fact that in many cases, a single ... a victory for one is a victory for both. And it's hard to get your head around that kind of selflessness. But I've heard it repeated so many times.

   3. CWChris Williamson6:21

      What about that? What about the degree of emotional connection between identical twins? Y- I mean, there's, uh, tales as old as time about they c- they've got secret languages and they can mind read and do stuff like that. Um, but have you found, uh, comparing it with normal siblings and fraternal twins, is there an, uh, an extra degree of connectivity, of emotional investment, of kinship, uh, as would have been predicted by that theory?

   4. NSNancy Segal6:51

      I, I think there's no question that there is an emotional connection that goes far beyond any kind of relationship. In fact, I would assert that the identical twin bond is closer than any other relationship.

   5. CWChris Williamson7:01

      Even more than mothers with children?

   6. NSNancy Segal7:03

      Yes. And I w- I say that because I have a study on the loss of a twin, on bereavement, and I wanted to understand two things. Do identical twins grieve more than fraternal twins, mirroring what you see in their relationships? And is there something unique about twin loss? And of course, this was all framed by evolutionary theory, in particular kinship genetics, and I did find that identical twins grieved more for their co-twin than they did for any o- the loss of any other relative, whether it was a mother, a father, a non-twin sibling, a grandparent, an aunt or uncle. Of course, when you get to those, you know, second-degree relatives, the, the genetic relatedness dips down.

   7. CWChris Williamson7:42

      I'm gu- I'm guessing that's the same for a son or a daughter as well then?

   8. NSNancy Segal7:46

      Yes. Yes. But ... Well, l- let me backtrack on that. I have very few sons and daughters, very few twins who've lost children, for which I'm very grateful. But that would be ... Theoretically, it would be a fascinating comparison because with identical twins, you share all your genes, with children, only 50%. Whereas for fraternal twins, you share half on average with your twin and you share 50% for sure with your child. So I would expect much greater variability among the paternals. So it's-

   9. CWChris Williamson8:15

      Very interesting.

   10. NSNancy Segal8:16

       Very interesting, but I really hope I never get to do that comparison because I don't want anyone to lose a child.

3. 8:22 – 16:22

   The Rare Occurrence of ‘Half Twins’

   1. CWChris Williamson8:22

      I ... One of the other very interesting things that I learned about when looking through your research is that there are times when a mother will release two eggs and will have multiple sexual partners within that, uh, pregnancy window, within that fertility window, and end up with ... I don't even ... What- what are the, the, the, like, half- half-twins? Like, what, what are they called?

   2. NSNancy Segal8:49

      Well, the medical term for that is superfecundated twins, which means that because she had two eggs released and she had two different partners, each partner got to one egg in that four-day fertilization window, and the children are really genetic half-siblings. But I regard them as a legitimate pair of twins because this can come out naturally and it can also come about through artificial reproductive assistance. You know ... A- as you know, and I've told you, I have a book that's coming out August 8th called Gay Fathers, Twin Sons: The Citizenship Case That Captured the World. And this is a case where two gay fathers who were very much in love with each other and married decided to raise a family. And so they contacted a donor and a surrogate and they each provided sperm to fertilize these eggs, and it turned out that the top two embryos were each, uh, in sep- each created by one father. And those are the ones they implanted. So they replay a naturally occurring situation.

   3. CWChris Williamson9:52

      Tell us that s-

   4. NSNancy Segal9:52

      It's very fascinating.

   5. CWChris Williamson9:53

      Tell us that story.

   6. NSNancy Segal9:55

      Well, what happened was there was a young man named Andrew from the United States who decided to get a master's degree at Tel Aviv University, and there he met another young man, Elad, and they fell in love and married in Canada in 2010.

   7. CWChris Williamson10:08

      Just go to ... Tel Aviv, Tel Aviv isn't, uh, fantastic for trying to get your gay wedding across the line.

   8. NSNancy Segal10:13

      Uh, not really, no. I- in fact, Israel now will recognize gay marriage, but they won't allow it in their country. If you marry elsewhere, it's recognized. At any rate, they moved to Canada because marriage, gay marriage, was allowed there in 2010, and Andrew also had dual citizenship. In 2016, they decided to have a family and that's when they gave birth these beautiful boys, Aiden and Ethan. And the problem became when the boys were four months old and they decided to move to Los Angeles, and when they tried to get the boys the passports at the consulate in Toronto, they were just hit with a, uh, a number of very rude and intimate questions, such as, "Where do these children come from? Who's the father of this one? Who's the father of that one?" Intimate details that they had no plans to reveal, not even to their parents. The only ones who knew were the DNA lab and the surrogate. Beyond that, nobody knew the relationship of the kids. So now their genetic linens are all hanging out on the clothesline, everybody knows, and so the upshot was that they issued a passport to the little boy who had ... who was created with the sperm from the American father and a tourist visa to the other one. And so this threatened to tear their family apart. Tourist visas are good for about six months. They are renewable, but it was a terrible situation. So when they did come to the US, it was about 2017, 2018, and that was when, when former President Trump issued these bans on Muslim immigration, so all the immigration attorneys were at the airports taking care of these cases. But they did find a wonderful group in New York called Immigration Equality, lawyers that are very concerned with gay couples, HIV-infected individuals, other minorities, and they work pro bono on behalf of these couples. And Andrew and Elad's case came about at the perfect moment because they already had three other couples, transnational, who had children outside the US. But...... Chris. Twins capture attention, and this case really got into the media because the idea of separating two little boys who were born four months apart is unconscionable. And, and that was a real threat to the family. So the case was the families named Davosh-Banks versus the US State Department and Rex Tillerson, who was then Secretary of State, later Mike Pompeo. It was a very high profile case that almost reached the Supreme Court. It took four years to resolve. There were moments when the government appealed. You have an appeal window of 60 days, and they would appeal on the 59th day after the circuit court fa- uh, ruled in favor of the family. Eventually, the case settled, no more appeals. And now they're living out here in California. I can't tell you what a lovely family they are. And all you see when you look at them are two really devoted parents and two very happy children. That's it. You don't see anything else.

   9. CWChris Williamson13:09

      Wow. What a story. How much of this do you think is, uh, concealed homophobia from, uh, organizations that maybe... Um, and then I guess actually, uh, a combination of concealed homophobia and concealed Islamophobia, uh, intersectionally combining to, to create this?

   10. NSNancy Segal13:30

       I, I think that is certainly one of the factors. And I think whether you're homophobic or not, if you just simply disagree with the idea of it, then I think that that can play a role, but there's also-

   11. CWChris Williamson13:42

       Well, it could be... Sorry, I, I... Maybe homophobia might be the wrong, the wrong term there, that just there's, there's less preference given. It's not like you need to discriminate against, but it's a slippery slope from, "Well-"

   12. NSNancy Segal13:53

       Right.

   13. CWChris Williamson13:53

       "... is the treatment the same?" I'm gonna guess that it would be treating somebody different on the basis of their sexual orientation.

   14. NSNancy Segal13:58

       Yeah.

   15. CWChris Williamson13:58

       Probably that's like a, a rough ge- uh, definition of homophobia. So it probably is. It probably meets the, meets the criteria. Not quite the same as going out of your way to call somebody a slur. But, you know, if you're not treating them the same way that you would do as a heterosexual couple or a couple that are, uh, both from a European country or whatever, um, yeah, maybe, maybe it does meet the criteria.

   16. NSNancy Segal14:20

       Yeah. So, yeah. So at, at any rate, I think that certainly plays into it. And then there's another element that I noticed that one of the lawyers brought to my attention, and that is that the government just seems, in some ways, to make things difficult. I don't know why, but they just seem to make things difficult for these families who just simply want to lead their lives. And so many politicians say, "Families first," and yet what about this family? And the wonderful thing about this case was it did settle in favor of the family, and it has been helpful to future families. The foreign affairs manual, which is what is relied upon in the consulates, was modified because of this. And it's still the case that officers have some measure of discretion in interpreting some of these guidelines and rules. But nevertheless, um, it's, it's gone far. And these two fathers could have taken an easy way out. They could have gotten a green card for the child. They wouldn't have had any publicity. But they were both very eager to make a statement and to leave some kind of lasting change in society. They both had difficult times growing up as gay men, as gay teenagers. They both... And so they know what it was like to suffer and to stay strong and to make a difference. And so that was an attitude they carried with them into this issue as well. And, and I, I think they're terrific. I mean, they're just terrific. Right now, they're, they're over in Europe having a vacation. They're doing what all families do. In fact, one of them said to me, "We're boring." Said, "All we do is we take our kids to Disneyland, we watch Netflix, we go to, you know, the market, and, you know, we're just boring people. It's just that we happen to be two gay guys." And, and they're right. They are boring, but I love them. (laughs)

   17. CWChris Williamson16:02

       I am very, very glad that you managed to find such an interesting story. And, uh, what was it, three identical strangers, you know, that, that managed to do something very similar with regards to just captivating people's attention. You said it earlier on, there's something about twins, especially identical twins and triplets, that are just, you know, so, so captivating. One of

4. 16:22 – 21:02

   How Do Twins Know They’re Twins?

   1. CWChris Williamson16:22

      the things that you brought up earlier on that's still playing on my mind was, you mentioned, uh, the, uh, kinship genetics prediction. Uh, that the, the closer you are genetically related to somebody, the more you should care, the more that you would be invested. How is it that twins know that they're twins in this case?

   2. NSNancy Segal16:43

      Well, that, that's a very good question, and I think they know when they can see the other one looking like them, or even if they... In the paternal twins, you know, there's someone they've grown up with, they'd been in the house. Now, in evolutionary psychology, there are two cues that have been talked about in terms of sibling, um, relatedness or, uh, s- knowledge of a sibling. One-

   3. CWChris Williamson17:06

      Is one of these the Westermarck effect? 'Cause this is my favorite.

   4. NSNancy Segal17:09

      Um, I wasn't gonna go there, but we can go there later, 'cause I think that's really fascinating. I have talked about that, and I'm gonna tell you some stuff that's gonna startle you.

   5. CWChris Williamson17:16

      Cool.

   6. NSNancy Segal17:16

      But, all right. Let me just go with this for a moment. So, so the, the two cues that have been talked about in terms of sibling knowledge, knowledge of a sibling, is maternal, uh, association. So if you see another baby with your mom, you figure that's a relationship to you. And the amount of co-residence. So if you live with a child, another kid, that means that that's probably yours. That's interesting, but it's not enough because most identical and fraternal twins live at home with the same mom, same dad, same house. And yet we still have these differences in social relatedness between the identicals and the paternals. Nobody teaches them that. So I think that it's recognizing similarities, and, and it goes beyond just the physical feature. Because as I told you earlier, I do studies of unrelated lookalikes who look as alike as identical twins, and they are nowhere as alike in personality, and very few of them develop close relationships that are lasting, where-

   7. CWChris Williamson18:14

      Just to interject there, what that would prove is that the reason that-... that identical-

   8. NSNancy Segal18:19

      The, the-

   9. CWChris Williamson18:19

      ... twins are the same is not because people treat them the same.

   10. NSNancy Segal18:22

       Yes. It... But, right, because they evoke similar treatment from others. So, see, I'm sort of turning the process around. I do think people treat identical twins more alike, but it's because they evoke similar reactions from people, and we call that evocative, uh, gene environment correlation in behavior genetics. That's what it's called. So, at any rate, I think that with identical twins, whether raised apart or raised together, they perceive certain similarities of themselves that draw them together. Beyond their appearance, it's their mannerisms, their interests, their temperaments, all those kinds of things. I- I've seen close relationships evolve in, in no time. I worked for nine years on the Minnesota Study of Twins Raised Apart, and I could see these things evolving very quickly between twins who recently met. And I actually have done, demonstrated this quantitatively. I had identic- like paternal twins reared apart tell me how they felt when they first met, how they feel now in terms of closeness, and their initial feelings of familiarity and current familiarity. The identical twins were significantly higher on most of those than the fraternal twins. But an even more revealing question that I asked, which I'm so grateful I put in, was I asked all the twins, "How do you feel in terms of closeness of familiarity to the adopted sibling you were raised with in your home?" Very few said very close. Very, very few. And that's rather counterintuitive. You'd think, "Well, I should feel closer to the people I was raised with." It's not so. It's just not so.

   11. CWChris Williamson19:57

       Uh, so what this, uh, counters a little bit is the theory that it's just to do with seeing your mother raise somebody, it's just to do with co-residency during the, that early years window. Because if it was the case, then the way that you look in terms of similarity, your, uh, personality type, that, um, level of resonance between you and someone that you meet in later life would have relatively limited impact. Also-

   12. NSNancy Segal20:23

       Oh, yeah.

   13. CWChris Williamson20:24

       ... one, one thing I've been thinking about, you know, in a, (clears throat) a modern world where we've got mirrors and we've got cameras and we've got a phone that's got high definition video recorder in it, we see ourselves. But for almost all of human history, we didn't see ourselves, right? How would we-

   14. NSNancy Segal20:40

       Okay.

   15. NANarrator20:40

       Yeah, I-

   16. CWChris Williamson20:40

       Other people would be able to say, "You look like them."

   17. NSNancy Segal20:43

       What about, what about lakes and ponds? You could look in there and kind of... It wouldn't be as sharp, but you still-

   18. CWChris Williamson20:48

       Mm-hmm, mm-hmm, yep.

   19. NSNancy Segal20:48

       ... get a sense of wh- what you look like.

   20. CWChris Williamson20:50

       That's right.

   21. NSNancy Segal20:50

       And, and I know that some of the, some of the older cultures had very shiny glass or metal, where they would look at. So, it's not like today, but y- you certainly could get a sense of, of what you look like. Now, I wanted to talk

5. 21:02 – 25:00

   When Separated Twins Are Both Gay

   1. NSNancy Segal21:02

      about, um, uh, the thing you mentioned before. So, the Westermarck effect. All right, so that is very, very fascinating, and I've, I've not documented this, but I have noticed that when identical twins are raised together and both are gay, they're almost never each other's partners. In fact, they have relationships outside the home virtually all the time. And that could be a result of, you know, familiarity breeds contempt, if you want to call it that. But there have been... There was a pair of identical twin men raised apart that we studied at the University of Minnesota, and when they met, they became each other's lovers. Now, it's only one case. I went back and looked at the biographical material in previous re-depart twin cases, and there were a couple of cases that kind of hinted at that sort of a relationship. So, I wonder if it works the same way. No one has really ever looked at that because the percentage of identical twins and fraternals raised apart is relatively small, but you could probably do it with siblings. Now, there is a concept in the adoption world called genetic sexual attraction, and it's been talked about mostly with mothers and sons who reunite and fathers and daughters. And it's not even that they necessarily have intercourse with each other, but this mother described this feeling she just wanted this close physical contact. And sometimes this does go into, um, sexual relationships. It can, but it doesn't necessarily have to. Now, where am I going with this? Because I've documented five or six cases of male-female twins who've been separated at birth and who meet and marry, and they describe a fierce attraction probably based on the similarities they perceive in one another. And the way that their relatedness is discovered is because they usually have a child with a genetic defect, 'cause remember that every parent carries a lethal recessive. And if you marry a sibling or you have, you know, two siblings carry the same lethal recessive, the chance of a child would be 25% if that couple got together. So, at any rate, i- it's devastating, of course, but some couples split up, some don't. It, it's very, very interesting. And I also, along those lines, noticed that when we had separated male-female twins in our lab in Minnesota, there was absolutely flirtation going on. There's no question about it.

   2. CWChris Williamson23:29

      Wow. Okay, so here's a question for you. What does the state think about accidental incest?

   3. NSNancy Segal23:39

      You know, I don't know the answer to that question. But because some of these couples are allowed to marry, and I don't think that they've been from this country, most of them have been from Europe, and far as I know, no one has forced them to separate. If they separate, it's, it's their own choice.

   4. CWChris Williamson23:57

      Isn't that interesting that we, we, we almost carve out a exception for the fact that we know there is a very small cohort, but not insignificant, of twins raised apart for one reason or another, fraternal twins. Because that, that's such a shame. I was thinking o- one of the things I wish that you'd been able to work out would have been, um, sexual aversion or an increase in the Westermarck effect...... if there was such a thing as identical twins that were different sexes. Um, it would be...

   5. NSNancy Segal24:27

      Oh, if they were raised, if they're raised together, I'll bet that's right. But these are twins raised apart-

   6. CWChris Williamson24:32

      Yes.

   7. NSNancy Segal24:32

      ... where the attraction comes in. Now, I think that that is something we have to worry about, and some countries have started worrying about this. Because now, you know, with all the sperm donors creating so many hundreds of children in some cases, you have to worry that if the mothers live in the same local area, these kids may be about the same age, and so half-siblings might get together and they might be attracted to one another just the way that separated twins and siblings are. Speaker 1: (tongue clicks) What

6. 25:00 – 35:19

   Craziest Similarities Between Separated Twins

   1. NSNancy Segal25:00

      have been- And it-

   2. CWChris Williamson25:01

      ... w- what have been some of the craziest similarities between twins-

   3. NSNancy Segal25:05

      Huh.

   4. CWChris Williamson25:05

      ... who have been raised apart that you've found?

   5. NSNancy Segal25:07

      Yeah. Well, I have to think about these twins, Oscar and Jack, who had the most amazing story. Oscar, they, they were born in Trinidad to a Romanian-Jewish father and a woman from Nazi Germany, Catholic. That, they were born in 1933. So, Nazism was just sort of on the horizon. The marriage s- uh, failed, and so one boy was raised in Trinidad with his Jewish father. The other raised in Nazi Germany and went into the Hitler Youth. And so when they met, of course they had very different political and historical understandings, but they both read books back to front. They both used to wash their hands before and after using the toilet. They both thought it was hysterical to sneeze loudly in elevators. And they both got very upset if they were in a restaurant and there was a, a vase of flowers in the middle blocking your view of the other person. Th- they used to collect rubber bands around their wrists. I mean, they had a lot of these very odd idiosyncratic matches. And a lot of people think, "Well, it's coincidence." I don't think so. I think these are hard scientific data. I honestly do. The trouble is, you can't start studying rubber band wearing-

   6. CWChris Williamson26:17

      (laughs)

   7. NSNancy Segal26:17

      ... around the world across cases. But what you can study, Chris, is you can study the frequency of these odd similarities in identicals versus fraternal. And I can tell you that we found them much more in identicals than in fraternals. In fact, in the Minnesota study, we had one pair of fraternal twin men who both had 18 tattoos. We counted them.

   8. CWChris Williamson26:38

      (laughs)

   9. NSNancy Segal26:38

      Now, I, sorry, at this point, we didn't look at the types. Were they flowers? Were they women? What were they? We didn't do that, but we found 18. And I actually have a paper that came out earlier in 2022 in the, in the premier issue of the Japanese Journal of Genet- of Twin Studies. And my students and I did this project where we looked at the similarities in twins from the Minnesota study and from previous and past studies. And of course, when a similarity is something like, um, using Crest toothpaste, I mean, nobody cares about that. Half the world uses Crest toothpaste. But we had a pair of twins that used a s- a rare Swedish brand called Vaddemerkam. And so you have to wonder, you know, "What attracts them to this wei- weird stuff?" So, maybe they like to do things differently, or maybe they like the taste. Who knows? Or maybe they have this affinity with Sweden. But the beauty of these kinds of things is that they give you new hypotheses about why you do what you do. For example, we had a pair of fraternal t- uh, identical twin males who both held the beer can of only Budweiser with their pinky finger underneath. Now, why would you do that? It could be because your hand is made a certain way, or you worry about spilling the beer and you want to be very secure about it. You just like the way it feels. Something like, well, you think it looks cool. At any rate, it gives us new ways of thinking about these kinds of things. And let's face it, all of us have odd behaviors that we do that we hope nobody finds out about. But I'm willing to bet you that they're not just there because they're there. They're there because of you, because of the way your body and your mind are constructed, and you prefer doing things that way than alternative ways.

   10. CWChris Williamson28:21

       Yeah. I, uh, I, I fear that there's a twin, uh, a- an unseen twin out there of me doing all of the embarrassing shit that I do private, privately and, and letting other people know about it. Um, (clears throat) I'm thinking about, uh, w- what you spoke about, that y- th- these things seem relatively arbitrary. What type of car do you drive? What sort of toothpaste do you use? How many tattoos have you got? But they're, uh, very discrete individual examples that explain an entire suite of traits that somebody has, right? So, (clears throat) as you said, with the can, is it because it feels good? Is it because that's the particular size of your hand and the can slips out 'cause you've got particularly small hands or particularly big hands or whatever, right? (clears throat) What it shows is a physical manifestation that's very obvious about, uh, uh, that represents something that's going on internally and sort of, uh, uh, biologically too. What it suggests is that if we were able to visualize thoughts on some super intelligent, fancy fMRI machine in 100 years time, the texture of their mind is probably likely to be similar. The sorts of ruminative thoughts that they would have, the things that they wish that they'd said or didn't say, the number of words that they say per minute, the number of "ums", "uhs" and "likes" that they speak. You know, the, a- all of this stuff is determined by a combination of, uh, your physical attributes, the morphology of your mouth, et cetera. But then also, w- what's the predisposition that you've got mentally?

   11. NSNancy Segal29:47

       Well, well, sure. I think that all comes into play. I, I absolutely do. And, and I'm, I'm not so impressed, as I said, with the common similarities. It's the rare ones that I find intriguing. And those are the ones we focus on. And so for example, we, I did something with names in that Japanese journal. Twins, how often they, they name their children the same name. And we looked at the frequency of how often names were that name in those years. So, you know, you can start to quantify some of this stuff and get some very interesting findings.

   12. CWChris Williamson30:15

       Wasn't there... Th- was it the Jim twins? They have some incredible case.

   13. NSNancy Segal30:20

       Yeah. The Jim twins did too. Unfortunately, both of them passed away. They're the ones who met at age 39 and actually launched the Minnesota study. They lived only 40 miles apart in Ohio.And they used to bite their nails. They described a headache syndrome as someone pounding on your head. They, uh, used to scatter love letters around the house to their wives. They had work- woodworking benches. They drove the same kind of light blue Chevrolet. They vacationed on the same three-block strip of beach in Florida, amazing they'd ever met. They had, uh, they had numerous similarities, and they named their sons James Allen and James Allen.

   14. CWChris Williamson30:56

       (laughs)

   15. NSNancy Segal30:56

       One Allen had an L, two Ls, one had one. I know, you can laugh about that, but why would you name... W- what goes into name-picking? Obviously, the other partner has a, a say in this too, but maybe because they were firstborn sons, they wanted to name their son after their own name, very traditional. And, or maybe the name Allen reminded them of somebody, like the way it sounded. I, I don't know, I'm just throwing out ideas. But it just gives you a new and fresh way of thinking about these things, not just chalking it up to random chance.

   16. CWChris Williamson31:25

       Didn't they have something to do with their marriages as well?

   17. NSNancy Segal31:29

       Yeah. So this is interesting. One of the Jim twins married Betty and divorced her, married Linda, divorced her, married Sandy. Now, the other one also married Sand- uh, Sandy, divorced her, married Linda. If I were Linda, I'd be a little nervous.

   18. CWChris Williamson31:45

       (laughs) Because Betty's coming around the corner.

   19. NSNancy Segal31:47

       If I mi- if I missed Sandy came into the atmosphere, I'd probably g- go running.

   20. CWChris Williamson31:51

       (laughs) So interesting. And again, you know, you think about all of the different inputs that we have on our behavior, all of the myriad interactions we've had with the world, the books that we read, especially if we've been raised apart, different books that we read, different whatever, whatever, whatever, and yet-

   21. NSNancy Segal32:09

       Well, they are. They read the same, they read similar books when they're raised apart.

   22. CWChris Williamson32:12

       Well, there we go. But it's just this-

   23. NSNancy Segal32:14

       Yes, they do.

   24. CWChris Williamson32:14

       ... it's this permanent gravitational pull toward your predisposition.

   25. NSNancy Segal32:19

       I think so. You know, we all have choices in life and we live in, most of us do live in, in communities and cities where there's lots to choose from. And yet there are certain things we choose and certain things we don't. And I think that's why identical twins are alike, because they pick and choose the same things that are compatible with who they are. And, and the very, again, another kind of counterintuitive but true finding is that genetics, genetic effects seem to go up as we age. And people think, "How can that be? It should be environment making more of an impact." But it isn't, because once you get away from home and you're not under the thumb of mom and dad anymore, you're free to pick and choose. And that's why the early studies of religious interest showed no genetic effects, 'cause they were studying children raised at home by their parents. So both twins had to do exactly what mom and dad said. But once they left the house, you began to see the genetic effects kick in, because then they would gravitate towards similar types of activities and really express themselves. And sports participation works the same way. Very little genetic effect when you're young and at home, starts to kick in when you become an adolescent.

   26. CWChris Williamson33:26

       Does a... I- is it IQ is 0.8 by the end of life, pretty much?

   27. NSNancy Segal33:31

       The heritability is about 80%, 75 to 80%.

   28. CWChris Williamson33:35

       Yeah. W-

   29. NSNancy Segal33:35

       Yes, and so this is another one that shows increasing genetic effects as you age, because you're constantly, you know, refining your interests, your activities, all that sort of stuff, that feeds into mental skill.

   30. CWChris Williamson33:46

       But you would presume a, a, a lot of people, the behavioral genetics deniers out there, would say that all of the different inputs you have, your nutrition, your hydration, the amount of vitamin D that you've got, where it is that you live on the planet, the kinds of things that you get exposed to, you know, all of these are going to, uh, in their eyes, it would mediate your ability to deploy your IQ, and yet behavioral genetics seems to rule all.
7. 35:19 – 43:25

   Do Twins Also Share Illnesses?

   1. CWChris Williamson35:19

      What about, uh, sort of psychopathologies, sch- schizophrenia, depression, anxiety, alcoholism, s- uh, o- other sort of maladies like that? What w- what is the, uh, insights that you've learned with regards to fraternal and identical twins?

   2. NSNancy Segal35:35

      Well, identical twins are more likely to match on all of those than fraternal twins. There's a genetic component in virtually everything you rattled off. Schizophrenia is about 40 to 50%. It's nowhere near one. The one that, the only psychopathologist that's really, uh, the strongest genetic effect I've seen is autism, about 70%, and that can also vary depending on whether you use strict or looser criteria. But bipolar disorder has a genetic effect. Dementia. Breast cancer, interestingly, does not. It's about 20% similarity in females. Very unique to...

   3. CWChris Williamson36:10

      Wow, so you could have, uh, you could have identical twins, one of whom does-

   4. NSNancy Segal36:14

      Who has a-

   5. CWChris Williamson36:14

      ... get breast cancer and one of whom doesn't.

   6. NSNancy Segal36:15

      ... one doesn't. Yeah, that's very, very interesting. You know, s- there's... And see, those cases are extremely informative for the general public, 'cause a lot of people think that twin research is only for twins, but it's a model if you're looking at human behavior in general. And so you could look at a pair of identical twins and so one has cancer, one doesn't. Why? Why...... what about the environment that triggered it in one twin and not in the other? And that's really important information by way of m- of prevention. Diabetes is another one. Y- you know, one twin has it, it's about a 50% match. Multiple sclerosis is another one. Twins, it's funny because identical twins are so alike, but they're less alike than people think they are. Both are really true. (laughs) I hate to say it, but it is.

   7. CWChris Williamson36:57

      What have you learned about twins that are raised apart and, uh, BMI or weight?

   8. NSNancy Segal37:06

      Yeah. So, it differs for males and females. The similarity is higher for males. With females, there are various hormonal effects, exercise, diet. So females are a little bit more flexible in that way. But body mass index, BMI, does have a genetic effect, as does height and weight, se- separately, yeah.

   9. CWChris Williamson37:25

      Yeah. It's, um ... That was one of the most interesting things that I learned, because a lot of the time, and, and this gets onto ... What is it that you call it? The, the gene environment covariance?

   10. NSNancy Segal37:35

       Uh, correlation?

   11. CWChris Williamson37:36

       Correlation, that's it. Um, that in a household, let's say that you have identical twins. It is very difficult once both of those twins are in that household to parse apart what is the contributing factor of the nurture element here and what is the contributing factor of the nature element here. You see fat parents with fat children, and you think that, that's because of their lifestyle. You know, look at, look at this. But there's a huge genetic component to people's weight, and you don't know how. I had Robert Plomin on the show, and he told me this really, really great insight I can't forget. He said he has a predisposition to overeat. He said he's a secret fatty. And what he means is that he walks past a bakery and the, the smell of bread to him is just so alluring.

   12. NSNancy Segal38:21

       Mm-hmm.

   13. CWChris Williamson38:21

       And he told me this thing, and he said there are many ways to get fat. What he means by that is there are unbelievable suite of different routes toward, uh, being any- anything that you want, right? Being conscientious, being industrious, being fat, whatever it might be. It may be that your, uh, ghrelin release is, uh, higher than typical. That's the, the hunger hormone released from your stomach. Uh, it might be that you comfort eat because of the way that your mental dysfunction is. It may be that you really don't like exercise. You, you, you are low on energy. It may be that, you know, pick ... Myriad of reasons of how people can gain weight. So when you look at, um, people who do gain weight, you presume that it's all from the same root, but it's not necessarily. It can come from different places.

   14. NSNancy Segal39:04

       No. It can come from multiple sources, of course. And see, that's the danger in studying intact nuclear families, because you can't separate out the genes and environment. They're all confounded. You know, for example, parents pass on both genes and environments to their children. So if the parents are very bright readers and the child is too, how do you know it's not the genes? How do you know it's not the reading experiences and some combination of both? That's why you have to apply these developmental designs that separate them out. So one, the very simple one is the classic twin, monozygotic or identical twins versus fraternal twins. Another are adoption studies. Twins raised apart. You want to disentangle the genes and the environment. That's what you want to do. Many developmental psychologists study parents and children, and they come to the conclusions that it's environmental influence, but it's not. It's all confounded. It would be as if I were sick and I took drug A and drug B and got better. Well, how would I know which drug made me better? I wouldn't know. See? It's the same exact thing. You can't figure out what's causing what.

   15. CWChris Williamson40:06

       The other interesting thing, I always think about this, is that, um, because you have a predisposition genetically to be interested in certain things and to behave in particular ways, and your children will do too. Therefore, your behavior, which is predisposed by your genetics, and your children's predisposition, and the environment that your behavior puts them into all start to exaggerate each other. Now, this isn't to say that children are one to one with their parents' traits. That's not the way that it works. But the point being that when you see particular outliers ... I have a friend here in Austin, Aubrey Marcus, the guy that founded Onnit. I'm pretty sure his father was ... H- h- his parental ... His actual biological father was some inventor guy. His stepfather was a, a very, very impressive businessman, and that was the person that raised him. His mother was a world champion tennis player, and he went on to sell this business for half a billion dollars at age 35.

   16. NSNancy Segal41:05

       Mm-hmm.

   17. CWChris Williamson41:06

       And you go, well, (laughs) it's not ... You've got the genetic components, you've got the foundations here, and then look at the environment that you grew up in. It's not, it's not a particular surprise that in adulthood you had a very high bar for yourself, super conscientious, very industrious, worked hard, and, and succeeded.

   18. NSNancy Segal41:22

       Yeah. Uh, I know. That's not surprising at all. On the other hand, you know, parents could have two children who are extremely different, and one child might thrive in the environment that's provided by their parents, and then one child will absolutely refuse to go into the family business. So siblings in a family differ by a great deal. And, and the home environment is not the same for all children. You know, parents can provide all the sports equipment you want, but one child may thrive on it and one child won't even go near it. One child may stay on the computer the whole night and the other child won't go near it. It's, everybody fashions their own environment, you know, within the setting that they find themselves in. I mean there's so many, so many majors we could all be, right? Universities offer tons of different majors, but we pick one or two that are interesting to us, and we, we don't even consider the other ones. Why is that?

   19. CWChris Williamson42:11

       It's not strictly a ...

   20. NSNancy Segal42:13

       I mean, my father was a lawyer, and I have no interest in being a lawyer.

   21. CWChris Williamson42:15

       (laughs)

   22. NSNancy Segal42:16

       My sister, my twin sister is a lawyer, but I have no interest in it.

   23. CWChris Williamson42:20

       Is there ... Have you looked at anything to do with birth order effect? I know that it's not strictly a, a, a twin, uh, relationship.

   24. NSNancy Segal42:29

       Yeah. The trouble- The trouble with birth order is ... Well, you can have birth order effects with twins. But if the parents treat the firstborn one as the older, that could have some sort of an effect.... with twins, however, you know, if the twins are born in cesarean section and one happens to be a minute old than the other, I- I think to make a big deal over that means nothing. Now, the only way that birth order can make an effect with twins is if it's a vaginal delivery and the first one has a much better situation than the other. Because the uterus changes with the birth of a baby, making it much more difficult for the second child. So that child may have, y- you know, more adverse influences as a young baby and p- provide ... And will need a little more catch-up period. So that's where birth order plays a real role. But in C-sections, it doesn't and it, and t- See, I think that a lot of these birth order studies with twins don't take that into consideration, just lump everybody together and it's, it's ridiculous.

   25. CWChris Williamson43:24

       Is there

8. 43:25 – 48:31

   The Ethics of Separating Twins at Birth

   1. CWChris Williamson43:25

      anything that you can learn from triplets that you can't learn from twins?

   2. NSNancy Segal43:29

      It depends on the configuration of triplets. If you had triplets composed of an identical pair and a fraternal, I love that kind of triplets, and I've worked with a couple of these, because what you find is that the identicals tend to be really close and really similar, and the fraternal feels like the odd man out. And I've seen that on many, many cases. If they're all identicals, y- you know, y- you know, i- i- I mean, it's, it's basically three pairs of twins so you can match everybody up every which way. And if they're fraternal, you can certainly learn a lot too. But I think that the most interesting one are same sex where two are identical and one isn't. And what I ... If I had to devise an experiment, just pick one up, I would never do this, but I would like triplets like that and I would give away one of the identicals.

   3. CWChris Williamson44:17

      Mm.

   4. NSNancy Segal44:17

      And I would see are they more like the identical that they weren't raised with or the fraternal? And I bet, you know, my money would be on the identical.

   5. CWChris Williamson44:25

      Wow. That would be so interesting. Yeah.

   6. NSNancy Segal44:28

      Very interesting, but I- I'm not saying anybody should ever do it. I don't think twins should be raised apart. So I want to be very clear on that.

   7. CWChris Williamson44:33

      Yeah. Y- y- ... What's the, um, ethics or how do you feel when, you know, you're observing a lot of these s- situations and you have what you've managed to identify in your opinion as the closest human to human bond on the planet? Literally, the closest that, that you can feel to somebody else and then they get raised apart. So what, uh, what are your, um, uh, feelings on the, the ethics and the discomfort around that? And then what happens when twins meet for the first time?

   8. NSNancy Segal45:00

      Well, the ethics are very interesting. And in my 2021 book, Deliberately Divided, I go into that a great deal. And this goes beyond three identical strangers. It's a really in-depth analysis of the Louise Wise Adoption Agency that had a misguided view that identical twins should be raised apart because they grow up with their own identities (laughs) . And then, the secret study that followed these children up until the age of 12 without telling them or their parents that they had a twin. So separating twins for that reason, this misguided developmental theory, I, I think is unconscionable. Now, I will say this. Sometimes twins get separated for more legitimate reasons. So maybe a mother dies in childbirth or the family can't afford to keep them. But the parents separate them or the families separate them with the children's best interest in heart. I'm still not condoning that, but I do think it's understandable. And twins have also gotten separated through odd circumstances. We had a pair where the twin was visiting her grandmother in mainland China and the other twin was in Taiwan, and because of political developments, they, they were raised apart. She couldn't go back and be reunited with her family, the one from mainland China. So these things can happen. Now, my perspective is that ... Oh, and also, I have this study on the twin children who were separated indirectly through the one child policy in China. And these are twins who were separated partly sometimes because the mother gives away one and keeps the other, and then maybe gives the other one away later, or they're brought together to an orphanage and then somehow they're separated because people don't realize they're twins or whatever. But my view and the view of my colleagues who are in this line of research, we believe in bringing twins together and we don't believe in keeping them apart for research reasons. In Minnesota, we would sometimes encounter twins who'd never met and we wouldn't keep them apart. You know, for research reasons, yeah, maybe you want to separate them. We would never do that. In fact, we made it an incentive of the study to bring them together so they could spend time together. And we would test them separately. You know, we told them not to discuss the test while it was still ongoing. All that sort of thing. And they took it very seriously. I have no doubt about that. But I'm, I'm completely against twins being raised apart. Sometimes private adoptions happen where a mother decides to keep one and give away another one. I mean, I think it's unfortunate these things happen, but I would be of the opinion to never separate twins. I- I just don't think it's right. I think it's, it's a violation of, of a birthright.

   9. CWChris Williamson47:31

      What is it like... Have you, have you been there when twins have met for the first time?

   10. NSNancy Segal47:35

       Oh, I have.

   11. CWChris Williamson47:35

       What's that like?

   12. NSNancy Segal47:35

       I have. I have. It's amazing. It's the most wonderful experience you could ever imagine. And twins do different things. Some jump up and down, some hug and kiss, some just kind of look at each other. Sometimes they, they touch their face and touch their twin's face at the same time. But it's amazing. It's sort of this moment of out of control glee. And you can't help but feel the same joy that they're feeling. After all, most of these people who are adoptees who never looked like anybody who raised them and suddenly for the first time, they're meeting this celebrated relative, an identical or a fraternal twin, and it's a big deal. It's a very big deal. I mean, I sometimes say to people, "What if you learned that you had a long lost cousin? Would you go look for them?" Well, modi- modest interest. How about an uncle or an aunt? Maybe. Parent? Absolutely. Identical twin? You bet. It's, it's irresistible. It's just irresistible.

9. 48:31 – 52:57

   Why Do So Many People Have an Issue with Behavioural Genetics?

   1. NSNancy Segal48:32

   2. CWChris Williamson48:32

      Why do you think it is that so many people have a problem with behavioral genetic explanations for the traits that we have?

   3. NSNancy Segal48:41

      I think when people hear the word genetics, they feel that whatever that trait is is non-changeable and is set in stone, and that could not be further from the truth. Behavior is, after all-... the expression of a gene in an environment, and if you modify the environment, you can affect the genetic expression. I will say that some traits are harder to change than others, but you can engineer an environment, you can work harder, you can get into training. Y- y- you're not stuck with, with things. Now, for example, we know that divorce has a genetic component because identical twins are more likely to divorce, both of them, than fraternal twins. But your g- your genes don't tell you to divorce. You make the decision. Maybe you have a difficult personality or you're very fussy about your partner or whatever the reason is, but you make the choice. Your genes don't tell you what to do. You're the one in command.

   4. CWChris Williamson49:32

      Yeah, I see, uh, a lot of this on the internet, um, especially coming out of the dating sphere, the, uh, black pill and the incel movement that William, in particular, studies. Um, you know, behavioral genetics, to me, was just w- it was the second-most fascinating thing that I learned about after evolutionary psychology. Uh, a- and I adored looking at this, not necessarily a conflict, but this tension between, uh, my predisposition and, and, and the outcomes that I got, what I had the raw, in terms of raw materials, and then what I had in terms of environment that impacted that. But a lot of people do get fatalistic after learning about behavioral genetics. They believe that they have a very heavily capped ceiling, uh, that it's, it's this sort of deterministic life that they're living now. "I am doomed to be X or Y or Z."

   5. NSNancy Segal50:21

      Yeah. No. That's, that's really not the case. I mean, maybe you're doomed to have brown eyes or hazel eyes, but even then, you can get colored lenses if you really wanna make the change. But let's face it, I mean, somebody who may be six feet tall will probably never be chosen for gymnastics. There are certain limitations, but I think that's good to know that. You know, it makes us predisposed toward more realistic decisions and lifestyle changes. So, I think it, I think it's good if you know that, say, your parents are alcoholics. Suppose you learn that. Well, you can use that information. You're not necessarily gonna be alcoholic, but you might watch how much you drink, drink a little more carefully, things of that sort. So I think it's, it's wonderful information that we can all use.

   6. CWChris Williamson51:00

      How do you conceptualize or, or explain to people this relationship of genes and environments when it comes to, to outcomes in life and, and how that should inform our behavior and, and the way that we sort of see ourselves and our efforts?

   7. NSNancy Segal51:14

      Well, e- exactly what I just said, that you can alter environments and affect genetic expression. I give examples of things like that. Y- you know, I'll tell you, the people who I find the most in- intelligent about this are the parents of fraternal twins and siblings. They know more about human behavior and have a more reasonable view ab- it than my colleagues, many of my colleagues. They just know that what works for one child doesn't necessarily work for another, and many of them went into parenting thinking that everything was environmental, and they come out of it with completely different ideas, as do reunited twins. I s- I interviewed every reunited twin in the Louise Wise Adoption Study, and a lot of them said that they really felt that behavior was environmental, but they'd never met a twin before. And suddenly, th- they're learning about themselves that their behaviors are not just coming out of nowhere, but they're coming out of somewhere. And it's, it's a great education. It's just a great education for them.

   8. CWChris Williamson52:13

      How much-

   9. NSNancy Segal52:14

      And, uh, uh, let me just mention, I, I also, uh, did a book recently this year on the twin children who survived the Holocaust. It's an annotated photograph collection. I think I told you about that.

   10. CWChris Williamson52:25

       Mm-hmm.

   11. NSNancy Segal52:25

       And, um, these are the twins who were in the Mengele experiments in Auschwitz-Birkenau in 1945, and I went with them to the 40th anniversary reunion in 1985. And, you know, why did these twins survive when some other ones didn't? It's an interesting question. Luck had a role here too, but a sort of resilience and strength, and the twin bond too. The strength of that bond gave them each kind of a will to live, which was so important, which non-twin survivors didn't have, um, the benefit of.

10. 52:57 – 1:04:14

    How Much Can Rearing Change a Child?

    1. CWChris Williamson52:57

       Mm. Y- y- thinking about the, uh, parenting side of this, how much can rearing change a child?

    2. NSNancy Segal53:07

       Well, I, I can't give you a number, but what I can say is that I think parents have a very important role, and I think it's different than how people conceptualize it. Parents do not mold you into what you are. I regard parental responsibility as being very sensitive to the child's individual tastes, temperaments, likes, dislikes, abilities, and interests. And I think if parents can be attuned to that and really help the child to become more of who they are and to maybe overcome some of their drawbacks like shyness or timidity in some situations, then I think that's a great responsibility. You know, it, it really pained me when, when parents, when mothers who were still pregnant are enrolling their children in these prena- prenatal programs of education. I, I mean, it, it's ridiculous. I think that good parenting is really sensitivity to the child and being very supportive and nurturing. So, I think parenting makes a huge difference. I think children who grow up with insensitive parents, uh, or, or multiple caretakers who don't take the time to really see what their interests are are the ones who are not going to benefit.

    3. CWChris Williamson54:14

       Yeah. Geoffrey Miller once tweeted that, um, every parenting book combined is less useful than one book on behavioral genetics for parents to read.

    4. NSNancy Segal54:23

       I think that's very well put. I would agree with that.

    5. CWChris Williamson54:25

       Yeah. Uh, it's, it's just... Uh, I try and look back, you know. I'm an only child, so I try and reflect on my own life, and I don't have, uh, another, uh, an A/B split test of me to be able to look at, to be able to compare. There's some parts of my personality that I do see from my parents, but there is so much that's different, like so much.

    6. NSNancy Segal54:45

       Hmm.

    7. CWChris Williamson54:45

       It's incredible. And I would say that my parents', um, predisposition, in terms of the way that they're set up and the environment that I grew up in was quite aligned. I, I don't, I don't think that they, um, uh, changed themselves massively when I was born, although, obviously-... all children will change parents. It's a massive life, life switch. But yeah, it's, uh ... I, I love the idea of helping a child to find out what is their passion, what is their calling, what it is-

    8. NSNancy Segal55:16

       Yeah.

    9. CWChris Williamson55:17

       ... that, that aligns most, uh, with them. Because, you know, for an individual parent to try and reverse engineer or to, um, prescribe in advance, uh, I always ... Uh, you know the classic story of the father that didn't get picked for the football team. "So, you know, my son, he's gonna be the football player and he's 2 years old throwing a football at Christmas and stuff."

    10. NSNancy Segal55:36

        Mm-hmm.

    11. CWChris Williamson55:37

        Um, that prescriptive role, in some regards is good, because it creates guidelines that children can follow, but if you continually having to re-force your child to do that, because all he wants to do is play music or draw or whatever, uh, you're, you're fighting a losing battle.

    12. NSNancy Segal55:51

        Yeah, yes you are. And that's why I think that parents of fraternal twins and near-in-age siblings are the ones that really understand human development, because fraternal twins can be extremely different. My sister and I went very, very different directions. I took ballet, she took drama lessons. We went to different schools, different summer camps that were more suited to what we wanted. And my parents were, were very good about that. They didn't force us to be together. It was easy, because children in their own way will tell you what's best for them if parents will only take the time to look.

    13. CWChris Williamson56:20

        Mm. That's a lovely insight. And I think when I first spoke to Plomin about this as well, he, he ... The sense that I got, I'm not a parent yet, but the sense that I got from a parent's perspective is that it alleviates a lot of the pressure, I think, that parents-

    14. NSNancy Segal56:38

        Yes.

    15. CWChris Williamson56:38

        ... feel.

    16. NSNancy Segal56:38

        Yes. I think that parents who are less well-informed about what parenting's all about feel they have to do everything. And if they just relaxed a little bit and paid attention and took the cues from the child, I think they'd be a lot better off and they'd be much happier and more effective parents.

    17. CWChris Williamson56:55

        Yeah.

    18. NSNancy Segal56:55

        I have no, no, uh, qualms about saying that.

    19. CWChris Williamson56:58

        Yeah, I think so too. Um, and, and there is (clears throat) ... You know, in a meritocracy, uh, if you are your successes, then it also means that you are your losses too. Right? And we know that people have very different ... As soon as you take the behavioral genetics pill, like forget equality of opportunity. Forget that, right? Way before equality of opportunity is equality of genetics, which is just not, it's not going to happen-

    20. NSNancy Segal57:23

        Yeah, uh-

    21. CWChris Williamson57:23

        ... between everybody. So, as soon as you take that behavioral genetics red pill, what you realize is that largely your child's outcomes in life are going to be determined by the partner that you chose to have them with. Right? A- and you can do things to improve that. You can make the quality of their life better. But if you're tige- momming your way to hope that you can create a 140-

    22. NSNancy Segal57:45

        Mm-hmm.

    23. CWChris Williamson57:45

        ... IQ child, I, it's-

    24. NSNancy Segal57:48

        No, you're gonna be disappointed. Keep, keep in mind too, though, that suppose you've got two parents who are very interested in dancing or sports or something like that, they could have a child with absolutely no interest in that whatsoever, because the genes reshuffle in every generation. And, and then also, what's popular in one generation may not be popular in another. And even if a child has a certain ability that aligns with that of the parents, there may be something else that's, that's grabbing everybody's attention in the generation into which the child is born. So, these things, you know, have, have all kinds of factors affecting them. Parents and children, I think, are actually less alike than people think they are. We do see similarities, definitely, but children are very different. And I think it's largely because they, they ha- they get different suites of genetics and they ... They're in environments and generations where things can be vastly different.

    25. CWChris Williamson58:40

        Yeah, I think I'm really seeing this in my generation. So, I would be pretty much slap bang in the middle of the millennials. And I would probably guess that aside from some times when there's been global pandemics like the Spanish flu or World Wars or Genghis Khans come through or something, that this block has had, from parent to child, the largest inflection point in terms of the difference of environment that we found ourselves in. You know, you have-

    26. NSNancy Segal59:09

        Yeah.

    27. CWChris Williamson59:09

        ... parents that grew up without the internet, children ... So, for me, I was, uh, not internet native, but I think the internet would have come online maybe when I was 11 or 12, something like that. So, I've got a little bit of time before that, and a good bit of time before smartphones, but relatively digitally native. But the difference, the difference in my, my dad's upbringing in the '60s and '70s and mine in the '90s and the 2000s is a, uh, different universe. So, yeah-

    28. NSNancy Segal59:34

        Yeah.

    29. CWChris Williamson59:34

        ... you know, even if you have, even if you were one-to-one with your parents in terms of your, uh, genetics, look at how different all of the different inputs are that you've got, the, the, the opportunities that you have, the influences, uh, the, the chance to actually display this behavior in a completely different way.

    30. NSNancy Segal59:50

        Yeah. Uh, uh, the differences are extraordinary. Uh, they are. There's no question about it. And, um, yeah, we can't account for everything, but I think we can count- account for a lot. (laughs)
11. 1:04:14 – 1:07:03

    The Family Dynamic of Bi-Racial Twins

    1. NSNancy Segal1:04:14

    2. CWChris Williamson1:04:14

       It's got me thinking, uh, this is only very tangentially related to your work. I've been thinking for a little while about interracial couples and then the children that they have. And I w-

    3. NSNancy Segal1:04:26

       Oh. I'm doing a study on that, but keep going. 2020-

    4. CWChris Williamson1:04:29

       Okay. All right. So my bro science, not your real science, we can get into that in a second. My bro science was, I would be very interested in looking at parental opinions and perspectives on race relations. Let's say that you have a, a, a white mother, Black father, and then mixed-race child, but, you know, the, uh, gene is relatively dominant so it's going to be a dark child. So, I would love to speak to the mother and, and work out what it's like to be completely uninvested in racial discrimination, uh, personally uninvested, you can altruistically be as invested as you want. And then immediately upon having a child for this to change, and he would be the second one, and this would be the craziest one, if you were able to have the, uh, I can't remember what the name was when you have, uh, two eggs that get released and two sperm that go at the same time. But if you-

    5. NSNancy Segal1:05:23

       Twins with different ages.

    6. CWChris Williamson1:05:24

       Yeah. But if you had that, but those were interracial, that there was, you had a white and a Black-

    7. NSNancy Segal1:05:28

       Well, okay. L- l- let me tell you something. I'm very interested in the so-called biracial twins too, and these are fraternal twins that are born to mixed-race couples. And I got interested in this because in one of my classes, I had a pair of fraternal twins, one looked very Hispanic and one looked very Caucasian. And they did have a Caucasian mother and a Hispanic father. And they told me that their life experiences were extremely different despite being raised at home and in the same communities. That everybody thought that the one who looked Hispanic was the dumb one when in fact it was just the other way around.

    8. CWChris Williamson1:06:01

       (laughs)

    9. NSNancy Segal1:06:01

       And so there have been many more mixed-race couples lately and they have fraternal twins. And so now I've, I've interviewed probably 10, 15 couples because I want to understand the different life experiences of the kids and what the parenting challenges are. And I also am trying to get at the topic of do you feel a greater kinship with a kid that looks more like you racially than the other one?

    10. CWChris Williamson1:06:25

        Mm.

    11. NSNancy Segal1:06:25

        And that's a very hard concept to get across. I mean, you can't say, "Who do you love more?"

    12. CWChris Williamson1:06:30

        (laughs)

    13. NSNancy Segal1:06:31

        You, you can't say that. But I, I wonder if I can somehow tease that out in maybe a less direct way 'cause it's, it's an interesting question. And I also wonder if there is less paternity uncertainty-

    14. CWChris Williamson1:06:41

        Yeah.

    15. NSNancy Segal1:06:41

        ... in mixed-race couples.

    16. CWChris Williamson1:06:42

        Yeah, yeah.

    17. NSNancy Segal1:06:43

        There, there might well be. I don't think anyone's ever looked at that. But that's something I can, I could think about at the same time. But it's, it's really, biracial comes from the press and the media. It's not a term that makes sense to me because they're not biracial. They may look biracial, but they're equally biracial 'cause they have the same parents.

    18. CWChris Williamson1:07:00

        (laughs) Okay. I understand that.

12. 1:07:03 – 1:11:34

    Common Criticisms of Twin Studies

    1. CWChris Williamson1:07:03

       Um, what are the...... common criticisms that you encounter around twin studies, whether it be, uh, methodology, conclusions, pushback, that sort of stuff. What- what's most common?

    2. NSNancy Segal1:07:17

       I- it's probably mostly methodological. People think that when twins are together, they learn from each other, that sort of thing, or they're not tested separately. And I think people- some people think that the conclusions are overdrawn. But I would argue that the critics have not done the studies themselves, and they probably never encountered a pair of twins. I mean, so- so many people who have these hard opinions don't have the experience to really make the appropriate judgments. And, you know, s- and- and also, so many studies that have used different populations, different subject pools, different protocols, converge on the same conclusions. In- in my book, 2012, where I give a whole overview of Born Together, Reared Apart, which is the Minnesota study, I reprint from one of our papers a graph showing the IQ correlation from four or five different reared-apart twin studies. One in England, one in Denmark, one in, um, the US, one in Sweden. Different populations, different time points, different protocols. And they all converge on the same basic conclusion, about .75 is the genetic effect.

    3. CWChris Williamson1:08:25

       (laughs)

    4. NSNancy Segal1:08:25

       And you- it's rare to get that kind of repetition, replication I should say, in the behavioral sciences. It's- it's a very robust finding.

    5. CWChris Williamson1:08:33

       Yeah. I was gonna say, you know, f- f- for the people who like to throw the term replication crisis around, and- and point the finger at fields of psychology and social sciences, which is very justified, the two places that you really shouldn't be pointing the finger at behavioral genetics and evolutionary psychology.

    6. NSNancy Segal1:08:51

       Right.

    7. CWChris Williamson1:08:51

       Because both (laughs) both of those...

    8. NSNancy Segal1:08:53

       Lots of repetition there, and lots of converging evidence. And- and I- I- I really love that, because it's different methodologies and different people. But, you know, even if you go outside of behavior genetics and evolutionary psychology, you can see studies done in social psychological theories, and they come out with the same thing but their interpretations are different. There's a wonderful study done in the '50s where they simply asked twins, you know, "Who would you miss most in the event of death, twin, mother?" And- and while there was some little variation against my studies, it- it was basically very remarkable that genetic relatedness was more aligned with g- higher levels of grief. So, if you look in that literature, you still see this stuff. It's just that the interpretation and the theoretical layering is so different.

    9. CWChris Williamson1:09:36

       What was their, uh, justification for it? What was their interpretation of that effect?

    10. NSNancy Segal1:09:41

        Um, you know, it really wasn't an interpretation. It was a sociological study. It was mainly to see what if, wha- what is out there.

    11. CWChris Williamson1:09:48

        Okay.

    12. NSNancy Segal1:09:48

        It- it didn't really have an interpretation. It was basically what if.

    13. CWChris Williamson1:09:50

        Got you.

    14. NSNancy Segal1:09:51

        But- but the what if aligns with the behavior genetic and evolutionary psychological interpretations.

    15. CWChris Williamson1:09:57

        Damn right it does, which is why we're interested in it, Nancy. What- 'cause you mentioned that just, you said about, um, the study that you'd done. Is your study one of the biggest or the biggest in terms of twins? Or is that Robert Plomin's study that he did-

    16. NSNancy Segal1:10:12

        No.

    17. CWChris Williamson1:10:12

        ... in the UK?

    18. NSNancy Segal1:10:12

        Which twin study are- are you referring to? The Minnesota study?

    19. CWChris Williamson1:10:15

        Yes.

    20. NSNancy Segal1:10:15

        Oh. No, the Minnesota study is not my study. I worked on it for many years, and I still work on it. That was Dr. Thomas Bouchard-

    21. CWChris Williamson1:10:22

        Got you.

    22. NSNancy Segal1:10:22

        ... the director who actually launched that. Now, keep in mind, that was the reared-apart study, so we ended up with 137 pairs.

    23. CWChris Williamson1:10:29

        Yep.

    24. NSNancy Segal1:10:30

        Uh, for more identicals than fraternals. Plomin's study is twins raised together, and he has thousands of pairs, so definitely gonna have more.

    25. CWChris Williamson1:10:37

        Yeah, I think it was every- every set of twins born in the UK between like 1991 and 1994-

    26. NSNancy Segal1:10:44

        Yeah. (laughs)

    27. CWChris Williamson1:10:44

        ... or something, right?

    28. NSNancy Segal1:10:45

        It's something like that. It's something like that. And- and those kinds of datasets are remarkable. But I will tell you honestly, Chris, that there's nothing I like more than being in a lab with twins and seeing it up close and personal, because you really see your data in action. And I think there's no substitute for that. And I remember at one of the International Twin Congresses, which are held every two years, I organized a film session where I showed films about different aspects of twinship. And I remember some people coming up to me and saying they loved seeing this because all they do is work with data. And, you know, I work with data too, a lot of it. But I also work with the real human stuff. And when I bring twins into the lab, I just love it, because again, just by acting naturally, these twins give you all kinds of new interesting ideas and- and new takes on human development.

    29. CWChris Williamson1:11:33

        Did you watch

13. 1:11:34 – 1:14:10

    ‘Tell Me Who I Am’ on Netflix

    1. CWChris Williamson1:11:34

       the Netflix documentary, Tell Me Who I Am?

    2. NSNancy Segal1:11:37

       No, I didn't.

    3. CWChris Williamson1:11:39

       Nancy, you must watch this.

    4. NSNancy Segal1:11:41

       I'm- I'm writing it down now.

    5. CWChris Williamson1:11:42

       You must watch it. For the people who haven't seen it, it is- I- I- I wonder if-

    6. NSNancy Segal1:11:48

       Oh, wait a minute. Wait a minute. Is this the one, I think, it's with identical twin men and they had a secret? Is this the one?

    7. CWChris Williamson1:11:55

       Yeah, they had a secret. They, one of the guys loses his memory, and then he has to be-

    8. NSNancy Segal1:11:59

       I did see it. I'm sorry. I- I did see it. I did see it.

    9. CWChris Williamson1:12:01

       Yeah.

    10. NSNancy Segal1:12:02

        Yes. And it's remarkable. I- I didn't know that, I couldn't remember that was the title. But yes-

    11. CWChris Williamson1:12:05

        Yeah.

    12. NSNancy Segal1:12:05

        ... I did see that. It's remarkable. Yes.

    13. CWChris Williamson1:12:07

        Yeah. For the people, I- I won't spoil it, um, but for the people who, uh, are interested in this, uh, Three Identical Strangers, absolutely fantastic film. Um, Born Together, Reared Apart, your book, uh, awesome, awesome breakdown of this. And then that, uh, that Tell Me Who I Am is harrowing.

    14. NSNancy Segal1:12:25

        Yeah.

    15. CWChris Williamson1:12:25

        And you see, you see... It- it, what got me thinking about it was you saying when you're in the lab and you see the twins and so on and so forth. And, um, yet on this Tell Me Who I Am, you see these guys reveal this lifelong secret to each other-

    16. NSNancy Segal1:12:39

        Yeah.

    17. CWChris Williamson1:12:40

        ... on set.

    18. NSNancy Segal1:12:41

        Yeah.

    19. CWChris Williamson1:12:41

        And it's the first time it's ever happened. It is...

    20. NSNancy Segal1:12:45

        Yeah. Yeah. It- it- it was remarkable.

    21. CWChris Williamson1:12:47

        It's crazy.

    22. NSNancy Segal1:12:48

        It w- it was a film that we talked about for a long time. And- and I will say, there's another film about the Louise Wise Adoption Agency that I think is also excellent called The Twinning Reaction, which didn't get as much attention as the others. It was made by Lori Shinseki, an independent filmmaker, that came out just about a year before Three Identical Strangers. Also very excellent and many of the twins are in- are in both films.You know, when you think about naturalistic observations, one of the best films I've ever seen was done on 16 millimeter, back in the '60s by my thesis advisor at the University of Chicago. And what he did was he filmed identical and fraternal twins once a month over the first year of life, and he looked at their reactions to strangers. So in every month, he'd show them with their mother where they're happy and playing, with a stranger, and maybe with this new toy and how they reacted to that. And I'm telling you, it- it was remarkable 'cause the identicals were so coordinated at that young age. Fraternals were so different. It was amazing. It- it's a beautiful film, and I wish more people would do film. It- it's- this is something that came up at the conference I was at just last week, the International Society for Human Ethology in Detroit. And it's a shame that more people don't use film. It- it really is. It- you can look at it so many times and get new ideas, and it's- it's- it tells things in a way that texts just can't.

    23. CWChris Williamson1:14:08

        Nancy Segal, ladies and gentlemen.

14. 1:14:10 – 1:16:07

    Where to Find Nancy

    1. CWChris Williamson1:14:10

       Nancy, I absolutely love your energy. I love your passion for your work. I'm very, very glad that you came up to me at HBESS and- and accosted me to one side. And, uh, I've been looking forward to speaking to you for ages, and I'm- I'm super, super excited to see what you do next. Where should people go if they're interested in the work that you're doing? What books should they start with? And- and what ones have you got coming out and all the rest of it?

    2. NSNancy Segal1:14:29

       Yeah. So I have a website with all my twin books and all my related material, and that is Doctor, D-R, Nancy Segal, so D-R-N-A-N-C-Y S-E-G-A-L twins dot org. And I update it very, very often. And I have eight books out now. My ninth one is coming out in August. That's Gay Fathers, Twin Sons: The Citizenship Case that Captivated the World. They might wanna look at my photo book on the Holocaust twins. There's a lot of interesting stories about twinship in there. And Deliberately Divided, certainly, Deliberately Divided, uh, Twins and Triplets Adopted Apart, Inside- The Inside Story, something like that. Uh, but- but if you're really, really new to twin studies, you might wanna check my 1999 book called Entwined Lives, where I cover many, many different topics on twins. I cover the biology, the psychology, uh, reproductive interests, legal cases. I- I work as a, um, an expert witness on- on legal cases about wrongful death, injury, custody, all kinds of things like that.

    3. CWChris Williamson1:15:35

       Wow.

    4. NSNancy Segal1:15:35

       Very, very fascinating. And right now, um, I'm gonna be on leave for a year, and I'm developing a new book proposal, which is going to be kind of a comprehensive book, kind of the- the tome on twin studies. So I'm excited about that.

    5. CWChris Williamson1:15:49

       Hell yeah. Very cool. Nancy, I appreciate the heck out of you. Thank you very much for joining me today.

    6. NSNancy Segal1:15:55

       Thank you, Chris. I'm glad I accosted you.

    7. CWChris Williamson1:15:57

       If you enjoyed that episode, then press here for a selection of the best clips from the podcast over the last few weeks. And don't forget to subscribe.

Episode duration: 1:16:07