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

how do you describe what you work on when somebody asks well I tell them that I'm a development of psychologist but my interests also cover Behavior genetics and evolutionary psychology and I'm passionate about twins because twin studies are simple and very elegant way of combining all three developmental psychology Behavior genetics 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 like into a candy store I've just had a wonderful ride and the ride is continuing 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 it's 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 in sales and do 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 can see how behavioral genetics comes in you know we're splitting apart genetically and environmentally what the contributing factors are uh but I I'm less sure about about the others 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 with 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 closer socially than fraternal twins are on average and so I thought that this was another level of analysis that I could bring to twin studies because many people say Well they're they're closer because they look alike and people encourage it but I don't believe that's the case because behavior is not built on appear as behavior is built on the brain and so I always felt there was some deeper level to this and so I've been able to use twins I've been able to use unrelated look-alikes 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 because they really Converge on the same thing you know I remember when I was doing my doctoral dissertation my first major study and I use 7 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 for 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 what is your explanation for why identical twins and fraternal twins had that difference for the people that don't understand am I writing saying that fraternal twins are essentially just simultaneously born brothers and sisters that's correct identical twins result when a single fertilized egg divides between the first and 14th 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 of 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 of kids we've been 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 deaf on the competitive side I wonder whether teams 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 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 yes I think that's right for example if you're a 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 is Twins and sports and it is amazing to see these matched levels of elite athletes you know it's extraordinary 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 their 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 what about that what about the degree of emotional connection between identical twins I mean there's uh tales as old as time about 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 extra degree of connectivity of emotional investment of kinship as would have been predicted by that theory 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 even more than mothers with children yes and I would 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 code twin than they did it for any of 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 I'm guessing that's the same for a son or a daughter as well then yes yes but well let me Backtrack on that I have very few Sons and Daughters very few twins 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 fraternal twins you share half on average with your twin and you share 50 percent for sure with your child so I would expect much greater variability among the fraternals very interesting very interesting but I really hope I never get to do that comparison because I don't want anyone to lose a child 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 like half half twins like what what are they called well the medical term for that is super fee condated 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 have siblings but I regard them as a legitimate pair of twins because this could come out naturally and it can also come about through artificial reproductive assistance you know 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 insept each created by one father and those are the ones they implanted so they replay a naturally occurring situation tell us that story 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 then he met another young man ilad and they fell in love and married in Canada in 2010. Tel Aviv Tel Aviv isn't uh fantastic for trying to get your gay wedding across the line not really no in fact in fact I 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 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 the DNA lab and the surrogate beyond that nobody knew the relationship of the kids so now their genetic learnings 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's created with a sperm from the American father and a tourist visa to the other one and so this threatened to tell their family apart tourist visas are good for about six months they are renewable but it was a travel situation so when they did come to the U.S 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 Allah's case came about at the perfect moment because they already had three other couples trans and National who had children outside the U.S 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 family's name DeVos Banks versus the U.S state department and Rex Tillerson who was then Secretary of State later Mike Pompeo it was a very high profile case it 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 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 there 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 wow what a story how much of this do you think is uh concealed homophobia from uh organizations that maybe and then I guess actually a combination of concealed homophobia and concealed islamophobia uh intersectionally combining to to create this I I think that is certainly one of the factors and I think whether you're a homophobic or not if you just simply disagree with the idea of it then I think that that can play a role sorry maybe homophobia might be the wrong the wrong term though 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 what is the treatment the same I'm going to guess that it would be treating somebody different on the basis of their sexual orientation probably that's like a a rough 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 both from a European country or whatever um yeah maybe maybe it does meet the criteria yeah so at any rate I think that's really 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 I 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 just that we happen to be two gay guys and and they're right they are boring but I love them I am very very glad that you've managed to find such an interesting story and uh was it three identical strangers you know that that managed to do something very similar with regards to just captivating people's attention he said it earlier on there's something about twins especially identical twins and triplets that are just you know so so captivating one of 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 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 well 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 fraternal twins you know there's someone they've grown up with they've been in the house now in evolutionary psychology there are two cues that have been talked about in terms of sibling uh relatedness knowledge of a sibling is one of these the Western Mark effect because this is my favorite um I wasn't gonna go there but we can go there later because I think that's really fascinating I have talked about that and I'm going to tell you some stuff that's going to startle you but all right let me just go with this for a moment so so the two cues 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-residents 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 same mom same dad same house and yet we still have these differences in social relatedness between the identicals and the fraternals 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 look-alikes 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 just to interject there what that would prove is that the reason that identical twins are the same is not because people treat them the same yes 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 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 evolved 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 identical and fraternal 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 think well I should feel closer to the people I was raised with it's not so it's just not something uh so what's 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 personality type that um level of resonance between you and someone that you meet in later life would have relatively limited impact also one one thing I've been thinking about you know in a 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 other people would be able to say you look like them what about what about lakes and ponds you could look in there and kind of it wouldn't be as sharp but you still have a sense of what you look like and I know that some of the some of the older cultures had very shiny glass or metal where they would look so it's not like today but you certainly could get a sense of of what you look like now I wanted to talk about um the thing you mentioned before so the Western Mark 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 read apart 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's really ever looked at that because the percentage of identical twins and fraternals raised apart as 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 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 because remember that every parent carries a lethal recessive and if you marry a sibling or you have you know with two siblings carry the same legal recessive the chance of a child would be 25 if that couple got together so at any rate it's devastating of course but some couples split up some don't 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 wow okay so here's a question for you what does the state think about accidental incest 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 as far as I know no one has forced them to separate if they separate it's it's their own choice isn't that interesting that 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 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 western Mark effect if there was such a thing as identical twins that were different sexes um it would be oh if they were raised if they're raised together I bet that's right but these are twins raised apart they're 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 another just the way that separated Twins and siblings are what has been what have been some of the craziest similarities between Twins who have been raised apart that you've found yeah well I have to think about these twins Oscar and Jack who had the most amazing story Oscar 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 failed and so one boy was raised in Trinidad with the Jewish father the other raised in Nazi Germany went to 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 sneezed loudly in elevators and they both got very upset if they were in a restaurant and there was a a Vaz of flowers in the middle blocking your view of the other person 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 around across cases but what you can study Chris is you can study the frequency of these odd similarities in identical versus fraternal and I can tell you that we found them much more on identicals than in fraternals in fact in the Minnesota study we had one pair of paternal twin men who both had 18 tattoos we counted them now I sorry at this point we didn't look at the types for the 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 genetic 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 rare Swedish brand called batty makem and so you have to wonder you know what attracts them to this 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 paternal 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 where 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 yeah I uh I fear that there's a twin an unseen twin out there of me doing all of the embarrassing that I do private privately and letting other people know about it um I'm thinking about what you spoke about there 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 very discreet individual examples that explain an entire Suite of traits that somebody has right so 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 you've got particularly small hands of particularly big hands or whatever right what it shows is a physical manifestation that's very obvious about uh that represents something that's going on internally and sort of 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 ears and likes that they speak you know all of this stuff is determined by a combination of your physical attributes the morphology of your mouth Etc but then also what's the predisposition that you've got mentally well sure I think that all comes into play I absolutely do and and 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 the stuff and get some very interesting findings wasn't the was it the gym twins there was some incredible case yeah the gym 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 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 them the same three block strip of beach in Florida amazing they'd ever met they had they had numerous similarities and they named their sons James Allen and James Allen one Allen had a nail two Wells one had one I know you can laugh about that but why would you name what goes into name picking obviously the other partner has a say in this too but maybe because they were first born 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 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 didn't they have something to do with their marriages as well yeah so this is interesting one of the gym twins married Betty and divorced her married Linda divorced her married Sandy now the other one also married sand Sandy divorced her married Linda if I were Linda I'd be a little nervous because Betsy's coming around I don't understand he came into the atmosphere I'd probably go running 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 and yeah they read the same they read similar books when they read it apart well there we go but it's just this it's this permanent gravitational pull towards your predisposition 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 because 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 at home starts to kick in when you become an adolescent does a is it IQ is 0.8 by the end of life pretty much the heritability is about 80 75 to 80 percent yes which is another one that shows increasing genetic effects as you age because you're constantly refining your interests your activities all that sort of stuff that feeds into mental skill but you would presume 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 you get exposed to you know all of these are going to in their eyes it would mediate your ability to deploy your IQ and yet behavioral genetics seems to rule all well genetics no genetics does not say it's completely genetic I mean there's nothing is a correlation of one I find the most fascinating thing is that there's so much out there that can make us different and yet identical twins are still remarkably alike whether they raise their part or raised together but again you know you certainly with nutrition I mean if one twin is exposed to a condition another one isn't you know there are cases where one had coveted one didn't that sort of thing so certainly with infections I mean there are many things that can make you different but it's not like it makes you different than every way you might be different in one area but very still very similar in others I've also had the opportunity to work with twins identical female twins where one felt like a male and actually went through surgical reassignment to become a male and yet the Twins were still remark will be alike in every other way except for this one fundamental difference and what was so wonderful to witness was just how welcoming the the non-change twin was you know she wanted her now brother to be happy and content and the brother wasn't for many many years what about uh sort of psychopathologies schizophrenia depression anxiety alcoholism uh other sort of maladies like that what what is the uh insights that you've learned with regards to Fraternal and identical twins well identical twins are more likely to match on all of those than fraternal twins there's a genetic component that virtually everything you rattled off schizophrenia is about 40 to 50 percent it's nowhere near one the one that the only psychopathologist that's really the strongest genetic effect I've seen is autism at 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 wow so you could have uh you could have identical twins one of whom just get breast cancer and one of whom doesn't yeah that's very very interesting you know so there's and see those cases are extremely informative for the general public see a lot of people think that twin research is only for twins but it's a model for 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 prevention diabetes is another one 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 I hate to say it but it is what have you learned about twins that are raised apart and BMI or weight yeah so it differs from males and females the similarities higher for males with females there are various hormonal effects exercise diet so female is a little bit more flexible in that way but body mass index BMI does have a genetic effect as does height and weight separately yeah yeah it's um that was one of the most interesting things that I learned because a lot of the time and this gets on to what is it that you call it the gene environment covariance of correlation 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 pass 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 Plowman on the show 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 smell of bread to him is just so alluring 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 Roots towards uh being any anything that you want right being conscientious being industrious being fat whatever it might be it may be that your ghrelin release is uh higher than typical that's the the hunger hormone released in your stomach 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 are low on energy it may be that you know pick your Myriad of reasons of how people can get gain weight so when you look at um people who do gain weight you presume that it's all from the same route but it's not necessarily it can come from places 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 as some combination of both so that's why you have to apply these developmental designs that separate them out so one the very simple one is the classic twin monopsychotic or identical twins versus fraternal twins another are adoption studies twins raised apart you want to disentangle the genes of 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 was sick and I took drug a and Drug B and got better 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 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 found it on it I'm pretty sure his father was his parenta is 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. you go well 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 succeeded yeah I know that's surprising at all on the other hand you know parents can have two children who are extremely different and one child might thrive in the environment that's provided by the parents and one child will absolutely refuse to go into the family business so siblings and family differ by a great deal and and the home environment is not the same for all children parents can provide all the sports that commit you want but one child May thrive on it 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 it's not there's so many there's so many majors we could all be right universities offered 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 it's nothing and I I have no interest in being a lawyer my sister my twin sister is a lawyer but I have no interest in it is there have you looked at anything to do with birth order effect I know that it's not strictly a twin uh relationship 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 were born in the cesarean section and what happens to be a minute old and the other 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 firstborn 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 you know more adverse influences as a young baby provide and will need a little more ketchup period so that's where birth order plays a real role but in C-sections it doesn't then and to 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 is there anything that you can learn from triplets that you can't learn from twins it depends on the configuration of triplets if you had trip was 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 you know 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 we are 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 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 wow that would be so interesting yeah 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 yeah what's the um ethics or how do you feel when you know you're observing a lot of these 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 you can feel to somebody else and then they get raised apart so what what are your um feelings on the the ethics and the discomfort around that and then what happens when twins meet for the first time 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 twin should be raised apart because they grew up with their own identities and then the secret study that followed these children up until the age of 12 that 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 that 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 family separate them with the children's best interests and 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 the study on the twin children who were separated indirectly through the one child policy in China and these are twins who are 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 in part you know for research reasons yeah maybe you want to separate them we would never do that in fact we made 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 a Birthright what is it like have you have you been there when twins have met for the first time 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 twins 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 or adoptees who never look like anybody who raised them and suddenly for the first time they're meeting this celebrated relative and 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 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 why do you think it is that so many people have a problem with behavioral genetic explanations for the traits that we have 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 you're not stuck with with things now for example we know the divorce has a genetic component because identical twins are more likely to divorce both of them than fraternal twins but 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 are the one in command yeah I see a lot of this on the internet um especially coming out of the dating sphere the black pill and the incel movement that William in particular studies um you know behavioral genetics to me was just what it was the second most fascinating thing that I learned about after evolutionary psychology uh and I adored looking at this not necessarily a conflict but this tension between uh my predisposition and and the outcomes that I got what I had the wrong 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 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 yeah no that's that's really not the case I mean maybe you're doomed to have brown eyes or hazel eyes and but even then you can get colored lenses if you really want to 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 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 going to 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 how do you conceptualize 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 the way that we sort of see ourselves and our efforts well as exactly what I just said that you can alter environments and affect genetic expression I give examples of things like that you know I'll tell you the people who I find the most intelligent about this are the parents of fraternal twins and siblings they know more about human behavior and have a more reasonable view of 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 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 they're learning about themselves that their behaviors are not just coming out of nowhere but they coming at us somewhere and it's it's a great education it's just a great education for them how much let me just mention I I also 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 and um these are the twins who are in the mangle experiments in Ash with 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 um thinking about the uh parenting side of this how much can rearing change a child well 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 really pained me when when parents when mothers were still pregnant or enrolling their children in these prenatal programs of Education I mean it's ridiculous I think that 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 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 yeah Jeffrey Miller once tweeted that um every parenting book combined is less useful than one book on behavioral genetics for parents to read I think it's very well put I would agree with that yeah it's it's just 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 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 don't I don't think that they um change themselves massively when I was born obviously all children will change parents it's a massive life life switch but yeah it's uh I love the idea of helping a child to find out what is their passion what is their calling what it is 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 you know the classic story of the father that didn't get picked for the football team so you know my son he's going to be the football player and he's two years old throwing a football at Christmas and stuff um that prescriptive role in some regards is good because it creates guidelines that children can follow but if you're continually having to reforce your child to do that because all you want to do is play music or Draw or whatever you're fighting a losing battle yeah yes you are and that's why I think that parents of fraternal twins and near and age siblings are the ones that really understand human development these fraternal twins can be extremely different my sister Knight went in 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 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 only take the time to look um that's a lovely insight and I think when I first spoke to Plowman 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 feel yes I think that parents who are less well informed about what parenting is 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 yeah I know no uh poems about saying that yeah I think so too um and and there is 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 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 and you can do things to improve that you can make the quality of their life better but if you're you know tiger momming your way to hope that you can create 140 IQ child you're going to be disappointed 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 can 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 to which the child was 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 had they get different swedes of genetics and they they're in environments and generations where things can be vastly different 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 parents that grew up without the internet children so for me I was 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 is a different universe so yeah you know even if you have even if you were one to one with your parents in terms of your genetics look at how different all of the different inputs are that you've got the the opportunities that you have that influences uh the the chance to actually display this behavior in a completely different way yeah the differences are extraordinary and 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 you know what it makes me think about I have a friend Johnny that comes on the show quite regularly and someone asked a question four or five years ago on the show and they said um if you could go to dinner with um four people alive or dead who would it be and you know you've got the the typical idea of thinking about it would be Mohammed Ali and would it be Socrates and would it be Plato and would it be Jesus and Johnny's answer was that he would love to sit down with all four of his great grandfathers because he thinks that he would learn an awful lot more about himself from sitting down with them than he would yes and this is a benefit that the internet has given us that we can track our families in many ways that other people never could and there's a real interest in that now too I regret the fact that I didn't ask my grandfather more questions about his coming over from Russia I think I would have learned a lot but still there's ways of tracking thing things and um and many twins have found each other because of the internet when I was in Minnesota we thought that we had exhausted every pair of weird apart twins in in English-speaking countries and that was so wrong it was so wrong so many have met on the Internet by posting a video not even knowing they were a twin just I I studied a pair of twins born in South Korea and one was raised in New Jersey and one was raised in a very Posh French suburb and the one from from New Jersey moved to LA was an aspiring actress put a video of herself online a friend of the other twin sought and said you look remarkably similar and that's what led to their reunion it's absolutely amazing and you know this gets back again to something we talked about a little earlier I think the idea of finding someone that looks so much like you or is so much like you now there are websites for finding people who look like you these unrelated look-alikes and not only that there are websites for finding a piece of art sculpture a painting a drawing in a museum that looks like you and we don't go looking for something that looks different than us children's imaginations of friends were always for someone similar and I think that's all such fascinating and very revealing information about human nature people who see identical twins are fascinated and I think the reason they're fascinated is because we all learn to expect individual differences in behavior and appearance and so we when we encounter identical twins to look so different it challenges our beliefs in the way that the world works and it fascinates most of us but it can still turn off some people who are nevertheless intrigued some people may say it's too much closeness too much similarity takes away from individuality but everybody is intrigued nevertheless and I think that's why whenever anything happens to identical twins it's in the news I mean it's in the news all the time and I you know I get these cases and I get context from journals all the time that want commentaries on unusual cases and in fact right now I'm working with the Guinness World Records book on compiling the update instead of twin records which is a lot of fun did you say that you've studied or managed to try and track down every pair of identical twins in the English-speaking world Minnesota study concluded we thought that we had had every pair right Indians being wrong it was a very naive conclusion because there were so many out there there were so many people who don't know their Twins and there were people who didn't have the means to find out if they suspected but now they do and there are people out there fraternal twins who will never find out because they don't have the advantage of mistaken identity so many twins meet I wouldn't say many but a number meet because of mistaken identity somebody confuses one for the other you know and then that's how it all comes about but fraternal twins don't have that advantage and so when I think back to that Louise wise adoption study of twin separated birth virtually all those identicals met through mistaken identity and the fraternals did not and I wonder were other fraternal twins out there who were separated and will never ever know and I think that's a shame 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 I'm doing a study on that but keep going 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 white mother black father and then mixed race child but you know the 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 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 two eggs that get released and two sperm that go at the same time yeah but if you had that but those were interracial that there was you had a white and a black okay 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 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 a dumb one when in fact it was just the other way around and so there have been many more mixed-raised 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 of the kid that looks more like you racially than the other one and that's a very hard concept to get across I mean you can't say who Do You Love More you can't say that but I wonder if I can somehow tease that out and maybe a less direct way because it's an interesting question and I also wonder if there is less paternity uncertainty in mixed-aged couples there might well be I don't think anyone's ever looked at that but that's something I can I can 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 because they have the same parents okay I understand that um what are the common criticisms that you encounter around twin studies whether it be methodology conclusions pushback that sort of stuff what's most common 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've 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 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 rear to Park which is the Minnesota study I reprint from one of our papers a graph showing the IQ correlation from four or five different read apart twin studies one in England one in Denmark one in the US One in Sweden different populations different time points different protocols and they all Converge on the same basic conclusion about 0.75 is the genetic effect and you it's rare to get that kind of repetition replication I should say in the behavioral sciences it's a very robust finding yeah I was going to say you know 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 a behavioral genetics and evolutionary psychology because both of those 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 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 while there was some little variation against my studies it was basically very remarkable that genetic relatedness was more aligned with higher levels of grief so if you look in that literature you still see the stuff it's just the interpretation and the theoretical layering is so different what was the uh justification for it what was their interpretation of that effect um you know it really wasn't interpretation it was a sociological study it was mainly to see what if what is out there they really didn't have an interpretation it was basically what if but the what if aligns with behavior genetic and evolution and psychological interpretations damn right it does which is why we're interested in it Nancy you mentioned there just you said about um the study that you've done is your study one of the biggest or the biggest in terms of twins or is that Robert bloman's study that he did in the UK yeah Minnesota study yes 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 the director who actually launched that now keep in mind that was a weirdo part study so we ended up with 137 pairs yep for more identicals and fraternals Plowman study is twins raised together and he has thousands of pairs so definitely going to have more yeah I think it was every every set of twins born in the UK between like 1991 and 1994 or something right it's something like that it's something like that and and those kinds of data sets are remarkable but I will tell you honestly Chris that there's nothing I like more than being in the 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 new takes on human development did you watch the Netflix documentary tell me who I am no I didn't Nancy you must watch this I'm writing it down now you must watch it for the people that haven't seen it it is I I wonder is this the one I think it's some of the identical twin men and they had a secret is this the one yeah they have a secret they one of the guys loses his memory and then he has to be right I did see it I did see it yes and it's remarkable I I didn't know that I couldn't remember that was the title but yes I do see that it's remarkable yeah for the people I won't spoil it um but for the people who are interested in this uh three identical strangers absolutely fantastic film um uh born together read apart your book uh awesome awesome breakdown of this and then that uh that tell me who I am is harrowing and you see you see 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 yeah on this tell me who I am you see these guys reveal this lifelong secret to each other yeah on set and it's the first time it's ever happened it is yeah it was remarkable it was crazy 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 Laurie Shinseki an independent filmmaker they 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 was remarkable because the identicals were so coordinated at young age fraternals were so different it was amazing it's a beautiful film and I wish more people would do film it's this is something that came up with 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 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 text just can't Nancy Siegel ladies and gentlemen 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 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 yeah so I have a website with all my twin books and one of my related material and that is Doctor Dr Nancy Siegel so d-r-n-a-n-c-y-s-e-g-a-l-twins.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 captured the world they might want to 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 um but but if you're really really new to twin studies you might want to check my 1999 book called entwined lies 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 an expert witness on on legal cases wrongful death injury custody all kinds of things like that 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 it yeah very cool Nancy I appreciate the heck out of you thank you very much for joining me today thank you Chris I'm glad I accosted you 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