Welcome back. This is the last module of the second unit. In which we talk about really, alternative research designs that the traditional research designs that behavioral geneticists have used. I've introduced twin studies. And last time, adoption studies. And today, I'm going to talk about the combination of, of the two. Twins who are adopted. Or what are called, Reared Apart Twins. This is a very rare type of study. There may be four or five, maybe six such studies ever really reported in the literature. And as it happens, one of these has been done here at the University of Minnesota. And I think, although, of course, I'm going to be a little bit biased. I think, arguably, this study, which is called the Minnesota Study of Twins Reared Apart or the acronym MISTRA. MISTRA is arguably probably the most visible behavioral genetic study. It's been reported in the popular press, quite a bit over the years. And actually helped make the University of Minnesota, at least the behavioral genetic research program here, kind of put us on the map. So again reflecting a little bit on the history to, to lead up to the study here. In about the 1960s, psychologists came back to start doing twin studies again. And in the 60s and the 70s, we're re, reporting their results. And they're reporting that pattern that I mentioned to you earlier. A very consistent pattern that monozygotic twins were more similar than dizygotic twins. And there was actually, the, the, that initial literature as it came out, was met with a bit of skepticism by the psychological field. These twins were all reared together. And the belief was that perhaps that consistent pattern really reflected some sort of environmental bias. That the, the assumption we talked about earlier, the equal environmental similarity assumption, was not being met. And a real illustration of this skepticism is captured by this I think beautiful quote by Walter Mischel. Walter Mischel is certainly one of the most famous personality psychologists of the 20th century. And he wrote a very influential introduction to personality textbook. And roundabout 1981 he stated in that text book and after considering the studies of reared together twins is well. Think of what would happen if we actually had twins that weren't reared together, but are actually reared in separate homes. Imagine how different they would actually end up being. Well, what Mischel didn't realize, is that actually two years prior to his publication of the book and this quote. Such a study had begun at the University of Minnesota by this man, Tom Bouchard. And this study ran for 20 years. And it began in 1979. It, it actually began by what really, I think, is mostly just a chance event. That really reshaped certainly his career and, and maybe also, to some degree, the field of behavioral genetics. In February of 1979, a graduate student here at the University of Minnesota, read a short article in our local newspaper about a pair of twins from Lema, Ohio. Who had been separated at the time of birth, reared separately. And then reunited at the age of 39. One of the remarkable thing about the twins is they both, when they had been adopted, their adopted parents, had both called them or named them Jim. So they came to be known as the Jim twins. Jim Lewis and Jim Springer. When they reunited at age 39, there were remarkable concordances in their biographies. They both smoked the same type of cigarettes, I think they were Salems. They both vacationed with their family on the same stretch of beach in Florida. They both had married wives with the same name. Divorced that wife and then married a second wife that both had the same name, which is a little bit spooky if you ask me. They both had the same hobbies, they both suffered from tension headaches. And it, it was really remarkable that these two men had all these similarities. If it were just the coincidences in their biography, probably MISTRA, we wouldn't be talking about it today. But what Bouchard and his colleagues did is actually systematically study not only the Jim twins. But almost 140 similar types of twins. Twins who were separated at or about the time of birth, and then reunited in adulthood. And asked the question, these individuals who really didn't know about for the most part, didn't know the other existed. When they were reunited, like the Jim twins. They were brought in really pretty closely after the time they were reunited at age 39. To what extent were they psychologically similar? And if they were psychologically similar, it really probably had to be their genetics that was the basis for that. Because they, they were reared in separate homes. This study is identified as one of the 40 studies by the psychologist Roger Huck in his book, One of the 40 Most Important Studies in Psychology. And I, I really can't argue with that conclusion. If you look at the, the twins and there's a, a, a book out now. And we'll put it on the web page if you're interested in reading about the study more. A, a book that talks a lot about MISTRA. Not only its scientific findings, but also just how it came, how it came to be. And what some of the more interesting twin pairs were like. But as Bouchard started collecting these pairs of twins. Other twins, in addition to the Jim twins, had really remarkable coincidences in their background. There were the firefighter twins who were reunited in their 30s and they're both volunteer firefighters who like John Wayne movies. There were twins that both wore seven rings on seven fingers. But Bouchard's conclusions weren't based just on these anecdotes that he was collecting. He, he, what he would do is he brought the twins here to the University of Minnesota for a full week of very rigorous psychological examinations, as well as medical examinations. And the first really major, I think, empirical publication for MISTRA, came out in 1988. And kind of indirectly addressed Mischel's challenge. What would reared apart twins look like? In this case they were looking at personality characteristics. So what's reported here are the correlations. And again recall zero is a lack of similarity. The perfect similarity would be one. And negative would be that they're, they're actually dissimilar. For reared apart monozygotic twins, which are labeled here MZA, and reared apart dizygotic twins. This is an early publication from the, the study, ultimately they studied about 140 twins. But in this case, they had about 70 pairs. These are the correlations. You, we see really virtually the same pattern that we saw with reared together twins. Monozygotic twins, even though reared apart, were consistently more similar in their personality, than dizygotic twins. And again these are the three broad dimensions of personality. So as we looked at personality characteristics, we saw the same pattern with the reared apart twins, or at least Bouchard did, and his colleagues. The same pattern with reared apart twins as we were seeing with reared together twins. But that doesn't quite answer what Mischel was asking. We, the, what Mischel was particularly interested in, we might see that same pattern. But it might be that the reared apart twins are not anywhere near as psychologically similar as the reared together twins. Probably the major publication to come out of MISTRA, was published in 1990 in the Journal of Science. And actually, I'm going to ask you to read this article. It, it'll be on our course webpage. It's an important publication for the field. And I'm, I'm actually just taking data right out of the article that I'm going to ask you to read. And what I'm reporting here does get directly at what Mischel was asking. And that is, are when the twins are separated and reared in different homes, are they remarkably less similar, than if they're reared together? And in this case I'm only going to report, which the, actually the article only reports, for the monozygotic twins. So in this case the blue correlations, are for monozygotic twins, a different sample of monozygotic twins, who were actually reared together. The red correlations are from monozygotic twins who are reared apart. And they're actually more data than this in the article that you'll read hopefully. But here, I've picked out I guess seven of these. Some are physical characteristics like weight and, and blood pressure. Others are psychological characteristics like personality and IQ. And, the point here, is that, well, Mischel is, was probably for the most part not, not correct in, in what he was expecting to see. As you see, the red bars really are not that much less than the blue bars. Growing up in different homes didn't lead them to be less psychologically similar. Now there's one major exception here. And I do want to highlight that, because we're going to come back to that. And that is IQ. For IQ, although there's still quite a lot of similarity for the reared-apart twins. They're not as similar as reared together twins. And that's an important observation when we come to IQ. Because that means that our home environments are, in part, shaping our IQs. That's why these twins are more similar than those twins. But despite what psychologists in the 80s would have expected. What MISTRA and actually, other studies of reared part twins showed. Is that for the most part, reared apart twins aren't all that less similar than reared together twins. There are some cases where they are less similar. But in, across a broad array of traits, they don't appear to be much less similar. Why has this study been so influential? Well, I think really three general findings will come out of came out of the MISTRA study. First, twins are similar even when they're separately reared. That strengthens the case for genetic influences. We've looked at twin studies, reared together twin studies, comparing monozygotic and dizygotic twin similarity. And we've seen that very consistent pattern. But now we're seeing a different pattern that's also consistent with genetics being important. That even when reared in separate homes, twins have some similarity. So, a way of confirming observations we're making, using different study designs. A second general finding that came out of MISTRA is that for many, not all, but for many of the traits that were studied, the reared apart twins were not a lot less similar than the reared together twins. That really, actually might be the most remarkable finding from the study. It implies that the environments we share, by virtue of growing up in a home with our siblings or our twins, may not be that influential. The third thing is the thing that I want to emphasize throughout the course. Is that, and, and we see it with reared together twins as well, is that reared apart twins are neverly, never psychologically identical. And that lack of psychological identity, because they have the same genotype, has to be due to their environment. So, these three general findings that the MISTRA study so nicely illustrates. Has really been the reason I think that it's been a highlighted study for the field. And as it turns out, those three general findings will map onto something that we're going to come to in a little bit later. We're going to start dealing with this next week in this course. The first finding that genetics is important corresponds to an influence of what geneticists call additive genetic factor, or A. The second factor that may be growing up in the same home, might not be that important. Is what behavioral geneticists will talk about as the influence, or maybe the lack of influence, of the shared environment. What we'll end up calling C. And the final finding that monozygotic twins, whether reared together or reared apart. Are never psychologically identical. Is, underlies the importance of a third general class of factors. Which we'll call the non-shared environment. We'll come back to these next week. But I just want to highlight, that MISTRA really underscores the importance of the, the relative importance of each of these three factors, what we'll come to know as A, C and E. Well, MISTRA certainly has its critics. And I think it's important to address these critics, but actually I'm going to leave that up to you. Because they're addressed in the article that you'll read. There are two alternative hypotheses for why the reared together twins might be psychologically similar. The first is that, they may have had contact with one another. And indeed, different twin pairs had differential degrees of contact. They weren't all separated of course, right at the date that they were born. Some of them were reared together maybe for a first few months, maybe for a year. And then Bouchard didn't study them immediately after they were reunited. So some of them had contact after they're, were reunited. And some of the critics of the study have worried that, well maybe they weren't reared together but maybe they had enough contact with one another to explain their psychological similarity. That's one possibility, alternative possibility. The other is that they were placed, they were reared in separate homes. But maybe the separate homes were themselves similar. Maybe they weren't randomly placed in separate homes. And maybe the similarity of where the two twins were placed, were the reason that they're psychologically similar. The article I'm, I'm asking you to read takes up these criticism. And comes to the conclusion that although they're important to consider, they really are not an explanation for the findings that are coming out of MISTRA. This brings us to the end of Unit 2. There are three major themes I've tried to play to play out in this week. First of all, that behavioral genetics, human behavioral genetics is really an observational discipline. And an observational discipline in which we like to make strong causal inferences, is going to try to take advantage of natural experiments. Twin studies, adoption studies, reared apart twin studies, are natural experiments. That we use to try to draw conclusions about whether genetics is important, whether growing up in the same home is important. And we'll see those being applied as we get into things like schizophrenia and IQ. Secondly, and we're going to again, this is, we're going to see this, we're going to build on this when we begin to look at specific phenotype. Some general, I would argue, some general patterns of findings are beginning to emerge. MZ twins are almost always more similar than DZ twins, even when they're reared apart. And we're going to, behavioral geneticists are going to include that that's probably almost certainly due to genetic factors. Adopted individuals are similar to their birth parents psychologically. Also evidence of genetic factors. For many but not all. And that's very important, for not all traits. Reared apart twins are not much similar, than reared together twins. And adopted siblings are not that similar for many traits. The rearing family environment, may not be as important a force in shaping our psychology as we might have imagined beforehand. But again, for some traits, it will be important. And IQ will be such a trait. And finally, monozygotic twins are never perfectly similar, because they're genetically identical. If they differ, they're not differing for genetic reasons. They have to differ because of their environment. The last thing that I tried to point out in this second unit. Is the importance, and it really goes along with the first. The importance, that this is an observational field. There are no, even though MISTRA is a very important study. There're really no in, in an observational science, there's no definitive study. So what we really look for is convergence of findings, across alternative study designs, and alternative studies. And it's only really when we see that convergence of evidence, that we really feel confident in making strong inferences. We feel confident that, or at least I do, that another behavioral geneticist. We feel confident that genetic factors are important In individual differences in behavior. Not just because studies of reared together twins. But because studies of reared together twins, because of adoption studies. And because studies of reared apart twins, all seem to be telling us the same thing. There's some convergence of findings. So next week we're actually going to start really getting into genetics. [SOUND] [BLANK_AUDIO]
