Welcome back. So today what we're going to do is we're going to talk about although this, this week we're really focusing on twin studies what we're going to talk today about is adoption studies. And the, the importance here is that, that inferences behavioral geneticists make about the influence of genetic factor don't ride on twin studies alone. There're other des, research designs that provide the same type of conclusions, and so it's important that we look at those. And, certainly, the most important other research design in behavioral genetics is an adoption study. And I'd actually like to begin with, with an anecdote. Actually a rather high percentage of the population is adopted. In the US and I'm sure this varies from country to country, but in the US roughly 2% of the population is adopted. And maybe some of you know that this very famous man who sadly passed away a few years ago, Steven Jobs was an adopted individual. he, his birth parents his birth father received a PhD from the University of Wisconsin in Political Science, and his birth mother, I believe had a Masters Degree in Speech Therapy, she was a speech therapist. And, they became pregnant with Steven Jobs, when they were students at the University of Wisconsin, they couldn't support raising him, so they placed him for adoption. And he was actually adopted by a working-class family. I believe it was Sunnyvale, Sunnyvale, California. Somewhere in California. His adoptive father was a machinist and his mother was a bookkeeper. His mother, actually, his adoptive mother never completed high school. It turned out that remarkably, and of course this man has a real remarkable life, but remarkably Steven Jobs parent, his birth parents, ultimately got married after they graduated schools and they had another child. And later in Steven Jobs' life, he came to know his biological sisters, full biological sisters. Her name is Mona Simpson, and she was actually quite success, or she is quite successful. She's a, a well known novelist, professor of English at the University of California Los Angeles. And Steven Jobs was so impressed with finding his long lost sister that he completely changed the way he thought about nature and nurture, and the quote here reflects that. Before he met Mona, that's his, his biological sister, he really thought that nurture was the pow, the most powerful force in shaping our psychology. After he met his very successful and creative sister, he actually recognized that genetics must also be part of the puzzle here. Adoption studies are in a sense, so easy to understand. They're much easier to understand than twin studies. They've been used in a lot of different ways, but I'm going to focus just on two of them here today. The first is to look at the similarity of what I'll call adopted siblings. These are individuals who were placed in adoptive homes, two individuals placed in adoptive homes that aren't genetically related to one another but are reared in the same home. And we can ask, well If they're rid in the same home but not genetically related to one another, to what extent are they psychologically similar? And then secondly I'm going to talk about parent-offspring adoption design. So I'll come to that secondly. Let's first talk about the adopted-sibling design. And a way of thinking about this is, it's a real extension of what we talked about when I introduced monozygotic and dizygotic twin. The natural experiment. And I said that if genetics were important, then monozygotic twins should be more similar than dizygotic twins. Because they share 100% of their, genome, and they only share on, on average 50%. If the rearing environment were important, they'd be approximately similar in their similarity. Now we can add in this new group, adopted siblings, who share none of their genetics, but share their rearing environment and it provides us another way of trying to confirm the inferences we're making here. If genetics is important, then, right, these should both be more similar than these ones who don't share their genotypes. If the rearing environment is important, then they should all be roughly equally similar. So adopted siblings provide us a way of trying to confirm outside the twin study design, itself, the inferences we're making in a twin study. And if you remember when we, I, first introduced this we looked at some data that I collected on height. And these are the correlations for height and Monozygotic and Dizygotic twins I gave you earlier. Well it turns out that here at Minnesota we've also been collecting a, a, sample of about 400 pairs of adopted siblings. Again, these are not genetically related individuals, but growing up in the same home. Well, you see that their correlation, it's not a zero correlation. There's some similarity in their height. But it's much less than both the dizygotic and monozygotic twins. Genetics seems, it seems to confirm what is not surprising here. That height, for height Genetics is important. What about looking at a psychological trait, like IQ? Well, again, I gave you this data before monozygotic twins. And again, we're going to come back to IQ. We're going to spend a whole week talking about behavioral genetic research in IQ. But this just to illustrate the extension of the design here. Monozygotic twins are more similar then dizygotic twins. We'd like to from that draw the inference that, that's because of genetic factors. Having the reared together adopted siblings here provides some confirmation of that. Again they're reared together just like these individuals are reared together but they're nowhere near as similar as these. They don't share a genotype. Genetics appear to be important. The rearing environment also somewhat important. There is some correlation here. And that's a point that, believe me, that we'll come back to quite a bit in this course. Other psychological traits, personality, we won't have the opportunity to talk a lot about personality in the course. But this is Again, correlations for personality characteristics. And data that we've collected here in Minnesota. Three broad personality characteristics. Positive motionality, negative motionality constraint. The correlations for monozygotic and dizygotic twins. That very familiar pattern of monozygotic twins being more similar than dizygotic twins. But where do the adopted siblings. Fall in. Well, their correlations are given in the green bar here. And you can see that there's actually very little similarity in individuals who grew up in the same home. These are individuals who were adopted in infancy, who grew up together, but have very little similarity in their personalities. Another way of thinking about it is that two individuals growing up in the same home, positive emotionality really taps into the degree to which you're happy or outgoing or extroverted. Two individuals growing up in the same home have virtually no similarity in the degree to which they're happy. Or are their outgoing unless they're genetically similar. That's pretty remarkable finding. I don't want to leave you with the notion that adopted siblings growing up in the same home have no psychological similarity at all, they do have some and that's very important. Here are some other traits that we've explored and again we're going to come back to IQ. Here are the correlations for IQ for how much. These are adolescents adopted siblings. How much they're using substances. Two different types of ex psychopathology acting out in inward-turning psychopathology. And what you see is across the board. There is some similarity. The correlation is not zero for each of these traits. It may not be as high as biological siblings or twins. But there is some similarity in certain psychological domains, for individuals who are not genetically similar, but grow up together. Something about their rearing home is shaping some similarity in a trait like IQ, a trait that will be very important for us later. That's the first design. Lets look at the second, parent-offspring resemblance, and here, I think, is where the adoption design is so easy to understand. When we look at intact nuclear families, then the resemblance between the biological parents and, or the parents in those families and the offspring they rear, could reflect genetic mechanisms of transmission, but also their shared environment. And just observing for example that high IQ parents are more likely to have high IQ offspring than non high IQ parents. We don't know if that's genetic or environmental because they share both of those or potentially share both of those mechanisms. But in an adoption study, in principle, we have separated the two. There's a set of birth parents, like in the case of Steven Jobs, his PhD. father and his Master's Degree mother, and there's his rearing parents, the working class family. We can ask, is there any similarity with His birth parent. That would reflect genetic methan, mechanisms of similarity versus similarity with his adoptive parents, which would reflect environmental mechanisms of similarity. Again, because I'm just trying to intro, introduce the alternative methods or designs here, I'm just going to talk about one study. But it's, I think, illustrative, not only the power Of the adoption study method but also the types of results that behavioral geneticists have been finding. This study, again, comes out of Sweden, takes advantage of the registry system in Sweden. It's done by Ken Kendler again and his colleagues in Sweden. In this case, the, the phenotype is drug abuse. They can go into the registry system, the public health system there and identify people who have a diag, diagnosis of drug abuse. They can also identify individuals who are adopted through that registry system. They found, remarkably, 18,000 adopted individuals. And they were able to track both their birth and the adoptive parents, who are also identified in the Swedish registry system, pretty remarkable system that they have there. They do this all confidentially of course, so we can ask them, we, we have these adopted individuals, or they did They don't actually see them, there are doing this all using the information in the registries but we can ask do these adopted individuals that they have drug abuse is that similar to their birth parents or their adoptive parents. We'll let's first look at their birth parents. So, this is the rate at which The offspring had a diagnosis of drug abuse if their birth parent had a drug abuse diagnosis versus they didn't. So these are adopted individuals, these birth parents didn't rear them so the only mechanism really that makes sense here is that some sort of genetic mechanism is going on. So the difference here reflects some sort of genetic factor in the parent offspring resemblance. Birth parents with drug abuse are more likely to have a child with drug abuse, even though they didn't rear them, than birth parents who didn't, who weren't registered for drug abuse. There's some genetic mechanism. But what about the adoptive parents? If you have a diagnosis of drug abuse in an adopted parent, does that increase the chance that their non-genetically related child would also have a diagnosis of drug abuse? The answer to that is also yes. The effect is not as big as the. Genetic effect. But the effect is still there. And given the sample sizes, a very large effect. The rate of drug abuse, if you had an adoptive parent with drug abuse was 6.8%. If you, your adoptive parent didn't have drug abuse, it was 4.5%. So, there's an increase risk of drug abuse If you have an adoptive parent with drug abuse, an environmental mechanism, as well as a birth parent with drug abuse, a genetic drug abuse. One of the real beauties of adoption studies is that it begins to tell us, not only about the genetics, but the environments that are important. And in this case, what you're seeing is that both the genetics and environment are important risk for drug abuse in offspring. We'll talk about adoption studies later when we get into IQ and into schizophrenia. In general, if you look at adoption studies, I'll just give you a very general conclusion. Adapted individuals bear some psychological similaraties to the birth parents that did not rear them. They also in some, but not all domains bear some psychological similarity to their adopted parent. Here we're seeing it for drug abuse. Later we'll see it for IQ, we will not see it for schizophrenia, for sometime, in some cases, we don't get that environmental transmission, in drug abuse we certainly do. Next time we'll look at really what is a combination of the two study designs we've talked about. Twin studies and adoption studies.
