Welcome back to this fourth module in week six. And in this module, what I want to do is kind of build on the biometric of behavioural observation of what appear to be the major contributors to individual differences in general cognitive ability, or intelligence. That is, previously this week, we talked about first of all that genetic factors appear to account for about 50% of the variance in general cognitive ability. 50% of individual differences in general cognitive ability appear to be associated with genetic factors. That's the heritability. Shared environmental factors account for roughly 35% of the variance. And non-shared environmental factors the balance, or 15% of the variance. Right. The three were going to add up to 100%. Now, it would, I think, be unsatisfying to just stop there. That's a description but it doesn't tell us really, what's going on? What is the under, what are the underlying factors that are contributing to this variance? Can we characterize them? What I'd like to do today in this module, is to begin to talk a little bit about how behavior genetic research aims to try further characterize the nature if these effects. To go beyond just estimating how important they are to try to understand what they are. The first thing I'm going to talk about is actually the, the last one here, the non-shared environment. And in the case of general cognitive ability, there probably isn't much to really be said about, the non-shared environmental component. The non-shared environmental component accounts for 15% of individual differences in general cognitive ability. If you go back to Week three, one of the things I told you is that necessarily in these bio-metrical analysis of twin data, for example, measurement error is included in the estimate of the non-shared environmental component. What is measurement error? When psychologists measure a trait or phenotype, they don't measure it perfectly. That is, if you measure something today and you come back two weeks from now, you won't necessarily get the same score. So if I gave you an IQ test today, and I gave you an IQ test two weeks from now. Maybe today you're a little bit sleepy. You didn't a lot, you're, you're a little bit tired. You didn't get a lot of sleep last night. Or maybe you're distracted because of stress in your home. And so when you come back two weeks later, you're in a better state, and you do better. The difference between those two administrations are just measurement error. They don't really reflect anything about your true level of general cognitive ability. We know from psychometric studies that about 10% of individual differences or variants in general cognitive ability is really just measurement error. And if 10% is measurement error and 15% is non-shared environment and that 15% includes measurement error, there really isn't a lot left there to be explained, only 5%. So, in the case of general cognitive ability there's not a lot of behavioural genetic research aimed at looking at this particular component. There are for other traits. In fact, previously last week we talked about the non-shared environment being very important for schizophrenia. And we'll come back to the non-shared environment. But at least for general cognitive ability it doesn't seem to be a very important component because most of it seems to be measurement error. The shared environment there's something very distinctive about it general cognitive ability or intelligence. The shared environment, which is the environment individuals share by virtue of growing up in, in the same home. That appears to be very important. Accounting for, 35% are roughly a third of individual differences in general cognitive ability. What about that shared family environment is accounting for or contributing this 35% of the variance? In fact, adoption studies are very well suited to answer that question. What about families contribute to individual differences in general cognitive ability. And the reason adoption studies are so good at this, is because in adoption's studies we don't have to worry about genetic similarity. Adoptive relatives are not genetically related. They're environmentally related. So, studying adoptive families is actually a way to focus in on these important environmental effects. And there are whole areas of behavioural genetics just focusing on studying adoptive families for this reason. So I'm going to talk about three important adoption studies in this regard. And the first one is going to show that on average, and I'll explain why this is important, on average, adopted children seem to do better in general cognitive ability than non, than their non adopted siblings. For some psychologists, they look at adoption as a quasi-intervention. Not a true intervention, right? No one's doing an experiment here. But it's kind of a quasi-intervention. That is in many cases, certainly not in all cases, but in many cases an adopted child, a child who is adopted, moves from a less advantaged home or situation or varying circumstance, to more advantage circumstance. And we might think about moving from a less advantaged to a more advantaged circumstantial as a quasi-intervention. As something that might benefit their psychological functioning. In this, in the, essentially meta-analysis of the relevant literature a, a well-known developmental psychologist, called Van, Ijzendoorm. I hope we, pronounced his name correctly. Van Ijzendoorm, who's a, a Dutch psychologist. Actually, collected all the relevant data. Where, he compared adopted individuals who had been placed in adopted homes, to their siblings, their biological siblings who did not undergo that transition. They stayed with the birth family. Again, in every case, it isn't the case that moving from a birth family to an adoptive family, is moving from disadvantage to advantage. But in some, and maybe many cases, it is a transition that is in some ways advantageous. Is that transition also associated with better performance and general cognitive ability? What's depicted here is my recreation of the results we poured into this paper. Here's general cognibility. In fact, they talk about IQ here. In the blue bar here, is the difference between the ado-, the individuals, the children who actually made that transition. They were placed in the adopted home. Compared to the performance in general cognibility to their, probably, either half siblings or full siblings, that didn't, weren't placed for adoption, but rather, stayed in the birth home. Here the metric is on a standard deviation difference. So on average, those siblings who were adopted Scored about one standard deviation better or higher on average than their sibling, who didn't get adopted. Stayed in the birth home. That's quite an, quite an increase in their general cognitive ability. For school achievement, the difference is about a half a standard deviation. Those are fairly large benefits in general cognibility associative from, going from maybe a somewhat disadvantage environment to an advantage environment. And the red bars would then Ijzerdoorn and his colleagues are reporting is the difference between that adopted individuals, in this case IQ, and the IQs of the siblings that he or she was reared in. And you can see they score a little bit lower, but not really significantly lower. The, the, the major result in this study is that individuals that are adopted are doing better, and actually quite a bit better, than individuals who didn't get adopted. And that's an environmental effect. The next classic study in this area, actually tries to ask, what about these adoptive homes seems to underlie that boost in IQ or general cognitive ability. And, what adoption research indicates is that it has to do with the socio-economic advantages of those adoptive homes. This is a study that actually came out of France. And, again, I apologize if I mispronounce the researcher's name Duyme et al, and what Duyme et al did is actually a very interesting study. What they did is they took a sample of individuals who were actually were removed from their birth homes because of neglect and maybe abuse. Most, in most cases, because of neglect. And before they were removed from the birth homes, at about an average age of four, they were given an IQ test. And on average they scored about 78 points on the IQ test. But they were removed from the homes and actually placed in an adoptive home and legally adopted by another family. And so the researchers came, actually 10 years later. That's the red bars here and remeasured their IQs and you can see these are the same kids before they were placed in the adoptive homes, afterwards. And you can see that, on average, their IQs increased about 14 IQ points. That's very consistent with the previous study by the Dutch researchers that I gave you before. Being placed in these adoptive homes is associated with better performance in general cognitive ability. The second thing though they did in this study, which really made it, I think a very important contribution, is ask what about these adoptive homes, underlie this increase 14 point increase. And what they focused in on was the socio-economic advantage of the home. They classified the adoptive homes as either working class families. Middle class families or professional families. These were the IQ's of the adopted children when placed in these adoptive homes. And the point here, the blue bars here, is that really there was no relationship. When they moved into these homes, on average, the IQ's are about the same. And they're all about 77 to 78. The question is what do they look like, what do their IQs look like ten years later. That's the red bars here. And what you see is that in every case, the adopted child is doing better than he or she was doing before they were placed in the adoptive home. So in every case, there's some advantage to their cognitive functioning, but clearly, the advantage is musk greater. In a, in a, socially economically advantaged home, then in one that has less economic and socio class advantages. The difference here is 20 points verses less than ten points down here. There are all benefits, but greater benefits here. What appears to be the basis for the increase here, is the socio-cultural advantages that it, that on average adoptive families have. The last study I want to talk about here is sometimes the study by Duyme or the previous study by Van Ijzendoorn, is used to argue well there are these potent environmental effects that are coming out of adoption studies. That's definitely true. Given the potent environmental effects, maybe genetics doesn't matter. That isn't true. Genetics still does matter. And I want to show this with yet another adoption study. So even though it's kind of the converse of what we talked about in the, in the last module. Even thought there's malleability, that doesn't mean that there isn't in-heritability going on. This is another French study, actually again by Duyme and a colleague of his, Capron. And what they did in this case is they looked at children who were placed in adoptive homes that were either working class or professional class. Professional class homes have greater economic resources, greater educational resources. This is again a French study. So the red bar is being higher than the blue bars would indicate an effect in that rearing environment. And you can see in both cases the red bars are greater than the blue bars. But the reason this is kind of an interesting study is that they also classified the social class back ground of the birth parents as either working class. Are professional class. And what you see is, not only is there an environmental effect, the red bars versus the blue bars. But there's also a birth background effect. A genetic effect. The performance here, when you're coming from a birth background of professional class, is on average higher than the corresponding bars here. So both the environment and the genetic background is important. Just because something is malleable, also does not mean that it's not heritable. In this module the last thing I want to touch on is saying something about, what can we say about the genetic factors, underlying genetic cognitive ability that account for 50% of the variants? I'm going to actually talk a little about this here but then pick up on it again in the second module. But, there's some interesting recent studies about this that I think are very important and kind of fit in with this module. The first is that the heritability of general cognitive ability, is actually varies as a function of the socio-economic status of the home. It's much higher in advantage homes, socially, culturally advantaged homes than it is in homes that aren't socially, culturally advantaged. And this was first shown by a psychologist named Eric Turkheimer who's at the University of Virginia in Charlottesville. And he actually, we don't have to get into the methodology of exactly what he did, but he actually used twin data to show this. And what he did here, and I'm going to focus here on, he actually shows both additive genetic, shared environmental and non-shared environmental effects in his analysis but in this case I want to focus primarily here, in this particular panel. The Additive genetic effect. What he's plotting here is, first of all, he arrayed the families. He measured their socio-economic status, their SES. Things about how much income did they have, how educated were the parents in the home. And he just scaled that from 0 to 100 in the various families. And then he actually, in the various families, estimated the heritability of general cognitive ability. And then he plots here these are the confidence bands in gray. But he plots here the estimated heritability as a function of socio-economic status of the home. And what you see is there's a sharp increase. General cognitive ability is not particularly heritable in socially, culturally disadvantaged homes. It is very irritable in socially advantaged homes. Why might that be? What Turkheimer and his colleagues hypothesized is that what socially, culturally advantaged homes is, one of the aspects of being advantaged is they can create for their children opportunities, maybe because they just have more income that other families can't easily create. And those opportunities allow those children to fully realize their genetic potential. These children down here, are not fully realizing their genetic potential. These children are, and they are realizing their genetic potential because the opportunities, those advantaged homes are able to create for them. It would be nice, it's kind of a very intriguing and important finding, can we show it in other ways? Well there is other ways that this has been shown, and I'm going to just highlight one of these. I think it's kind of a clever way. This is actually done from a, a, bio, a psychologist names Jeanette Taylor. Who's at Florida State University in, in Tallahassee. And in her case, she's not actually looking at general cognitive ability, she's looking at reading achievement. But it's kind of a an elegant study. And again, she's looking at the heritability, the contribution of shared environmental effects and the contribution of non-shared environmental effects to individual differences in reading achievement. In this case, we're talking about children who are in first and second grade, when they're just starting to learn to read. She has a measure of how effective their teachers are. These are twins in various classrooms throughout Florida. And she was actually able to measure teacher quality. We don't need to get into that. But it's actually a very good measure of teacher quality. Teachers up here are very high quality teachers, very effective in teaching reading. Teachers down here are less effective in teaching reading to their students. Again, I'm going to focus on the graph for the genetic. Note how the genetic effect increases with teacher effectiveness. Genetic factors are more important when teachers are effective than when they're ineffective. It's the same phenomena that Turkheimer observed. What effective teachers are doing, they're creating opportunities, or at least this is the interpretation Taylor gives to her study. They're creating opportunities for their students to fully realize their genetic potential. That's why the heritability is higher here. What ineffective or relatively ineffective teachers are, are they limiting the opportunities to fully realize the genetic potential of their students. Thus, the heritability is less high in these particular range. So, general cognitive ability is heritable. But, then heritability, as we talked about in the third module, or I'm sorry the third unit of this course is not a fixed constant. And in fact varies in interesting and important ways in term, in relation to the genetic, I'm sorry, the social class background of the home. Next time we'll explore further aspects of the genetics bases of general cognibility by trying to see if whether or not we can identify the generic factors that contribute to that. [SOUND] [BLANK_AUDIO]
