 Welcome back to the last lecture this afternoon. Our next speaker, Dr. Robert Ploman, is recognized as an outstanding investigator in theorist and behavior genetics. He's been amazingly prolific in the number of articles, papers, and books he has authored, and there's universal agreement among his peers that his work has been both groundbreaking and innovative. Dr. Ploman became interested in behavior genetics while taking it as a required course when he was a graduate student in psychology at the University of Texas at Austin. He quickly realized the importance of bringing together both genetic and environmental research strategies in the study of human development in a field that had been largely dominated by environmentalism, the legacy of the American behaviorists. His position after receiving his PhD was at the Institute of Behavioral Genetics at the University of Colorado at Boulder, the only one of its kind at the time. Dr. Ploman and his colleague, John DeFries, began work on what has become known as the Colorado Adoption Project that involves tracking more than 2,400 adopted children from infancy to adulthood, a group key in determining the culture and biological influences in development. This project has been remarkably productive with over 150 publications since its inception. In 1986, Dr. Ploman moved to Penn State where he and Gerald McLaren launched a study of elderly twins reared apart and twins reared together and developed mouse models to identify genes in complex behavioral systems. In 1994, he moved to the Institute of Psychiatry in London where he and Professor Sir Michael Rutter set up the Social Genetic and Developmental Psychiatry Research Center where he is currently Deputy Director and undertaking new research that involves the study of all twins born in England between 1994 and 1996. Recently, he has turned his attention towards the study of molecular genetics to identify genes for psychological traits. His research has always emphasized that individuals are not passive recipients of environmental influence, but individuals that select, modify, and create environments in accordance with inherited predispositions. What has been called the nature of nurture and the title we chose for our conference has been a paradigm-changing influence for psychology and he has helped to create a new understanding and a more balanced view of the influences of nature and nurture and human development. Please join in welcoming Dr. Robert Ploman. Well, thank you, Dick, very much. That was a very nice introduction. And that introduction, plus the first article in the brochure that you received today by Tim Robinson pretty much says it all, so if you don't get what I say now, all you have to do is read that and you're in business. I'd also like to thank President Dennis Johnson for his speech this morning. You remember about his grandchildren and I think it's great to be in an area where the basic science that you're studying, issues of genetics and environment as they affect behavioral development, those basic science questions are applied science issues to people like President Johnson with his grandchildren and your children and even yourselves, part of understanding yourself, is understanding the issue of nature and nurture. When I say the word nature, what do you think about? People often think about very warm, fuzzy things like how beautiful it is outside today and leaves are changing and all of that and also with the word nurture. Nurture also connotes warm, fuzzy things like mothers and babies, but when you put those two words together, people have shown it. If you say nature, nurture, undergraduate psychology students say controversy and it's only that way because people think about it as nature versus nurture and really the theme of my talk today is that the nature and nurture wars are over almost everyone recognizes that both nature and nurture are important in behavioral development. Now that may be a truism but it's actually a deeper thought than that. It's not just saying oh well genes and environment are both important so can't we all be friends? It's really the science of it says that genes are important and environment is important and furthermore and the main thing I really want to get across is that we understand a lot more about behavioral development if we bring these genetic and environmental strategies together. I'm always curious what people think. In the media it's often assumed that people are environmentalists and behavioral geneticists like me are the bad guys that are disillusioning them of their environmental beliefs of the blank slate and that everything you do to your children as a parent has to do, everything that happens to them is about the environmental treatment that you give them. But I think the man on the street is smarter than that. So I do wonder of individual differences in height and I assume most people accept that that's largely due to genetics. As Jerry Kagan was just saying we're just talking about what happens on average and certainly if you starve a child put them in the dark closet that Jerry Kagan was talking about even a child that would have been very tall could be quite stunted in growth. But we're not talking about that we're talking about the normal range of genetic and environmental variation in this room. And is there anyone who doesn't believe that genetics mostly account for individual differences in height? So I'm not going to talk about that because I think everyone does accept that height is almost entirely due to genetic factors to inherited differences among us. Again, as Eric Kandel and Jerry were talking about we're not talking about our species and why we are about five foot six or seven on average as compared to chimpanzees who are smaller or gorillas who are larger or rhesus monkeys who are much smaller. We're saying in our what causes these individual differences in height and you all agree that genetics plays the largest role. I thought I'd talk instead about weight. I'd use that as an example of some of these points. Because just think about it now. Nature nurtured. What do you think? Do you think it's largely due to environmental factors or is there a genetic component to weight? Well just remember what you think and see how you think about it after I tell you about it. So I'll use weight as an example of these sorts of designs that allow us to say empirically how much is genetics important and how much is environment important. And then we'll talk about the behavioral things that maybe interest you more. I'd also just briefly like to mention common medical disorders. What do you think? Nature, nurture, cardiovascular disease, breast cancer, ulcers? You don't have to tell me. Just kind of get it in your head as to what you think. And then what about once you get into behavior people think, oh well that's so ephemeral and hard to measure. How could there be much genetic influence there? And then finally what about normal traits, not just disorders. What about normal variation like personality? Is there genetic influence or not? So I'll be talking about those issues beginning with weight and along the way I'd like to mention eight misunderstandings about nature and nurture and how they fit together. The very first one I thought I could get into when he was talking about his tapestry and that because there are many metaphors that people use to try to make this point that you can't separate the effects of nature and nurture because both nature and nurture are essential. I mean how can you have behavior if you don't have genes and you don't have environment? Therefore isn't it nonsense to talk about the relative influence of genes and environment? Well that's true. Here's one of the metaphors. The area of a tango is a product of its length and width. So isn't it stupid to say how much of the area of that rectangle is due to length and how much of it's due to width? There is no area unless there's length and width. But when you think about genes and environment that's exactly the mistake people are making and here's the point Jerry also emphasized this point that we're not talking about one rectangle or an average rectangle we're talking about individual differences. Differences between individuals in our species and the extent to which genetic and environmental factors are important. So in terms of areas of rectangles those areas you can actually say how much of the area differences are due to length and how much of the differences are due to weight. Moreover the differences... I'm having trouble moving this here. Here we go. The differences can be called... The width can be the same for everybody. You can hold the width constant and the area of the rectangles will differ as a function of length. Similarly you can hold the length constant and the differences in area will be solely due to width. This is all because we're talking about not one rectangle but many rectangles. So if you think about weight people vary in weight from the boy on the left who's very thin to the boy on the right who's very thin in between. So what causes those differences in weight? The second misunderstanding, let's use weight as an example, is people will say how can genetics be important because everybody knows if you don't eat you lose weight. It's obvious isn't it? So how can genetics be important? Well the answer is that genetics is talking about what is. It's saying of the individual differences in this room in weight to what extent are genetic and... for those differences. Some of you are on diets and there's lots of environmental differences among you but given those differences that normally occur to what extent would this snapshot in this room and weight measurements be due to genetic differences? So behavioral genetics isn't about what could be. It's absolutely true if you don't eat you will lose weight but those of us who diet and try to lose weight we sometimes gain our weight back again but at any point now let's take the weight of everybody that's important and how much is environment. So the fact that if you don't eat you lose weight doesn't matter behavioral genetics is talking about what is not what could be and it's certainly not talking about what should be. I'll talk about that later. A third misunderstanding is that how can genetics be important because there's an epidemic of weight in most advanced cultures in the world and America as in many things is leading the epidemic of weight. Well those changes have happened too rapidly to be due to genetic factors so environment must be important in that trend but that doesn't mean genetics is not important. The trait we know most about is height and you know height has been increasing generation by generation for 50 years. Well the heritability the genetic influence on individual differences in height has not changed so even though the average height of generation by generation their resemblance to their parents is just the same it hasn't been changing and that makes the larger point the second point that's also a contentious issue about race differences, class differences, gender differences or cohort differences that the causes of average differences between groups are not necessarily related to the causes of individual differences within groups. So the reason why on average our population increases in weight but that has nothing to do with the question of whether individual differences within each of those cohorts is due to genetic or environmental influences. So how do we know? The point of these studies is you can't just assume what's heritable you have to use these techniques to assess it because I'll show you examples where your intuitions as to what ought to be heritable are wrong. The two major methods that are used are the twin study where we compare identical options study where we compare non-adoptive and adoptive relatives so I'll tell you about both of those methods briefly identical twins sometimes called monozygotic meaning one zygote a single egg that's fertilized with one sperm and then early in development in the first few days of life typically that fertilized egg splits and becomes two individuals with the same DNA in each of those zygotes. They're actually, you know, people worry about identical twins are more clones than clones because they're clones that grow up in the same womb and they're the same age throughout life whereas if you were cloned your clone then would be placed in some womb and it would grow up in a different womb but also in a different cohort from you and there are cohort effects. So identical twins are more clones than clones and about 1% of all birth are twins identical twins 2 thirds of what we call fraternal twins or dizygotic twins these are two separately fertilized eggs so these are just two eggs that are happen to be fertilized at the same time so they're like any brother and sister in that they share 50% of their genes they're 50% similar genetically so the twin method consists of comparing the resemblance of identical twins to the resemblance of fraternal twins for many many pairs for one pair you can't say here's one pair but there can't be any genetic influence what we're talking about are differences in the population on average and the extent to which genetic and environmental differences account for those differences that we observe so if genetics is important you'd have to predict that identical twins will be more similar than fraternal twins oops I hope that isn't a terrible problem very good did it overheat this is hot stuff okay so the twin method is one way of answering the question empirically about genetic and environmental influence so I'll use weight as an example what if weight were entirely due to nurture if you understood what I just said you'd realize that identical twins because the two-fold greater genetic similarity of identical twins shouldn't matter if genes aren't important you follow that? so identical twins and fraternal twins ought to be just as similar now what if it's entirely due to nature genetics then you'd expect identical twins to be about twice as similar as fraternal twins and if all the individual differences in weight are due to genetics you'd expect identical twins to be 100% similar genetically because they're 100% similar genetically that correlation if you don't know what a correlation is it's an index that goes from 0 to 1 0 means no resemblance at all 1 means perfect resemblance identical the other design, that's the twin design the adoption design is more powerful in some ways because it almost experimentally separates genetic and environmental influence parents and their offspring share genes as well as environment so when we say that things are because of genes or because of environment the adoption method separates that looking for genetic relatives who only share genes but not environment and environmental relatives who share environment but not genes and this is a social experiment that's happened since the 1930s here where adoption agencies exist so that unwed mothers relinquish babies for adoption at birth and those babies are adopted are just as genetically related to their birth parents biological parents as any kid is to its parents and then it's as related environmentally to these adoptive parents and that's also true for siblings a third of adoptive families adopt a second child those two children are genetically unrelated to one another but they share the same home in addition there are biological unwed mothers who relinquish more than one child for adoption they're genetically related to one another even though they're reared in different homes so the adoption method neatly cleaves separates the genetic and environmental influence that's normally confounded in a family study so with an adoption design what if weight is entirely due to nurture all that matters is whether you grew up with somebody you shared the same environment so we'd expect adoptive relatives on the right to be just as similar as non-adoptive whereas if you were adopted apart from your relative like your parent you don't share that family environment therefore you shouldn't be similar in weight if what's important is nurture but what about nature you'd expect a very different pattern of results what's important is whether you share genes not whether you share environment so if genetics entirely accounts for weight you would expect these adopted apart relative be just as similar for weight as non-adoptive relatives who share genes and environment and you'd expect adoptive relatives not to be at all similar because they don't share genes so what are the results for twins here are the results over many studies fraternal twins are about half as similar as identical twins suggesting substantial genetic influence on individual differences in weight but is it all genetic no because they're similar for weight they're about 80% similar so the differences within identical twins has to be explained environmentally because they're genetically identical to one another well those are the twin results suggesting substantial genetic influence but also providing evidence for non-genetic environmental influence I did want to point out that identical twins are amazingly concordant for obesity as well as weight identical twins reared apart that's what people often think about when they think about twins identical twins reared apart well there's only a few hundred pairs that have been studied in all the world because it's obviously a very rare occurrence but there's considerable data on identical twins reared apart for weight and as you can see identical twins reared together so these are the data I showed you before and here are the data for identical twins reared apart showing that together the other adoption results are much larger studies and parents in offspring correlate about 0.25 for weight now that could be either genetic or environmental but what the adoption method does is that this entangles that by studying genetically related individuals parents who adopt their children away at birth and as you can see those children even 20 years later are just about as similar to their birth parents as our kids and even more surprisingly is that adoptive parents who adopt these children very early in life and give them the nutrition and the living styles that we often think are associated with weight those kids aren't at all similar to their adoptive parents in weight so when you put these data the same things true of siblings adoptive siblings who grow up in the same family but don't share genes aren't at all similar for correlate about 0.3 something 0.33 a bit more than parents in offspring so when you put these data together here's the sort of picture you get where the pie represents the differences in weight in a population in the populations we've studied Caucasian mostly North American and European populations and you find that genetic factors account for about say 2.3 of the variance but these data also provide the best evidence that we have for the importance of environmental factors because even in the case of weight which is much more highly heritable than most of the behaviors I'll show you even in the case of weight about a third of the variance is due to environmental factors and later on I'll emphasize this distinction between shared environment and non-shared environment but the point I'm trying to make here is that weight accounts for maybe about 2.3 of the variance in weight is that what people thought? I think there's a lot of no's there so I hope I convinced you that genetics is important but I want to say right away that just because genetics is important you can do about it as we said before if you don't eat you do lose weight when you find genetic influence it really is just influence it doesn't mean that genes determine anything so genetic risk factors it means that if you come from a family where there's a lot of obesity you're probably at well you are very likely at increased genetic risk for becoming obese if you eat the same sorts of things that everybody else does your friends might not become obese but you're at greater risk for that and it doesn't mean it's bad by the way the general thinking about it evolutionarily in which we evolved where it was very important to be able to store fat efficiently but our problem in society is having these stone age genes in a modern society with fast food restaurants everywhere you turn and so in a larger sense I think it's important to recognize that genes aren't destiny but it's part of understanding who we are and who our children are knowing that genes are important for some of these traits even like weight is much due to genetics but it is another misunderstanding is if genetics is important there cannot be equality now this doesn't sound people aren't too uptight about it personality or intelligence people might have gotten a bit more worried on this score but I think it's good to bring it up in terms of weight are we going to discriminate against people because there's genetic influence on weight well of course not I think there might actually be more understanding of it if we it's not just a matter of lacking self-control some people find it tremendously more difficult not to gain weight than other people for genetic reasons but in the larger sense the founders say said that all men were created equal they weren't so naive as to think that all people are identical when they had eyes they could tell people different weight and height and they probably knew they differ in terms of depression and intelligence equality before the law was the fundamental thing that they were after and the recognition that if everybody were identical you wouldn't need a democracy there are many differences it's really that the essence of democracy is that you treat people equally before the law despite their differences there's a lot to say about this like equality of opportunity now that's a trickier one but maybe we can get into is that you're only studying genetics because you're trying to push a conservative political agenda and that really is very wrong obnoxious really in a way it's to impute political motives for the science of it I come from an old fashion point of view where I don't believe science is politics I think what we're trying to do is as dispassionately as possible examine the evidence for important issues in our and that there isn't a necessary connection between research and that policies depend on values as well as information and one can only hope that you make better decisions with information than without information but most of the time I think people are quite willing to make policy decisions with no information at all but you know when you're planning you're going to go seriously wrong in terms of making an impact on this very important problem of our society a lot of these issues that I've just are presented brilliantly in a book that just came out last month by Steve Pinker called The Blank Slate he examines historically the reasons why we've been so reluctant to accept a more balanced view of nature and nurture and I strongly recommend it now I'm going to just take about three minutes here five minutes to tell the truth to grasp a bit because most of what I do now is molecular genetics but I decided in my talk today not to talk about molecular genetics because it doesn't fit the theme of the conference quite as well when you study genes themselves it's great to identify specific genes responsible for this because of the evidence for the strong genetic influence on it but it doesn't in itself molecular genetics tell you anything about nurture once we identify genes they'll help us a lot in understanding the developmental interface with nurture but right now all the work is in terms of trying to find genes but I couldn't help but say a few things about it when I talk to journalists I usually end up by saying we're talking about genetic influence on some language problem of kids one of the things I study now invariably the headline comes out the gene for language and you're trying to say it's exactly what you don't want to say because for complex traits of the sort we're talking about here like obesity or common medical disorders or depression, hyperactivity anxiety are influenced by many genes and that has some important implications it means that the trade isn't determined it's a single gene like if you have the gene for Huntington's disease you'll die from it it doesn't matter what your other genes are it doesn't matter what your environment is it's hardwired deterministic and the problem is that when people think about behavioral disorders they think that same way and as a result of that complexity these genetic effects are only influences they're those complexities or risk factors they don't determine our behavior from a molecular genetic point of view this last point is very important it's been very difficult finding genes for these complex traits because I think there are many genes involved so any one gene has a small effect which means it's much more difficult from a single gene perspective you undoubtedly when you first read about genetics we're reading about Mendel there are seven single gene characteristics so if you get this form of one gene you will have wrinkled seeds they're necessary and sufficient that is those pea plants would only have wrinkled seeds if they've got that form of the gene and you don't find these highly deterministic and hardwired when we're talking about complex traits we're not talking about either or things you're not either obese or not or depressed or not or alcoholic or not we're talking about continuously distributed characteristics you don't wake up one day alcoholic it's a very long progression and there are many people in the borderline area well from a genetic point of view it's particularly different from a distribution that most distributions that is most common disorders are probably the extreme of continuous distributions so from a genetic point of view what that means is this is a slide showing a red green a gene and a yellow gene and what it's saying is both of those genes are associated with higher values on this trait let's call it weight so are necessary or sufficient there are some people up here who are very heavy who don't have either gene there's lots of people of middle way to have one gene or the other if there are many genes involved they're going to contribute quantitatively to the trait so from a molecular genetic point of view it has a very different approach we're not just going to look for families where they have the disorder because it's not a matter of is that there may be no common disorders from a genetic point of view common disorders may be merely the quantitative extreme of the same genetic and environmental factors that operate throughout the distribution and people like that in a way because you're thinking about obesity now not as something out there that other people have but it's part of the same ideological continuum that we're all on so that's one important issue in terms of molecular genetics the largest issue is that it's been taking much harder to find genes we can find genes for rare severe disorders but for the common disorders which are the vast number of the things that hurt us in life there's no evidence that these are single gene characteristics there are many genes involved but what we don't know is some genes that maybe account for 5 or 10% of the differences to the truth that for complex disorders there are probably many genes involved each of which have very small effects and the implication of that is that it's going to be very difficult to find those genes so that's where we are on the molecular genetic side I have no doubt that we will find many of those genes in the single genes but when we find those genes then the fun will begin because we'll begin to understand how the genes is only the first step and what the next decades are going to be about is understanding how those genes work not just at the molecular level that Eric Kandel talked about this morning that's what most people are doing if you've got a gene you try to understand its product in a cell and what goes on in this what's very exciting about functional genomics that is how do genes work is to think about a different level of analysis and to study how genes work at the level of the behavior of the whole organism how the gene affects an organism during development when does it affect it early or late and then how does it affect the organism's interaction genomics the important point here is that understanding how genes work isn't just at a molecular biology level but it can also be at a behavioral level and as someone else said earlier what's most exciting about all of this is that DNA will help to integrate the behavioral sciences into the life sciences as these bottom up approaches meet the top down approaches in the brain okay so that's my little and return to this pie diagram of weight I was focused on this two thirds of the pie that's due to genetic differences I'm now going to focus on this other third that talks about environmental influences and the first point in this understanding I want to make about this is that when you say genetic influence is important it doesn't mean the environment is not important and which is what I'll be talking about now and that genetics provides new ways of thinking about how the environment works and the first topic I'll talk about is non-shared environment I think two of the most important findings of non-shared environment has come from genetic research and the first one is this topic of non-shared environment if you think about weight for example what are our theories of the type of food you learn to eat and the lifestyle how sedentary for example the lifestyle was of your family but two kids growing up in the same family should have experienced that same environment then if that's so important what are the environmental influences they make family members similar well one way to estimate them directly is by looking at adoptive relatives adoptive relatives what we showed before we're not looking at the genetics now we're looking at what these data tell us about the environment and they say that parents in offspring where the children grow up in that family don't resemble each other at all for weight similarly for adoptive siblings their correlation for weight is about zero so these are kids growing up in the same family and yet they're not at all that shared environmental influences can't be important that what's important largely is the environment but it's a different type of environment it's called non-shared whatever it is it's making children in the same family different from one another one way of estimating it is to ask about the difference between identical twins if identical twins differ it might be due to genetics it has to be environmental and if they grow up 20% of those differences are due to non-shared environment so that's why we showed when you look at all the literature on weight that about a third of the variance is due to environmental factors but most of that is due to non-shared environment and not much is due to shared environment and in fact gender is probably most natally than are other siblings so that most of that estimate is due to the twin studies if you take twin studies out as in those adoption studies all of the environmental influences seem to be due to non-shared environment so the first point I want to make is that by saying non-shared environment is important it doesn't mean that parents don't have an effect it does mean parents don't ask why children in the same family are so different in weight why is it that the environment whatever it is is making two kids in a family different not similar in terms of weight and the answer to this is going to to come from research that looks at more than one child per family so that's the topic of non-shared environment and what I want to do now is that I want to talk about the results for these other areas because as you'll see the results are somewhat similar in making those points so in terms of medical disorders these are twin results for the major common medical disorders like in case you can't read it breast cancer, heart disease ulcers and these are MZ the point I want to make these twin studies to assess rather than assume genetic influence because if I had asked you what about ulcers, is there genetic influence there how about ulcers compared to heart disease compared to breast cancer where is there more genetic influence I know what you would have said because I've done this ulcers people think are due to stress therefore there's not much genetic influence but in contrast ulcers are actually one of the well you might say how can this be I mean your infections has to do with whether you get an infection now it doesn't, it has mostly to do with your susceptibility, your vulnerability to ear infections and that has a strong genetic component similarly with ulcers they have to do with stress but we all experience stress whether we get ulcers or not is to some extent due to genetic differences among us well on the other side of BRCA1 and 2 that cause breast cancer but those are single gene types of breast cancer that are very rare very severe and they appear very early identical twin concordances for breast cancer among female identical twins where at least one has breast cancer are about 15% that means 85% of the time when one identical twin gets but because of all the interest in molecular genetics nobody's really paying attention to this and saying the vast majority of the reason why one woman gets breast cancer and the other doesn't is not genetic there's no way you can argue with identical twin concordances that are so low lower than you find for just about any medical disorders most of the reason most of them are things like hypertension and heart disease where they show modest genetic influence now if you keep the differences in mind here look at the average difference between the blue and the yellow they show you the common behavioral disorders, mental illnesses the first thing you notice is that there's greater differences between identical and paternal twin concordances there's more genetic influence on common mental biological therefore they must be more genetic but again you can't assess you can't assume what's heritable you have to study it and for whatever reason behavioral disorders are more heritable I think it's because behavior is farther downstream and there's more opportunity for many different genetic systems brain, physiology to enter into that down again along the lines of assessing rather than assuming a good example is autism Professor Michael who was a rudder who was mentioned as the person who co-founded this new center in London with me was studying autism he was a socialization researcher he really thought that most of the important factors in mental illness are environment and especially early in the year if you did a twin study of autism you'd expect paternal twins to be just as similar as identical twins but in contrast after he did the research he found that identical twins are amazingly highly concordant about 60% concordant for autism there have been three subsequent studies all of which found the same result one of the most highly heritable mental disorders and as a result there are now international consortia trying to identify specific genes responsible for autism but the concordance for identical twins isn't 100% the news 10 years ago was the concordance for autism for identical twins is 60% for identical twins for autism is only 60% 40% of the time autistic identical twins where one is autistic the other is not they're discordant there can't be any genetic explanation for that it has to be environmental so even in the case of autism these data provide the best evidence we have for the importance of environmental influence and that those influences have always been assumed to be highly heritable but actually it's quite modestly heritable compared to other behavioral disorders so is it just disorders a lot of people think that we're all the same genetically except for a few rogue mutations that make us different but if you look at normal dimensions of behavior you find the same than for identical twins suggesting genetic influence on personality traits like neuroticism and extroversion on cognitive traits like spatial reasoning or verbal reasoning Jerry Kagan was talking about vocabulary memory always shows less genetic influence than other traits those of you getting older and having senior moments will be pleased to know and general intelligence also has that the environment largely works in a non-shared way so in summarizing those data genetics is important for nearly all these complex traits a bit more for some like say ulcers a bit less for others at the same time is that these data provide the best evidence we have for the importance of the environment but that environment works in a way that none of us hadn't expected that is whatever it's doing it's making two children growing up in the same family different from one another rather than similar so when I said there were two findings from genetics about the environment that I think are the most important findings of nurture and that's the notion that there's a correlation between our genetic propensities and the experiences that we have in technical terms in the type environment correlation and what it's about is genetic influence on exposure to environment so here's that mother and her child again we think of parenting as a pure environmental factor but it doesn't have differences among women that affect the way they interact with their baby some women are just more nurturant or sociable or warm and loving some are more controlling whereas the second way in which genetics can enter is in the baby babies certainly differ in their cuddliness for example very early in life whereas Jerry Kagan was talking about in terms of the infant we talk about three types of genotype environment correlation the first is called passive where the child passively inherits genetics that are correlated with the environment so if there's genetic influence on sociability that's what we think that mother we just saw to be more warm and cuddly and smiling with the baby as well as giving that genes and environment that are correlated with the development of that trait sociability but it's sort of passive the child isn't doing anything about it it just passively gets these genes and environment the second type is called evocative where it's not just limited to genetically related people anybody can react to a child or to you of your genetic propensities so if you are a smiley shy or behaviorally inhibited the converse is true so that your genetic propensity is setting up a correlation with the experiences that you receive in life and even more profoundly the third type of genotype environment correlation is called active and that is that we actively create environments that are correlated with our genetic propensities if you've ever seen a musically gifted child you know if you take away a piano or they'll hang out with other kids who are musical, they'll listen to radios kids can create environments that are correlated with their genetic propensities now there are two aspects to research on this topic of the nature of nurture and the first is to ask if genetics actually influences or is correlated with environmental measures now at first this seems a number of books on the shelf in the home well how can that be genetic I mean those books don't have DNA so how can you find genetic influence on number of books on the shelves in a home can you think about that well the answer is it's not like the weather where we don't have anything to do about it books on the shelves don't just get there by themselves parents put books on the shelves and all of our measures of the environment that we use are parenting measures measures of social support, life events classroom experiences all of them can be subject to genetic influence so there's been quite a bit of research on that beginning about 20 years ago with my first student David Rowe who studied adolescence perceptions of their parenting and so in the twin study he found that identical twins perceive more similar parenting in terms of maternal warmth than do fraternal twins and that was true of both mothers and fathers suggesting genetic influence on adolescence perceptions of their parents parenting towards them well since then there have been dozens of studies like this I've done a study over the last 10 years on non-shared environment and adolescent development we studied 700 families across America who had not only identical twins and fraternal twins but other sort of genetically distinct family groupings like step families siblings and genetically unrelated kids it just gives you more power in these analyses and what we found like everyone else is that all positive behavior or negative behavior about the fathers behavior these are heritabilities the average heritabilities are about 30-40% just about as heritable as personality traits and similarly if you ask the parents about their parenting towards the children you get a similar result that is genetic influence substantial genetic influence on their interactions between parents and children so it isn't all perceptions we used a task that's widely used in developmental psychology where you ask parents and their adolescent kids what problem do you have as a dyad and you know there's no end to it if you have adolescence you'll know what I mean you could quickly generate a list of problems that you have with your adolescent kid so then later on in the two hour home and then we go away and rate the videotape later and you'd think people would be inhibited by the videotape but you don't see any sign of that sometimes we had to go in and break it up but the neat thing we found is that then you can analyze the parent's behavior to the kids and the kid's behavior to the parent you get an interesting result that a child's behavior towards the parent is still significantly heritable it suggests to me that most of the genetic influence in the parent-child relationship is coming from parents responding to genetic differences in their children rather than creating differences in the children so there have been a lot of studies along these lines for peer groups and work environment social support life events most psychological important on environmental measures and genes are important on outcome measures like kids development isn't it possible that genes mediate the relationship between environmental measures and outcome measures and so in NEAD that study I described we did a lot of analyses of this sort for example maternal negativity whether the mother is hostile and conflicted with the adolescence antisocial behavior to what extent does that correlation mediated genetically we can answer that question because this study was embedded in a genetically sensitive design and what we find is that most of that correlation is mediated by genetic factors about two thirds of it there is also environmental mediation to the multivariate genetic model fitting that gives us those results but there have been quite a few studies now along those lines and they consistently support that sort of conclusion not just for family environment and psychopathology but also outside the family social support as it's correlated to oppression so the two big questions about nature of nurtures and behavioral outcomes and the answer there is also yes to some extent so the implication here I think is really profound if you accept that genetics contributes to our experiences then it moves you away from this passive view of the environment the old stimulus response view that the environments out there modify and even create environments and recreate in-memory environments it's those experiences that are important and that's I think where that's how genetics works in development and it's a I think a very important direction for research and developmental psychology so what I've been trying to talk to you about with this topic of nature and nurture is basically what genetic research tells us about the environment I first tried to convince you that genetics is important because if you don't believe that then this idea of nature and nurture you know doesn't make any sense because there isn't any nature well nature is important but I think increasingly people accept that thought it worked it largely works in a non-shared way making two kids in a family different from one another not similar finding at the interface of nature and nurture is the nature of nurture genetic influences on environmental measures and these are the themes of our large interdisciplinary research center which is quite a mouthful but it does convey what we're trying to do it's saying nature and nurture wars are over both of them are important so we need to bring together social that is environmental and genetic strategies to help us understand the development of complex behavioral influences on behavioral development and if you remember one thing as you go from explicit to implicit memory in terms of Eric Kandel's talk if you remember one thing about the talk today it's that the conjunction between nature and nurture is and not first us so we're talking about nature and nurture thank you