The Joe Walker Podcast - The Doyen Of Behavioural Genetics On Untangling Nature And Nurture — Robert Plomin

Episode Date: February 22, 2021

Robert Plomin is one of the world's leading behavioural geneticists. He is currently MRC Research Professor in Behavioural Genetics at the Institute of Psychiatry, Psychology and Neuroscience at King���s College London.See omnystudio.com/listener for privacy information.

Ladies and gentlemen, boys and girls, swagmen and swagettes, welcome back to the show. It is great to have you back and we have a fascinating episode in store for you today. The longest standing controversy in psychology is the tug of war between genetics on the one hand and environment on the other. In this conversation, my guest helps to unravel the Gordian knot of nature versus nurture. Robert Plowman is perhaps the leading figure in the field of behavioral genetics alive today. More than 800 papers have his name on them, and he is one of the most cited psychologists of the 20th century. He is most famous for his twin and sibling studies. For example, his ongoing Twins Early Development Study, or TEDS,

has followed more than 10,000 pairs of twins born in the United Kingdom since 1994, following them from infancy into early adulthood. Robert Plowman is currently MRC Research Professor in Behavioral Genetics at the Institute of Psychiatry, Psychology, and Neuroscience at King's College London, and he is the author of many books, including most recently, Blueprint, How DNA Makes Us Who We Are. In the nature versus nurture debate, Plowman's view isn't the only one, but given his achievements in the field, it's certainly one that's worth considering. So, without much further ado, please give it up for the great Robert Plowman. Robert Plowman, welcome to the Jolly Swagman podcast. Well, thank you very much. I've listened to a lot of your podcasts and I'm rather honored to be part of that illustrious group. Although I must say I'm a bit intimidated as well because

I know nothing about economics or business, which is the topic of many of your podcasts. But I think you know that too, don't you? I do. And I'm equally, if not more honored to have you on the show. I also know very little about economics, I must confess. I know a little bit about business. And I know even less about behavioral genetics. So this is a really great learning opportunity for me, and I'm sure for many in the audience as well. And you'll have to forgive my ignorance on a lot of these issues. Well, you know, I do think having said that, though, that I don't know anything about economics and you're being falsely modest, because if I mentioned a bubble to you, I think you could go off for the next hour, couldn't you? But for me, what's interesting about genetics is, you know, you think

of swagmen. Well, my swag is genetics. And what's interesting about genetics, just like swagmen, is it goes anywhere. And one of the more exciting areas it's going to is behavioral economics, for example. A lot of areas of science, especially the life sciences, that haven't considered genetics. My main target there is education. I mean, it's just amazing to me, learning ability and that sort of thing is the most heritable traits around, most influenced by genetics. And yet, you wouldn't think genetics exists if you looked at training books for teachers. So it's really exciting to bring a new dimension to areas of research. And so that's my swag.

I love it. It's a great swag. So it's been over two years since Blueprint was published. What have those two years been like for you, Robert? And what's the reception been like? Well, great question. It's my big question when I published this book. I've been in the field for over 45 years, and I kept my head down for several decades, because it's a very contentious area, as you can imagine. When I was in graduate school in psychology in the 1970s,

textbooks did not mention genetics. I mean, you can look at textbooks of the time and look for schizophrenia, for example, and genetics wasn't mentioned. It was thought to be due to what your mother did to you in the first few years of life, which is incredibly wicked, isn't it? So we can go into that later. But over the 44 decades subsequently, so much research piled up that I think most honest scientists who aren't blinded by ideology have to accept the data. I mean, if science is anything, it's empirical. And so I think I was right to say, don't argue with people. Just collect the data, keep piling up the data.

And I think as a result, most psychologists do accept a substantial role for genetics on most psychological traits. So that's changed a lot. But I'm also glad I waited to write this book because something I'm sure we'll get into is the DNA revolution. In the last decade, it's going to change everything. And it's going to be relevant to all areas of society, not just psychology. So that's very exciting. Nonetheless, when the book came out two years ago in hardback, I was really quite worried. Some friends of mine said this is a professional suicide note, because there's still a lot of people who have this knee-jerk reaction,

environment good, genetics bad. And so I've been tremendously pleased with the reception. So huge sigh of relief. I mean, I really was honestly very worried. I mean, at my stage of my career, I don't give a shit. You know, if people didn't like it, I was just going to tell it the way I saw it and not pulling my punches for once in my life. So I was really pleased. I've given well over 100 sort of talks to public audiences. There's none of that negativity. The general reaction you get is people acknowledge they just didn't know about any of this stuff. So in academia, there's some areas like sociology, maybe education a bit, who are still, you know, pushing back. But it's like shooting fish in a barrel. I mean, they haven't got a prayer because the data are just

so strong. And the DNA revolution is really going to make people sit up and pay attention, because you can argue about these twin studies and adoption studies and family studies that together, we'll talk about those I'm sure, but together they provide this evidence base for the conclusion, which is in the title of my book, Blueprint, How DNA Makes Us Who We Are, and it should add as individuals. It's explaining why people differ in mental health and illness, in personality, in cognitive abilities and disabilities. It explains about half of the differences between people, which, you know, is huge. So, although there's been some blowback from some areas of the social sciences, on the whole, even in academia, I've been very pleased by the reception of the book.

I still get a letter a week from people saying it really changed their lives. You know, it made them understand as a parent why they don't seem to be able to exercise control over it. You know, that they don't determine the way their children turn out. You know, that's an important message that comes from this, you know, not that you can't make a difference. It's just in the ordinary course of things, I mean, yeah, if you lock your kid in the closet, they're not going to do so well at school, right, but within the normal range of what parents do, they don't make much of a difference environmentally. They make a difference environmentally. They make a difference genetically.

And it doesn't mean you're going to throw your hands up and say, I can't do anything. But it's really important for parents to recognize they have much less control than they would think, given the thousands of parenting books out there, none of which mention genetics, which to me is the most important thing parents need to know. And just one more bit of this while I'm on this riff, and that's about, say you think of mental illness, 1% of the population becomes schizophrenic in their lifetime. You don't know someone's schizophrenic until late adolescence, early adulthood. So here's your kid going along, doing reasonably well. Maybe they get a little withdrawn in adolescence,

but then at 21, whatever, they're diagnosed as schizophrenic. Well, you were told that's because of what you did in the first few years of life, which is really wicked. What can you do about that? Because, you know, you can't go back, you can't go back in history. And so parents of mentally ill children, offspring, are big supporters of genetic research. And it's important for parents to know that's a concrete example. I mean, if you think you have, you're completely in control of molding your child to be what they want you them to be, on the whole, because you're genetically similar, they'll kind of turn out on the average pretty well. But what if your child becomes schizophrenic? I mean, it's important to know you're not at fault

for that environmentally. So there's a lot of ramifications of the stuff we'll talk about. And just to come back to your question, these are just examples of how I, really the reception has been better than my wildest dreams, really. And it's what I wanted. And it's starting a discussion about the DNA revolution and how are we going to handle this in society. So the last two years have been wonderful. I'm thrilled that must have been a liberating feeling to put something into the world that you knew might be controversial and then to survive yeah well it's just I just do feel I've been lucky I was lucky I was asked by a publisher to write this book 30 years ago

and I was you know lucky I said no mostly because I was a chicken. At that time, I would have been crucified. But I'm lucky in other ways that I waited and now the DNA revolution came along, which no one anticipated 20 years ago. No one thought we'd be anywhere near the stage we are now with the whole genome sequenced and knowing all the millions of DNA differences between people. So, you know, that's astounding. And it's even more fine-grained luck because I was working on this book just as the DNA revolution was really hitting the ground in terms of application. And so some of the biggest studies that are still the big ones today, two years later, were just coming out at that time. So I was able to really ride the wave, you know, of this revolution of DNA advances. So

I just do feel lucky really throughout my career, but the book was in especially fortunate timing. Because as you say, just as it was coming out penguin was being very brave about publishing it it was Alan Lane which is the hardback publisher and several of the staff you know as the publishing enterprise is really quite left-wing and you know there's been several cancellations of authors and so there was some staff that said, you know, we can't publish this. And to the credit of the chief, he said, have you read the book? And they said no, obviously. They just knew this is going to be bad because it's by me. And he said, read the book, come back and we'll talk. And no one came back.

So I thought that was great. And the point was that it was good that the timing was, you know, tricky. I mean, by now, if it came out, people would say, yeah, we sort of know a lot of that stuff. But when it came out, it was really dodgy. You know, it was just at the tipping point of whether people were going to accept this, or if they were just going to rebel against it and cancel it, and all of that sort of stuff. So again, luck, I think, as many of your speakers have said, even in economics, and even in physics, I love that talk by the, what's his name, starts with a G, the German

physicist you had on, Nobel laureate, who talked about uncertainty. Yeah, yeah. Uncertainty and the problems with Bayesian prediction. You know, the idea you just get more and more data. The turkey problem, as he called it, which is a great metaphor. And many other speakers talked about the role of luck. And so that's something we'll come back to because I think that's largely the way the environment works, you know, is idiosyncratic, stochastic sorts of events. Yeah.

Which is super interesting. I do want to talk to you about that. So we can talk about some of the better criticisms of the book a little later but but what what's the most common straw man version of it and what's your response to that straw man well the worst is the first major review which was in nature and it was by this guy who's a historian of science. He's not a scientist, but he's a historian. And the basic line there was, this is old-fashioned determinism and it's fatalism.

And sort of the last line is a review of, this is the world that Plowman wants. I don't want any part of it. So it was like he never said anything about the data, never argued with the science. He just said, I don't like the message. Well, that's not the way we work in science. You can't just say, I don't like the way those results came out. So I'm going to clobber you. The best review I had of my book was by this lefty in England from a famous communist family, David Aronovich. And he wrote a five-page spread in

the Sunday Times, which is a big newspaper here. And in it, he said, it's a very positive review. And in it, he said that he's amazed at the alacrity with which people move from the science to the message. You know, they can't criticize the science, so they just go on to criticize the message. And my objection to that is I don't have a message. I say many times in the book, genetic influence is influence. It's not hardwired, deterministic, innate,

which is the main mistake people make. If something's genetically influenced, well, can't do anything about it, you know know just throw up your hands and say we'll be the way we'll be not at all you know a good example is in the book I talk about my polygenic scores these you know the revolution in DNA was to realize that there are thousands of tiny DNA differences that account for heritability of traits you you know, the genetic influence, and you can put them together in a polygenic score. Well, I provide the first profile of

polygenic scores of anyone in this book, and it's for me. And my highest polygenic risk is for obesity and body mass index. And, you know, so people would say, well, people might be surprised to learn that body weight body mass index is highly heritable it's about 70 percent heritable which means of the differences between people that you observe which you could say oh that's just due to the environment you know it's just due to exercise and that sort of thing six seventy percent of those differences are due to inherited dna differences and we can predict about 10 percent of those differences are due to inherited DNA differences. And we can predict about 10% of those differences. So I have a very high polygenic score for body mass index. So the

point here is, what does that mean for me? Does it mean I just say, oh, well, I'm a genetic fatty, I can't do anything about it. But to the contrary, nobody reacts that way. For me, it's been very motivating because i realize it's not just like you know your skinny listeners who say well just get a grip don't eat so much don't be a pig you know it's that it's a lot easier for me to put on weight and it's a lot harder for me to lose weight and so i know from my genetic risk i'm in a lifelong battle of the bulge it's not just you know six pounds from christmas. It's not just, you know, six pounds from Christmas. It's a pound a week. You know, it's invidious. It just creeps up and it doesn't go down. And so,

as a result, I've organized my environment around that. I just don't have junk food in the house, for example. And, you know, I watch what I eat more. I get on the scale every morning. And, you know, so I think this shibboleth of, you know, this knee-jerk reaction saying, oh, genetics is bad because it'll just make people give up and say there's nothing they can do about it. I think it goes the other way. I mean, if you knew your kid had a genetic tendency for alcoholism, if you know this right,

it doesn't mean they're determined to be alcoholic. It just means compared to other kids, they're more likely to become alcoholic. And what that would mean, if they go out and binge drink with their buddies, you know, in adolescence, they're more likely to become addicted to alcohol. I mean, we can probably all become addicted if we drink enough alcohol over a long enough period of time. So isn't that good to know? Because you can just tell your kid, you don't have to give them ant abuse or something. You just say, there's just information for you. You just got to be more careful than other kids. And you can't become alcoholic if you don't drink a lot of alcohol over a long period of time. So why not be smart and just moderate your alcohol use just to avoid that risk?

Low tech, you know? So I just see so much good coming out of this. And that's what I try to emphasize in the book, in my subsequent writing, is because, you know, there's so many doom bongers out there saying the sky's going to fall if we start testing ourselves for DNA. Well, the genie's out of the bottle. 27 million people have paid to have their genotypes done. And many countries are now beginning to think of this as kind of a universal sort of a thing that they'll provide, especially in national health services like in England, because you can predict with DNA, you can predict who's going to have a

heart attack. And all of medicine is moving away from, wait until you have a heart attack, and then we'll try to fix you, to say, you got to prevent these things from occurring. And there's a lot we can do to prevent heart attacks. But the more intensive ones are expensive. And you can't do it for everyone. But if you could know who's at risk you can just start with low-tech information saying you know everyone hears that you're supposed to eat well and exercise but you better pay attention because you've got this genetic risk and you're at a say five fold greater risk than other people of having a heart attack and you know if I told you that you might pay attention to, you know, if I told you that, you might pay

attention to it. You know, we all hear that message and we all ignore it. But if you knew it was personalized to you, that might make you sit up and pay attention. But you can go beyond that then to body scans and things that are more predictive with the whole goal of preventing these heart attacks. Because, you know, you don't really fix heart attacks you don't fix obesity you don't fix alcoholism but you can prevent these things and so I'm just tremendously excited about this and I don't understand why people are so negative you know any big advance I'm sure you'd agree can create problems that's why we have to have these discussions but I hope the book would give people a level of DNA literacy so that we can have

honest, you know, adult conversations about these things. Sure, there's possible misuses, labeling, and, you know, I don't know, and government security breaches. There's things we got to worry about. But there's so much good that can come out of this. I just think it's going to happen, regardless of what people think. You know, parents are the big market now. They're testing their kids. The national policy in China is that by next year, they're expecting to have 50% of all their newborn children not just tested for genotypes, but sequenced, where you sequence

the whole 3 billion base pairs of DNA. Now, that's scary because, you know, that's China. And, you know, that isn't just for medical prediction and prevention. You know, that's for monitoring. Sure. It's like facial recognition, which is the same thing that's very advanced in China. So, yeah, there's cons, but there's a whole lot of pros here. And I feel like I have to hit those pros very hard as an antidote to all the doom mongers out there. When did the DNA revolution begin?

Well, in the first 30 years of my career, I was doing these twin and adoption studies showing that genetic influence is important. And at some point, you kind of say, well, everything's heritable. It isn't very interesting to say, oh, here's a trait nobody's studied, let's ask if it's heritable, because everything's heritable. So at that point, I thought, well, the next step clearly has to be to identify some of these genes. So in about 1990, I began doing that. In the late 80s, we began to be able to identify differences in DNA itself. Up to that point, we had to use markers, you know, like blood markers. They're single gene markers, but they're not DNA differences. They're a physiological measure that is closely related

to DNA. But the big change was in the late 80s, we were able to identify differences in DNA. And that really took off in the 1990s. And then new sequencing techniques developed so that by 2000, we were able to sequence most of the 3 billion base pairs of DNA. Right after that, and it's a great example of blue skies research because all the big advances that came from sequencing the human genome were unanticipated it was just thought this is a cool thing to do and you know that's why thousands 2,000 researchers were involved in this effort and because they knew good things had to come of of this and one thing that came of it was to identify all the DNA differences between people and there's millions of them so we're 99% our 3 billion base pairs of DNA 99% plus of those steps in the spiral staircase of DNA are

the same for all of us that's what us human. 1% or so differs between us. That's what makes us individuals. And that's what I'm studying. So you've had a couple people on talking about evolutionary psychology, for example. That's talking about human nature, who we are as a species compared to other species. That's a great perspective to have, but the individual difference perspective is not necessarily related to that. They're both genetic, but the evolutionary differences are things that have been, they're so important, like bipedalism and frontal vision, they're made the same for everybody. You don't allow variation. Whereas a lot of our societal concern about say learning disabilities in kids or mental health problems, that's about differences between people. And so by being able

to identify these DNA differences, we're able to actually identify the genes responsible for this ubiquitous heritability of all complex traits and common disorders. So all of those technological advances were part of this. And it was only in about the late 2000s, just about 2007, that the first big study that came out that showed if we have large enough samples, we can identify these tiny DNA differences that make a difference in all complex traits. So it wasn't just one point, but it's been building. And that's what I love about this genetic stuff. You know, it's so progressive and cumulative. And as a social scientist, I really appreciate that because so much of the rest of social science, it seems to me, is very faddish. You know, it's like you go off, this is a fad, you know, like you recommended, say, growth mindset and grit. Well, these sorts of fads come up because they're easy answers.

You know, you're going to fix kids' educational problems just by having them look in the mirror and say, you're great. You know, you can do anything you want to do. I mean, as America proved four years ago, anyone can become president. But I think we, well, there's so much I can say on that, and I'm babbling on a bit too much. So I'll stop there with that but that the dna revolution is as you can see here from my voice um very exciting yeah and especially exciting because as you say we can we can put together a large enough sample size that we can still have a statistically significant small effect so we can see the little effects in those differences between individuals. Yeah. And it took us a while to learn that, you know, because the first studies, like the ones I did for the first 15 years, like in the 1990s,

were what we call candidate gene studies. Because the technology hadn't come about that allows us to genotype, that is to look at DNA differences across the whole genome, we had to do it one DNA difference at a time. Very expensive, very time consuming to do one DNA difference. So what people did, like me, is they said, well, let's look at a few genes that are relevant. They call candidate genes, like hyperactivity.

I'm interested in developmental sort of phenomenon. And you know that kids with hyperactivity. I'm interested in developmental sort of phenomenon. And you know that kids with hyperactivity are treated with Ritalin, you know, a methylphenidate. It's an amphetamine, basically. And so what are the pathways, the neural pathways involved in that? Well, it always goes through dopamine, dopamine receptors. So how about finding some DNA differences in dopamine receptors, and we'll genotype those. Well, so there were literally thousands of those studies. That's all we could do in the 1990s, where you genotype a few DNA differences in so-called candidate genes. Well, that's been genetics contribution to the replication crisis,

which is the biggest problem in all the lives, in all science really, that things don't replicate because it's a huge area of interest in research. But those candidate gene studies did not replicate. And we could go into the reasons for that. The replication crisis is tremendously important in drug studies, everywhere. But genetics got its act together to realize we could only in those days because it was so expensive the genotype we had relatively small samples at most you know a few hundred people well i don't know if your listeners are how sophisticated they are in statistics but one basic sort of thing is uh small samples, you can only detect big effects. Well, the flip side of that is if you look at a lot of genes or several genes, chances are one of those might be statistically significant, but it's not really significant.

You only had power to detect big effects. But what if, and this is the case, the biggest effects are so much smaller than anyone ever thought. You had no chance of detecting them. All you could detect were false positives, and then you report them, and they won't replicate because they're not true. So it seems stupid, but a lot of science made that mistake. And so what really changed was in the mid-2000s, a new technology came along. So this was entirely technology-driven.

But because of the human genome sequence, it all kind of followed from that blue sky sort of research, is the SNP chip. So a SNP is a single nucleotide polymorphism. That's one base, one step on the spiral staircase of DNA. And as I say, over 99% of those steps are the same for all of us. Sometimes one step differs. That's called a single nucleotide. That's what the DNA backbone is about.

Polymorphism, which means multiple shape. So it's a difference, a DNA difference. The thing about this, so I was doing those two SNPs, but instead of doing them one at a time, this miniaturization was developed, which on a quartz crystal, you could grow probes of DNA. So you get a short sequence of DNA, say 20 base pairs, and then you get the difference too. So one step is different, so you get probes for that. And so you can miniaturize that on a plate the size of a postage stamp and measure millions of these SNPs, many times over, so that they're incredibly reliable.

They're very cheap. When they first came out, they were like $10,000, but now they're like $40 to get a chip that measures all the SNPs in the genome for one individual. And when you send in your swab, you know, your cheek swab to one of the, or spit to one of these companies like 23andMe for genotype, that's what you do. You give them a few cells, they can amplify those cells, and then they can measure with this SNP chip all the DNA differences, how you differ on several million of these SNPs compared to me. So that was the thing that really turned the corner. And then what we found from those studies called genome-wide association studies, instead of looking at a candidate gene or two, you look at everything in the genome. And that's when we found there were no big effects.

All those candidate gene studies, that never showed up. What it is, is many, many small effects. The biggest effects account for 1% of the variants. And that's the one SNP that is related to body mass index. And so when that came out in 2007, people thought, well, who cares? I mean, 1% of the variance. Turns out that's far and away the biggest association, the biggest effect size. So most effect size, they're so small, it's like 0.02%, that's 0.0002% of the variance,

which is 100%, the differences between people. So, when people say that, they say, oh shit, that's going to be tough, because if you're a molecular geneticist and you want to study gene-brain-behavior pathways, and you've got a DNA difference that accounts for so little variance, that means there's going to be thousands of these DNA differences that account for the trait you're interested in. So how are you going to be able to trace that in the brain? And I think the answer is going to be very hard. But people like me, we said, we've always known there were a lot of genes involved. Let's put them all together, weight them by their effect size. And that's this polygenic score I

mentioned before. So that's really turned the corner. And that's what people are going to know about genetics in the next few years, is that you can get your polygenic propensities for hundreds of traits, medical traits as well as psychological traits. So it really is an exciting time. So one folk model, probably the main folk model that people have in relation to genetics is nature v. nurture. Can you unpack that? Yeah it's good it's a it's a

fundamental misunderstanding um so as i said uh the title of my book is blueprint how dna makes us who we are and it should say as individuals because one of your interviewees, Nicholas Christakis, is it? Yeah, the author of the other Blueprint. Blueprint. We came out at the same time, these books. I know, yeah. But what he's talking about is the blueprint of human nature. That is, this is the kind of between-species level, the normative approach. What makes us who we are as a species.

That has to do with the 99% of DNA that's the same for all of us. I'm interested in the 1% of DNA that makes us different. So my book should be called How DNA Makes Us Who We Are as Individuals. It's trying to explain why we differ in personality. So it's completely different perspectives and perspectives aren't right or wrong, they're just more or less useful. And if you're trying to answer questions about individual differences, the evolutionary perspective isn't going to take you very far, because that's saying how we're all similar. So that's the nature side of it. We're talking about

inherited DNA differences that make us difference as individuals and that's nature too but it's the nature of individual differences rather than the nature of say the human species which is the evolutionary perspective so on the nurture side though it's even more interesting should I go into that now or place yeah okay when when someone says nurture people think about sort of systematic effects of family environment they think of mothers cuddling their kids and parents flashing cards to their kids to learn vocabulary it's these systematic effects and um say in psychology, which is my area, we've known forever, well, I guess throughout history, people know that things run in families. You know, weight, height, obviously runs in families. And psychological traits, like schizophrenia, run in families.

But psychologists didn't have any trouble with that. They say, yeah, that's nurture. That's the way the parents are treating the kids. That's what makes them who they are. They never thought about genetics. Well, what's interesting about genetics is that it can obviously explain why family members are similar. But what's, because first degree relatives, parents and offspring and siblings are 50% similar genetically. But what's cool about genetics is it predicts differences within families. So if a trait is heritable, you don't predict everybody's the same unless they're identical twins who are genetically identical. You predict that they'll be different as well as similar.

So that's an important point, like for parents to. Their kids aren't going to be just like them because they're 50% different genetically. So genetics predicts differences, but the environment doesn't. Nurture doesn't. Psychologists assume that the way the environment works, it's doled out family by family. It makes kids in a family similar because they have the same parents. But what we've learned is that genetics can account for the similarity in families. The environment's important, you know, like genetics accounts for about half of the differences between people. That means the environment accounts for the other half. But it's not the environment that psychologists have always thought was important. It's not nurture. It's not shared effects of

growing up in the same family. And the way you can show that is with twin studies, but easier to understand as an adoption study. So if you take, there's been dozens of studies where you look at kids who've been adopted away from their parents at birth. And then you take, there's been dozens of studies where you look at kids who've been adopted away from their parents at birth, and then you compare those kids to their biological parents who they didn't see after birth. They share genes though, the same 50% of the genes that parents normally share with their kids. But then you can compare those adopted kids to their adoptive parents with whom they share family environment. Those adoptive parents give the kids their food and nutrition and examples of lifestyles. And so it separates nature and nurture, which normally runs together in families. And if you

take body mass index, what's fascinating is that if you just take a sample of parents and offspring, the correlation between parents and their children as they grow up to be adults is about 0.35. I assume people know a correlation goes from zero to one. One is perfect resemblance. So 0.35 is the correlation just in between parents and their offspring who share genes and environment. There's no good word for it. You don't want to say normal families because adoptive families object to that. But you know what I mean. And so is it nature or is it nurture? Forever and still, some people think, well, it's nurture, obviously.

Well, it could be nurture. But what if it's nature? And it turns out it's all nature. It's all genetics. The correlation between adopted kids and their birth parents is 0.35. The correlation between adopted kids' weight and their adoptive parents' weight is zero. So that shows that what runs in families is genetic. The environment's important, but it's not this environment given by systematic effects of the parents' nurture of the kids. And so the question then is, well, then what is the environment? And it's not what we thought it was. And what it is,

is something that makes kids growing up in the same family different. That's called non-shared environment. So that's one of the biggest findings from genetic research, that the environment works very differently from the way we thought it worked. And we don't know what these non-shared environmental influences are. We spent 30 years trying to find them, but we haven't found them. And I've come to believe it's sort of idiosyncratic, stochastic effects. They're important. They make a difference.

But they're things like Bill Clinton always used to say he got into politics because he shook JFK, John F. Kennedy's hand, when he was 16. And that just convinced him he wanted to be like that charismatic politician, JFK. And, you know, it's an important event. He wanted to be like that charismatic politician, JFK. And, you know, it's an important event. And there are black swan events like that too, you know, that unforeseen events. They're really important. But how could you measure them? How could you predict them, you know?

They are kind of stochastic. And it's not too much of an exaggeration to call them chance really um and and that's the way the environment largely works i believe in these non-systematic ways so the environment's important but it's not the systematic effects of nurture it's this non-unsystematic role of chance non-shared environment yeah so when you say the environment's important it's not in the way that people commonly think which is that like proactive human agency where parents are actively making choices about how they for example rear their children it's contingencies which can snowball in really important ways because our lives are path dependent things so yeah examples great i mean well and you know

like another example maybe someone is um you know nearly hit by a bus that they're crossing the road and and they they narrowly escape and and maybe that makes them a bit more neurotic or something like that yeah or a lot of my friends you know given that i'm getting up there in age you know they i know i have three friends who had a mild heart attack and they said it was the best thing that ever happened to them they you know they didn't they they're in good health they're actually quite athletic and all that but they said it was great because it made them take stock of their life and it really was a tipping point in their life where they just decided you know they've had they're not going to die a happier person because they

published one more paper for example you know that they realized work-life balance is important and so there's so many examples of that and I think it's Interesting when you talk to a public group or even if I ask you about it I know my life was governed by these chance turning points and I could describe them but most people I think I don't know if this is true for you, but you look back on your life and there were these sort of You know the film sliding doors you know where just one little event you get on this train or an everything hinges on that everything follows from that and at the time you don't even know that's a big deal but looking back you say oh that really was a turning point now the difficulty here is people often tell

histories about their life that make it look like this was all planned and systematic. But, you know, when people are honest with themselves, I find they often say that there were these chance events, a particular teacher, a particular event, or a peer, or they met this person, or they had that accident. So how about you? What happened? Is it when you look back on your life, what made you be where you are today? Wow. Well, there are some big hinges. So one important one without lowering the mood too much, but our dad got passed away from bowel cancer when I was 14 I think 14 and I was at that point going to like a local kind of Catholic school but in Australia the Catholic school system is is not especially fancy it's sort of like just above the public school system so you pay a little bit of money but not a lot and at that point i was like all right i'm taking myself to private school so i

applied for a scholarship and got into the the boarding school that he and my grandfather went to uh in sydney and that just sort of opened the world up to me. But that would probably never have happened if he hadn't have passed away from bowel cancer. So that's one example. So he didn't want you to go to the private school? Well, it just didn't really occur to me. It just didn't occur to me. Yeah. Yeah. It was not that he didn't want me to he would have supported it but that sort of triggered it how about you interesting well my big example i grew up in the catholic school system in chicago and yeah um you know like you where you pay just a little bit of money my

my parents were poor and um uh what's interesting to me looking back on it is that from an early age I like to read we didn't have any books in our house literally and I my sister didn't like to read I went to school I love school you know I just thought it was fun I love learning about this stuff and this the Catholic schools weren't bad you know and my sister had a lot of trouble yet here we both grew up in the same family my My parents didn't push me. They sort of helped her a little bit. But, you know, they were kind of hands off. They wanted us to do well, but they didn't push us at all in school.

Yet I did very well because I was in the Catholic school system. I don't know why. I don't know if this is true in your school, but they tested the shit out of you. So you got lots of testing done. So as a result then, I got scholarships to go to this academy for high school. And then I got scholarships to go to university, DePaul University in Chicago. And being an inner city boy where I worked from the age of eight, they said, go to university, I had no plans to go to university, I was making too much money as a high school student. Yeah, I took I was working full time

as a high school student, just taking classes full-time as a high school student just taking classes that kind of fit in. And so when they said, we'll pay you to go to university and pay all the fees and everything, I thought, oh, that's a scam. And so I went to university. And then I had this wonderful advisor. I ended up in psychology after being in English and film, just taking things that kind of interested me and fit my schedule. I wasn't doing this for, you know, some to develop an occupation, but I just hated philosophy, which I was in for a while and decided I was an empiricist and I would like psychology instead. So I ended up in psychology and I had this wonderful advisor who

said, what about graduate school? And I honestly had never heard of graduate school. You know, none of my family went to university, let alone graduate school. So he helped me apply. And University of Texas at Austin came along. And they said the magic words will pay you to go to graduate school. I said, fine. And it turns out they had the only program in behavioral genetics in the world. I had no idea about it.

I didn't even know about it when I got to university in the autumn. And we were just told you have to take these compulsory courses called core courses at the time. And one of them, you know, like in perception and cognitive and clinical and all of that. And one of them, the only place in the world, was behavioral genetics. And so that was a big chance event. And the 40 kids, you know, 40 new graduate students in this class, it completely floored me. I thought it was so brilliant.

I had never heard of genetics in psychology. And here they're showing that, mostly in animal studies at the time, genetics is very important. So it just flabbergasted me, you know. And I knew at that moment that's what I wanted to do. And yet 39 other students never did anything with it. So that's what I don't understand, you know. I mean, they all had this opportunity, too, to see this new area coming along. And none of them were interested. And I honestly don't know

why it turned me on so much. But again, it seemed lucky. I mean, very lucky that I ended up at Texas at Austin, because I never would have gotten in genetics otherwise because genetics wasn't in the game at that time. So that's a good example of a huge turning point in my life that was total chance. It had nothing to do with me. But where I come in, just as you came in with applying to that private school, is something in me made me say, wow, that's for me. And I bet you there's genetics in that too. Maybe it was, in your case, motivational. You must have been intellectual. You must have done well at school or you wouldn't have gotten into this private school with the scholarship. So that's where genetics enters into this. And that's the kind of third big finding. So the one big finding

is genetics is important for all traits. It's the major systematic force that makes us who we are. The second point of the book is that the environment's important, but it doesn't work the way we thought it worked. It's this non-systematic chance, non-shared environment. The third finding is what looks like systematic effects of the environment are actually genetics in disguise. So you could say going to that private school, that's an environmental factor. But actually, was it? You were selected on the basis of genetic traits. You did well at school, intelligent, even personality sorts of things. probably look motivated to them so the effect that the private school probably wasn't added value at the private school we've done research that shows it's largely a self-fulfilling prophecy of selection

you select kids who do well at school who are bright who have to get going all that and they do well at school it's not added value the private school so that that's the third finding. It's called the nature of nurture. That there's genetic influence on most of the environmental measures that we use in the social sciences. Like life events, for example. So this is relevant to business and occupations. You know that what we call the environment is often very substantially influenced genetically

because the way genes work is not to just, you know, if you put DNA on the table, it doesn't do anything. It has to be in a cellular environment and in a body and in an evolutionarily expected environment. You know, again, put kids in a, lock them in a closet,

and they're not going to develop very well. But given the normal range of environments, genetics is what drives things along systematically. But the way they work is not just like a master puppeteer pulling our strings. They're not deterministic or hardwired. They're just nudges. And, you know, for example, the most highly heritable cognitive trait is vocabulary. And people say, what? I mean, how can the vocabulary be heritable? You just, you have to learn words. Well, the thing is, some kids pick up words. They're interested in nuances of words. I have one grandchild who has six grandchildren. One of them always wants to know about nuances of words. Why did you use that that word what's the difference with that word and so

she's going to develop this great vocabulary was most of my other grandchildren is whatever who cares you know what I mean you know they don't care about using language precisely and you see so the genetics is making us not making us it's nudging us towards selecting environments. She hangs out with kids, the one who likes vocabulary, hangs out with kids who are kind of verbally oriented. They're actually writing poetry and stuff like that. You select environments, you modify environments,

like in a school environment, you can get more or less out of it. And then you even create environments that are correlated with your genetic propensities. So that's what we mean by the nature of nurture. And it's also a very important finding that could only come out of genetic research. Because if you just assume the environment's all important, you're never going to find out these two big findings about non-shared environment and the nature of nurture. So I think it's important for people to realize it's always easy after the fact to kind of attribute things that happen to the environment. But I'd like people to stop and think about, well, what about genetics? And especially with

parents and their kids. Yeah, if you're cool and you have cool kids, you could say, well, that's because that's the environment. But you can say what about genetics because what's more important for parents is when you're cool and your kids end up being uncool and they get into drugs and trouble with the law and they don't do well at school you know is that you too did you do that you know probably not and so um it's important for parents to recognize that genetics is a lot more important than they think and that they have less control over their kids ultimate outcomes than they think but that's not to say parents are unimportant they matter a lot it's just that they're not molding their kids to be what they want them to be. And my message is parents should relax more than they do with all these books,

thousands of parenting books telling them, don't do this, don't do that. You know, the books disagree with each other. It must be a nightmare to be a parent. Because all the things in the newspaper, everything is oriented towards making you anxious. You know, that's what captures your attention. Oh, don't do this and don't do that and God, you know, parents must be frozen with

fear about doing the wrong thing. So it's important to know it doesn't much matter what you do. Your kids are going to be all right. But that doesn't mean you don't do anything. It means you have a relationship with your child. It's just like with your partner. If you're only nice to your partner, you do good things for them because you want to make them what you want them to be, that's going to be a disaster. And it's the same thing with your kids. You know, you do nice things for them because you want them to be happy. You want life to be nice for them. You tell them, you know, if you do those things, people aren't going to like you. And I think life will be better for you if you don't do those things but

you're doing it because you love them and you want it to be a nice relationship rather than doing things for them that make them be what you want them to be so my message to parents is just to relax and part of the enjoyment of being a parent a parent is watching your children become who they are genetically, rather than thinking you're going to make them be what you want them to be. It seems like your research would have some profound implications for the idea of meritocracy. Have you thought through that? Yeah, that's not quite a third rail. The third rail here is ethnic differences. But meritocracy is a pretty hot topic, as you can imagine. And I think one thing to say is a lot of it has to do with policy issues. And there's no necessary

policy implications of genetics. You can have a right-wing perspective, a left-wing perspective, that sort of thing. Requires a separate value judgment. Yeah. And so I would say the one thing I'm interested in particularly about meritocracy is the idea of equal opportunity. And what's an interesting policy issue related to meritocracy is that if people can understand what we've said so far, maybe they'll understand this, that heritability is an index of equality of opportunity.

And so if you think of education, for example, if there are environmental factors like privilege, wealth, access given by your parents, for example, that's unequal opportunity. If you get rid of these things that are environmentally different, and you make true equal opportunity, you're diminishing the environmental effects. And then, relatively speaking, the genetic effects are going to be bigger. You're not changing the genetic differences. So that's why with more equal opportunity heritability increases and that may be

why countries with greater educational opportunity have lower heritability to some extent. I'm sorry, higher heritability if there's equal opportunity. And so the United States, for example, has the lowest heritability of learning ability sorts of traits. And education seems to be quite unequal in the United States. So, you know, it's all locally controlled and each school district does their own thing. In contrast, the UK, and I think Australia is kind of in between, the UK has a national curriculum where teachers are told week by week what they're supposed to be teaching their kids.

So that should diminish those school differences between kids, and if that's true, then it should increase heritability. So heritability is an index of equality of opportunity, but what's really important for people to understand, and this is where you get more towards the third rail, it doesn't mean equality of outcome. And you've talked about that, and I'm sure your listeners know the issues there, but it's just amazing how many people think that unless you have equality of outcome, you know, there is no equality. Well, you can give equality of opportunity. But if you recognize the importance of genetics, you're not going to have equal

outcomes. I mean, any teacher teaching in England, you teach 30 kids in these state schools, you know, you're giving the kids, you're doing the best you can with each kid, but these kids just vary tremendously from those where you barely show them something like in math and they're off and doing it and other kids just struggle with it. You know, so I think genetics hits you over the head when you get to see a lot of children develop. And that's why it's said that actually that a neat aphorism is parents are environmentalists until they have more than one child. Because with the first child,

you don't have children, do you? No, no, no, not at that stage yet. Well, if with the first child, people are surprised to know that one of the more heritable temperament traits is shyness early in life. And so if you ask parents of a child, is your child shy? And the child's shy, you ask them why. They'll give you one of two answers. And one is, I took her out too much when she was young. The second is, I didn't take her out enough when she was young. Because with the environment, it's one of the problems with the environment.

You can explain anything after the fact. But then if you have a second child, because it is heritable, you'd expect those children to be different. So if one was especially shy, you would expect on average, the next one not to be so shy. And that's when parents say, wait, I didn't do that. You know, if you took kids out a lot when they were young you did it for both and if you didn't take them out you did it for both so that's when people get hit between the eyes with genetics and there's many famous authors like my favorite this Norwegian writer who writes these cult books and it's like Proust Ian levels of detail about psychological life. Karl Ove Norsgaard, he's a huge hit in Norway, and then his books have been translated into English and many other languages. It's 7,000

pages of his, it's sort of autobiography, but it's more like an intense psychological description. So as he has these kids, he's just describing where from the get-go, they're just so different. You know, one very outgoing and confident and another, where if you just look at her the wrong way, she starts to cry. You know, so it's a good thing to remember for parents that they're environmentalists until they have more than one child, because you can explain everything environmentally with one child. But then you see the second child and you say, I didn't do that.

These kids were different from the get-go. How should we think about intelligence? What is intelligence if not the ability to survive in the real world? Like Herb Simon had a famous analogy. He used a pair of scissors to describe ecological rationality or in his case bounded rationality but you know one blade was rationality or cognition and the other blade was the environment and you can't really talk about cognition without the context of the real world.

Yeah. So how should we think about intelligence? Yeah. Well, that example of Herb, that was Herb Simon, wasn't it? That you just said? Yeah. Yeah. He doesn't talk about individual differences, does he?

I mean, you know, and Kahneman, Tversky, one of my gripes with economics, the reason I didn't like it at university, was that I thought it was just so rational, and I thought they needed a heavy dose of psychology. Well, they've gotten it. All the Nobel Prizes in economics are in psychology, as far as I can see. But then the other thing is individual differences and this level of uncertainty. For one individual, you can't separate nature and nurture. But when you look at individual differences between people, all those differences could be genetic or all of them could be environmental, the differences.

So with individual differences in weight, it's possible that all the differences between us could be due to the environment. Now, no one ever has trouble with that. They don't say, oh, well, but it could interact with genetics. You know, they're willing to accept the environment. But it's also true on the genetic side. All of the differences could be due to genetics. And you really see that with our, I started out doing animal research because it's much more powerful, like mouse studies. You can manipulate genes and you can manipulate the environment and you can't do either of those with humans, really, very much.

So with animal studies, though, you can get genetically different, say, strains of mice who are selected to be different genetically, and you can raise them in different environments that you control in the laboratory environmentally. So that all the differences between the mice could be due to those environmental manipulations. But also, all the differences could be genetic in the sense that it doesn't matter which environment

the genetics comes through. And then the interaction is the statistical interaction between genes and environment. So that's to say, the effects of genes are conditional upon the effects of the environment. They depend on the environment, or the environmental differences depend on genetics. Either way, it's that there's a conditional relationship between them. So there can be environmental main effects, genetic main effects, and there can also be interactions, but it does not imply that you can't separate out genetic and environmental differences. So I think the key factor is to

tell people we're not talking about cognition in the human species, we're talking about differences between people in, say, cognitive abilities. And those could be all genetic, they could be all environment, or they could be due to a statistical interaction between genes and environment but you certainly can separate out the effects of genes and environment and i know we've covered a lot but one i think one thing i want to make sure i mention i might as well do it now is that what i'm saying uh in terms of these three findings, genetics, non-shared environment, and the nature of nurture, what I'm saying is that if you were switched at birth in the maternity ward and raised by a different family,

what I'm saying is you would be much the same person that you are now because the systematic forces are inherited DNA differences and they wouldn't change for you. Now, you know, if you think about that a bit, you know, I'm saying even though you grow up in a different family with different parents, go to a different school, have different friends, I'm saying you'd be much the same person that you are. And that isn't just hypothetical. And this is the point I wanted to get to. There's this documentary film a couple years old now that won an award at Sundance. It's called Three Identical Strangers, and it's available on streaming services. And it's the remarkable, it's an anecdote,

it's one case, but it's a remarkable case of three identical triplets. So identical twins come when the same fertilized egg splits in the first few days of life. So these two individuals have the same DNA. Sometimes one of those zygotes, which is a fertilized egg, splits again. So you get three identical clones of one another. So there were three young men. The story starts with one man, Bobby, who grew up in a very wealthy area of Long Island outside of New York with very wealthy parents, a doctor and a lawyer. And he went to university in upstate New York at age 19. And on the first day of university, Bobby is being called

Eddie. Everyone comes up and says, oh, Eddie, so good to see you. And he thought it's some sort of weird psychology experiment or something. Then he met Eddie. And Eddie is like looking in the mirror. It was a clone of him. And they quickly worked out they had the same birth date and they had been adopted at birth. And the publicity that came from this led to a third one, a triplet. And the film is about how remarkable these guys

are. Physically, you can't tell them apart. But even psychologically, you know, in psychopathology, they're all quite depressive. One actually commits suicide later in life. And in terms of academics, they're similar too. They're a type of student, very different from you and me, I think, who they're bright, they're well-read they just don't like school they don't like the restrictions of school and when they got together they all quit University and set up a nightclub in Manhattan which made a million dollars in the first year you know it was like them finding their niche and their niche wasn't in academic learning they just they were intrapreneurs really that's what they liked is the sort of the thrill of business starting a

business and all of that so it's really a remarkable illustration of the points I'm making because they grew up in as different environments as you could find as I said Bobby grew up in this very wealthy environment and one of the other boys grew up in a immigrant family and then the other one grew up in kind of a middle-class family where the father was a secondary school teacher and they differed in parental styles as well you know so they were very different environments nature nurture but then they ended up being very similar to one another, nurture. So it's well worth watching as a dramatic illustration of the points I'm making.

The problem is, and the reason I hesitate to recommend it, is the last half of the film goes dark. And you might ask yourself, well, why were these identical twins separated and didn't know about the existence of the others. And it turns out this was a really, this is the 1950s, a terrible example of experiments going bad. Back then you didn't need ethical approval to do experiments, and so some crazy psychiatrist said, wouldn't it be cool now we take these identical triplets and we adopt them in

very different family environments and see how similar they become and yeah i know oh god so i i important to emphasize the people that sort of research can't be done now and there's ethics committees all over the place but um they did do it, and not just with that set. There were at least five or six other pairs. There's a book going to come out this summer, I think, by Nancy Siegel at Fullerton, California. And that's a very terrible story, but it's too bad because it spoils the first half of the film, which was, for me, a perfect illustration

of the points I'm trying to make. Yeah. IQ seems to be informative for very low IQs. Is it informative when it comes to high IQs? So very bright people are different the way everybody's different in psychopathology and in personality and all the other stuff. And being very bright doesn't guarantee that you're going to be successful or motivated.

It takes work as well as basic intelligence. And sometimes I think being really, really bright can be a curse as well as a blessing because i knew one guy went to graduate school was one of the brightest people i know he got perfect scores on these graduate record exam tests that you use to get into graduate school but he was just so bright and knew it he could never do anything because it was it sort of wasn't he was looking for the big problem he was going to solve, but he never actually got there. You know what I mean? Because

whereas people like me who I never thought I was very bright, I know I work hard. And I think Einstein was right about 99% perspiration, you know, 1% inspiration. And I do think genetics is important. You need a certain basic skills. But I think in graduate school, most everyone's bright enough to do it. I mean, especially in psychology. We're not talking physics or maths here, you know, where you really, I think it's more pure intelligence

or a type of intelligence anyway. But, you know, they're bright enough. The difference, I'm sure, and the difference I look for in selecting graduate school students is, yeah, they got to be bright enough. But that's not what makes the difference it makes the difference is more motivation personality maturity more and more I find you know just it's a marathon

rather than a sprint you know and you need people who are going to be there day after day they just keep plugging away at this stuff and you work hard enough and if you're lucky things happen you know so um i don't know how i got off on that long tangent but i'm sure it was related somehow if genes correlate with iq and iq correlates with performance are those correlations transitive in other words does it necessarily follow that genes correlate with performance? Yeah. What's interesting is another finding that I mention in the book that I didn't talk about today is what I call generalist genes.

Genetic effects are very general. So it isn't like there are genes for, say like, even math or humanities or general learning ability, which is what we mean by intelligence. To a large extent, the same genes are affecting all of those things. What makes them different, like, you know, what makes you, you know, some people say, oh, I'm good in math, or I'm not, I'm good in verbal. But actually, because of generalist genes, you're probably pretty good in both. You just know you're better in math, you like math more. But it's not like you're verbally retarded or something. You know, you're probably a lot better than average. You just notice the difference in yourself. And so genetic effects are largely general. And we've shown, I'm particularly interested in educational achievement because it wasn't studied very much. And I knew that it's the business end of intelligence, cognitive ability, you know, which in these intelligence tests involve abstract reasoning and things like that. But where it hits the road is when it comes to educational achievement.

And what we've shown is that about half of the genetic influences on educational achievement can be accounted for by general intelligence. The other half, about half of that, is due to personality traits that are heritable. And then there's maybe a quarter there that is something else that we can't yet explain. So it's interesting how much genetic overlap there is. And the most surprising, we now know this at a DNA level as well, that when you find genes for general cognitive ability, they'll explain a lot, they'll also relate quite a bit to how well you do in English,

how well you do in math, how well you do in all educational subjects. But where it's really shocking is in psychopathology, where in psychiatry we separate the first level. I mean, if you come in very disturbed, you're brought in by the police because you're having hallucinations or whatever. The first division they make is what we call psychosis, which is severe mental disorder. But the main division there is between, say, bipolar affective problems, you know, depression and mania versus schizophrenia, which is more like pure thought disorder. So that's the very first distinction. Until recently, you could be diagnosed as both bipolar and schizophrenic, just because of the way the diagnostic rules were set up.

But the first time we found genes about 10 years ago for schizophrenia, the shock was every gene you find for schizophrenia also predicts bipolar. So even at that very specific DNA level, there's a lot of genetic overlap. So what it suggests is that genes give you a general propensity towards going off the rails. But which way you choose to go off, whether it's more cognitive, like schizophrenia, or, you know, which includes paranoia and delusions, or more effective disorders, like, you know, getting depressed or manic, that seems to be more environmental. Most of the genetic effects are general rather than specific so that's that's an unanticipated cool kind of finding called generalist genes is the topic

i've heard people say that because of the curse of dimensionality well the curse of dimensionality sort of cripples our ability to make inferences beyond monogenic effects how do you think about that yeah it's the biggest problem you know that when you say genetics of people people are thinking mendel you know mendel you know who 19th century monk who found out how genes work in heredity, you know, by studying single gene characteristics. So there are thousands of single gene characteristics in humans. These are necessary and sufficient for the development of the disorder. So just like Mendel's pea plants, where wrinkled, whether you have wrinkled or smooth seeds is due to a single gene. A mutation causes the normal

smooth seeds to be wrinkled. And it's deterministic and hardwired. And the same thing's true with single gene disorders in humans. There's 7,000 or so of them, most of them very rare. But say like Huntington's disease, which causes this neural degeneration that Woody Guthrie died from, it's a single gene disorder on the tip of chromosome six. It's just a mutation. And it's necessary and sufficient in that it's necessary that you cannot get Huntington's disease, which is this long-term neural degenerative disease, unless you get that gene. And it's sufficient in the sense that you only get the disease if you have the genes. So necessary and sufficient, hardwired, deterministic. And that's the way people learn about genes. The thing is, though,

when we study complex traits, like learning ability or personality or common disorders, all the common disorders, you know, diabetes, heart disease, they're all heritable, but none of them are due to a single gene. They're due to many genes of small effect. Which is why you say that they're quantitative, not qualitative. Exactly right. That is the point, that that they're quantitative, not qualitative. Exactly right. That is the point, that it's all quantitative rather than qualitative. And the DNA revolution is making that abundantly clear, that we're not finding a gene for this and a gene for that. Even though, and this is the hard part that you mentioned, even though genes work the way Mendel said they worked, you know, they are inherited as these discrete alleles. The thing is, the guy who founded what we call quantitative genetics in 1918,

Sir Ronald Fisher, realized that there was no discrepancy between what Mendel was saying and what applied geneticists knew in agriculture and in animal husbandry. And that is, they said, there's nothing like discrete categories here. Butterfat, content, and milk. Everything you measure is quantitatively normally distributed in a bell-shaped curve. So initially they said, well, this Mendel stuff, which was rediscovered in the early 1900s, we don't know what that's about, but it can, but maybe it's just the pea plant peculiarity, because we know there can't just be one gene, because these things are quantitative. So they said there has to be lots of genes.

But this guy, R.A. Fisher, brought them together in 1918 by saying, no, each gene could be inherited the way Mendel said it's inherited, but it's just that even if you have three or four genes affecting a trait you'll very soon reach a normal distribution you know it's just like you know flipping coins each you either get a head or tail each time but what if it takes ten coins or a hundred coins you flip all of those and you get you quickly get say if you flip a hundred you know it's 50 50 heads so you'll get a lot of 50 50s and 49 51s you'll get this normal distribution and that's what we're doing with genes we're inheriting alleles it's like flipping alleles instead of coins so it's a very important distinction. And the one implication

of it that I find very interesting is I think it's going to be the end of diagnosis and qualitative approaches to medicine. Because from a genetic point of view, and genetics is the major systematic force, if you've got thousands of these tiny DNA differences in these polygenic scores, they're always perfectly normally distributed. They have to be. So there's no cutoff point at which you have a genetic risk for cardiovascular disease or obesity or anything. It's perfectly normally distributed.

It's quantitative. That doesn't make it less important. It just means that all this stuff in psychiatry about diagnosing whether or not you're schizophrenic you know that's the medical model which makes sense with kovat or an infectious agent because that's like a single teen it's a single environmental cause and you either have it or you don't like you're not supposed to get you don't have kovat if you don't have the infection right and so a diagnostic approach is so important in medicine you know that's so that's good but it's been the major thing holding us back in psychiatry because

they're pretending that you're either schizophrenic or not. Whereas any working clinician knows it's not the case. You don't wake up alcoholic one day or depressed. This is even in an individual. It's a slow accrual of these symptoms. So I think it's a very important message that it's a matter of more or less, not either or. And a neat aspect of this is, it's not those schizophrenics over there and us normal people. We all have literally thousands of genes that put us

at risk for schizophrenia. It's a quantitative issue. How many do you have? And how does that interact with your environment? So it's such an important way of thinking about these things. And I do think it's kind of neat to think, well, we all have genes for schizophrenia. It isn't like us normal people. And I don't know why that does appeal to me a lot. But the more important application, I think, is that I think it'll be the final nail in the coffin

of the myth of the medical model in psychiatry, as well as in common disorders in medicine. You're not hypertensive or not. It's totally normally distributed. And even at the symptomological level, like, say, cholesterol in the blood, anything you can measure will be quantitative. And statins don't just reduce the risk of hypertension and hypertensive. It works totally throughout the distribution. So if you have a low cholesterol level like I do, you'll still lower it even more with statins.

It's just quantitative. And it's such a different way of thinking about illness and cures. You don't cure something if there is no disorder. You ameliorate symptoms, you reduce risk quantitatively. So I can understand why people like black and white categories, you know, okay, you're schizophrenic, can we cure your schizophrenia and make you normal, you know, but it's just really wrong. And I think it creates a lot of problems. And it's really holding back the science, I think. And really led us into some very wacky treatments decades ago.

Whereas now, obviously, it's much more about sort of managing the symptoms rather than trying to cure someone, as you say. Yeah. So what's next for Robert Plowman? I mean, what are you working on at the moment? What are your plans for the next few years? Well, yeah, good question. I want to take it, you know, I'm 72

and someone might think it'd be graceful if I left the scene now, but I've been waiting so long to find genes that, you know, there's no way I'm going to throw in the towel now because this is where the excitement starts because we can use genes to predict behavior. And what's cool about these polygenic scores is you can predict, DNA doesn't

change throughout life, which is a topic we might get into. People say, what about gene expression, epigenetics? But the inherited DNA sequence does not change systematically during life. What that means is I can predict obesity in newborns just as well as I can predict it in adults. So that ability to be able to predict behavior means you can study the interplay, the developmental interplay between genes and environment. That's what I'm particularly interested in doing. You know, tracing how they interact with one another,

and also how genes use the environment in that way I was talking about, the nature of nurture, to kind of create and select and modify environments that foster our genetic propensities. And I'm especially interested in the relationship with parenting, because it just appalls me that of these thousands of books out there, there's only one book that really talks about genetics at all. But all the popular books, it's as if genetics doesn't exist. And you think of the implications for parents on individual differences. There's no one-size-fits-all treatment for anybody, any kid. You can't tell parents, this is what you must do for your kid, even if it's like night waking.

Kids are different. They have trouble sleeping at night for different reasons, and some of that's genetic. So I think the ramifications are there's just so there's just so much to do and there's so many ways that this can advance science because psychology has for a century ignored genetics. So now you bring genetics in and it's so synergistic because everywhere you look you say, you guys don't know anything. You've ignored genetics. You've pretended that everything's environmental

yeah so i'm gonna go out feet first i guess well hopefully that's in a in a very long time to come but uh i'd love to to continue the conversation on another occasion you've been so generous with your time and thank you so much for coming on the show well it's my pleasure and uh i hope you continue to do so generous with your time and thank you so much for coming on the show. Well, it's my pleasure and I hope you continue to do so well with your podcast. I mean, just wonderful to see, you know, in this age of unpleasantness and unreason, you know, it's nice to see just open, honest discussions about stuff. I just love it. And congratulations to all your audience for being loyal followers, because we need a lot more of them in the world. I hope you enjoyed that conversation as much as I did. Two things before you go. One,

if you want to read the transcript or the show notes for this episode, you'll find them on my website, thejspod.com. Number two, please subscribe to the show. It means that you won't miss new episodes like this one, and it also makes it easier for other people to find us, and I would appreciate your help. The audio engineer for the Jolly Swagman podcast is Lawrence Moorfield. Our dehydrated video editor is Al Fetty.

I'm Joe Walker. Until next week, thank you for listening. Ciao.