How Do Genes Influence Our Behaviour? - Robert Plomin | Modern Wisdom Podcast 353

1. 0:00 – 1:42

   Intro

   1. RPRobert Plomin0:00

      Well, for IQ, siblings correlate about 0.3 in childhood, about 0.4 later on. How much do these adoptive sibs correlate? Because they grow up in the same family, they have the same parents. Zero. So the fact of growing up in the same family isn't making them similar. (wind blows)

   2. CWChris Williamson0:20

      You turned my world upside down last year-

   3. RPRobert Plomin0:23

      (laughs)

   4. CWChris Williamson0:23

      ... when I read Blueprint. I, uh, I've been wa- looking forward to speaking to you ever since I read that book, and I'm hoping that today I'm going to be able to deliver the same uncomfortable, topsy-turvy world that I was, I, I sort of slowly ingested about 12 months ago. So I'm looking forward to seeing what the audience make of the insights that we're gonna get from today.

   5. RPRobert Plomin0:46

      Yeah. Well, that's, that's terrific that you got it, you know? I, I, some people I think just get turned off. They just say, "Whoa, this is too weird." But, um, it, it really is so rewarding for me when people, you know, persist with it, they're willing to deal with these difficult topics. And then when you get off on the other side, it isn't so bad. It's actually exciting. It's a new way of seeing the world, I think.

   6. CWChris Williamson1:08

      I thi-

   7. RPRobert Plomin1:08

      So that's terrific. I'm really glad to hear it, Chris.

   8. CWChris Williamson1:10

      ... totally correct, like it is a whole new world. And you, you're also right to say that today there'll be some uncomfortable insights, especially when we're in a meritocracy, you know, a meritocratic society that's capitalist and you are your achievements, to hear that there are these immutable truths that you perhaps didn't choose, there are influences on you that you didn't elect. These things are uncomfortable. But I, you're also correct that it's very liberating if you take it just a little bit further, it's so liberating to learn. So, okay, we've

2. 1:42 – 4:22

   What are Behavioural Genetics?

   1. CWChris Williamson1:42

      danced around it. How would you describe behavioral genetics to someone who's never heard it before?

   2. RPRobert Plomin1:48

      Well, behavioral genetics is like medical genetics in it's not the genetics of medicine, it's the genetics of behavior. And behavior is essentially psychology. So we're dealing with the major domains of psychology, like psychopathology, personality, cognitive abilities, even getting into education, educational achievement. But the main thing is we're focused on individual differences. Why are some people schizophrenic and others not? Why are some children reading-disabled and others not? And it's an important distinction, because, um, genes, uh, um, we're 99 point say 9% similar for all our DNA. Three billion base pairs of DNA, we have exactly the same DNA at ... These are the steps in the spiral staircase of the double helix of DNA. We're, we're identical for well over 99% of those bases. But for at least 0.1% or so, which still means millions of these steps in the spiral staircase, we differ. And so what we're asking in behavioral genetics is the extent to which those differences in inherited DNA sequences make a difference in our behavior. Do they make us more likely to be susceptible to schizophrenia or depression or alcoholism, or do they affect our personality? So it just can't be emphasized enough that we're talking about individual differences. The other 99.9% of the DNA is the same for all of us. That's what makes us human. And those are also important questions. You know? Is that, that, is that why, for example, humans are natural language users, or we walk on two feet, which is very rare. We have eyes in the front of our head for depth perception. So those are questions about universals. Why is the human species like this or like that? Those are terrific questions, but we're not looking at that. We're asking about why people differ and the extent to which inherited DNA differences make them different.

   3. CWChris Williamson3:53

      It's crazy to think that all of the differences that we have come down to that 0.1%. All of the idiosyncrasies, the way that we speak, the nature, the texture of our own mind, the interests that we have, any of the medical predilections that we have with regards to our behavior. Especially given that I've got a big interest in evolutionary psychology, which is looking at that 99.9%.

   4. RPRobert Plomin4:17

      Yeah. Yeah.

   5. CWChris Williamson4:17

      And then your field just focuses on the tiny little final bit.

3. 4:22 – 17:52

   Nature & Nurture

   1. CWChris Williamson4:22

   2. RPRobert Plomin4:22

      Right. So it would be perfectly reasonable to think that these ... this small amount of DNA difference doesn't make a difference. And psychologists always assumed inheritance wasn't important. They, from Freud onwards, assumed that we are what we learn. You know, it's the environment that makes us who we are, and that's called nurture. And especially the family environment. You know, when I was in graduate school in the '70s, textbooks actually said at the time that schizophrenia is caused by what your mother does to you in the first few years of life. And, you know, that's reasonable, because schizophrenic mothers tend to have kids who are more likely to be schizophrenic. But what they didn't realize is that parents and offspring are 50% similar genetically. So the issue is, to what extent do inherited DNA differences account for some of these differences we observe? And you don't need DNA. It was only in the last 10 years we were able to use DNA. For the last 100 years, we've been able to use methods like the twin method that compares identical and non-identical twins, adoption studies where you study genetically related people reared apart, like birth parents and their adopted-away children, or conversely then, adoptive parents of adopted children who share nurture, environment, but not nature. And so the shock was, in the '70s and '80s, that all of this evidence kept coming up with a fi- a general finding that in ... individual differences in psychological traits are very substantially due to genetic influence. We now say about half of the differences are due to inherited DNA differences. And the excitement now is with the DNA revolution, we're able to begin to find some of those DNA differences which will allow us to make predictions at the level of the individual, which is gonna be a very big thing.

   3. CWChris Williamson6:15

      50%.

   4. RPRobert Plomin6:17

      50% of the differences are due to inherited DNA differences. Now, first, that means the other half is not due to DNA differences, it's due to the environment. But there's a big story there in t- that the environment isn't what we always thought it was. So, we can get onto that later. But the... We call it heritability, the extent to which genetic differences make a difference for a trait. And there's some important misconceptions-

   5. CWChris Williamson6:43

      What do you... When you say trait, what's a trait?

   6. RPRobert Plomin6:45

      Uh, yes. A trait is a measure of individual differences.

   7. CWChris Williamson6:48

      What would be an example?

   8. RPRobert Plomin6:49

      So like physical height, weight, psychological, psychopathology, personality. Okay. So, um, when we say that these... that, uh, heritability is 50%, we're talking about differences between people. So the easiest one, take weight. People are often surprised. You say height. How heritable is height? Well, people aren't surprised to hear it's very highly heritable. How highly heritable? At least 90%. So that means of the differences you see between people and height, about 90% of the differences are due to inherited DNA differences. So the first misconception is that that's not you. You didn't grow 90% because of your genes and the last 10%, uh, because of the environment. And as funny as it sounds, you scratch the surface of what people know, and most people are making that mistake. So we're talking about differences between people in the population. Okay, so high- highly heritable, 90%. But how heritable is weight, say body mass index? Um, a lot of people think, yeah, maybe there's a little genetic influence, but it's mostly due to the environment. And it's not. It's 70% heritable. So of the differences you see between people and weight, about 70% of the differences are due to inherited DNA differences. So that's kind of shocking to people, and it makes, um, a, a couple of points. One is, again, we're talking about differences between people in a population, given their environmental differences, you know, like some people are exercising and watching their diet and all of that, and other people, you know, just let it all go. But it's... And given the genetics that's there too, different populations differ genetically. You know, there's immigration, emigration across time. We're just describing differences as they exist in a particular population at a particular time. We're not talking about what could be. So with weight, for example, and this is the second misconception, if it's genetic, it's deterministic, it's fatalistic, and that's true of the thousands of single gene disorders. Like if you have this mutation in a gene at the tip of chromosome four, you know, we have 23 pairs of chromosomes, our three billion base pairs of DNA are chopped up into these 23 blocks we call chromosomes. So at the tip of chromosome four, there's a gene for Huntington's disease, which is what Woody Guthrie had. It's, uh, a, a, a long-term degenerative disease that doesn't show up till later in life. (laughs) So if you have that mutation for Huntington's disease, you will die from Huntington's. It is deterministic, hardwired. Unless something else kills you first, no matter what your diet is, there's nothing you can do to prevent it. Now, so it is deterministic, and that's the way people learned about genetics. That's what Mendel studied with his pea plants. These are hardwired, deterministic, single gene, necessary and sufficient disorders. However, when we get to psychological disorders and most common medical disorders, they're not like that. They're not due to a single gene. They're due to thousands of tiny DNA differences. And that changes the story from determinism to probabilistic propensities. It gives you a risk. So, um, so that's the second misconception. And... Go ahead. Sorry, I'm, I'm rabbiting on here.

   9. CWChris Williamson10:15

      Not at all. You've got a quote in the book I think that summarizes this beautifully, and it says, "DNA isn't all that matters, but it matters more than anything else, and it matters more than everything else put together in determining who we are."

   10. RPRobert Plomin10:28

       Right. Well, that's the heritability of 50%. If you look across all psychological traits, on average, they're about 50% heritable. Physiological traits, you know, weight, more heritable, 70%, height, even more heritable.

   11. CWChris Williamson10:41

       I need to stop you there. The heritability of weight being 70%, there are a lot of guys and girls listening that do fitness, there'll be PTs, there'll be dieticians that work incredibly hard to try and get themselves to their optimal BMI, to get their athletes down to a weight and a body fat percentage that they're supposed to.

   12. RPRobert Plomin11:00

       Mm-hmm.

   13. CWChris Williamson11:00

       And you're saying that the best diet regime would have been to have different parents.

   14. RPRobert Plomin11:05

       Well, absolutely. I mean, that would make-

   15. CWChris Williamson11:07

       (laughs)

   16. RPRobert Plomin11:07

       ... the biggest difference. But see again, the point I was getting to here is that we're describing what is in this population at this time with people, some people who are fitness nuts or really watch their diet and all of that, and other people who don't. We're saying of those differences in weight, how much are due to inherited differences? And the answer is more than half, 70% on average across many different countries, for example. But it's also true in the UK. It's about 70% heritable. Now the point though, the third point is, it doesn't... It's, it's a confusion between what is and what could be. We're describing a particular population. We say on average, 70% of the differences are due to genetic differences for weight. But that doesn't mean you can't control your weight, your own weight. It's, it's what is in the population. It's not what could be for one individual. Most obviously, if I was locked in a room and not allowed to eat, I would lose weight. And it's... Part of the problem too is people think, you know, I do have... We now have these genetic scores. We can predict about 10% of these differences in body weight with DNA alone now. It's about 70% heritable. So we've just started doing this, but, you know, predicting 10% is not bad.... I mean, there aren't a lot of other things that will predict BMI to that extent. So it, you know, it's a start, right, with this BMI. So my highest risk score for what we call polygenic, this DNA composite score, is for BMI. So I'm really meant to be a genetic fatty.

   17. CWChris Williamson12:39

       (laughs)

   18. RPRobert Plomin12:40

       But again, you know, people say, "Oh, well, you're just gonna give up and say you can't do anything about it." But, you know, to the contrary, I find it's very motivating. I know why I keep putting on ... It's invidious. You know, I put on a few pounds every year, but then you don't lose those pounds. And, you know, for some of us, they g- tend to go to the belly and, you know, and, and you know, people say, "Well, just pull your socks up," you know, "Just don't eat so much. Exercise more." It's easy for thin people to say, but if you have this propensity to put on weight, um, I think really what it is, it's not even physiological. I think it's psychological. We've done some research saying that the genetic propensity is more, um, we, we talk about sy- satiety, feeling full.

   19. CWChris Williamson13:26

       Yeah. Yeah.

   20. RPRobert Plomin13:26

       I go out with people, we're eating at a restaurant, pray God we can do it again pretty soon, but (laughs) you know, and I, I'm full and, but there's food on the table. We're talking away and before you know it, I've eaten that food.

   21. CWChris Williamson13:39

       (laughs)

   22. RPRobert Plomin13:40

       You know, I'm not hungry.

   23. CWChris Williamson13:42

       Well, that's, that's totally correct because for even when you're talking about particular traits, the individual ways that you can contribute to that trait manifesting can occur in a number of ways. Let's say that, um, that 70% could be contributed to from some people who don't like exercise-

   24. RPRobert Plomin13:57

       Mm-hmm.

   25. CWChris Williamson13:58

       ... some people who do have greater ghrelin release or leptin release or whatever-

   26. RPRobert Plomin14:02

       Yeah.

   27. CWChris Williamson14:02

       ... in the stomach that encourages them to feel hungry. Maybe some of them have bigger stomachs. Maybe this particular selection of traits is associated with having a larger stomach, or what, pick your route moving forward, whatever it might be. They just have a, an all-or-nothing mentality when it comes to food.

   28. RPRobert Plomin14:18

       No, exactly right. There's lots of different ways in which these genetic effects can come in. It's highly unlikely to be a simple pathway. It won't be.

   29. CWChris Williamson14:26

       Not, not everyone gets fat in the same way.

   30. RPRobert Plomin14:28

       That's right. And another major cue here that you didn't mention is, um, uh, responsiveness to food cues. So, you know, I can't... I used to like to make bread. I can't do it because the smell of fresh... and my mouth is watering now just even thinking about it.
4. 17:52 – 22:39

   How Genetics Are Studied

   1. RPRobert Plomin17:52

      10 years from now.

   2. CWChris Williamson17:53

      How do you study this? Let's say that one of the first things that I thought upon swallowing the huge industrial-sized red pill that I had to reading your book was, "Yeah, but..." I just had all of these "yeah, buts" in there. "Yeah, but how are they studying this?" So what's... How are you able to separate out all of the different genetic influences on traits?

   3. RPRobert Plomin18:15

      Well, there's two questions there. One is, how do we measure it? The other is, how do we separate out genetics and environment? On the first bit-... I would just say that, um, I- I- I particularly like to study cognitive abilities because you can measure them, you know, like spatial ability and memory ability, and you can measure them accurately and their maximum performance. You know, so you take this test and you'd be trying to do as well as you can do on it. And your scores today will be highly correlated with your scores next month and next year. They're highly reliable, these sorts of scores. The problem with other sorts of measures like personality is if I ask you, "How shy are you?" Well, you think of, "Oh, but what context do you mean?" So we try to ask questions about many different contexts. You know, like were you at a party with strangers, which is the kind of key aspect of shyness. The shyest person on Earth is not shy with pers- of someone they love, they live, you know, they live with or they- they're very familiar with. Shyness, anxiety doesn't enter into that. So it is difficult to measure, but I... Without going into it in great detail, I would just say, um, psychologists have spent a century trying to measure these things, and I think they do pretty well at it. Um, but now the issue of how... Okay, so now you've got a measure. I mean, weight's easy. People differ. And they, for most of these traits, they differ in what we call the normal distribution, a bell-shaped curve. So for weight, there's some people who are extremely obese and there's some people who are extremely thin. Most people are in the middle. That's this bell-shaped curve. That's the individual differences that I'm talking about. And if I use the word variance, that's a statistic that describes the extent to which people differ, the variance. The- So you describe this distribution with a mean, the average, which is in the middle of this bell curve, and then this statistic of variance, which describes the extent to which people vary around that mean. Because a distribution, I don't know if y- you can see it here, a distribution that spreads out has a lot more variance than a distribution that's tight like this. So, um, so the way we study variance and why people differ, as I mentioned, involves methods from a century ago called the twin study, which compares identical, i- and non-identical twins. So identical twins are clones of one another. Their DNA is exactly the same. Fraternal twins, or non-identical twins, like any brother and sister, are f- 50% similar genetically. So of the DNA that differs, that 1%, they're similar for about 50% of that. So if a trait's influenced by genetics, you'd have to predict that identical twins are more similar than non-identical twins because they're twice as similar genetically. So that's the twin method. And the adoption method's even more straightforward. In families, nature and nurture runs together. So the fact that, uh, parents who are schizophrenic have kids who are more likely to be schizophrenic i- is always assumed to be nurture, but it could be nature. There could be genetic influences there. And one way to do, to tell that is to separate nature and nurture. So you can have birth parents who are s- become schizophrenic later in life who relinquish kids for adoption, and those kids are adopted away in an adoptive home where the parents are unlikely to have schizophrenia. So that is a direct estimate of the extent to which parent-offspring resemblance is due to genetics. And the converse side of it is just as neat. You've got adoptive parents of adopted children. They share nurture with those kids. They adopt them early in life, so they're the environmental parents of those kids, but they're not genetically related to those kids. So these two methods, what's nice is they're very different. They each have different problems, but the convergence of evidence from both of these measures, methods is- is really very impressive. And so that's how we get to this conclusion that across... If you take all psychological traits, say in twin studies, you get an average heritability estimate of 50%, which is just extraordinary given that 30 years ago, most psychologists would have said, "Nah, there, there's really no important genetic influence."

5. 22:39 – 27:39

   Biggest Ever Twin Study

   1. RPRobert Plomin22:39

   2. CWChris Williamson22:39

      How many twins have you studied? Or how many people have you used in these adoption studies, in these twin studies? Am I right in thinking that you have been part of the biggest ever?

   3. RPRobert Plomin22:50

      You know, when I came to England in 1994, part of the deal was they gave me a grant to study... to put together a huge sample, 10,000 pairs of twins at birth from birth records.

   4. CWChris Williamson23:01

      10,000 pairs of twins.

   5. RPRobert Plomin23:03

      Yeah.

   6. CWChris Williamson23:03

      20,000 people.

   7. RPRobert Plomin23:04

      Yeah. One, one percent of all twin births are twins and there's, say, 7,500 births a year, at least there was back then when I started this 25 years ago. So that's, you know, just about what you'd expect. And a third of those are identical all around the world, and that means two thirds are non-identical. So, um, we studied these kids 14 times between the ages of infancy at two through adulthood at 25. We most recently studied them at 25. They were all born in '94, '95 and '96. So we started with about 21,000 sets of twins. We excluded some because of illness, especially death. We, we spent a lot of time making sure we didn't contact... Imagine if you had a- a new birth of twins and one of them died, it wouldn't be too cool to get a message saying, "Oh, would you like to participate in this exciting new study of twins?" So we spent a lot of time making sure we didn't do that. And so we ended up with about 85% participation rates, which in this sort of s- s- study, you know, is- is amazing. But that's because parents of twins know they're special. And-

   8. CWChris Williamson24:16

      Is this... Sorry, is this just in the UK?

   9. RPRobert Plomin24:18

      Yep.

   10. CWChris Williamson24:19

       Okay. So we're, we are-

   11. RPRobert Plomin24:20

       Well, it's just England and Wales.

   12. CWChris Williamson24:22

       Okay.

   13. RPRobert Plomin24:22

       Scotland had their own thing.

   14. CWChris Williamson24:23

       Okay. Is there any criticism around the fact that the heritability that is represented in England and Wales-... wouldn't scale across the rest of the world?

   15. RPRobert Plomin24:32

       Now, it's a great question because remember I said we're describing what is in a particular population at a particular time. So it's an empirical question, but there have been studies around the world. There's been three million pairs of twins studied around the world in about 3,000 different reports. And it could be the results are very different, but it turns out they're not very different.

   16. CWChris Williamson24:54

       (laughs)

   17. RPRobert Plomin24:56

       And, you know, that's really remarkable and I always struck... I study cognitive abilities and in India, you have studies in rural India where people are mostly illiterate, and then you have very urban societies in India. The results don't change much, you know, they're still coming up with very substantial heritability. And it didn't have to be that way, and it'd be quite interesting if it weren't that way, but on balance, it's quite... The most remarkable finding in, uh, in relation to your point is that the results are so similar across many very different countries.

   18. CWChris Williamson25:30

       Did you find or see any groups which are less heritable? Is there an area on the planet that seems to be statistically decreased?

   19. RPRobert Plomin25:38

       Well, the one that's been of interest in the last decade or so is not different populations, but within a population, the thought that kids from very deprived backgrounds, lower socioeconomic status backgrounds, the heritability is lower is what, what they were saying. And it kind of makes sense because you think the environment is so overwhelming, you know, at the extreme end of social-

   20. CWChris Williamson26:11

       Discomfort. Yeah.

   21. RPRobert Plomin26:13

       All right. And so that was an interesting notion, but there's been a dozen studies since, and they generally don't confirm it. The one thing that's left is the guy who found it initially is in America. He's done several subsequent studies where he says he still finds it. And so the possibility exists that maybe it's less heritable for low-SES kids in America, but not in the rest of the world, which is Europe, Australia, Southeast Asia. And, you know, there... Again, it would be a great story if it's true. I'm kind of dubious that it's true. This is a guy kind of hanging on to a finding that everybody wanted to believe because it's a really cool finding, you know, gene-environment interaction. The idea different strokes for different folk. But, um, it could make sense because in, uh, the US, um, it's the most decentralized education system in the, uh, uh, developed world. So every little school district, they just make all their own decisions. So you could imagine that creates a, a lot of environmental variance. And then you could imagine that the kids in the lowest SES schools are in the bottom of that pile, perhaps. So if it were true, it would be interesting. So I guess the point I'm making, I don't have any... I don't have any skin in this game of trying to say it's the same result everywhere. In fact, I find it really interesting if we could find groups or countries where the results are very different.

6. 27:39 – 36:32

   Do Genes Influence Behaviour & Health?

   1. CWChris Williamson27:39

      Doesn't seem to be that way though. Okay. So-

   2. RPRobert Plomin27:41

      Not so far.

   3. CWChris Williamson27:42

      How, how do genes influence our behavior? Like is there a violin playing gene and a premature ejaculation gene and a dog-loving gene?

   4. RPRobert Plomin27:50

      Yeah, that's what people tend to think about. You say genetic and they think single gene. Well, for the single gene disorders, it is a single gene. You know, I mean, Huntington's, we know pretty much what that gene does and how it affects the, the brain. It, it starts creating, um, we call them repeat sequences, but you know, it, it messes up the gene by reproducing not what it's supposed to reproduce, but extra bits. And those extra bits just start mucking up the proteins it creates. And then eventually the brain just starts to degenerate as a result of having all this muck around. But when you get into complex traits and common disorders like heart disease or, um, or obesity or psychological traits, there's no example of a single gene disorder. And if there are thousands of genes involved, each contributing a tiny bit of risk, um, what are the chances you're going to find an intervention that works? Because, you know, people still think of the brain in this kind of simple-minded neurologizing way. This does that, this bit of the brain does that. But, you know, I think, uh, if there's thousands of genes, they're going to work at the level of the brain and they're going to make it very difficult to find any pathways. It's just a... you know, and which kind of makes sense, you know, from an evolutionary perspective if- if- you... If you want to have a species evolve, you're not going to just say, "Oh, well, let's make it simple for neuroscientists and have this one simple pathway that makes all the difference." That would be disastrous really. What you would do as natural selection is take advantage of all the DNA differences that are there, and you'd select for behavior, you'd select for people who are, say, brighter and solve problems more quickly, and you'd take advantage of all the DNA variation that exists everywhere, not even just in the brain, in the body as well. So I- I think it does make sense. It- it's a... it's not a happy story for molecular biologists who want to do a reductionistic-

   5. CWChris Williamson30:02

      Yeah.

   6. RPRobert Plomin30:03

      ... approach to gene. This gene does this and that does this in the brain, and then that causes this in behavior. So... But as a psychologist, I'm interested in the behavior, you know, and, um, so it's okay by me. And what's exciting now is we can predict these behavioral differences with DNA itself.

   7. CWChris Williamson30:21

      I guess what you're saying there, the fact that it's... it provides a challenge for interventions, what you're referring to is that if you wanted to go in and edit the genes to make someone-... a thing-

   8. RPRobert Plomin30:33

      Yeah.

   9. CWChris Williamson30:33

      ... if you wanted to try and manifest a trait, you don't just get to go and poke one of them. You actually have to poke a lot of them. And I'm guessing that the 10% that you're now able to predict BMI, uh, in life is because you've managed to bundle together around about one-fifth of the genes that are, uh, uh-

   10. RPRobert Plomin30:54

       Yeah.

   11. CWChris Williamson30:54

       ... responsible for causing that weight.

   12. RPRobert Plomin30:55

       Yes. Yes. Well, I agree with the second part of what you said. About the first part, it makes interventions difficult. I don't think so, because an important, um, uh, I don't know if it's a law, but, I mean, for me, it's just about a law, is that cures aren't necessarily related to causes. Now, you always think if you find out a cause, then you fix it. Now, that's true with single gene sorts of things. It's true with single environmental agents like SARS, um, 2, and COVID. You only get COVID if you get infected with this virus. So you wanna know who has it, who doesn't have it, it's dichotomous, and then you pick the people who've got it and you think, "Well, what can we do to prevent other people from getting it, to make the course of the illness less bad, to stop people from dying?" So, you know, definitely knowing the cause helps a lot in knowing the cure. But now, what if you take common disorders and psychological traits where we've got thousands of genetic differences? There is no single cause. There's a whole gemish of causes, and I think it's gonna be very difficult to have these causes tell you what to do about cures. But fortunately, cures don't... are often, most often, not related to causes. So if a kid has a reading disability, neuroscientists often think they're looking for the hole in the brain, they're looking for the bit of the brain that misfires, you know, f- and, um, long story's there. But if there's thousands of DNA differences involved, I think it's just some kids have more trouble learning to read. It's not that they're dyslexic, you know. If you wanna make... medicalize it, you give it a, a Greek or Latin name, and then, then you say, "I'm sorry, madam, your child has dyslexia." You don't say they have reading problems because a psychologist could tell them that. A- and similarly with hyperactivity. You don't say, "Your kid has poor attention span." You say, "Your kid has hyperkinetic disorder." You know? 'Cause it medicalizes it, and then you think there's a simple cause, and then you think there's gonna be a simple cure.

   13. CWChris Williamson32:59

       What people like is giving the name to it wrangles the chaos into order, right? Okay, it's a thing. I know that it's a thing. I think you've got a quote that says, "There are no disorders, there are just quantitative dimensions."

   14. RPRobert Plomin33:11

       Yes. That's this bumper sticker of the normal... the abnormal is normal. What the genetics su- suggest is that... more than suggest, it really, I think, necessarily implies that if there's thousands of genetic differences affecting a trait like reading disability, those genes are normally distributed. So some people have a lot, just by chance, of those DNA differences that make it more likely that they'll have problems learning to read. Doesn't mean they're, you know, gonna have reading disability or be diagnosed with it. Just, it's a propensity. And what I like about this is it's, it's gonna be the nail in the coffin of diagnoses. So in medicine, the illness model, medical model, you know, it worked really well when you've got simple causes. So you wanna find out what caused the cholera, someone figures out it's bugs in the water, you know? And then you stop the bugs in the water and you cure this. But it doesn't work that way for common disorders or quantitative traits. And although it might make people feel better to say, "Ah, I know why I've been having so much trouble in life, I have dyslexia," you know, or whatever, and it... but it's, it's g-... the truth has got to be better, and that is that there is no... it's just all quantitative.

   15. CWChris Williamson34:26

       Yeah. So-

   16. RPRobert Plomin34:26

       It's not a matter of either or.

   17. CWChris Williamson34:27

       To drive that home, there's no point along this normal distribution at which after this point somebody becomes labeled dyslexic or dyspraxic or whatever it might be. There are a whole bundle of traits that are normally distributed. Some people have a particular combination-

   18. RPRobert Plomin34:44

       Mm-hmm.

   19. CWChris Williamson34:44

       ... of those which has created-

   20. RPRobert Plomin34:45

       Yeah.

   21. CWChris Williamson34:45

       ... a meal, and that meal is a restriction in their ability to read. But, as we said before, that could come from a number of different pathways as well. The same ways you can gain weight by not liking exercise or by liking food too much, or by doing both, or by any other number of things-

   22. RPRobert Plomin35:00

       Mm-hmm.

   23. CWChris Williamson35:00

       ... you can be not very turned on by reading, or you can find it hard, or you can struggle to gain vocabulary, or you can da-da-da-da-da-da-da. And then the medicalization that you've got where you give particular terminology, what you're doing is bundling common disorders or orders into a title which combines those traits together, and, and that's the outcome that you get.

   24. RPRobert Plomin35:23

       And it's dichotomous, you know? It's-

   25. CWChris Williamson35:25

       You are or you aren't, yes.

   26. RPRobert Plomin35:26

       ... either or... You are or you aren't. And what's bad... what I like about this normal distribution, this quantitative idea is that it's not like those schizophrenics and us normal people. You know, we all have thousands of genetic risk factors for schizophrenia. It's just a question of how many you have and how you, uh, interact with the environment, 'cause even if you have a very high score, it doesn't mean you're necessarily gonna be schizophrenic, um, partly because we're only explaining about 15% of the liability to become schizophrenic. So it's not deterministic, it's probabilistic, but I... there's a lot of advantages to thinking about these things quantitatively because you're not trying to cure a disorder. There's no disorder. You're not trying to cure it. You're trying to alleviate symptoms quantitatively, you know? The, the, the, the output here... what you wanna do is not just say, "Okay, they're cured." It's not gonna happen, you know? And so there's many ways in which I think it is important. I think this medical model has been holding back psychological research.

7. 36:32 – 50:09

   Heritability of Different Traits

   1. CWChris Williamson36:32

      I wanna give you a list of a bunch of different things that I've come up with, uh, and we're going to see if you know how heritable they are, or if they are or if they aren't. Uh, well, they, they all will be, as we've alrea- already identified. Uh, so aggression or antisocial behavior, stuff like that.

   2. RPRobert Plomin36:47

      Yeah. Well, that's an interesting one. Aggression...... it, it's hard to measure, but if you just do it the usual way with self-report personality questionnaires, most personality measures, including aggression, are less heritable than other traits, like cognitive traits. They're about 40% heritable. I mean, 40%, 50%, not much difference, but, you know, it's not 100%, it's not 80%, and it's not 10% or 20. It's- you know, it's substantial, but it's not the whole story. But psychopathy is interesting because early in life, it seems to be very highly heritable. And you wouldn't think you could measure it early in life. It's not... These are the kids who... My colleague, Essie Viding at UCL, has studied this for a long time. It- it's more technically called, um, callous unemotional psychopathy. These are the kids who tear wings off flies. They'll, they'll hurt animals, not, not 'cause they like to hurt things. It just, it doesn't, you know, it doesn't bother them. And so psy- psychopaths aren't out to hurt you either, even as adults. They want something, and if you're in the way, you know, they'll push you aside, because it just... there's no empathy there. So I think that's a really interesting one and it remains... uh, it's not shown, but early in childhood, it's- it's very highly heritable. Then when you get into middle adulthood, it gets mixed up with delinquency, which is almost normative. Shoplifting, you know, doing stuff when you're an adolescent, destroying, vandalizing property. You know, I'm not saying it's a good thing, but, you know, so many kids do it. Some people have said it's actually predictive of better mental health later, but that's a different story. But the point is, these kids who are cruel and doing bad things, they get sucked up into this adolescent delinquency thing, but then they come out the other end being more psychopathic, whereas the normative sort of usual delinquent behavior in adolescence tends to drop out.

   3. CWChris Williamson38:48

      Okay. IQ.

   4. RPRobert Plomin38:50

      That is one of the more highly heritable traits. It's probably... it- it's interesting. Over the lifespan... Well, first of all, we used to say it's 50% heritable, but almost all those studies involved kids, just because it's easier to study twins and adoptees when they're living at home. But then when you got to, um, adults, you find that the inheritability of IQ increases linearly throughout the lifespan. 20% in infancy, 40% in childhood, like the early school years, 60% in young adulthood, and some people say even 80% later in life. Now, that's really interesting. How can heritability change? But it makes the point we're just describing differences as they exist in a particular sample. And so if you look at young samples versus old samples, heritability now consistently... We've done meta-analyses across all these things, it consistently goes up in an almost linear way.

   5. CWChris Williamson39:51

      Why do you think that is?

   6. RPRobert Plomin39:52

      Well, it- it... Nobody knows for sure. I think, and I think most people think, it's because genetics isn't... it isn't like hardwired in the brain. Um, it's not... What it is, i- it makes you use your environment differently. So if you s- if you study these really bright young kids and say, "What are they doing?" It's... they're asking questions. They go into a room and they wonder about the angles at the corners of the room. You know, they just use their environment i- in a better way. Uh, they get a lot more information out of it. The classroom is a good... the teachers can teach something to kids, but some kids will get so much more out of it than others. And I think as you go through life then, you... it's called, this is called gene-environment correlation. As you go through life, i- it's not that... it's not that the heritability is there at the moment of conception, you know, and it doesn't change. It- it makes you, um, use your environment differently so that you select environments, modify them, and create environments correlated with your genetic propensities. So kids who are academically oriented, they hang out with other academically oriented kids, they read books, they're interested in intellectual things, whereas other kids have other appetites. And increasingly, I think it's appetites. It's not aptitudes, it's not this hardwired, um, you know, brain that's making the difference. It's just these sort of psychological appetites, you know. It's what you like and what you like you do, and you tend to get better at that so that the differences snowball until later in life. Um, you know, see, my parents were 97 until they died a couple years ago and they were in an old people's home, and you really see the differences there. I mean, some of these older people are still very active intellectually. You know, they don't lobotomize themselves on television. They argue with people, they read the newspapers, you know, they're really alive and the differences seem to be even greater, you know, later in life. So I think that's what happens. It's snowballing. These little genetic effects become bigger and bigger as you go through life selecting and modifying and even creating environments that are correlated with your genetic propensities. But-

   7. CWChris Williamson42:10

      Are there any traits that do the reverse of that?

   8. RPRobert Plomin42:13

      Um, we don't know of any. So when heritability changes, it goes up. Some people say that's true for body weight as well. Um, most of the time, like personality, there's no evidence that heritability changes across the lifespan. So, um, it just... Anyway, so cognitive ability is more heritable than personality, maybe 60%.

   9. CWChris Williamson42:37

      Uh, academic outcomes, is that the same?

   10. RPRobert Plomin42:39

       Uh, no, it's not. You know, the correlation between how well you do at school and your IQ is about 0.5 in the hundreds of studies that have looked at this. But, um, one thing that's interesting is in the early school years-Educational achievement, which in England is great. You know, they have these national tests. Not great for the kids maybe, but it's great for researchers because, you know, they're the most tested kids in the world. So you get very good educational achievement data, at least for what tests are measuring. And they're substantially more heritable in the first school years, like 60% heritable as compared to IQ, which is 40% heritable. And I think that's really interesting. But educational achievement stays at about 60% heritability all the way through GCSEs and A levels, whereas IQ is going up and up and up, and they cross somewhere in adolescence.

   11. CWChris Williamson43:31

       Ah, that's so interesting. So you don't have as much of an increase in heritability over time with academic outcomes as you do with IQ?

   12. RPRobert Plomin43:40

       Yes. And so, um, yet again, I don't know why, but I wonder if it ... This raises, uh, bring- It's worth going into this, like why is that? Because it raises another issue I think that's important and that is that I think what... Educational achievements, what teachers teach. We have a national curriculum and there, teachers have to teach certain things on certain days. You know, it's very prescribed. And so kids who come to school without much background, they very quickly do their phonetics, get into reading, but no one teaches IQ. I think they ought to, because IQ is general reasoning, abstract reasoning, the scientific method, I think. And I think we need a, a, a heavy dose of that. People need to recognize the importance of thinking logically and taking new facts and coming up with hypotheses and realizing you don't believe them, you test them, and you have to test them. So I think that has a lot to do with IQ. We don't teach it. So as a result, I think when kids come to school, you know, um, they're ... Well, they're not, um, they're not getting the, the full possibilities for ex- expressing their genetic propensity. So again, it's just that, again, we're describing what is in a particular population, in this case, the early school years, the, you know, and then going on through key stage two, three, four. Um, and one other thing I'll mention is, you know, Michael Gove, when he was, uh, Secretary of Education, uh, what, almost a decade ago now, he instituted this idea of, of the phonetic screening test. You know, a lot of the Tories, they think it's a ... Whatever was in the '50s, the good old glory days, that's what's gotta be good. And they taught reading by phonetics then. And somehow in the '60s and '70s, educators began to teach reading through word recognition and, you know, recognizing whole words and not worrying so much about spelling and phonetics. Well, so Michael Gove said, "Teachers gotta teach phonetics." And he instituted this test, a four-minute test of phonetics. And it's really kind of a cool test. Two minutes where you read age-appropriate words. At seven, they're like dog, cat, you know? And, and then as fast as you can, as many words as you can in two minutes. And then there's a, a list of matched non-words. So these are not words, they're like tep, T-E-P, um, gep, you know, G-E-P. They're phonetically and linguistically matched, but the only way you can say what the word is if you can sound it out phonetically. And so Michael Gove thought this is gonna be a test of how well the teachers are teaching, and he was gonna name and shame those schools that didn't do phonetics. It's the most heritable test we have. So at seven, when these kids have to take this test, that test is 70% heritable, which is amazing given that it was... No one even questioned this. They said, "Well, okay, it's a phonetics test. So kids didn't learn phonetics by themselves, so this is a test of how well the teachers have taught phonetics." But instead what it says is some kids pick it up a lot better than others. I'm convinced there's individual differences all over the place. I bet you there are some kids who would learn to read better with whole-word reading. But we force all these different-shaped pegs into this one round hole of the national curriculum, and I think that's the biggest lesson to learn in education. And teachers know it. You can't stand in front of a class of 30 kids and not recognize that some of them pick stuff up very fast and others just need a lot more help. So I'm particularly keen on education because that's the business end of these cognitive abilities. So I keep distracting you. We, we just said IQ-

   13. CWChris Williamson47:29

       All right, so next one. Next-

   14. RPRobert Plomin47:30

       ... changes during the lifespan, but 50% heritable al- on average.

   15. CWChris Williamson47:34

       Got you. Next one, penis size. Did anyone research penis size?

   16. RPRobert Plomin47:39

       There have been studies on it, but I'm not aware of genetically, um, sensitive studies.

   17. CWChris Williamson47:44

       Shame.

   18. RPRobert Plomin47:44

       Yeah.

   19. CWChris Williamson47:44

       Someone should do that. Diabetes.

   20. RPRobert Plomin47:47

       Yeah, that's been studied a lot. And it's, maybe... It's tricky when you're dealing with these disorders. Diabetes isn't a disorder, it's a quantitative trait, right? And y- um, so many of these disorders are, like heart disease, they're not disorders. So hypertension. These are pretty normally distributed traits. And things that work, work quantitatively too. So when you've got a dichotomy, it makes it much more difficult to say how heritable it is, because all you've got is a zero and a one.

   21. CWChris Williamson48:18

       At what point does diabetes become diabetes?

   22. RPRobert Plomin48:22

       Well, but you take it for what it is and then you create these very complicated statistics called liability. Right? Uh, it's a liability to the disorder 'cause you recognize it's not really a disorder. But if you look at simple concordance, you know, um, that's like if one identical twin has schizophrenia, what's the chance that the other one does? And even though you don't believe it's a dichotomy like that, and the answer is about 50%, the identical twins are similar. And non-identical twins, their concordance for a diagnosis of schizophrenia is very much lower, about 7%.... now, they're- they're half as similar, genetically, as identical twins. So you would've expected them to be about 25% similar because identical twins are 50% similar, but they're only 5%. But it's just because in a way- because th- these things are not very useful statistically when you're dealing with a dichotomy. It makes it, makes it trickier, but the evidence is still very clear that genetics is important.

   23. CWChris Williamson49:27

       Got you. What about, uh, a happiness set point or sort of self-reported, uh, life happiness?

   24. RPRobert Plomin49:34

       Well, there- there's a lot of work about, um, depression and, um, wellbeing, which is what a lot of people mean by happiness, a sense of wellbeing. Um, it- it's all a tricky business, but if you look across all those studies, they're about 40% heritable when you measure them quantitatively. At least with happiness, you're not saying people are either happy or not. So you measure it quantitatively, and when you do for wellbeing, um, you find that about 40% of the differences between people can be ascribed to these inherited DNA differences.

8. 50:09 – 55:57

   Seeking Happiness

   1. RPRobert Plomin50:09

   2. CWChris Williamson50:09

      That's crazy when you think about how much work people put into trying to make themselves happy. You know, it's one of the- the most common conversations that podcasts have. I actually, I actually quite err away from having it on this show, uh, especially after reading, uh, your book, but also generally it's just a bit of an icky topic to me to talk about happiness and this generation of it as if that's the only thing really that people should be aiming for in the world. There's a lot of other contributing factors to this sense of wellbeing. Have you got meaning in your life? Do you have connections? When does that become happiness? So on and so forth.

   3. RPRobert Plomin50:41

      Yeah. Yeah.

   4. CWChris Williamson50:42

      But, yeah, it's, uh-

   5. RPRobert Plomin50:42

      Well, I suggest people do some meditation training or something, you know, to recognize that you don't become happy. You've only got this instant.

   6. CWChris Williamson50:50

      You be happy. Yeah.

   7. RPRobert Plomin50:51

      And you either... You're- you can be happy, be here now, that sort of thing. I mean, as hokey as these things sound, like y- we mentioned Sam Harris, we were talking before, and you know, I think his app, Waking Up app is- I- it's really changed my life in a lot of ways. I- I was in philosophy and- and I- I took against it because it's not empirical. Um, I can go into that a bit, but psychology is actually the empirical side of philosophy, but it can only deal with things you can test, right? And-

   8. CWChris Williamson51:17

      Psychology is the empirical side of philosophy. I like that.

   9. RPRobert Plomin51:21

      Right. Well, it was because I was at a place at DePaul University in Chicago that specialized, um, in phenomenology. Now, that's the branch of philosophy that talks about the is-ness of things, like the desk-ness. What is it that's the essence of a desk, you know? Okay, fair enough. But after I heard this about the third time, I kept saying, "Well, there's these huge arguments about it." And I'm saying, "How do you know this guy's right or that guy's right?" There's gotta be some way to test it, and I ran into a stone wall because I realized finally that if you can test it, it's no longer philosophy. And I asked, "What is it?" It's psychology, if you can actually test it. So at that point I decided, "Well then great, I'll go into psychology," which is what I did. And I've- I've sort of been anti-philosophy.

   10. CWChris Williamson52:07

       Well, you've come full circle now.

   11. RPRobert Plomin52:09

       I have, yeah. Maybe that's a result of getting older or meeting Sam Harris and, you know-

   12. CWChris Williamson52:15

       Perhaps.

   13. RPRobert Plomin52:15

       ... it's- it's not the... You know, philosophy went bad in the '70s. It went into linguistics and, you know, it's not like... I'm really into stoicism, which is the most ancient, um, philosophy around Confucianism. And I think it's very practical psychology what they're talking about there. Well, modern philosophy, you know, is not that. I mean, it's really dealing with this very abstract mathematical linguistic sort of stuff. Fine, you know, everybody do their own thing, but there's gotta be room here for philosophy in the old sense. You know, the ethical and moral and what does it mean to be human and how- how can I be happy or, uh, become happy and, you know. So I think it's a great point and, um, having said that, uh, I agree completely, you know, that people are obsessed with becoming happy and that's a losing proposition in a way. You know, the- the Stoics talk about this. William Irving has written some great stuff about stoicism and he- the Stoics, you know, were talking about many, many centuries ago. Uh, they talked about hedonic adaptation, and if you live life because you'll just be happy if you can get X, Y, or Z, the new car, the new house, the new job, but then you get it and yeah, you're a little bit happier for a while, but then there's hedonic adaptation. You get used to it. And again, it's not making you happy. In fact, if it could have made you happy, if something could have made you happy, you've been spending your life trying to be happy and it hasn't made you happy, you might get the idea trying to get what you don't have is not the way to go. And the Stoics say it's the other way. It's to say, um, use these techniques like negative visualization to want what you have and to realize what you have you may think is shit, but you'll say there's about a billion- 10 billion- billions of people on earth who would do anything to trade lives with you.

   14. CWChris Williamson54:17

       But that's the thought experiment, right? Like the- the things that you now have are those which only once you dreamt of and when-

   15. RPRobert Plomin54:24

       Yes.

   16. CWChris Williamson54:24

       ... you actually, when you reframe stuff like that. Yeah, I, um, I had Rupert Spira on the show recently, non-dualism guy.

   17. RPRobert Plomin54:31

       Oh, yeah.

   18. CWChris Williamson54:32

       Uh, I found him very, very clear and precise with how he put across non-duali- non-duality as a philosophy, which is-

   19. RPRobert Plomin54:39

       Mm-hmm.

   20. CWChris Williamson54:39

       ... can get a bit, get a bit messy at times.

   21. RPRobert Plomin54:41

       I'm still having trouble with that. You know, I'm- I'm struggling with it. Sam Harris has a new whole lecture series by someone on this non-dual-

   22. CWChris Williamson54:48

       I think it might be Rupert. So he, he's definitely got-

   23. RPRobert Plomin54:50

       Oh, it is. You're exactly right. It is. So I started that today.

   24. CWChris Williamson54:53

       Very softly spoken British man.

   25. RPRobert Plomin54:55

       Exactly. I started listening to that today.

   26. CWChris Williamson54:57

       Okay.

   27. RPRobert Plomin54:58

       Even with Sam, I still have trouble with this i- Maybe I have too big an ego to deny myself

   28. NANarrator55:03

       (laughs)

   29. CWChris Williamson55:03

       Separate yourself from the experience. Yeah. Well, I mean-

   30. RPRobert Plomin55:06

       Yeah.
9. 55:57 – 58:41

   Heritability of Sexual Preference

   1. CWChris Williamson55:57

      two more for you. Um-

   2. RPRobert Plomin55:58

      Okay.

   3. CWChris Williamson55:58

      ... is infidelity heritable? Have you ever been able to look at this?

   4. RPRobert Plomin56:04

      Um, well, David Buss, you know, studied it, a good friend of mine and from an evolutionary perspective. But, um, divorce has been studied and that shows heritable influence.

   5. CWChris Williamson56:15

      Do you know how much?

   6. RPRobert Plomin56:16

      Uh, not, you know, not a lot. Maybe 30% or so.

   7. CWChris Williamson56:19

      That's (laughs) that's quite a lot.

   8. RPRobert Plomin56:21

      Yeah.

   9. CWChris Williamson56:23

      (laughs)

   10. RPRobert Plomin56:23

       Um, and again, it's not because you have genes for divorce. You know, you say that there's heritable influence on divorce. People say the divorce gene.

   11. CWChris Williamson56:31

       (laughs)

   12. RPRobert Plomin56:31

       Or you talk about aggression, the warrior gene, for example. Uh, and it's not that. It's like what makes people get divorced? Well, I think a lot of it has to do with, um, joie de vivre, good things, you know. You get, maybe you get bored, you're a sensation seeker, or you just really like the fireworks of love and ro- romance. These may have been the things that made someone attractive in the first place, but it could be that those same things make them more at risk for, um, uh, divorce. So I don't know of a study of infidelity. I'm sure there are some though, but it's not something I have looked into.

   13. CWChris Williamson57:12

       What about sexual preference? The gay gene is something that people have talked about-

   14. RPRobert Plomin57:17

       Yeah.

   15. CWChris Williamson57:17

       ... for a very long time. What does-

   16. RPRobert Plomin57:18

       Yeah.

   17. CWChris Williamson57:18

       ... how does this come out in the research?

   18. RPRobert Plomin57:20

       Well, see that got started, you know, when the DNA revolution was just happening, it was way premature and it wasn't true, you know, that there's a gay gene. But, um, Michael Bailey at Notre Dame has done most of the work on this. And there's, there is genetic influence on sexual preference. And I know some people get very upset about that, but, um, I think most gays are happy to accept that because it means it isn't just, um...

   19. CWChris Williamson57:48

       A lifestyle, fashion choice.

   20. RPRobert Plomin57:49

       Yeah, ex- exactly. Yeah. Which i- in the current identity politics day, it seems to be getting to be more, more like that.

   21. CWChris Williamson57:57

       Yep.

   22. RPRobert Plomin57:58

       But there is a genetic component. I worked at an adolescent treatment center where we had three, um, gay boys when I was in graduate school. And, you know, they just tell you this story from early in life, they just really knew they were different and they hid it. They tried their best to be daddy's boy and everything. And then fortunately, and by the '60s or so, it got a, a little bit easier for people to come out. So again, I think it, it's i- important to recognize there is a genetic tendency. It doesn't mean everybody who is gay has this genetic tendency. It's just overall in the population of gays, there does seem to be a genetic propensity, but it doesn't mean you're determined. It's not hardwired. It's just like all these other traits.

10. 58:41 – 1:03:22

    Do Children Behave Like Their Parents?

    1. RPRobert Plomin58:42

    2. CWChris Williamson58:42

       The thing that I'm interested in, eh, here when talking about the genes is, is a child's behavior like an aggregate of their pa- of how their parents' behavior manifests? So, or can you have genetic influences on behavior which kind of come out of nowhere? So could you have two very calm parents whose DNA combines to make an easily pl- prone to anger or violent child? Obviously we're talking on average here.

    3. RPRobert Plomin59:05

       Yeah. Well, it's a good point because a lot of people think, "Well, you get your genes from your mother and your father, so surely you have to be a blend between them." But the thing is, these are discrete units. That's what Mendel figured out long ago. Genes don't just blend. They're, um, they, they're discreet. So you can have zero, one or two, we call them alleles, form of a, of a particular gene. Now you look at polygenic scores that involve thousands of these, those scores will be deli- um, normally distributed within a family. I mean, we can show this and we've always known this to be true. So that means that, um, say parents where one is very highly educated and the other isn't, it's not like the kids are all going to be in between. They're going to have a whole range of individual differences, including some that are some of the brightest, you know, they have the highest genetic scores and some that have the lowest. And what I like about this is there's a concern about right now about genetic castes. You know, like the Indian caste system. And the idea is that by, uh, meritocracy is getting us into genetic castes because the Silicon Valley people marry each other and they have these super bright kids. But what's, I don't think it's true as long as there is mobility because if, say two parents, IQ is, um, mean of 100 and we'll call standard deviation of 15. So it means if you're at the 85th percentile, um, you have an IQ score, not of 100, but of like 115, and two standard deviations, an IQ score of 130. The average IQ of people with PhDs is 130. So suppose you have two parents with IQs of 130, what's, uh, gonna be the average IQ of their kids? It's not 130, it's 115. It's 50% heritable. So the kids will regress to the population mean of 100. So on average they'll have a considerably lower IQ than their parents. And, and then secondly, there's this big distribution of scores. Kids in a family with the same parents have genetic scores that differ a lot, not as much as anybody, any random people in the population, but a whole lot. So that you can get kids in the same, in a family with the same parents where one is genetically w-... has got all the goods and the other doesn't. And this is really comes home to me because my, my sister never liked school, never... was late to learn to read, didn't like to read. Still doesn't much like to read. Whereas I read early, not because my... My parents didn't have anything to do with this. N- neither of them went to high s- or they just barely finished high school in the Depression in the United States. So just on my own, I started reading even before I went to school, I got books from the library. And I always loved school because it was easy. I was good at it and, you know, got rewards for it. My sister just didn't like it. And yet we have the same parents, we have the same nurture and people say, "Well, but you've got the same genes too," when we don't. We can show this now with the DNA. And, you know, I think it's an important point to recognize that when university-educated parents have kids who don't want to go to university and it's like the end of the world. But then, do we want to force kids in, you know, with all their different shapes into these round, this one round hole of this golden yardstick of academics? I think there's a big movement now away from that. Um, so we might talk more about that later.

    4. CWChris Williamson1:02:29

       Yeah, it's so interesting. That, that point, I, I never even realized that you, as a set of parents providing traits to your child, you're, you're competing or you're sort of almost aggregating them against where the center of that normal distribution for the population is. So if you're an outlier on either side of that, it's either going to drag down or drag up on average from wherever you are.

    5. RPRobert Plomin1:02:54

       Yes. And, and then the other part of it though is that there'll be a big range of your kids don't all have that one mean score. They-

    6. CWChris Williamson1:03:01

       It's not everyone is 450 in IQ. Yeah, yeah, yeah.

    7. RPRobert Plomin1:03:04

       They, they vary a lot, you know, and, um, I think that's hard for some parents to accept. Like, with my sister, we thought, "Well, you know, she just wasn't trying hard enough." But, you know, again, it's appetite. She just didn't like it, you know, she just didn't like academic training. She went on to do a good life. She was a lab tech in a hospital. She did save people's lives by doing these blood

11. 1:03:22 – 1:09:54

    Non-Genetic Impacts on Behaviour

    1. RPRobert Plomin1:03:22

       tests very carefully and, and she's very good with, you know, fine motor stuff. She just likes that and she's good at it, and the world's a better place for it.

    2. CWChris Williamson1:03:32

       All right. So outside of genetics, what are the other influences on our behavior? How do they slot together?

    3. RPRobert Plomin1:03:39

       Um, so you're, you're talking about the 50% of the differences that aren't due to genetics. That's the other big story that we haven't touched on because psychology for a century just assumed everything's nurture. The way you are is the way your parents treated you. You know, I mentioned schizophrenia before. But also kids do well at school because they have parents who did well at school. Why is that? Well, the parents help them to do well at school. It's all environmental. Well, now we know half of the differences are not... are genetic. The half that aren't genetic are not what we thought they were. They're not due to these systematic effects of parenting. Two... They make two kids in the same family as different as kids in different families. So the environment's important, but it's not this nurture, the systematic effects of the environment that psychologists always assumed was so important. And I know it's, it's hard to get your head around that, but, um, you can s- you can see it in, uh, many different types of studies, but the easiest way to see it is adoptive families, a third of them adopt a second child. So these two kids are genetically unrelated to each other, but they grow up in the same family. Well, for IQ, siblings correlate about 0.3 in childhood, about 0.4 later on. How much do these adoptive sibs correlate? Because they grew up in the same family, they have the same parents. Zero. So that's... So the fact of growing up in the same family isn't making them similar, yet the environment's important. And what is it? We call it non-shared environment. That is, it's something that's not shared. It's not shared by kids growing up in the same family. So you can start to think of things once you start thinking this way, you got to ask, um, what makes kids in a family different? And you can think of things like peers, you know, when your kids get into adolescence, you can see that makes a difference. Accidents, illnesses, um, things like that. But after 30 years of looking for these things, we haven't found them. So one of the points of my book Blueprint is I've come to conclude what's called the gloomy prospect. I don't think it's so gloomy, but it's just... it's the role of chance that, um, of the important environmental factors are sort of idiosyncratic. You know, they're... we call it stochastic.

    4. CWChris Williamson1:06:07

       What do you mean by...

    5. RPRobert Plomin1:06:08

       They're just s- chance events. So, um, I always think of Bill Clinton says he got into politics because at the age of 16 he shook JFK's hand, John F. Kennedy's hand. And that just really made him say, "I, you know, I want to go into politics." I mean, maybe it's just a retrospective history, but there are events like that where, you know, when people do their autobiographies and they look back on their lives, they say, "Ah, that was a real turning point. That teacher at school, that biology teacher," or, "This event where I was humiliated in the playground," or, you know, there are these events that you can't just measure because they're kind of unique to an individual at a particular time. That's what I mean by idiosyncratic. It's the sliding doors sort of phenomenon. There's several current books out, current novels. One that I just finished today is called The, um, Midnight Library, which is, uh, by Matt Haig, H-A-R-I-G. He was the guy who wrote, um, what is it? Uh, 20 Reasons Not to Die. He's a depressive. But this book is about alternative endings and, you know, how things could just change a little bit, but then that is a t- a tipping point that leads to other things and it could end up very differently. Lionel Shriver's new book too is, um, about that, about alternate endings in life. So I think-... um, and there's a great book by Melvin King, who was the former Bank of England head, um, that- that's called, um, uh (clicks tongue) not Random Chance. What is it called? Uh, ugh, shoot. I'm blocking. It's a great word, but, um, it's like Super Chance. You know, it's that we need to recognize that chance plays a much larger life, uh, role in life. Physicists are getting into this too, you know, the idea that things are essentially unpredictable in, at some level. And I think it's good for us to know that. Like in Matt Haig's book, the woman who wanted to commit suicide and goes to this library and tries out alternate lives, ends up coming back to her own life, having realized that every life could go many different ways. And it's again, what we were talking about with, uh, meditation. It's all you've got is what you're experiencing this instant. Everything else is either a thought or a memory that came from ... It's, it's, you know, it- it's sensations. It's not you that created these things. These are just sensations in your brain. So I don't know, maybe I, I, I don't know, you might think I've been taking some psychedelics or something, but. (laughs)

    6. CWChris Williamson1:08:42

       No, no, I get it. I mean-

    7. RPRobert Plomin1:08:44

       I'm, I'm ... I like it when these things all come together like that.

    8. CWChris Williamson1:08:46

       I agree. Yeah. The synchronicity is beautiful and that, it, it lends credence to the theory as well, right? That if you have these particular narratives that coalesce, it's the same as when people talk about Buddhism and Stoicism and meditation and new world practice and Confucianism, you go, "Okay, well, if multiple different parties from different times-"

    9. RPRobert Plomin1:09:05

       Yeah.

    10. CWChris Williamson1:09:05

        "... from different geographic areas with different cultures all arrive at similar sort of conclusions, you've probably got a fairly good amount of backup that that might be right."

    11. RPRobert Plomin1:09:15

        Exactly right. And that's why I'm, I'm resolved to get a sense of non-dualism, but I'm having a hell of a time.

    12. CWChris Williamson1:09:23

        Insane.

    13. RPRobert Plomin1:09:23

        I mean, I've only been at it a few months-

    14. CWChris Williamson1:09:25

        Yeah.

    15. RPRobert Plomin1:09:25

        ... but, um, I find it really difficult, but I'm beginning to see, at least Sam Harris is saying, you don't get it all at once. You know, it comes ... Some people have an epiphany, but for most people, you just get it a little bit more and a little bit more. But it's exactly as you say. I mean, every ancient philosophy comes up with this. So I think we al-

    16. CWChris Williamson1:09:45

        Dissolve the ego. There is no self. Yeah. Be present. Find happiness in the moment. Yeah. All of these different things you, so you're so right. So there's the, my favorite

12. 1:09:54 – 1:23:38

    Educating Children on Genetics

    1. CWChris Williamson1:09:54

       sentence in the entire book that I think kind of drives this home. So we've put people into a coffin, we've put a couple of nails in, and then this is the dirt that goes on top I think, saying parents matter, but they don't make a difference.

    2. RPRobert Plomin1:10:07

       Yeah.

    3. CWChris Williamson1:10:07

       What does that mean?

    4. RPRobert Plomin1:10:09

       Well, I'm, I'm glad, I think ... Are you saying you liked it or?

    5. CWChris Williamson1:10:11

       Oh, I loved it. I, this is-

    6. RPRobert Plomin1:10:13

       Okay.

    7. CWChris Williamson1:10:13

       I live for this stuff. Yeah.

    8. RPRobert Plomin1:10:15

       Right. Um, because, uh, that's the four pages in the book that have by far gotten the most attention. So much so that I was going to write another book that would just focus on genetics and parenting. Are, are you a parent?

    9. CWChris Williamson1:10:27

       Uh, no.

    10. RPRobert Plomin1:10:28

        Uh-huh. But, um, uh, when you become a parent or you know people who are parents, there are thousands, literally thousands of parenting books. They don't mention genetics. Whereas I have no doubt that genetics is the single most important thing that parents need to know. That is not that it's all deterministic, not that they can't do anything about it, but they have much less control over their kids' outcomes than they think they have. Because genetics is genetics and the environment isn't the environment we thought it was. It's not. If it's chance and stochastic events, idiosyncratic events, parents don't have control over that. So I think they need to relinquish control to a greater extent and to fi- spend more time figuring out what their kid likes to do and what they're good at and helping them do it rather than preordaining my kid's gonna be an Olympic athlete or a professional musician. Y- it's not that you can't do it. You know, the tiger moms, these shows, you can make kids do stuff to a certain extent, but why? I think it's, it's analogous to like if you, if you have a partner and you pick them because you say, "Well, there's some pretty good raw material here, but I'm gonna make them into what I really want them to be." You know, it's a disaster 'cause you have relationships because you love people. And when you love people, you want to do good things for them. You want life to be nice for them, on their terms. And so same with k- kids. I think, you know, it's better to focus on your relationship. It's a long relationship. And some of this tiger parenting or helicopter parenting is counterproductive to the relationship. And so I just think it's better for parents to realize they don't have nearly as much control as they think they have. And it's better to go with the flow. It's not to say you can't change things, but it's awfully good to recognize what kids, their appetites as well as their aptitudes, and to help them do what they want to do, to be like a resource manager, to give them opportunities to find out what they like to do. So-

    11. CWChris Williamson1:12:37

        Is there a way-

    12. RPRobert Plomin1:12:38

        ... that's me talking off my soapbox now.

    13. CWChris Williamson1:12:40

        Is there a way to game the stochastic idiosyncratic model?

    14. RPRobert Plomin1:12:46

        Well, I think it's partly what meditation is about, is to realize that things that happen to you, they're just happening. There are these events in the world, they don't have anything to do with you. These are things that are happening. And you, you know, you don't want to, um, read too much into them. You just say, like the Stoics would say, this is a challenge. They talk about stoic challenges instead of just saying, "Oh God, not again. This is happening to me. Uh, I've lost my job, or I have to go on furlough. I've got COVID." You know, you can take that and say, "Ah, life is crap." Or as the Stoics would say, "Think about it as a challenge." You know, and do, do what you can with what you've got is their motto and do it now and make a plan. And don't waste your time with negative emotions because they don't do any good.

    15. CWChris Williamson1:13:36

        I was talking more...... from the, uh, perspective of the parent. So let's say-

    16. RPRobert Plomin1:13:43

        Mm-hmm.

    17. CWChris Williamson1:13:43

        ... that this, there are these chance incidents which occur in young people's lives. They can shape them in unbelievably dis- disproportionate ways. Uh, as a parent, presumably one of the things that you could look to do with your child, there would be a big difference between a parent who sends their child to the same routine week in, week out for 18 years, and a parent that encourages the child to do a bunch of different things. The outcomes have to be different for that child, because the number of opportunities for different idiosyncrasies and stochastic inference events to occur is m- wildly different. The one that-

    18. RPRobert Plomin1:14:24

        Mm-hmm.

    19. CWChris Williamson1:14:25

        ... does go and do summer camp and, uh, e- every summer for, you know, throughout all of the years of school, and the one who is encouraged to go to this sport and then this sport, as opposed to, "You will be a boxer. You will be a this thing." Like, that has to have it. So what I'm thinking about is, for the parents that are listening or for the fu- the people that want to have kids in the future, what are some of the ways that you think people could maximize that kind of, uh, stochastic advantage, I guess?

    20. RPRobert Plomin1:14:49

        Well, it is, it, it seems, like, oxymoronic to talk about systematic unsystematic events-

    21. CWChris Williamson1:14:55

        (laughs)

    22. RPRobert Plomin1:14:57

        ... which is what we're doing here. I think it's more important for parents to recognize there's just, shit happens and stuff will happen. And, you know, some things, uh ... So what we're saying is these things are heritable, and they don't show shared environmental influence much at all, especially for personality and psychopathology. And, um, that includes these parents who are doing what you say, who give their kids lots of opportunities or don't. But again, it's, it's what is rather than what could be. So if you want your kid to be a sprinter or a, a musician, you can get the best teachers around, you can do as much as you can do, but you gotta say at what cost, you know? And I don't think we do that enough. And to recognize you're better off going with the genetic flow than spending a lot of time figuring out how you're going to systematize chance, because you really can't.

    23. CWChris Williamson1:15:49

        That's a really, really good takeaway. I use Tiger Woods as an example a lot because he had such an extreme childhood and has continued the sport through. But look at the externalities that he's had in his life, like just hugely public marriage failures. He's fallen asleep on the side of the road because he's been on, uh, antidepressant drugs. He recently rolled his car and broke, like, everything. So yeah, I think, um, you're totally correct. The price that people pay for extreme performance within narrow domains that they may not have chosen themselves, especially when it's, uh, deployed on them by a parent in early life, you do not know the potential externalities, the cost, the suffering that's going to occur from that. And I love the idea of genetic flow, of look, like, I am here to provide resources, to be open, to move with the child, to allow them to do what they want. I have some wisdom. I can say, uh, "Maybe trying to do free running off the top of a building at four years old is a bad idea, Timmy. Like, maybe we'll ..." You know, there, there are certain things that you know that are better and are worse. But also, yeah, I, I love the idea of, of being sort of like a, a kite in the wind, right? You're holding the kite. You can let it out, you can pull it back, but you allow the kite to kind of choose its own direction based on where it wants to go.

    24. RPRobert Plomin1:17:03

        And you recognize that there's very different sorts of kites.

    25. CWChris Williamson1:17:06

        Yes. Yeah. There's, there's big ones. There's small ones.

    26. RPRobert Plomin1:17:08

        And first off, it's kind of figuring out what's, what kind of kite you've got and what they like. You know, rather than in ... These parenting books are really, they're bad. I mean, you know, they want you-

    27. CWChris Williamson1:17:18

        What do you disagree with most about the parenting books?

    28. RPRobert Plomin1:17:20

        Just about everything.

    29. CWChris Williamson1:17:21

        Okay. (laughs)

    30. RPRobert Plomin1:17:21

        I mean, they mostly are all implying that parents are completely in control, and it's always by Dr. So-and-so. So they appeal to authority, but they don't appeal to data. Very few of these books have any evidence base. There's a few now starting to come out. But parents then ... It's really bad for psychology because all you gotta do is go to the book shop, pick up two books from that pop psychology shelf about parenting. And one will, Dr. So-and-so will say things very dogmatically about, "You must do this about sleeping and eating." And the other one will say things dogmatically too, but that are completely different. And neither one is based on evidence. And the evidence is that these things don't have much of an effect, partly because kids are so different. You know, what do you do about night waking? I say the answer is, it always depends on the kid. And, you know, you sort of go with the flow of what works for you and the kid. You don't do things because some doctor, so-and-so said, "This is what you must do." Because you can bet it's wrong.

Episode duration: 1:42:07