Making Sense - Sam Harris - July 17, 2020


#211 — The Nature of Human Nature


Episode Stats

Length

1 hour and 12 minutes

Words per Minute

158.0778

Word Count

11,453

Sentence Count

648

Misogynist Sentences

2

Hate Speech Sentences

5


Summary

Robert Plowman is a professor of behavioral genetics at the Institute of Psychiatry, Psychology, and Neuroscience at King's College London. He previously held positions at the University of Colorado Boulder and at Pennsylvania State University, and was elected a Fellow of the Academy of Medical Sciences and of the British Academy for his groundbreaking work in behavioral genetics. And he s the author of the fascinating book, Blueprint: How DNA Makes Us Who We Are. In this episode, we talk about the birth of Behavioral Genetics, the taboos around studying the influences of genes, in particular in human psychology, controversy surrounding the topic of group differences, the first law of behavior genetics, the concept of heritability, nature and nurture, the significance of non-shared environment which is genuinely perplexing, and the prospect of this will land us in some Gattaca-like dystopia: heritability and equality of opportunity, the implications of genetics for parenting and education and other social policies, and other topics. This is important science, and this is a fascinating conversation. And I bring you Robert's interview with me. Robert is one of the most influential people in the field, and one of my good friends, Dr. Robert's book is a must-listen-to-book, so you won t want to miss this one. Thanks to Robert for being on the podcast, and for being kind enough to let me bring you his interview. . And as always, I never want money to be the reason why someone can t listen to the podcast. If you can t afford a subscription, there's an option at Samharris.org to request a free account, and we grant 100% of those requests, and you can't afford it, no questions asked asked? No questions asked, no question asked, 100% asks asked, you get it all the time by Sam Harris and as always I never wants money, I do not want money, you can do it, I just say so, I'm not going to be a millionaire, right? - Sam Harris, I love you, I know you do, I really do, right I do I do that, I'll say so. - Thank you, thank you, right, I said so, right?? - I'm making sense, I mean really, really? - Thanks, Sarah, Sarah? - Sarah? -- Sarah? -- -- Thank you? -- Sarah, Amy?


Transcript

00:00:00.000 Welcome to the Making Sense Podcast.
00:00:08.340 This is Sam Harris.
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00:00:27.580 other subscriber-only content.
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00:00:49.220 Okay, just the briefest housekeeping here.
00:00:52.180 Just to say that we have finally posted the bonus questions I have long been promising
00:00:58.240 to subscribers.
00:01:00.380 Those can be found on my website if you're logged in, or also in the subscriber feed near the
00:01:07.040 related episode.
00:01:09.620 And I haven't done these for every episode, but there are many going back quite a ways.
00:01:15.160 For people like Nicholas Christakis, Donald Hoffman, Eliezer Yudkowsky, Yuval Noah Harari, Jack Dorsey,
00:01:24.460 Jaron Lanier, Johan Hari, Jonathan Haidt, Matt Taibbi, Neil Ferguson, Nick Bostrom,
00:01:32.400 Preet Bharara, Preet Bharara, and Stephen Fry.
00:01:36.860 And so if you look in your subscriber feed, going back, you will find those, and as well
00:01:42.980 on my website, if you are logged in to your account.
00:01:47.700 Okay.
00:01:50.060 Today I'm speaking with Robert Plowman.
00:01:52.920 Robert is a professor of behavioral genetics at the Institute of Psychiatry, Psychology, and
00:01:57.720 Neuroscience at King's College, London.
00:02:01.060 He previously held positions at the University of Colorado Boulder and at Pennsylvania State
00:02:06.200 University.
00:02:07.280 He's also been elected a fellow of the Academy of Medical Sciences and of the British Academy
00:02:12.280 for his groundbreaking work in behavioral genetics.
00:02:16.100 And he's the author of the fascinating book, Blueprint, How DNA Makes Us Who We Are.
00:02:22.340 And Robert and I get into many of the interesting and fraught questions here.
00:02:25.940 We talk about the birth of behavioral genetics, the taboos around studying the influences of
00:02:33.400 genes, in particular in human psychology, controversy surrounding the topic of group
00:02:38.980 differences, the first law of behavioral genetics, the concept of heritability, nature
00:02:45.340 and nurture, the significance of non-shared environment, which is genuinely perplexing, the
00:02:52.060 way genes can shape our environments, epigenetics, genetic influences on complex traits, dimensions
00:03:00.260 versus disorders, the prospect of this will land us in some Gattaca-like dystopia, heritability
00:03:07.640 and equality of opportunity, the implications of genetics for parenting and education and other
00:03:15.560 social policies, DNA as a fortune-telling device, and other topics.
00:03:21.700 Anyway, it's a fascinating conversation.
00:03:24.360 This is Important Science.
00:03:26.800 And now I bring you Robert Plowman.
00:03:34.600 I am here with Robert Plowman.
00:03:36.580 Robert, thanks for joining me.
00:03:38.240 Well, it's my pleasure.
00:03:39.220 It seems like I've known you because I've listened to so many of your podcasts.
00:03:42.140 Nice.
00:03:42.940 Well, I have read your book.
00:03:45.360 Let me properly introduce your book first because it's a fantastic introduction to everything
00:03:50.720 we're going to talk about and there's no way we will exhaust its interest.
00:03:54.320 So people should read your book.
00:03:55.880 The book is Blueprint, How DNA Makes Us Who We Are.
00:03:59.940 And we'll track through the case you make here pretty systematically.
00:04:06.060 But, you know, first I should say you really are one of the most revered people in this
00:04:12.520 field of behavioral genetics.
00:04:14.820 And this is a field that is still somewhat under the radar for people, I think, intellectually.
00:04:21.320 I mean, people know that we had the Human Genome Project some decades ago.
00:04:26.620 And I think there's this vague sense still, somewhat analogous to the sense everyone had
00:04:34.300 that artificial intelligence never amounted to anything.
00:04:37.500 And then all of a sudden it amounted to a lot.
00:04:39.940 But people have a sense that this genetic revolution hasn't really arrived.
00:04:45.760 And yet behavioral genetics is this field in which we're discussing the role the genes
00:04:50.480 play in determining who we are in the most basic sense.
00:04:54.340 I mean, really the nature part of human nature.
00:04:57.120 And your book is just a great introduction to that and its implications directly for psychology.
00:05:03.000 But before we get into the data and your argument, maybe you can summarize your background a little
00:05:09.760 bit.
00:05:09.960 How did you get into this work?
00:05:12.520 It depends how far we go back.
00:05:13.920 But I'll start at university.
00:05:18.000 You know, I think one of the things I hope we get to talk about, I've heard on several of
00:05:21.140 your podcasts is about the role of chance and genetics has a new kind of spin on chance.
00:05:27.720 And I went to the University of Texas at Austin because I was an inner city kid in Chicago.
00:05:32.660 None of my family went to university, let alone graduate school.
00:05:35.680 But I had this wonderful advisor who helped me apply to graduate schools.
00:05:39.160 And being a good inner city kid, when the University of Texas offered to pay for me to go,
00:05:43.700 I said, well, that sounds like a good deal.
00:05:45.200 So I went to the University of Texas in psychology, but they, unknown to me, had the only program in
00:05:52.320 behavioral genetics in the world.
00:05:53.920 It had just started at that time in the early 1970s.
00:05:57.920 And this is one of these chance events that everyone in those days, I don't know about when
00:06:04.000 you were in graduate school, but in those days you had to take core courses.
00:06:07.320 So you had about two years worth of courses you had to take in clinical and perception.
00:06:12.220 And this, everyone had to take this course in behavioral genetics.
00:06:16.660 Forty other students were in there and it floored me.
00:06:20.600 You know, I just saw this evidence for the importance of genetics.
00:06:23.720 Most of it was from animal studies at that time.
00:06:26.180 And I just knew right away, that's what I wanted to do the rest of my life.
00:06:29.300 Yet none of the other students took it up.
00:06:31.340 So what is that about?
00:06:32.780 You know, I don't know, but it was really a turning point in my life.
00:06:36.000 And I went, it was very lucky because most of the behavioral geneticists in the world were
00:06:40.960 there at that moment.
00:06:43.080 And I was really at the beginning of the application of genetics in psychology.
00:06:49.180 And, you know, back then it was actually dangerous to be doing genetics in psychology because
00:06:53.120 psychology was completely dominated by environmentalism and nurture.
00:06:57.000 So I kind of grew up with the field and everything, you know, I learned a lot of stuff about genetic
00:07:03.300 influences.
00:07:03.960 I'm sure we'll talk about genetic influences on environment and developmental changes.
00:07:08.400 There's a lot we learned.
00:07:10.520 And I thought, great, that was terrific.
00:07:12.280 And I'm happy with my career.
00:07:13.820 And then along came the DNA revolution.
00:07:16.280 And that's what's really changed everything.
00:07:19.360 And it's all relatively new.
00:07:22.080 So I don't think that's what's going to have the impact on people.
00:07:25.140 Because you can argue with these twin studies and adoption studies, but you just can't argue
00:07:30.800 with DNA.
00:07:31.820 And that's what's new.
00:07:33.180 And that's what's really going to make a difference.
00:07:35.140 Yeah, so we're not just talking about things like height and weight, obviously.
00:07:40.060 We're talking about personality characteristics, things like how nice a person you are and how
00:07:45.420 outgoing and how neurotic and how happy, how empathic, how prone to violence, and also just
00:07:52.720 core capacities like intelligence.
00:07:55.580 And, you know, whether you think about that narrowly in terms of IQ or much more loosely in
00:08:01.340 terms of educational achievement, we're really talking about everything we can care about in
00:08:08.940 ourselves and our children and in people we interact with in society.
00:08:15.260 And the punchline here is that, as you say in your book, that DNA isn't all that matters,
00:08:22.680 but it matters more than anything else.
00:08:24.440 And it matters more than everything else put together in determining who we are, which
00:08:29.620 is a, you know, on its face, again, a very provocative statement.
00:08:34.560 Even today, I mean, in the beginning of your book, you write two sentences that fairly floored
00:08:41.280 me because I'll actually read them.
00:08:43.460 You say that you delayed writing this book in part due to cowardice because you recognized
00:08:49.860 how dangerous this used to be.
00:08:52.340 And you say it might seem unbelievable today, but 30 years ago, it was dangerous professionally
00:08:57.600 to study the genetic origins of differences in people's behavior and to write about it
00:09:01.940 in scientific journals.
00:09:03.340 It could also be dangerous personally to stick your head up above the parapets of academia and
00:09:07.280 talk about these issues to the public.
00:09:08.720 Now, Robert, either you are a time traveler from the future and you wrote this book in
00:09:14.200 2050, or you're living on Mars right now, because in my world, anything less than a full
00:09:21.660 commitment to the blank slate is still taboo.
00:09:25.720 I mean, there are people who are trying to cancel J.K.
00:09:28.280 Rowling right now for just admitting that biological sex is a thing.
00:09:33.320 This is the environment we're in at a minimum on social media.
00:09:37.580 Do you really not perceive this to be a fraught territory now?
00:09:43.920 Well, as I say in the epilogue to the book, I was very nervous about this book coming out.
00:09:49.380 My friends said it was a professional suicide note, but I saw lots of signs that things are
00:09:55.280 changing over the years.
00:09:57.260 Back when I was in graduate school, the textbook said that schizophrenia was caused entirely
00:10:02.560 environmentally and even worse by what your mother did in the first few years of life.
00:10:07.580 Genetics never got a look in.
00:10:09.940 So you had to be very careful about even suggesting that something might show genetic influence.
00:10:14.860 But in the 40 years since, there's been a mountain of evidence from twin and adoption
00:10:19.760 studies and family studies that's convinced most scientists that many traits, in fact, I would
00:10:26.540 say all traits in psychology show significant genetic influence.
00:10:30.400 And it's not just statistically significant.
00:10:32.760 We're talking about a lot of influence, like explaining about half of the differences
00:10:37.640 between people.
00:10:39.060 So I think things have changed a lot.
00:10:41.520 And I've experienced that when I've talked to the public.
00:10:45.060 Mostly the reaction I get is that not hostility, but just ignorance.
00:10:50.040 People say, well, I didn't know about that.
00:10:51.520 It makes great sense.
00:10:52.440 In fact, most of the public I talk to are surprised there's a big controversy.
00:10:56.680 They say, you know, it sounds so reasonable and there's a lot of evidence behind it.
00:11:01.700 So I think things have changed.
00:11:04.120 And so I was wondering who the people are you've been talking to that are still blank
00:11:08.720 Slaters.
00:11:09.760 Again, there's resistance in some quarters on the far left politically, generally, that
00:11:16.900 biological sex is even a thing, right?
00:11:20.260 I mean, this is what J.K. Rowling has just run into, or that intelligence has anything
00:11:25.880 to do with IQ and is whatever intelligence is, whether IQ or not, that that would be at
00:11:33.160 all heritable.
00:11:34.840 And then when you start talking about group differences for any trait we care about, it
00:11:40.560 just becomes utterly toxic politically.
00:11:43.240 And the truth is that there's no ethical or perceived ethical sweet spot here, because
00:11:48.340 if you ascribe differences between groups to, you know, I mean, again, to take the most
00:11:53.900 fraught topic here is that, you know, IQ differences across racial groups, however defined, you know,
00:12:00.940 Charles Murray's territory.
00:12:02.260 This is just the plutonium of social science.
00:12:05.960 And even acknowledging that these differences exist is taboo in some circles.
00:12:11.200 They have to be artifacts of testing or, you know, any other metric you'd be using.
00:12:16.760 But once you get past that, then they have to be due to racism.
00:12:21.380 And once you look past that, let's say comparing, you know, Asians to whites on IQ tests, are
00:12:29.800 you now alleging that there's some anti-white racism that is benefiting Asians on these tests?
00:12:35.080 That begins to look a little weird.
00:12:36.660 But now everyone, again, is jumping out of their skin with political discomfort.
00:12:42.540 And the truth is there is no way of accounting for these group differences that people are
00:12:47.560 comfortable with.
00:12:48.180 I mean, genes are the worst answer, but environment and culture and family situation, that's also
00:12:55.540 a bad answer.
00:12:57.160 People just don't want to say that they don't want to draw any invidious comparisons between
00:13:03.140 groups on any level.
00:13:05.480 We will inevitably touch this territory, if only to comment on why we're not wading further
00:13:11.920 into it.
00:13:12.460 I just want to offer a warning to both of us and to our listeners that there is no avoiding
00:13:17.960 these topics on some level.
00:13:20.120 Because, again, with the best of intentions, with no interest in specific things like IQ differences
00:13:28.780 among groups, say, the moment you begin to study things like intelligence or anything else
00:13:35.740 you care about at the level of the genome's implications for how people develop later in
00:13:41.600 life, or just begin to tease out the difference between contributions from the environment and
00:13:47.720 contributions from DNA, you get ambushed by these topics that make people incredibly uncomfortable.
00:13:57.040 And even, and this is something we'll get to, you know, toward the end of our conversation
00:14:00.480 where we talk about the social policy implications of all of this, but, you know, in a world where
00:14:05.680 we have completely solved our political and social problems, let's just deposit a world where
00:14:13.600 there is no inequality, there's zero inequality of opportunity, everyone gets to go to the
00:14:18.820 best schools, and, you know, everyone is equally wealthy and has equally conscientious parents,
00:14:25.160 and there is nothing wrong at the level of society.
00:14:28.720 Well, then in that world, every difference in outcome between people will be ascribable to
00:14:35.420 differences in genetics, and that hardly seems fair to people either.
00:14:39.240 So, it's very difficult for people, given certain assumptions, to find any spot of comfort in
00:14:46.240 this conversation, and I think you and I can see some daylight past all that and talk about
00:14:52.100 how we're comfortable with what we're learning about human nature here, but just, you know,
00:14:57.640 warn us and warn our listeners that there's a kind of uncanny valley that we have to pass through
00:15:02.660 here where things seem to be threatening at the level of, you know, ethics and politics.
00:15:09.240 Could I speak to that?
00:15:10.820 Please.
00:15:11.000 I think there's, you've raised an awful lot of issues there, but just a couple of the
00:15:14.980 main ones, and you're right, the third rail is group differences, and in the paperback
00:15:21.440 edition, which came out last year of Blueprint, I have an afterword where I describe, talk about
00:15:27.880 my reactions to the response to the book, and one of those is why I didn't talk about group
00:15:34.500 differences, and I just mentioned briefly in the book, but I discuss it more in the
00:15:39.180 afterwards, that the most important point to realize is there's no necessary connection
00:15:44.020 between the causes of average differences between groups and individual differences.
00:15:49.140 Right.
00:15:49.200 So, individual differences in a trait like intelligence could be very highly heritable.
00:15:53.240 That doesn't necessarily imply that an average difference between, say, ethnic groups
00:15:58.440 is also heritable, but more than that, the reason I've stayed away from group differences,
00:16:04.240 there's sort of three reasons.
00:16:05.920 One is that there's much more variance, you know, I assume your listeners know variance,
00:16:10.580 it's just a statistic measuring how much people vary.
00:16:14.620 The vast majority of the variance on these traits is within groups rather than between groups.
00:16:19.860 Mm, right.
00:16:20.380 And so much so, like, you know, boys are better at math than girls, and girls are better at
00:16:25.940 verbal, that accounts for 1% of the variance.
00:16:28.580 That means if you know whether a child's a boy or a girl, you don't know anything about
00:16:32.040 their verbal ability or their mathematical ability.
00:16:34.720 So, differences within groups are far more important.
00:16:38.740 The second reason I don't study it is that we don't have any killer methodologies to answer
00:16:45.580 the question of genetic and environmental causes of average differences between groups.
00:16:52.720 But in contrast, we have very powerful methods for understanding the causes of individual
00:16:59.040 differences within groups.
00:17:01.720 And then the final reason is, I don't think I have to study everything.
00:17:05.480 And that's not just, you know, I'm not just being facetious there.
00:17:09.640 I think it's an important point.
00:17:11.060 In your discussion with Murray, which I thought was brilliant, by the way, you know, it's what
00:17:16.320 ought to happen, you know?
00:17:17.380 These are difficult issues.
00:17:18.940 I thought you discussed them very fairly.
00:17:21.220 But towards the end of your interview with Charles Murray, you asked him, but why do you
00:17:26.120 persist in studying these average differences between groups?
00:17:30.260 I think you even said something about it.
00:17:32.220 It seems to be, you didn't say frurient, did you?
00:17:35.640 But you did ask him about that.
00:17:37.840 I thought his answer was very unsatisfactory.
00:17:40.240 Yeah.
00:17:41.060 And so early on, I said, look, there's lots of important things to study.
00:17:45.600 Why are some people schizophrenic and others not?
00:17:48.460 And most of the variants that we're trying to explain with genetics is within groups.
00:17:53.400 So why focus on the politically explosive issue of average differences between groups
00:17:58.800 when we don't have powerful techniques to definitively answer the question of the
00:18:05.480 etiology of those differences?
00:18:07.320 And that's why I think there's so much heat and so little light there.
00:18:11.340 Yeah, yeah, I agree.
00:18:14.100 But just, again, a point of caution, and I think there's just, there's no avoiding this.
00:18:20.480 The reality is, you know, I am still digging out from the consequences of having had that
00:18:27.720 conversation with Charles.
00:18:29.100 Is that right?
00:18:30.540 Yeah.
00:18:30.960 Oh, really?
00:18:31.580 Yeah.
00:18:31.860 So it's like, that's at least a year and a half, something like that.
00:18:34.880 That was number 73, and you're up to 210.
00:18:37.420 Yeah.
00:18:37.700 Okay, yeah.
00:18:38.160 So maybe it's, you know, it's two years.
00:18:40.420 But, you know, he spent the last 25 years of his life not overcoming the effects on his
00:18:46.480 reputation of having written The Bell Curve.
00:18:48.320 You know, at this point, I'm reconciled to never coming out from under the shadow of having
00:18:54.800 touched that topic because of the response to that podcast.
00:18:59.400 I mean, people wrote articles and promoted them on social media to the limits of their
00:19:05.700 abilities, essentially saying that I was a racist for having had that conversation and
00:19:11.820 what I said in it, and it's maddening, but that's the environment we're in now, where
00:19:18.760 people who certainly are discussed as being real journalists and who you would think would
00:19:25.140 have reputations for some sort of integrity and intellectual honesty to protect will smear
00:19:32.320 you as essentially a Nazi for even touching this topic.
00:19:37.280 And the point I was making with Charles, you know, which was really the reason why I
00:19:41.560 spoke to him in the first place, he was not born of real interest in IQ, much less, you
00:19:48.020 know, racial differences in IQ.
00:19:51.000 But I'm interested in our inability to speak honestly about facts as we understand them.
00:20:00.040 And for years now, I've been seeing that there's certain things that will just spring out of
00:20:04.940 the data that we can't avoid, right?
00:20:08.640 Whether you're looking for them or not, if you want to understand
00:20:11.160 intelligence, and you're not at all interested in differences between people per se, but
00:20:19.120 you certainly don't want to put any, you know, ethical weight or moral weight on, you know,
00:20:23.320 human worth based on differences in intelligence, but the topic is still going to be forced upon
00:20:28.880 you.
00:20:29.140 And so, you know, we just have to get comfortable with that.
00:20:31.820 And, you know, I'm very comfortable that we understand what the political right answer
00:20:37.440 is in the end.
00:20:38.620 I mean, we know we want people to have equal opportunities, and we know we want people to
00:20:43.260 be treated as moral equals at the level of fairness in our society and in notions of
00:20:49.120 justice.
00:20:50.020 And we want to correct for the greatest disparities in good and bad luck insofar as we can do that.
00:20:58.240 And so much of this, the ethical punchline for me is that this is all due to luck in
00:21:03.720 the end.
00:21:04.120 I mean, you don't pick your genes, you don't pick your parents, you don't pick your environment
00:21:07.400 either, right?
00:21:08.100 There's nothing that you pick, you know?
00:21:10.400 And so, if you're a good person who cares about the well-being of others, and you realize
00:21:15.560 that, you know, there but for the grace of happenstance, you could have been in any other
00:21:21.040 possible situation on earth, it's through no wisdom of my own that I wasn't born in
00:21:26.840 the middle of a civil war in Congo, then you should be committed to making the world as
00:21:33.440 good a place and as fair a place as you can make it.
00:21:36.240 And that dictates a certain kind of politics and a certain kind of ethical commitment to
00:21:40.880 treating people fairly.
00:21:43.300 But people don't see that you can be, I mean, honestly, there are people who listen to this
00:21:48.340 conversation, and despite what I just said, and I could rattle on in this vein for an hour
00:21:54.780 and a half, and the punchline will still be, those two guys are Nazis.
00:21:59.760 That's the environment we're in, and it's a very dispiriting reality.
00:22:04.140 And it's only because I have taken elaborate pains to inure myself to the blowback to these
00:22:14.040 kinds of conversations that I even can have them.
00:22:18.300 Honestly, in any other role in society, I mean, had I been a professor at a university,
00:22:24.760 had I been a normal journalist who had a boss, I think I would have lost my job based on the
00:22:31.120 blowback from my conversation with Charles Murray.
00:22:34.840 And that's just a sobering reality of the environment we're in.
00:22:39.300 Well, I'm so sorry to hear that, though, because, I mean, your whole podcast is about just having
00:22:43.480 honest conversations about topics.
00:22:45.880 Now, you know, that is probably the hottest topic you could pick.
00:22:50.720 You can talk about genetics of schizophrenia, and people don't get upset about that.
00:22:56.380 You can even talk about cognitive abilities, but if you talk about reading disability,
00:23:01.120 nobody sweats that, no problem.
00:23:04.300 So, intelligence just is like a red flag to a bull in some ways.
00:23:09.400 And then, by getting into average differences between ethnic groups, I mean, there you've
00:23:15.020 got it.
00:23:15.420 So, that's the worst, well, the best case for your podcast to be able to talk about difficult
00:23:22.460 topics.
00:23:23.060 But I don't go there because of the reasons that I mentioned.
00:23:26.820 And there's an awful lot to learn about individual differences.
00:23:30.780 And in the end, I think they're very important.
00:23:33.600 You know, why are some kids reading disabled?
00:23:35.320 And why do some people become schizophrenic or not?
00:23:37.980 So, you really did go to the third rail on it.
00:23:41.920 And I am amazed to hear, though, that you're still getting blowback.
00:23:45.420 I avoid it because I don't do social media.
00:23:47.720 And in the academic press, things are, you know, really going the genetic way.
00:23:54.080 If you look at grants funded, for example, I mean, genetics is, there aren't that many
00:23:58.520 behavioral geneticists, but they dominate research funding in psychology.
00:24:02.820 They dominate the most highly cited papers in psychology.
00:24:06.660 So, I am an optimist, though.
00:24:08.560 And I have a sense that you're not quite as much of an optimist as I am.
00:24:11.860 But I can look at this history.
00:24:13.900 Or I spend too much time on social media.
00:24:16.640 Maybe that's right.
00:24:17.960 I mean, I just don't do it for that reason.
00:24:20.840 I mean, it just gets you down.
00:24:22.840 I don't even, long ago, I decided I wouldn't even respond to emails or to even publish criticism
00:24:30.020 of my work because I found, even back then, 30 years ago, before social media, a lot of
00:24:36.260 the critics weren't honest critics.
00:24:38.460 I mean, they would say, well, what about this?
00:24:40.700 And you say, okay, well, we've done research on that.
00:24:42.500 And I say, yeah, but then what about this?
00:24:43.980 And what about that?
00:24:45.000 And a lot of them, I realized, had nothing better to do, whereas I had science I wanted
00:24:50.240 to do.
00:24:51.100 And I did feel, in the end, if psychology was going to be an empirical science, in the
00:24:57.260 long run, if you take a very long view, getting the data is what matters.
00:25:02.580 And I hope in the end, you know, students of psychology will read about behavioral genetics
00:25:07.980 and nature and nurture and say, well, what's all the fuss about?
00:25:10.040 Of course, genetics is important.
00:25:12.420 So I am an optimist, and I do look at things kind of with my rose-colored glasses, but I
00:25:16.820 see huge change.
00:25:18.880 I haven't been called a Nazi for 20 years.
00:25:21.260 That's great.
00:25:23.520 Let's let that be either the motto or the epitaph for this conversation.
00:25:27.900 All right.
00:25:30.280 So I'm going to don your rose-colored glasses here, and we will proceed, because there's
00:25:36.400 fascinating science to talk about.
00:25:38.360 And if people don't understand our intentions here, they will be unreachable by the powers
00:25:44.780 of human speech.
00:25:45.960 What is the first law of behavioral genetics?
00:25:48.900 The first law of behavioral genetics is that everything is heritable.
00:25:53.560 By that, I mean individual differences in traits of cognitive abilities and disabilities,
00:25:58.460 personality, mental health, and illness.
00:26:01.000 Those traits, those individual differences all show significant and substantial genetic
00:26:06.960 influence.
00:26:08.320 Right.
00:26:08.440 And so we should clear up some confusion that people naturally have around this concept of
00:26:14.560 heritability.
00:26:15.520 And then we're going to go into how we know all this based on adoption studies and twin
00:26:21.260 studies and all the rest of the actual science.
00:26:23.740 But let's talk about this concept of heritability.
00:26:27.380 How are people confused about it?
00:26:30.180 Yeah, well, it's great you brought that up, because that six-syllable word is the most
00:26:35.480 misunderstood word around, because it includes the word heritable, somehow involves genes
00:26:41.280 and DNA.
00:26:42.380 So people have a lot of different notions of it.
00:26:44.860 But in behavioral genetics, and I should say, by behavioral genetics, I mean what we call
00:26:49.340 quantitative genetics, like twin and adoption studies and now DNA studies.
00:26:54.420 And it's the same techniques you'd use if you were studying medical disorders, for example.
00:26:58.540 So it's not peculiar to psychology or behavior, but these are the epitome, in a way, of the
00:27:04.360 complex traits and common disorders that's the focus of the DNA revolution now.
00:27:11.200 So heritability describes the, it's a descriptive statistic, and like all descriptive statistics,
00:27:18.700 like means and variance, it can change in populations over time.
00:27:22.740 But it describes the extent to which differences that we observe in a trait, say like body
00:27:28.440 weight, body mass index, to what extent are those differences due to inherited DNA differences
00:27:35.220 between people, in this population, at this time?
00:27:40.520 There are many misunderstandings, and probably the most common one is for people to think,
00:27:48.280 well, they confuse what is with what could be.
00:27:51.940 So we're describing what is, in a particular population, the extent to which people differ
00:27:57.400 in body mass index, and to what extent is that due to diets and exercise or inherited DNA differences.
00:28:07.040 So we're talking about differences.
00:28:09.300 And we find, people might be surprised, that about 70% of the variance of body mass index
00:28:15.420 in the Northern European populations that we study is due to inherited DNA differences.
00:28:21.420 So that's often a shocker for people.
00:28:23.220 We've done surveys, and people think there might be some genetic influence, but they think
00:28:27.140 it's more like 30% or so.
00:28:29.220 But 70% is a lot.
00:28:30.740 It's not 100%, but that's a lot of the differences between people in body mass index are due to
00:28:36.900 inherited DNA differences.
00:28:38.220 But that's what is, and it doesn't imply what could be.
00:28:44.160 So, you know, one of the most interesting things I found about doing my DNA and getting
00:28:49.240 these polygenic scores that we'll talk about later is that I have a very high polygenic
00:28:54.200 score for body mass index.
00:28:56.500 I'm quite heavy.
00:28:57.500 I'm at the 70th percentile of weight.
00:28:59.800 But what's interesting about this is some people say, well, if you learn that you got bad
00:29:04.580 news and your genetic risk for alcoholism or, in this case, for obesity, you'll just give
00:29:10.680 up and say, oh, well, there's nothing I can do about it.
00:29:13.140 But the point is we're describing what is, not what could be.
00:29:17.280 And certainly, if you locked me in a room and didn't give me any food, I'd lose weight.
00:29:21.020 Or more than that, if I had a bit more self-control or motivation, I might not eat like a pig the
00:29:29.460 way I would do, you know, given free access to food.
00:29:33.080 So, you know, the differences between what is and what could be, and the other caveat,
00:29:37.920 there's a bunch of them, but the other caveat I think that's important is we're dealing with
00:29:41.960 the normal range of genetic and environmental variation.
00:29:45.500 That is, the range of variation that we can study, which is fairly representative populations,
00:29:51.060 maybe 95% of the population.
00:29:53.720 But it doesn't include the genetic extremes of single gene mutations, for example, nor does
00:30:00.860 it include the environmental extremes, say, of abuse and neglect.
00:30:05.420 There are many wrinkles here.
00:30:08.660 I guess the two further points I would want to make about this concept of heritability
00:30:12.200 that are related to what you just said.
00:30:14.840 So, even if something were highly heritable in general, in any specific case, it may not,
00:30:23.020 in fact, be expressed.
00:30:26.000 I mean, you take like alcoholism.
00:30:27.380 I don't know what the contribution of genetics is to alcoholism.
00:30:31.700 I don't remember if you mentioned it in your book, but...
00:30:34.320 It's not real high, but it's, say, 40%, something like that.
00:30:37.160 Right, yeah.
00:30:37.680 Let's say even if it were 100%, right, even if it were just determined by DNA, in a world
00:30:43.820 without alcohol, it would not find expression, right?
00:30:46.900 So, the role of the environment in any individual's case, or even in any group's case, if you find
00:30:52.100 an island of proto-alcoholics, but where, you know, where alcohol has not been discovered,
00:30:57.220 you'll see 0% alcoholism among people who have the genome that would determine 100% alcoholism
00:31:04.940 in another context, right?
00:31:06.800 So...
00:31:07.160 Yeah, but, you know, but not even going to that extreme, the differences between what is and
00:31:12.280 what could be.
00:31:12.980 So, when we say alcoholism or alcohol abuse is 40% heritable, we mean of the genetic and
00:31:19.200 environmental differences that exist in this population at this time, inherited DNA differences
00:31:25.040 contribute about 40% to that liability, you know, the variance in alcoholism.
00:31:30.900 And even if you say, even as you said, if it's 80% or 100% heritable, if I say, okay,
00:31:37.860 I know my genetic risk for alcoholism is high, but I also know you can't become alcoholic unless
00:31:42.560 you drink a lot of alcohol.
00:31:44.200 So, I could take that information, say, even from DNA, risk for alcoholism, and say, well,
00:31:50.220 I've got to be more careful, because if I drink as much as other people, I'm more at risk for
00:31:55.760 becoming alcoholic than they are.
00:31:58.080 And you can't become alcoholic if you don't drink a lot of alcohol.
00:32:01.880 Yeah, yeah.
00:32:02.860 So, this covers things like alcoholism.
00:32:05.080 It probably doesn't cover everything that interests us, but it's relevant.
00:32:08.680 And also, we should talk about or mention the fact that differences between people we're
00:32:14.500 talking about when we're talking about heritability.
00:32:16.300 We're not talking about things that everyone shares, which are also genetically determined,
00:32:22.520 which is having a head, or having arms and legs, right?
00:32:25.600 Or being bipedal, you know, or having something, some, you know, bilateral symmetry.
00:32:29.980 I mean, these are things that virtually everyone has who is intact at birth, and we don't talk
00:32:36.080 about the heritability of having arms and legs, right?
00:32:39.760 Yeah, that's such an important point.
00:32:41.940 And we have, say, six billion base pairs of DNA, and 99% of those are the same for all
00:32:49.080 of us.
00:32:50.040 And that's what makes us human.
00:32:52.240 We're talking about the 1% of DNA sequence differences, base pairs of DNA, the extent to
00:32:59.940 which those differences between us make a difference.
00:33:03.100 And the answer is, they make a big difference.
00:33:06.160 But it is differences.
00:33:07.720 So if you say height is 80%, 90% heritable, it doesn't mean I grew to six, what, six feet
00:33:16.520 because of my genes, and the other four inches were added by the environment.
00:33:21.680 We're only talking about differences between people, why I'm very tall, and other people
00:33:27.800 are not so tall.
00:33:29.560 Genetics is largely responsible for those differences between people.
00:33:34.900 It really is a critical point.
00:33:36.820 So thanks for bringing that up.
00:33:38.740 Yeah, yeah.
00:33:39.480 So we're talking about, in the case of, we have the 3 billion base pairs in each half
00:33:44.560 of the genome.
00:33:45.300 So we're talking about 30 million base pairs that account for the difference between us.
00:33:52.540 And as you say, we're 99% identical to one another.
00:33:56.000 Although we are, if I recall, we're 50% identical to the banana.
00:34:00.500 So I don't know how much comfort to take there.
00:34:02.520 Exactly right.
00:34:03.300 So let's talk about the confusion that is even more common on the concept of nature and
00:34:11.560 nurture and how to differentiate those.
00:34:13.860 And one of the more fascinating points in your book comes in this discussion of the nature
00:34:19.880 of nurture.
00:34:20.960 What's the confusion here around nature and nurture and how we can demarcate them?
00:34:25.560 Well, there's that larger issue of just separating nature, that is inherited DNA differences, and
00:34:31.460 nurture, that is environment.
00:34:32.820 And there's a lot we've learned there.
00:34:34.800 But the topic of nature of nurture is a different topic.
00:34:39.480 So what would you prefer to start with?
00:34:42.820 Let's differentiate nurture and environment because people think it's one thing and then
00:34:47.900 they're, you know, the parents are either horrified or happily exonerated when they learn the punchline
00:34:55.180 here.
00:34:55.500 So let's talk about first, what are the contributions to individual differences beyond DNA?
00:35:03.580 We'll talk about nurture and unshared environment, and then let's talk about the nature of nurture.
00:35:11.280 Yeah, great.
00:35:12.000 Good.
00:35:12.500 Well, we talked before about the first law of behavioral genetics, that everything is heritable.
00:35:17.180 And we can get more precise than that and say, on average, across all the traits that have
00:35:23.080 been studied, about half of the differences between people, half of the variance of these
00:35:28.500 traits can be ascribed to inherited DNA differences.
00:35:33.100 Now, 50% is a lot, you know.
00:35:35.240 This is effect size, the idea of how big of an effect it is, not just as it's statistically
00:35:40.220 significant.
00:35:40.980 In psychology, it's rare to find anything that explains 5% of the variance.
00:35:47.020 So 50% of the variance is off the scale, but it's a lot less than 100%.
00:35:51.980 And the other 50% is actually not due to genetic differences.
00:35:59.000 But what we've learned is that it's not nurture in the sense that people have always assumed
00:36:05.500 it was.
00:36:06.200 From Freud onwards, nurture was thought to be what happens in families, particularly parents
00:36:13.360 and what they do to the kids, like schizophrenia is caused by what your mother does to you in
00:36:18.080 the first few years of life, was the line when I was in graduate school.
00:36:23.100 So what we've learned is, I think, almost more important, what we've learned about nurture
00:36:30.360 than nature, because that other 50% is not due to systematic effects of the family environment.
00:36:40.620 So it's probably best if I just give you one piece of data on that, that makes that point.
00:36:46.980 Yeah.
00:36:47.160 Just take BMI and parents' body mass index.
00:36:50.780 Parents and their children correlate about 0.3 is when the kids grow up.
00:36:55.100 I mean, at birth, there isn't any correlation at all, but they correlate about 0.3.
00:36:58.660 Is it nature or nurture?
00:37:00.540 Well, it was always assumed to be nurture, and that's not a dumb hypothesis.
00:37:04.940 I mean, parents give the kids the food, they model lifestyles and that sort of thing.
00:37:09.600 But the adoption studies showed that when parents adopt a child who's not genetically related
00:37:16.060 to them, the correlation between those parents and their kids for body mass index is zero.
00:37:22.800 Right.
00:37:23.780 Similarly, children growing up in the same family correlate about 0.3 or so.
00:37:28.660 In body mass index could be, it's reasonable to think it's nurture, but if those children
00:37:34.300 are genetically unrelated, their correlation is zero.
00:37:37.800 The other side of the adoption design is to take genetically related people adopted apart.
00:37:43.420 These adopted children who correlate zero with the body mass index of their adoptive parents correlate 0.3 with the body mass index of their birth parents, whom they never saw after the first week of life, who had no influence over their environment.
00:37:59.300 So that's the sort of evidence that for decades was used to say genetics is important.
00:38:05.360 But then people realized, you know, in the 70s and 80s, that it's telling us something very important about the environment.
00:38:13.820 Whatever the environment is, it's not making kids in the same family similar to one another.
00:38:20.080 It's not making kids similar to their parents.
00:38:23.500 And that's what I called in 1987, non-shared environment.
00:38:28.360 It's important.
00:38:29.700 It's making a big difference.
00:38:31.640 But it's not what we thought it was.
00:38:33.800 It's not due to shared family environmental influence.
00:38:37.440 So what is it?
00:38:38.980 Well, for 30 years, we've been trying to figure that out.
00:38:42.640 Like, what is it that's making two kids in the same family different?
00:38:45.840 You know, for example, parents don't really treat their children the same.
00:38:51.380 I don't know about you and your daughters.
00:38:52.560 If you ask parents, they say they do.
00:38:54.660 But if you ask the kids, you'd swear they're growing up in different families.
00:38:58.500 And if you videotape interactions between parents and children, you do see that parents aren't treating their kids the same.
00:39:05.800 I mean, like your friends, when they're sufficiently high, would probably admit to this.
00:39:11.020 I mean, some kids are just more lovable and cuddly than others, you know?
00:39:14.700 So anyway, there are these possible parental differences in treatment.
00:39:19.320 And it turns out, we did a 10-year study of this called NEAD, Non-Shared Environment and Adolescent Development.
00:39:25.720 And we find, yep, sure enough, differential parental treatment correlates with differences in children's outcomes within a family.
00:39:34.400 So you take siblings, you know?
00:39:35.740 And so the parents who say are more, if you look at the relationship between parental harsh discipline and children's antisocial behavior, in a family, the child who is more antisocial, the parents are more harsh in their discipline.
00:39:54.680 Well, as always, these correlations in psychology have always been assumed to be environmental.
00:40:01.680 But I think all your listeners know the adage that correlation does not imply causation.
00:40:07.200 Is it necessarily the case that the parents' discipline of the child caused the antisocial behavior?
00:40:13.480 Or is it possible that the parents' behavior is reflecting the children's behavior?
00:40:19.160 And you can put this in a behavioral genetic design.
00:40:21.480 And what you find is that about half of those correlations are due to genetic differences.
00:40:27.040 So this is where the nature of nurture comes in.
00:40:30.780 And it kind of took me off the track, though, of non-shared environment.
00:40:35.720 And the punchline there is after 30 years of trying to find these systematic sources, we haven't been successful.
00:40:41.960 I know in one of your conversations with Paul Bloom, you mentioned, you know, Judith Harris's book in the 90s, which really popularized a lot of these concepts, but really results.
00:40:52.560 But then also proposed maybe peers are important.
00:40:55.860 And that's another reasonable hypothesis.
00:40:57.600 You know, your daughters probably won't end up having the same friends.
00:41:01.360 Maybe one of them has more academically oriented friends and the other has more athletically oriented friends.
00:41:07.160 That could be a source of difference.
00:41:08.920 But since Judith Rich Harris proposed that, people have also looked at that.
00:41:13.820 And again, there's correlations there.
00:41:16.380 Kids who are more antisocial have friends who are more antisocial, you know, in a family.
00:41:21.580 So the sibling who is more antisocial is more likely to have friends who are also more delinquent.
00:41:27.600 But again, is it cause or effect?
00:41:30.660 And it turns out that, you know, kids select friends.
00:41:34.560 If they're antisocial, they select friends who are like them in that score.
00:41:39.020 And about half of that is due to genetic differences.
00:41:42.540 So that's what we mean by the nature of nurture.
00:41:44.500 But it's also why we haven't found systematic sources of non-shared environment.
00:41:49.460 Whenever we find something that looks like it's causing differences between kids and a family, it ends up being a genetic difference in disguise.
00:41:58.560 So after 30 years, I came to this what we call gloomy conclusion that non-shared environment is essentially idiosyncratic, stochastic, not systematic.
00:42:09.380 So that half of the variants for psychological traits are due to these environmental factors, but they're essentially random chance stuff happens.
00:42:21.720 Okay, so this is all, I think, more important than may be obvious to people at first pass here.
00:42:29.540 So I just want to linger on this topic.
00:42:31.200 So first, what you're saying here is that virtually half of everything we care about in human nature, you know, in our psychology, you know, whether it's susceptibility to various psychopathology, and we'll talk about how we think about disorders and whether the disorder framework is the right framework here.
00:42:52.120 But for virtually everything in psychology and in, you know, human difference one could care about, you know, from intelligence to, you know, big five personality traits to susceptibility to things like depression and schizophrenia, the punchline here is something like 50% of human difference.
00:43:15.220 It's often on either side, it's often on either side of that halfway mark, I mean, sometimes it's 60%, sometimes it's as high as 80%, you know, later in life for things, is accounted for by genes, and the other half is environment, but it is not the environment that parents or anyone else can systematically control.
00:43:37.260 And for the environmental component of things, very often half of what is ascribed to the environment is actually genes in disguise because people, based on their own genetic proclivities, wind up shaping their environment.
00:43:56.320 So, I think this is an example you use in your book, you know, you could ask someone, you know, how often does it rain where you live?
00:44:02.640 If ever there were an environmental variable that has nothing to do with DNA, well, you know, the weather is certainly that, but then you ask yourself, well, you know, people are free to move, right?
00:44:14.540 People can pick the climates in which they live, and maybe some of that is being driven by genetic proclivity, right?
00:44:21.980 There's some people who just hate living where it rains, right?
00:44:24.740 You know, I count myself as one of those people.
00:44:26.940 It's not an accident that I don't live in Seattle.
00:44:29.120 And so it is with everything else, you know, how much TV do you watch as a kid?
00:44:34.000 How often do you read?
00:44:35.200 How often do your parents read to you?
00:44:37.520 This all seems like it's a pure statement of an environmental influence, you know, i.e. nurture, and yet when you strip out the influence of genes, you find that genes are accounting for half of those so-called environmental differences among people.
00:44:54.480 I should just pause there, Robert, to ask, did I summarize that point correctly?
00:45:00.080 Yes, I thought that was great.
00:45:01.460 And the point for people to take home is correlation does not imply causation.
00:45:05.560 So parents who read a lot to their kids have kids who do better at reading at school.
00:45:10.160 And if you don't think about these issues, you might say, sure, it's environmental.
00:45:13.640 But I hope after this discussion, people at least pause a minute and say, well, wait a minute now, you know, who are these parents who read a lot to their kids?
00:45:22.380 And who, you know, who are these kids who do better at reading?
00:45:25.180 It could be due to genetics, or increasingly, I think it's due to parents responding to genetic differences in their kids.
00:45:33.540 I have six grandchildren, and I thought, with the first two, I thought, you know, what they're supposed to do is sit there and let you read to them.
00:45:40.340 I remember you talking about reading Harry Potter to your older daughter.
00:45:44.160 Well, that's what I thought grandchildren were supposed to do.
00:45:46.080 And with one grandchild, exactly right, I could read to her all day long, and she'd say, oh, please read some more to me.
00:45:52.220 But I've got another grandson who it would almost be abusive for me to make him sit there and let me read to him.
00:45:59.520 He wants the rough-and-tumble play.
00:46:01.020 So, increasingly, I think, as parents, we're responding to differences we see in our kids.
00:46:06.640 And given that you have two kids, I wonder if you experienced that, this wonderful phrase that's been attributed to six different people.
00:46:13.840 Parents are environmentalists until they have more than one child.
00:46:17.900 Right, right.
00:46:18.360 You know, with the first child, you can explain anything environmentally.
00:46:21.460 That's the problem with environmental hypotheses.
00:46:23.560 You can't explain anything after the fact.
00:46:26.200 But then you have a second child, and almost every parent notices that there's big differences between these children.
00:46:34.600 And you say, I didn't do that.
00:46:36.620 Have you experienced that?
00:46:37.840 Well, there's also one enormous environmental difference, too, which is the second child is growing up in the presence of the first, whereas the first had, in our case, five long years of being an only child.
00:46:51.700 So, it's hard to figure out how to factor that in, but that's a non-negligible influence there.
00:46:58.920 But yeah, I am noticing they're impressively similar in some ways, but they are clearly different people.
00:47:06.400 The genetic deck got shuffled.
00:47:08.780 Yeah, that's exactly right.
00:47:10.200 In case people haven't realized this, you know, the first-degree relatives, like parents and offspring or siblings, are 50% similar genetically.
00:47:18.040 Right.
00:47:18.300 But that means they're 50% different genetically.
00:47:21.380 So, genetics predicts that kids in a family will be different.
00:47:26.100 These socialization environmental theories, they have a lot of trouble explaining.
00:47:31.380 Why are two kids in the same family with the same parents so different, when, presumably, it's these parents that are causing differences in the kids' development?
00:47:41.500 Yeah, so, again, there are implications for parenting here and social policy, education.
00:47:50.780 We'll get to those in the back half of our conversation.
00:47:53.920 But, you know, all of this, again, is, this is a bit of a high-wire act to talk about these things without having people freak out.
00:48:00.760 But we are really just talking about the facts of human psychology insofar as we have come to know them.
00:48:08.840 And no doubt we will be wrong about certain things.
00:48:13.360 Certain assumptions will be proven wrong in the fullness of time.
00:48:16.080 But the idea that genetics doesn't account for a lot of what we care about in human nature, the door seems to be closed to that thesis.
00:48:29.220 I mean, the blank slate thesis is no longer on the table.
00:48:32.280 And, you know, it's empowering in some ways.
00:48:35.820 It pushes your intuitions around in others.
00:48:40.240 And we'll talk about those effects.
00:48:43.120 But we should talk a little bit more about how we know this.
00:48:46.880 Before we get there, could I just kind of summarize what we were saying?
00:48:50.600 Because we covered a lot of topics, and a lot of those are very big issues for people, you know.
00:48:54.620 Yeah, yeah. Go for it.
00:48:54.980 And so, what Blueprint is, there's three main points.
00:48:59.200 First is, everything's heritable.
00:49:00.940 So, inherited DNA difference is a comp for a lot of the differences.
00:49:04.840 Of the rest of the variants, it's not genetic.
00:49:07.300 It's environmental.
00:49:08.780 But it's not the environment we thought was important.
00:49:10.860 It's this non-shared environment.
00:49:12.920 And then, when we find correlations, like between parents reading to kids and kids reading ability at school, you can't assume that's environmental.
00:49:21.160 They're often genetic effects in disguise.
00:49:22.920 So, I find what helps people put this together is if I tell you that if one of your daughters had been switched at birth in the maternity ward and raised in a different family, she would have grown up to be very similar to who she is, even though she was raised in a different family.
00:49:41.060 And that's not hypothetical, because we have studies of identical twins reared apart.
00:49:46.720 And this wonderful documentary that won an award last year called Three Identical Strangers, about three identical twins, and just how similar they are despite being raised in quite different family environments.
00:49:59.480 So, it's a dramatic illustration of this point, because your daughter would be her identical twin.
00:50:05.380 She's still 100% genetically who she is, even though she's raised in a different family.
00:50:10.540 So, I think that helps people to understand it, that we'd be very much who we are, even if we had been raised in a different family with different parents.
00:50:21.740 Right.
00:50:22.000 Okay.
00:50:22.260 Although, we're going to have to land back on this topic and give some account of why being a good parent still matters.
00:50:28.180 Absolutely.
00:50:28.900 So, we'll have to get there.
00:50:30.520 So, okay.
00:50:31.240 But before we do, let's talk a little bit more about these studies, adoption studies, twin studies, adoption studies with twins.
00:50:39.660 And we have, so let's just remind people of the biology here.
00:50:42.620 We have two different types of twins.
00:50:45.100 There are monozygotic twins and dizygotic twins, identical and fraternal twins.
00:50:50.040 And identical twins share the same DNA.
00:50:54.420 They're 100% identical, barring some surprising mutation genetically.
00:51:01.140 And whereas fraternal twins are like ordinary siblings, they share 50% of their DNA, but they just share the same environment all the way down to the womb.
00:51:13.980 So, in these studies where you can compare identical twins to fraternal twins, and you can really strip out the influence of shared environment.
00:51:26.200 Because, again, you're looking at one group that has identical DNA and one group that has only 50% similar DNA, and yet shared environment.
00:51:36.000 And then you have these other studies where you have identical twins separated at birth and raised in different families.
00:51:43.200 And you are a pioneer in doing this work.
00:51:47.000 And maybe, I don't know if you want to talk about the Colorado Adoption Project, or I don't know how you want to enter this.
00:51:53.000 But let's talk a little bit more about the logic of these experiments and why they have been so compelling.
00:51:58.580 Well, that was a great description of the twin method.
00:52:01.980 But the punchline there is that if a trait, take like musical ability, which hasn't been studied very much, you know, and it's hard to measure.
00:52:10.500 But what we'd be saying is if genetic influences are important, you'd have to predict that identical twins would be more similar in their musical ability than non-identical twins.
00:52:20.280 And the extent to which they're more similar than fraternal twins, I say non-identical because in UK they call them non-identical rather than fraternal.
00:52:30.160 So if a trait like musical ability is heritable, you'd have to predict that the MZ, monozygotic twins, are more similar than the dizygotic fraternal twin.
00:52:40.060 And the extent to which identical twins are more similar estimates the magnitude of genetic influence.
00:52:46.780 So as you said, that's a pretty powerful test of genetic influence.
00:52:51.220 But the main assumption there is called the equal environments assumption.
00:52:54.780 What if identical twins are treated more similarly than non-identical twins?
00:52:59.500 Well, that's been studied.
00:53:01.240 It seems to be a fairly safe assumption.
00:53:03.840 You get identical twins reared apart are just as similar as identical twins reared together, for example.
00:53:10.920 But it still is an issue.
00:53:13.280 But the neat thing is we have this other method that's completely different called the adoption method.
00:53:18.140 And that's a wonderful situation to be in because the adoption method also has its possible, well, it has its assumptions and possible flaws, but they're completely different.
00:53:29.120 And these two methods, the twin method and the adoption method, converge on this conclusion that everything that we study in psychology is heritable.
00:53:37.580 So the adoption method, though, is in some ways more powerful.
00:53:41.340 You can really see it with identical twins reared apart.
00:53:44.420 But they're very rare.
00:53:46.480 So much more typical are biological parents who adopt their child away at birth.
00:53:52.360 And then you can study those adopted children and their adoptive parents who give them their family environment, but not their genes.
00:54:00.040 They're not genetically similar to them.
00:54:01.740 So it's another powerful way of getting at genetic environmental influences.
00:54:07.180 And I gave you the example of body mass index and how adopted children don't correlate with their adoptive parents in terms of body mass index, even though they share food and lifestyle.
00:54:18.660 Whereas parents who share genes and environment with their children correlate about 0.3 for body mass index.
00:54:25.080 And the real killer data is that these adopted children correlate 0.3 for body mass index with their birth parents who they never saw after the first week of life.
00:54:37.980 So I think together, that's a very powerful indication, not only of genetic influence, but of the unimportance of what we call shared environment.
00:54:47.780 You know, that traditional view of nurture.
00:54:50.500 Right.
00:54:50.760 Which is, we should just pause to acknowledge how counterintuitive this is.
00:54:54.500 We're talking about parents who have their own eating habits, which they then lavish upon their children from birth onward.
00:55:04.260 And it turns out those habits, stripped of their underlying genetic cause, is not what contributes to the body mass index of a child as he or she grows up.
00:55:20.620 Yes, exactly right.
00:55:21.540 So now, what about epigenetics here?
00:55:25.740 Is there anything to say about what we know there?
00:55:29.220 Yeah.
00:55:29.700 When I give a public lecture, it's sort of the first question I get is, yeah, but what about epigenetics?
00:55:34.860 You know, the environment changes genes.
00:55:36.560 Well, you know, as I say in the book, you only inherit differences in DNA sequence.
00:55:44.140 You start life as a single cell with half, 3 billion base pairs of DNA from your mother and 3 billion from your father.
00:55:52.240 And that DNA is the same DNA in the trillions of cells in your body.
00:55:56.580 We do pick up some mutations as we go along.
00:55:59.260 But the genes that are expressed of those 3 billion nucleotide bases of DNA in the double helix of DNA, we don't have the same DNA expressed in all of our cells.
00:56:17.520 You know, the cells in your liver do different things from the cells in your blood and from the cells in your brain.
00:56:22.940 And that's gene expression.
00:56:24.620 Different bits of DNA are turned on and off in response to the environment.
00:56:28.940 But what we inherit are the DNA differences.
00:56:34.760 And if a DNA difference correlates with an outcome like schizophrenia or alcoholism or reading disability, then that means that that DNA difference was expressed somewhere.
00:56:47.860 And it's making a difference.
00:56:50.320 But some, you know, people have really used epigenetics, which literally means above genetics, beyond genetics, to try and argue against Mendelian genetics.
00:56:58.940 And I think there's, after the initial excitement about epigenetics, I think people are calming down about it and realizing, yeah, gene expression is important.
00:57:09.380 Everything between inherited DNA and behavior is important.
00:57:13.300 We call that expression transcriptomics and tabulomics and the brain.
00:57:21.160 Everything in between DNA and behavior is important to understand.
00:57:24.140 But it's important to realize all we inherit are DNA sequence differences.
00:57:30.880 Right.
00:57:31.060 And if they're making a difference in terms of traits and if they're correlating with differences, individual differences in traits, well, then they're being expressed on some level.
00:57:40.740 Yes, that's right.
00:57:41.480 And the neat thing about DNA is you don't need to know anything about what goes on in between the DNA and the behavior.
00:57:49.020 Right.
00:57:49.860 To be able to make these predictions.
00:57:52.040 But that's not to say all of these other things are not important.
00:57:55.980 But I just do, I'd like to argue against this idea that epigenetics somehow invalidates genetics because it doesn't.
00:58:03.140 Yeah, there's another detail here which is interesting and has important implications, and it's that we're not tending to talk about single genes having some overwhelming trait effect.
00:58:19.200 We're talking about thousands of genes contributing tiny effects to any one of these traits, whether it's a susceptibility to schizophrenia or intelligence or anything else that interests us.
00:58:31.880 And that has some significance.
00:58:37.060 Well, it has, you tell me what significance you see.
00:58:40.780 I mean, the one thing that jumped out for me immediately, which I believe you mentioned in your book, is that it gives a somewhat less than hopeful picture that any single drug target will be a high leverage target for us in improving ourselves in whatever way we might hope to.
00:59:00.420 Yeah.
00:59:00.940 Well, the most important thing we've learned from the DNA revolution in the last 10, really 5 years, is that genetic influence on complex traits and common disorders of the sort we've been talking about are not due to one gene, certainly.
00:59:16.080 We've known that for a long time.
00:59:17.260 But they're not due to 10 genes or 100 genes.
00:59:19.620 They're probably due to thousands of tiny, tiny DNA differences.
00:59:23.520 Now, first, I'd like to say, though, that there are thousands, some people say 7,000, 10,000, single gene disorders.
00:59:32.820 These are like Mendelian hardwired deterministic disorders, like Huntington's.
00:59:40.680 They're necessary and sufficient.
00:59:42.860 So if you have the gene for Huntington's, you will die from Huntington's unless something kills you first.
00:59:47.900 And you only have Huntington's if you have the gene for Huntington's disease.
00:59:53.900 And that's the problem.
00:59:54.880 Everyone learns about genetics from Mendel.
00:59:57.120 And Mendel was studying disorders in pea plants, like wrinkled seeds, you know.
01:00:02.000 And so they're hardwired and deterministic.
01:00:05.720 And he showed through that that that's the way genes work in heredity.
01:00:10.780 But what's important to realize is that despite these thousands of single gene disorders, many of which are extremely debilitating, lethal for the people who have them, they're very rare, one in 100,000, one in 500,000.
01:00:27.040 So they're very rare, fortunately, and don't really contribute much to the heritability of the traits that we study.
01:00:35.620 The heritability of complex traits and common disorders, medical as well as psychological, are due to thousands of tiny DNA differences.
01:00:49.440 And that's a drag in some ways.
01:00:51.680 If you're trying to do a bottom-up approach, as neuroscientists would want to do, where you go from genes to brain to behavior, it's going to be very hard if each of those DNA effects are so tiny.
01:01:03.420 You know, you're going to definitely have to get away from a modular approach to neuroscience, where you think, you know, this gene does this, and then that has that effect.
01:01:13.220 You know, it's going to take more like a systems network sort of approach to be able to deal with the brain from this perspective, which we talk about as polygenic.
01:01:23.380 That is, every trait is influenced by many, many genes.
01:01:26.420 And that would include traits in the brain, you know, neurotransmitter levels, whatever.
01:01:31.040 But the other word that's important is pleiotropy.
01:01:36.020 Every DNA difference has many, many effects.
01:01:40.500 So, you know, you name these genes based on a disorder, you know, like this gene caused diabetes, but then you find out that gene affects hundreds of other things.
01:01:52.040 So, this polygenic point that you're making is critically important, and it's really hard for people to understand because they're still thinking about genetics from a single gene, hardwired, deterministic perspective.
01:02:07.100 Yeah, so there's a lot there.
01:02:09.080 So, let's break apart a few of these concepts.
01:02:11.820 So, yeah, there's an analog point to make about the brain.
01:02:15.240 There are very few parts of the brain that only do one thing, where you can say this is the part of the brain that, you know, recognizes faces, right?
01:02:23.200 And this, it does nothing else.
01:02:24.840 Well, you know, even fusiform cortex does other things.
01:02:27.800 So, the real picture is, you know, of pleiotropy, where any one gene, in this case, contributes to many traits, and also, and this is a point you make in the book, our concept of disorders, like schizophrenia, is itself misleading.
01:02:48.540 And it makes sense to talk more in terms of dimensions for traits, as opposed to these kind of terminal disorders.
01:02:56.300 And you use an analogy, which really drives home the point, with height, you know, and maybe you want to talk about height and the imaginary problem of giantism to clarify this concept.
01:03:08.320 Okay.
01:03:08.580 It is just a hypothetical example, but it does make the point that suppose you decided you've got a new disorder here, giantism.
01:03:14.420 So, people over six feet, five inches, they're giants, and everybody else is normal in height.
01:03:20.300 And yet, you find that all the genes, there's been thousands that have been identified, you know, thousands of DNA differences.
01:03:27.820 They all work, they don't, there aren't like a separate set of genes that cause people to be giants and different from the rest of people.
01:03:36.580 All of this is quantitative.
01:03:37.840 It's a matter of more or less, that is any DNA difference that is more prevalent in the giants, it will be distributed in the distribution.
01:03:47.380 So, people who are higher than average are more likely to have that DNA difference.
01:03:51.860 So, the DNA research, I think, puts the nail in the coffin of diagnoses.
01:03:57.940 Now, you might say, well, that's just a stupid example.
01:04:00.280 I mean, why would anyone divide height, which is so normally distributed, into a dichotomy?
01:04:08.000 But I think that's what we're doing with most other disorders.
01:04:12.180 You know, depression, no one thinks depression, you wake up one day and you're depressed.
01:04:17.100 Depressive symptoms are almost, they're quantitatively distributed.
01:04:21.440 And you never find genes for a disorder.
01:04:26.280 Any gene you find is distributed through the population.
01:04:30.240 Like, more concretely, one of the first of these effects that were identified using these new approaches called genome-wide association was a DNA difference that was associated with body mass index.
01:04:42.580 So, this gene had an A and a T, you know, the four nucleotide bases of DNA, A, C, T's, and G's.
01:04:51.320 And in the old, in thousands of years ago, we were all TT.
01:04:56.060 But then someone got a mutation that was an A.
01:04:58.900 And that A seemed to have been adaptive.
01:05:01.620 The story used to be that it allows you to conserve fat.
01:05:04.760 And in the Stone Age, that would be a good thing because you never knew when your next meal was coming.
01:05:09.540 But now, that makes you more likely to become obese in a fast food nation.
01:05:16.840 So, if you have two A's, you're three pounds heavier than someone who has one A.
01:05:22.260 And if you have no A's, well, that one A makes you three pounds heavier than someone with no A's, TT.
01:05:29.160 So, there's a six-pound difference between TT and AA.
01:05:32.280 That's what we mean by an association.
01:05:34.700 So, that was found for obesity initially.
01:05:37.100 But then they found that that DNA difference works quantitatively throughout the distribution.
01:05:44.880 That is, if you and your sibling, you have an A and they don't, you're likely to be, if we get a lot of siblings like that, three pounds heavier on average.
01:05:56.380 But that only accounts for 1% of the variance of body mass index.
01:06:03.220 And when that was published in Science in 2007, people, oh, well, 1%, I mean, what's that?
01:06:08.800 Turns out, it's one of the biggest effects that we can find for complex disorders, complex traits in common disorders.
01:06:15.480 So, it's so important to realize that these polygenic scores, that is, you can put these thousands of DNA differences together, because any one of them just doesn't account for enough variance to predict or to try and understand it mechanistically.
01:06:32.480 But you can put them all together, aggregate them in a polygenic score, and make pretty substantial predictions.
01:06:42.640 Like, we can predict 25% of the variance in height and about 10% of the variance in weight by putting all of these together.
01:06:51.620 So, for weight, this one DNA difference I was talking about accounts for 1%, but then these other DNA differences account for 9%.
01:07:01.540 So, altogether, you can predict about 10% of the variance.
01:07:04.960 But these polygenic scores are all necessarily perfectly normally distributed, because it's the central limit theorem of statistics.
01:07:16.000 You know, you flip a coin, and you flip 100 coins, and you get this normal distribution of heads and tails.
01:07:22.860 And that's what you're doing.
01:07:24.000 You're flipping alleles.
01:07:25.300 You know, you either have one allele or the other allele, or two of them.
01:07:29.140 So, these polygenic scores are perfectly normally distributed, so that the genetic liability for everything, any disorder, autism, schizophrenia, coronary heart disease, it's perfectly normally distributed.
01:07:42.660 So, I think that is really, I think, ought to put the nail in the coffin of diagnoses, because I really believe in psychiatry and psychology.
01:07:51.280 These diagnoses have held us back tremendously, and all of the DNA studies, these genome-wide association studies, are case control studies.
01:08:02.200 So, the whole game is to find these people who meet these, what I think are arbitrary diagnostic criteria, and you call them cases, like schizophrenics, and everybody else is a control.
01:08:15.440 Right.
01:08:16.060 And that's really held us back, because it's just simply not true.
01:08:20.060 Yeah, because everybody else who's normal, so-called normal, could be just like the 6'3 person who's not classed as a giant, but still shares all of these increased height probability genes.
01:08:32.560 And it means that we all have thousands of genes for schizophrenia.
01:08:38.320 Right.
01:08:38.680 It's just quantitative.
01:08:40.200 And I think, you know, if you have a very high, we call it polygenic score for schizophrenia, it probably takes, we all have stresses that would freak us out.
01:08:49.920 And as you've mentioned several times in your podcast, if you did have a genetic propensity towards schizophrenia, you probably ought to be careful about some of the psychedelics, for example.
01:08:59.380 Right.
01:08:59.580 Or some of the evidence suggests a high-THC sort of marijuana could also be dangerous in that situation.
01:09:07.240 It's like alcoholism.
01:09:08.200 You know, if you have the genetic propensity, it doesn't mean you're going to become alcoholic, or you're necessarily going to become schizophrenic.
01:09:14.140 You're just more likely to be, and given the stresses and strains of life, you're more likely to be tipped over the edge than someone else.
01:09:24.200 Yeah.
01:09:24.700 And these genes are very likely contributing to who you are in noticeable ways that puts you on this spectrum, which has schizophrenia as its terminus.
01:09:38.240 So, like, these genes for height that would render a giant 6'5 or beyond are also operative in you at the height of 5'10.
01:09:50.460 It's just you have a different complement of, and we're now talking about many, many genes for any one of these traits.
01:09:57.040 Exactly right.
01:09:58.140 The picture is, I think the phrase you used is that the abnormal is normal.
01:10:01.920 I mean, we're all on every spectrum that we could posit exists in the population.
01:10:08.680 We're all somewhere on it, and whether we have a symptomology that's interesting or not is the only difference, right?
01:10:16.160 So it gives us a finer-grained way of thinking about human difference and the boundaries between what is considered, you know, normative or normal and pathological.
01:10:30.680 I mean, it's common to—I think you referenced this in your book—ever since Aristotle, the analogy between madness and genius has been drawn, and I think probably too much has been made of that.
01:10:42.940 But this is susceptible to, in the end, a genetic analysis.
01:10:47.120 I mean, we can look at the genotype of whatever we want to call genius and the genotype of whatever we want to call madness and just see how much genetic real estate they share.
01:10:57.160 No, that's really right.
01:10:58.580 One implication I find quite interesting, too, is I'm basically saying there are no disorders.
01:11:02.940 They're just quantitative dimensions.
01:11:04.840 Right.
01:11:05.280 And one implication of that, then, is if there's no disorder, there's nothing to cure.
01:11:10.280 It's not like you're cured, yes or no.
01:11:13.260 It's all quantitative.
01:11:14.360 It's a matter of more or less.
01:11:15.540 We're alleviating symptoms rather than curing a disorder.
01:11:20.220 It all has to do with psychology-aping medical sciences, where, you know, a lot of this does work if you have a simple cause, a simple environmental cause.
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