« Making Sense with Sam Harris

#211 — The Nature of Human Nature

2020-07-17 | 🔗

In this episode of the podcast, Sam Harris speaks with Robert Plomin about the role that DNA plays in determining who we are. They discuss the birth of behavioral genetics, the taboo around studying the influence of genes on human psychology, controversies surrounding the topic of group differences, the first law of behavior genetics, heritability, nature and nurture, the mystery of non-shared environment, the way genes help determine a person's environment, epigenetics, the genetics of complex traits, dimensions vs disorders, the prospect of a GATTACA-like dystopia and genetic castes, heritability and equality of opportunity, the implications of genetics for parenting and education, DNA as a fortune-telling device, and other topics.

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This is an unofficial transcript meant for reference. Accuracy is not guaranteed.
What colors make a test? Podcast SAM Harris, just a note to say that if you're hearing this you're not currently on our subscriber feed and will only be hearing partial episodes of the podcast, if you'd like access to full episodes, you'll need to subscribe is samharris dot. Org. There you'll find our private rss feed to add to your favorite food along with other subscriber. Only content and, as always, I never wanted money to be the reason why someone can't listen to the podcast. So if you can't afford a subscription, there's an option, Samharris dot, org to request a free account and we grant one hundred percent of those requests. No questions asked: okay, just the briefest housekeeping here, just to say That said, we have finally posted the bonus questions. I have long been,
promising to subscribers. This can be found on my website if your logged in or also in the subscribe or feed near the related episode. And I haven't done these for every episode. But there are many going back quite a ways for people like Nicklaus, Chris Talkers Donald Hoffman Israel, Caskey, evolve no Harare, Jack Dorsey, journal near Johan hurry Jonathan Height, matter maybe Neil Ferguson, Nick Bostra, Pre Pereira and Stephen FRY, and so if you look in your subscriber feed, goin back, you will find those and as well on my website, if you are log in to your account. Ok, today must begin with Robert ploughman Robber today ass, her behavioral genetics at the Institute of Psychiatry
college in Neuroscience- Atkins College, London. He previous they help positions at the University of Colorado, bolder and Pennsylvania. State University has also been alive a fellow the academy, a medical sciences and of the British Academy. His groundbreaking work in behavioral genetics and is the author of the fascinating book, Blue print. How DNA makes us who we are and Robert. I get into many of the interesting and fraught questions here we talk about the birth of behavioral. Genetics, The taboos around studying the influences of genes, in particular in humans, ecology, controversy, surrounding the topic of group differences, the first, Behavioral genetics, the concept, perishability nature and nurture. The significance of non shared environment, which is genuinely perplexing the way genes, can shape our environments, epoch, genetics,
Genetic influences, Uncomplex trades dimensions, verse these disorders, the prospect of this one land, us in some Gatwick alike, to stop here, irritability and equality of opportunity. The implication of genetics for parenting and education and other social policies. DNA is a fortune telling device and other topics anyway, is fast any conversation. This is important science and bring Robert Schuman I am here with Robert Ploughman robber. Thanks rejoined me where's my pleasure. It seems like I know you because I've listened to so many of your pot guess nice. Well that I have read your book. I let me properly introduce your book first, because this affair,
tacit introduction to everything we talk about and then there's no way we will exhaust its interests. So people should read your book. The book is blue, and how DNA makes us who we are and will track through you're the case you you make here pretty systematically, but I should say, you really are one of the most the people in this field of behavioral genetics and that this is a field that is still somewhat under the radar for people. I think intellectually, and people know that we handy human, genome project. Some DEC ago, and I think there's this- this vague sense still Someone analogous to the sands. Everyone handed artificial intelligence ever amounted to anything. Then all of a sudden, it amounted to a lot, but people have a sense that this Netteke revolution hasn't really arrived and yet
Having genetics is this field in which we were discussing the role, the gene means play in determining HU. We are in the most basic sands, really that the nature part of human nature and your book is it just a great introduction of that at its implications directly for psychology, but before we get into data and you and your argument. Maybe To summarize your background of all. But how did you get into this work? The princess? we go back button I'll start at you at university, you know, I think the things I hope we get to talk about it. I've heard on several of your podcast is about the role of chance and genetics. Has it a new kind of spin on chance and went to the University of Texas Austin, because I was an inner city kid in Chicago. None of my family went to university, let alone graduate go, but I had this wonderful adviser who helped me apply to graduate school and being a good inner city kid. When the University of Texas offered to pay for meeting.
No, I said well, it sounds like a good deal, so I went to diversity of Texas in psychology but Day known to me. We had the only programme in being able to networks in the world. It had just started at that time in the early nineteenth seventies, and- and this is one of the least chance events that everyone in those days I don't know about when you were in graduate school, but in those days you had to take core courses, so you had about two years worth, of course, as you had to take in clinical and perceptual and this everyone had to take this course and behavioral genetics, forty others, were in there and it floored me in. I just saw this evidence for the importance of genetics most it was from animal studies, at that time- and I just knew right away- that's what I wanted to do the rest of my life. Yet none of the other students took it up. So what? that about you know I don't know, but it was really a turning point in my life and I went it was very lucky because
most of the behavior geneticists in the world. Were there at that moment, and I was really at the beginning the application of genetics in psychology- and you know and it was actually dangerous to be doing, genetics and psychology, because psychology was completely emanated by environmentalism and nurture. So I kind of grew up with the field and everything. You learned a lot of stuff about genetic influences, I'm sure we'll talk about genetic influences on environment and developmental changes, theirs We learn, and I thought great that was terrific, an unhappy with my career and then along came the DNA Revolution and that's what's really changed everything and it's all rout, relatively new. So I don't think that's what's gonna heavy impact on people, because you can argue with these twin studies and adoption studies but you just can't argue with DNA and that's what's new and that's what's really gonna make a deal.
And yet we are not just talking about things like height and wait. Obviously, we're talking about personality characteristics, things like nice, a person you are and how I go in and how neurotic and how happy? How empathic how prone to violence and also just core capacities like intelligence? and in a way. What do you think about that narrowly in terms of iq or much more Firstly, in terms of educational achievement, more we talk about everything we can care about in ourselves and our children. And in people we interact within society and the punchline. Here is that, as you say in your book, that your dna isn't all that matters, but it matters more than anything else and it matters more than anything else put together. Determining who we are which is eight on his face again, a very profound.
Could have statement. Even today. May you, in the beginning to your book, you write a two sentences that fairly floored me because artery you say that you? U delayed writing this book in part due to cowardice, because you recognised how dangerous this used to be any say if it might seem unbelievable the day for thirty years ago, it was dangerous professionally. To study, the genetic origins of differences in people's behaviour and to write about in scientific journals also be dangerous personally, to stick your head up above the parapet of academia and talk about these issues to the public, now Robert either. You are a time traveler from the future- and you wrote this book in twenty fifty or you're living on Mars right now, because in my world anything less than a full commitment to the blank slate is ill taboo. I mean that people who are trying to cancel J K rolling right now forget
admitting that biological sex is a thing. This is the environment wherein at a minimum social media so, like you really not perceive this to be. Fraught territory, now well us I, the epilogue to the book. I was very nervous about this book. Coming out. My friends said it was had professional suicide, note but I saw lots of signs that things are changing over the years back when I was in graduate school, the textbook said the schizophrenia was called entirely, environmentally and even worse by
your mother did in the first few years of life, genetics never gotta look here, so you had to be very careful about even suggesting that something might show genetic influence. But in the forty years since there has been a mountain of evidence from twin and adoption studies in family studies that have convinced us convince most scientists that many traits- in fact I would say all traits in psychology- shows significant genetic influence and it's not just the typically significant we're talking about a lot of influence like explaining about half of the differences between people. So I think things have changed a lot and I've experienced that when I've talked to the public, mostly the reaction I get. Is that not hostility but just ignorance people, so I didn't know about that. It makes great sense, in fact, most of the public. I talk to our surprise. There's a big controversy, they say sound so reasonable and there's a lot of evidence behind it. So I think things have changed.
I was wondering who the people are. You ve been talking to that are still blank slate again. There's resistance in some quarters on the far left politically, generally that biological sex, is even a thing right, and this is what Jackie Rolling has just run into or then that in time, regions has anything to do with I q and is a what, ever intelligence is whether I q are not, then that would be. At all heritable anyway you're talking about group differences for any trade we care about, it just becomes utterly tie exact, politically and and the truth is it no ethical or perceived ethical sweet spot here, because if you ascribe differences between groups to em, if again Take the most fraught topic here is that you know I q differences across racial groups, however defined
you, know Charles Marie's territory. This is just the plutonium of social science and even acknowledging that these differences exist is taboo in some circles: have to be artifacts of testing or or any other metric you'd be using, but once you get pass that, then they have to be due to racism and once you Look past ATLAS, comparing you know Asian. Two white Son IQ test Who are you we now alleging that there's some anti white racism that is benefiting Asians on these tests that began look a little weird but now everyone again is jumping out of their skin, with political discomfort and the truth is. There is no way of accounting for these group differences people are comfortable with him, and genes are the worst answer, but environment and culture and family situation. That's also a bad answer. People just don't
and to say that they dont want to draw any invidious. Comparisons between grew, hopes on any level. We will inevitably touch this territory if only to comment on. Why were not waiting further into it? I just I just want offer a warning to both of us and or listeners that is no avoiding these topics on some level because, again, with the best of intentions with knowing dressed in specific things like you differences among groups say the most, you begin to study things, intelligence or anything else. You care about at the level of the genome, the implications for help people develop later in life or just begin to tease out the difference between contributions, from the environment and contributions from DNA. You get ambushed by these topics that make people incredibly uncovered.
And even at this, and they will get to you, know till the end of our conversation. We talk about the social policy implications of all this, but in a world where we have come, Politely solved are political and social problems Let's just a part of the world where there is no inequality in this equality of opportunity. Everyone gets to go to the best schools and you know, One is equally wealthy and has equally conscientious parents and there is nothing wrong at the level of society- will then in that world. Every difference in outcome between people will be ascribed all to differences in genetics and that hardly seems fair to people either, so it is very difficult for people given certain assumptions to find any spot of comfort in this conversation, I am, I think you and I can
see some daylight passed all that and talk about how we are comfortable with what were learning about human nature. Here I just wish to warn us and Warner listeners that there's a kind Uncanny valley that we have to pass through here where things seem to be three name at the level of veto, ethics and politics? Could I could I speak to that, placing has you you raise them. Off a lot of issues there, but just a couple of the main ones and you're right. The third rail is group differences and in the pay back addition, which came out last year of blueprint. I have, and afterward. Where I describe talk my reactions to the response to the book, and one of those is why I didn't talk about group differences, and I said I just mentioned briefly in the book, but I discuss it more in the after word
that the most important point to realise this has no necessary connection between the causes of average differences between groups and individual differences individual differences in a trait like intelligence could be very highly heritable that doesn't necessarily, fly that an average difference between say? Ethnic groups is also heritable, but more than that and I ve stayed away from group. Differences is a sort of three reasons. One is that There is much more variants. You know I stimulus and has no variant suggests a statistic measuring how much people very the vast majority. The variants on these traits is with in groups rather than between groups. In my end, so much so like you know, boys are better at math and girls and girls are better verbal that account through one percent of the variants that mean
If you know whether a child, a boy or girl, you don't know anything about the verbal ability or their mathematical ability, so differences within groups are far more important. The second reason I dont study is that we don't have any killer methodologies to answer the question of genetic and environmental causes of average differences between groups, but in contrast, we have very powerful methods for understanding the causes of individual differences within groups and then the final reason is. I dont think I have to study everything and that's that's not just you know
I'm not just being facetious there. I think it's an important point in your discussion with Murray, which I thought was brilliant by the way you know of it, it's what ought to happen. You know these are difficult issues. I thought you discuss them very fairly, but towards the end of your interview with Charles Murray, you asked him, but but why do you persist in studying these average differences between groups? I think you even said something about it. It seems to be, you didn't say fury and did you, but you did in it it s about that. I thought his answer was very unsatisfactory here here and so Early on, I said, look, there's lots of important things,
study. Why are some people's gets? A frantic and others not and most of the variants that we're trying to explain with genetics is within groups. So why focus on the politically explosive issue of average differences between groups when we don't have powerful techniques to definitively answer the question of the ideology of those differences, and that's why think there's so much heat and so little light there year here I agree, but just again appointed caution- and I think that just there's no. Avoiding this. The reality. As you know, I am still digging out from the consequences having had that conversation with Charles is that yeah those yeah yet so it's like that's least a year and a half a billion That was number seventy three in Europe too, to ten here. Ok, I so may, as may be seen as two years, but he spent.
Twenty five years of his life, not overcoming the the effects on his reputation haven't written the Bell curve, this point I'm reconciled to, ever come out from The shadow of having touch that topic because of the response to that pop gas and people wrote articles and from them on social media? Today, the limited Our ability is essential. They say that that I was a racist for having had that common play Shania what I said with in it and maddening, but its that's the environment, wherein now, where people who certainly are discussed as being real journalists and who will you, think what have reputations for some sort of integrity an intellectual honesty to protect, will smear you as essentially, Nazi for even touching this topic and the point I was making with Charles
which it was really. The reason why I spoke in the first place. It was not born of real interest in IQ, much less dear racial differences in IQ, but I'm interested in our inability to speak honestly about food acts as we understand them, and for years now in saying that there are certain things that will just sprang out of the data that we can to avoid right, whether you're looking for them or not. If you want to understand intelligence and you're, not at all interested in differences between people per se. We certainly want to put any ethical weight or meet immoral moral weight on human worth, based differences in intelligence, but the topic is still gonna be forced upon you, and so we just half get comfortable. That, and you know, I'm very comforting, all that we
understand what the political right answer is in the end, and we know we want people to have equal. Opportune it is. We know we want people to be treated as morally at the level of fairness, society in and in notions of justice, and we want to correct for the greatest disparities in good and luck, insofar as we can do that so much of this, the ethical punchline me is that this is all due to lock in the end. You don't pick your genes, you don't pick your parents, figure, environment, either right, there's nothing exactly that. You pick you know, and so, if you're a good person who can is about the well being of others. And you realize that they are but for the grace of happenstance, you could have been in any other possible situation on earth its through no wisdom of my own- that I wasn't born in the middle the civil war in Congo. Then you should be committed to
making the world as good a place and his fair places, you can make it an that dictators. Kind of politics and a certain kind of ethical commitment to treating people fairly but people don't see that you can become an honestly. There are people who Listen to this conversation and despite what I just said- and I could read along in this vein for an hour and a half and the punch line will still be there two guys or not. Is there the environment wherein and it's very dispiriting reality, and it only because have taken elaborate pains to in Europe myself to the blow back to these kinds of conversation, There are even can have them. Honest. In any other raw in society and had I been a professor at a university, had I been eight a I'm a journalist who had a boss
I think I would have lost my job based on the low back. From my conversation with Charles Murray and That's just a sobering reality of the environment, wherein in. Well, I'm so sorry to hear that, though, because I mean you hold podcast is about us having honest conversations about topics. No, you do you know that is probably the hottest topic you could pick. You can talk about, genetics of schizophrenia and people don't get upset about that right. You can even talk about cognitive, a bill. These. But if you talk about reading disability, nobody sweats that no problem, so it in Halogens just is like a red flag to a bull in some ways and then, by getting into average differences between ethnic groups, I mean there, you ve got it. So that's the worst well, the best case for your podcast to be able to talk about difficult
books, but I dont go there because the reasons that I mentioned and doesnt off lot to learn about individual differences, and in the end, I think there are two very important you know. Why are some key reading disabled and why do some people becomes gets a frantic or not? So you really did go to the third rail on it and and I am amazed to hear, though, that you still getting blow back. I avoided because I don't do social media, yet India in the academic press, things are you really going the genetic way. If you look at grants funded, for example, I mean Genetics is, they're out that may be able to notice, but they dominate research funding in psychology. They die many of the most highly cited papers in psychology. So I am an optimist. Though, and I have a sense that you're not quite as much of an optimist as I am better I don't look at me. I just entering much time on social media. Maybe
that's right, I mean I just don't don't do it. For that reason, a minute just get you down, I don't even I have long ago. I decided I wouldn't even respond to emails or to even published criticism by work, because I found- Even back than thirty years ago, before social media, a lot of the critics weren't honest critics have eaten, they would say What about this? Is that ok, what we ve done, research on that as yet it. But then what about this? And what about that? And in a lot of I realized, had nothing better to do, whereas I had signed so. I wanted to do and I did in the end. If psychology was going to be an empirical science, in the long run. If you take a very long view, get the data is what matters and I hope in the end you know of students. Psychology will read about being able to networks in nature, nurture urgent sabre. What's all the fuss about amid, of course, genetics is important, so
I am an optimist and I do look at things kind with my rose colored glasses, but I see huge change been called a nazi for twenty second group what's that the heater the motto or the epitaph for this conversation our eyes, I'm I'm an old dawn euros the glass is here and we will proceed because it fascinating science to talk about, and if people. Don't understand our intentions here. They will be unreachable by the powers of human speech. What is that first law of behavioral genetics. First love: able genetics is that everything is heritable. By that I mean individual differences in traits cognitive, listen, disabilities, personality, mental health, an illness, those traits those individual differences, all shows significant and substantial genetic influence right, and so we should
clear up some confusion that people naturally have a round this concept of heritage lady and then an outward we're gonna go in how we know all this based on You know adoption studies and twin studies and all the rest of the actual science. But let's talk about this concept of Herod ability? How are people confused about it? Yeah? It's greatly brought that up, because that six syllable words the most misunderstood word around because it includes word haired abode, somehow involved genes and dna, so people have a lot of different notions of it, but in behaviour, genetics and, I should say, behavior genetics? I mean what we call quantitative genetics like twin and adoption study and now, DNA studies at its the same techniques used. If you were studying medical disorders, for example, so it's it's not peculiar to psychology or behaviour.
But these are the epitome in a way of the complex traits and common disorders that that's the focus of the DNA revolution. Now so Herod ability describes the it's a descriptive statistic: and, like all descriptive statistics like means and variants, it can change in populations over time, but it describes the extent to which differences that we observe in a trade say, like body weight body mass index. To what extent are those differences due to inherited dna differences between people at in this population? At this time, the missile, either many misunderstandings and probably the most common one, is for people to think well that they confuse what is with what could be so we're describing what is in a particular population, the extent to which people differ in Body Mass index and to what extent is that duty
diet, son exercise or inherited dna differences. So we're talking about differences, and we find people might be surprised that about seventy percent of the variants of Body Mass index in in the northern european populations. That we study is due to inherited dna differences. So that's often a shocker for people. We ve done surveys and people think there might be some genetic influence, but they think it's more. Like thirty percent or so, but seventy percent is a lot. It's not a hundred percent, but that's a lot of the differences between people in body. Mass index are due to inherited dna differences, but that that's what is, and it doesn't imply what could be so you're one of the most interesting things I found about doing my dna and getting these politics course it will talk about later. Is that my I have a very high polytechnic score for body message,
I'm quite heavy. I met the seventieth percentage of weight, but what's interesting about this is some people say what you learn, that you got bad news in you, genetic brisker, alcoholism or in this case for obesity, you're just give up and say about nothing. I can do about it. But the point is we describing what is not what could be and certainly you lock me in a room and give me any food, I'd lose weight or more more than that. If I had a bit more self control, motivation. I I might not eat like a pig. The way I would do you know given free access to food, so the differences between what is and what could be, and the other caveat there's a bunch of empathy.
Other cabbie. I think that's important is we're dealing with the normal range of genetic and environmental variation. That is the range of variation that we can study, which is fairly representative populations. Maybe ninety five percent of the population, but it doesn't exclude- include the genetic extremes of single Jean mutations, for example. Nor does it include the invite mental extremes, say of abuse and neglect. Their many were wrinkles hereat legacy to four point? I want to make about this concept of hair debility their related to what you just said. So Even if something were highly heritable in general. In any specific case, it may not in fact be expressed me take it alcoholism immaculately. I don't know what the contribution of genetics is alcoholism. Remember if you mentioned in your work, but it
It's not real, hybrid say it's a forty percent something right there middle, let's say even if it were a hundred percent right, even villages determined by DNA, world without alcohol it would not find expression, rights, then get role environment in any individuals Kayser, even in any groups case, if you find an island of protein, alcoholics, but where you know where alcohol has not been discovered, you'll see zero. And alcoholism among people who or have the genome, would determine a hundred percent alcoholism in another context right so yeah, but you know but not even going to that extreme. The differences between what is in what could be soon? We say: alcoholism or alcohol abuse is forty percent heritable, we mean of genetic and environmental differences that exist in this population at this time inherited dna differences contribute about forty percent. Today, liability the variants in unwholesome and even if you set, even as you said it,
eighty or a hundred percent heritable. If I say ok. I know my genetic research for is high, but I also know you captain come alcoholic unless you drink a lot of alcohol, so I could take that information. Even from dna risk for alcoholism and say? Well, I've got to be more careful because, if I drink as much as other people are more at risk for becoming alcoholic than they are and you can't become alcoholic. If you don't drink a lot of alcohol yeah yeah. So this covers things like alcoholism. It probably doesn't cover everything that interests us, but its relevant and also we should talk about or me. Mention the fact that differences between people- talking about when we talk about Herod ability, what we're not talking about things that everyone shares, which are also genetically determine just having a head or having arms and legs right or being by people in our having something some genome I lateral symmetry, and these are things that virtually every
One has, who is it intact at birth, and we don't talk about the Herod ability of having arms and legs yeah debts that such an important point- and we have say six billion base pairs of dna and ninety nine percent of those are the same for all of us and that's what makes us human we're talking about. The one per cent of dna sequence, differences base, pairs of dna RE extent to which those differences between us make a difference and the answer is they make a big difference, but it it is different, since, if you say height is eighty ninety percent heritable, it doesn't mean I grew to six. What six feet because of my genes and the other four inches were added by the environment, were only talking about differences between
but why I'm very tall and other people are not so tall? Genetics is largely responsible for those differences between people. It really is a critical points. Are thanks? bringing that up yeah near so we're talking about it. In the case of the three billion base pairs in each half of the genome, so tiny, thirty million base pairs that account for the difference between us and as you, they were ninety nine percent identical to one another. Although we are, if I recall, where fifty per cent identical to the banana, so I wonder how much comfort to take their but exactly right. So, let's talk about you confusion that is even more common on the concept. Nature and nurture and and how to differentiate those, and when one of the more fascinating points in your book comes in this discussion. The nature of nurture. What's the confused
here around Natura nurture and how we can t market them well There's that larger issue of two separate in nature, that is inherited dna differences and nurture. That is environment. And this a lot we ve learned there. But the topic of nature of nurture is a different topic. So what would you, prefer to start with less differentiate, nurture and environment, because people thing is one Hang in there, you have it Parents are either a whore. Fight or or happily exonerated when they learn the punchline here. So let's talk about four What are the contributions to individual differences? beyond DNA, we'll talk about an nurture and shared environment.
And then there must talk about the nature of nurture yeah great good. Well, we talk before about the first love behaviour, genetics that everything is heritable and we can get more precise than that and say on average, across all the traits that have been studied about half of the differences between people. Half of the variants of these traits can be ascribed to inherited dna differences. Not fifty percent is a lot. You know this is affect size. The idea of how big of an effect it is not just as it statistically significant in psychology, it's rare to find anything that explains five per cent of the variants of fifty percent of the variances off the scale, but it's a lot less than honour per cent and the other fifty percent is actually
Not due to genetic differences, but what we ve learned is that it's not nurture in the sense that people have always assumed it was from Freud onwards. Nurture was thought to be what happens in families, particularly parents, and what they do to the kids. Like schizophrenia is caused by what your mother does too. You know first few years of life was the line when I was in graduate school. So what we ve learned is, I think, almost more important. What we ve learned about nurture then nature, because that other fifty percent is not due to systematic effects of the family environment, so it's probably best. If I just give you one piece of data on that
makes that point you just take me: am I an parents, body mass index parents and their children correlate about point three is when the kids grow up I mean at birth. There isn't any correlation at all, but the correlate about point three: is it nature or nurture what was always assumed to be nurture and that's not at a dumb hypothesis. Emmy parents give the kids the food they model lifestyles and that sort of thing, but the adoption studies show that when parents adopt a child whose not genetically related to them, the correlation between those parents and their kids for body mass indexes, zero wrote some. Similarly, children growing up in the same family correlate about point three or so in body mass index, could be it reasonable think it's nurture, but if those children are genetically unrelated, the correlation is zero. The other side
the adoption design is to take genetically related people adopted a part. These adopted children who correlate zero with the body mass index of their adoptive parents. Coralie point three with the body index of their birth parents, whom they never saw after the first week of life who had no influence over their environment. So That's the sort of evidence that for decades was used to say, genetics is important, but then people realize in the seventies and eighties, that its telling us something very. Port and about the environment? Whatever the environment? Is it's not making kissing the same family similar to one another? It's not making kids similar to their parents and that's what I called in nineteen, eighty seven non shared environment, it's important! It's making a big difference, but it's not what we thought it was its,
due to shared family environmental influence. So what is it well for thirty years, been trying to figure that out like what is it that's making two kids in the same family different in, for example, parents don't really tree there to their children. Same about you about your in. If you ask you asked parents, they say they do, but if you ask the kids it's where their growing up in different families and if you videotape obsolete interactions between parents and children, you do see that parents are treating their kids. The same I mean like your friends when their sufficiently high, probably admitted, as some in some kids are just more lovable incur cuddly than others. You know so anyway. There are these possible parental differences in treatment, and it turns out we did a ten year study of this
called any ideas on shared environment, an adolescent development and we find yet sure enough. Differential parent till treatment correlate with differences in children's outcomes within a family. So you take siblings, you know and so that parents, the parents who say are more if you look at the relationship between parental, harsh discipline and Children's anti social behaviour in a family, the the child, who is more anti social, the parents are more harsh in their discipline, will, as always, these correlations in psychology have always been and soon to be in our mental. But I think all your listeners know that the adage that correlation does not imply causation is it necessarily the case that the parents, discipline of the child, caused the anti social behaviour, or is it possible that the parents behaviour is reflecting the children's behind
and you can put this in a behavioral genetic design and what you find is that about half of those correlations are due to genetic differences, So this is this is where the nature of nurture comes in, and I a kind of took me off the track, of non shared environment and the punchline there is, after thirty years of trying to find these systematic sources. We haven't been successful. I know in one of your conversations with Paul bloom you mention due to terraces book in the nineties, which really did popularized a lot of these concepts, but really resolves, but then also propose. Maybe peers are important and that's another reasonable hypothesis. You know, you, your daughter's, probably won't end up having the same friends. Maybe one of them has more academically oriented friends and the other has more f
ethically oriented friends than could be a source of difference. But since Judith with REACH, Harris propose that people have also looked at that and again, there's correlations their kids, who are more anti social, have friends who are more anti social. You know in a family, so the sibling who is more anti social, more likely to have friends who are also more delinquent. But again, is it cause and effect, and it turns out that in a kids select friends if their anti social, select friends who were like them in that score and about half of that is due to genetic differences. So that's what I mean by the nature of nurture, but it's also- why we haven't found systematic sources of non cheered environment whenever we find something that looks like it's causing differences between kids in a family, it ends up being a genetic difference. In the skies, so after thirty years I came to this what we call
the only conclusion that non shared environment is essentially idiosyncratic, stochastic, not systematic, so that half of the variants for psychological traits are due to these environmental factors, but their essentially random checks stuff happens, okay, so this is all I think, more important than may be obvious to people at first pass here says one link on this topic with the first What you're saying here is that virtually half of everything we care about in Cuba. Nature view our psychology, whether its susceptibility to various cycle, pathology and we'll talk about What I mean, how we think about disorders and and whether that is order framework as the right framework here, but virtually everything
in psychology and in inhuman difference, but one could care about enough from an intelligence to in a big five personality, trades, to susceptibility to things like depression and schizophrenia punch line here is something like fifty percent of human difference. It's off on either side of that halfway mark and sometimes it sixty percent some as his hide, eighty percent only later in life for things is accounted for by Jean and the other half is environment, but it is not the environment, that pair and saw anyone else can system. Ironically, control and. Or that the environmental component of things very off and half of what is ascribed to the environment is actually
genes in disguise, because people based on their own genetic proclivities, windup gaping their environment? So by because example using your book in either someone you. How often does it rain, where you live ever there, weren't environmental, very but that has nothing to do with DNA while it over the weather is certainly that. But then you ask yourself well who are free to move right. People can pick the climate in which they live and me be some of that has been driven by genetic proclivity right some people who just hate living where it rains right. I you know, I count myself as one of those people it's not, accident. I don't live in Seattle and so it is with everything else. You know how much tv watch as a kid. How often do you read? How often do your parents read to you? This all seems like it's 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 or accounting for her of those so called environmental differences among people. Pause their Robert task. It did I summarised that point correctly. Yes, I thought that was great and the point to for people to take home is correlation, does not imply causation, so parents who read a lot of their kids have kids who do after reading at school, and if you don't think about these issues must assure its environmental. But I hope, after this and people at least pause a minute say: we're waiting now, you know who are these parents who read aloud to their kids and man who, who are these kids? You do better at reading. It could be due to genetics, or increasingly, I think, its due to parents responding to genetic differences in their kids. I have six grandchildren and I thought
the first two I thought you know but disposed to do is sit there and let you read to them. I remember you talking about reading Harry Potter two year, older daughter. Well, that's what I thought gradual must also do end with one grandchild exactly. I could read her all day long and to say: oh, please read some more to me, but I ve got another a grandson who we're almost be abusive for me to make him sit there and let me, to him. He was the rough and tumble play so increasingly, I think, as parents were responding to differences, we see in our kids and given that you have two kids, I wonder if you experience that this wonderful phrase that's been achieved. The six different people. Parents are environmentalists, till they have more than one child hurt. You know with the first child, you can explain anything environmentally, that's the problem with environmental hypotheses. You can explain anything after the fact, but don't you have a say, and child and every parent notices that there's big differences between these children.
And here I didn't do that they have experienced the weather. It is also there there's one enormous environmental difference to which is these second child is growing up in the presence of the first, whereas the first hand, in our case five long years of being an only child. So it's hard to figure out a factor that in but it as a non negligible influence there, But yet I am noticing their impact. Simply similar in some ways, but they are clearly different people. The genetic deck got shuffled yeah this the right in a case, parent people haven't realised this. You know the first degree. Relatives like parents and offspring or siblings are fifty percent similar genetically right. That means there. Fifty percent different genetically, so genetics predicts that kids in a family will be different. They're, not these socialization environmental fairies. They have a lot of trouble. It's
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, Here so again, there are implications for pair team here and social policy education we'll get to those in the back half of our conversation, but All of this again is there, a bit of a high wire act to talk about these things without having people freak out. But we are really just talking about the facts of human psychology in insofar as we have come to know them, and no doubt, you'll be wrong about certain things. Certain assumptions will be proven wrong and in the fullness of time by the idea that genetics doesnt account for a lot. Of what we care about in human nature. The door seems to be closed to that thesis him in blank slate.
Thesis is no longer on the table, and you know it. Howard. In some ways it pushes you're. Intuitions around in others, and we will talk about those those effects, but we should talk a little bit more about how we know this before we get there. Could I just have summarised what, but we were saying, because we heard a lot of topics and a lot of us are very big issues. For example, you know cover, and so what blueprint is cited as mean three main points. First, is everything's heritable, so inherited. Dna differences account for a lot of the differences of the and the rest of the day It's it's not genetic, its environmental, but it's not the environment. We thought was important: it's not shared environment and then, when we find correlations like between parents, reading two kids and kids reading ability at school
You can't assume that's environmental there, often genetic effects in disguise, so I find what helps people put this together is is, if I tell you that it one of your daughters, had been switched at birth in maternity ward and raised in a day from family she would have grown up to be very similar to who she is, even though she was raised in a different family and that's that's not hyper, medical because we have studies if identical twins reared apart and this wonderful document three that one and award last year called three identical: strangers: faceted three identical twins and just how similar they are, despite being raised in quite different family environment, so that your dramatic illustration of this point, because your daughter would sit, would be her eye article twenty still one hundred percent genetically who she is, even though she is raised in the different family. So I think that It helps people to understand it. That term we'd be very much
HU. We are even if we had been raised in a different family with different parents. Ok I'll we're gonna have to land back on this topic and give some account of. Why being a good pair still matters so we absolutely have to get their so ok, but before we do, let's talk a little bit more about these daddy's adoption studies, twin studies, adoption studies, with twins, and we have also was just remind. While the biology here, we have two different types of tat and their manners I gotta twins and dies. I got a twentieth, identical and fraternal twins and Identical twins: Your share the dna there. A hundred per cent identical barring some Pricing mutation genetically end, whereas for Colonel twins are like ordinary siblings. They share fifty. And of their dna, but they just share the same environment all the way down to the the womb. So in the
studies where you were, you can compare identical twins two fraternal twins. Ere, you can really strip out the influence of shared environment because, again you're looking at one group that has identical dna and one group that it has only fifty percent similar dna and yet she environment, and then you have these other studies where you have identical twins supper did at birth and raised in different families, and you a pioneer in doing this work and maybe, if you want to talk about the Colorado Adele in project or an
want to enter this. But bill was talk a little bit more with the logic of these experiments and why they have been so spelling without was a great description of the twin method and but the the punchline there is that if a trait take like musical ability, which hasn't been studied, very much you and it's hard to measure, but what we'd be saying is of genetic influences are important. You'd have to predict that identical twins would be more similar in their musical ability. The non identical twins and the extent to which their more similar then fraternal twins, I say not identical cousin in UK. They call them not identical roundhead fraternal. So if, if a trait like music abilities
heritable you'd have to predict that the M said Manas. I gotta twins are more similar than the dies. I got it for tunnel twin and the extent to which identify twins are more similar estimates, the magnitude of genetic influence. So, as you said, that's a pretty powerful test of genetic influence, but the main assumption there is called the equal environments shit. What if identical twins are treated more similarly, then not identical, twins. Well, that's been studied. It seems to be a fairly safe assumption. You get identical. Twins reared a part are just a similar as identical twins, reared together, for example, but it still is is an issue. But the neat thing is: we have as other method, that's completely different called the adoption method and that's a wonderful situation to be it
because he adoption method also has its possible, who has its assumptions impossible flaws, but there completely different and these two methods, the twin method in the adoption method converge on this conclusion that everything's, that we study insight. Quality is heritable. So the adoption method, though, is in some ways more powerful. You can really see it with identical twins road apart, but they're very rare. So much more typical. Our biological parents who adopt their child away at birth, and then you can study, does adopted children and their Adele. The parents who give them their family environment, but not their genes, they're not genetically similar to them. So it's another powerful way of
adding a genetic environmental influences, and I gave you the example of Body Mass index and how adopted children dont correlate with their adoptive parents in terms of Body Mass index, even though they share food and lifestyle, whereas parents who share genes and environment with their children correlate about point three four body mass index and the real killer data is that these adopted children Coralie point three four body mass index with their birth parents, who they never saw after the first week of life so happy together. That's a very powerful indication not only of genetic influence but of the unimportance of what we called shared environment. You know that traditional view of nurture right, which is, we should just pause acknowledge how counter intuitive this is. We're talking about parents have their own eating habits. Which they then lab,
upon their children from birth onward, and it turns out those habits stripped of their underline genetic code, cause is not what contributes to the boy Mass Index of a child, as here she grows up. Yes, exactly right. So now what about them? Happy genetics here is anything to say, About what we know there, yet, when I give a public lecture, it's so to the first question I get is yeah, but what about epic? You know the environment changes genes well as I say in the book, you only inherit dna see differences in dna sequence. You start life as a single cell with half through billion base pairs of DNA for your mother and three from milk billion from your father and tat
DNA is the same dna and the trillions of cells in your body. We do pick up some mutations as we go along, but the genes that are expressed of those six billion state, three billion dna difference, Nucleotides basis of dna in the double helix of dna. Different. We do not have the same dna expressed in all of our cells into the cells in your liver do different things from the cells. Your blood and from the cells in your brain and that's Jean expression. Different bits of dna are turned on and off in response to the environment, but we what we inherit the dna differences and if a dna difference correlates with an outcome likes
It's a friend. You are alcoholism or reading disability. Then that means that that dna difference was expressed somewhere and is making a difference. But some people have really used happy genetics, which literally means above genetics beyond genetics, to try and argue against men, Delian Genetics and, I think, there's after initial excitement about ever, I think people are coming down about it and realizing. Yet Jean expression is important. Everything we'd inherited dna and behaviour is important. We call that expression. We transcript how makes and tallow mixing it and Wayne. Everything in between dna behaviour is important to understand, but it's important to realize all we inherit our dna sequence, differences right and if they're, making a difference in terms of traits and if a coral
with differences, individual differences in trades, will then there being expressed on some level. Yes, that's right. And then neither about DNA. Is you don't need to know anything about what goes on in between the dna and behaviour bravely like these predictions? But that's not true say all these other things are not important, but I just do I like to argue against the site the idea that epigenetic somehow invalidates genetics, cousin resin, were. The others another detail here, which is interesting and has important implications, and it's that were not tending to talk about single genes, the having some overwhelming trade effect, we're talking about thousands of genes contributing tiny effects, any one of these trade, whether it susceptibility to score- for an hour- intelligence or anything else and interests us and that that has
some significance: why has you tell me what what significant, you see him. It was one of the one thing they jumped for me immediately, which I believe mention your book is that it gives a somewhat less than hopeful picture that any single drug target will be a high leverage to for us in improving ourselves in whatever way we might help to develop them the important thing we ve learned from the DNA Revolution in the last ten really five years is that genetic influence on complex traits and common disorders of the sort we ve been talking about are not you, two one gene? Certainly, we ve known that for a long time, but they're not due to ten genes, are a hundred jeans they're, probably due to thousands of tiny tiny. Dna differences, not first I'd like to say, though, that there are thousands, some people say: seven thousand ten thousand single, Jean DE so
murders. These are like men, Delian, hard, wired, deterministic disorders like Huntington's, isn't that you give it their necessary and sufficient? no, if you have the gene for Huntington's, you will die from Huntington's unless something kills. You first, and you only have Huntington's if you have the gene for honey intense disease and that's the problem. Everyone learns about genetics from Mendel and member was studying disorders and p plants like wrinkled seeds, you know, and so their hard wired and deterministic, and he showed through that that that's the way genes work
in heredity ready but what's important realise is that despite these thousands of singleton disorders, many of which are extremely debilitating lethal for the people who have them they're, very rare one in a hundred thousand one in five hundred thousand so they're very rare, fortunately, and dont really contribute much to the Herod ability of the traits that we study the hare debility of complex traits and common disorders. Medical as well as psychological, are due to die thousands of tiny dna differences and that's a drag in some ways. If you're trying to do a bottom up approach has neuroscientist Siena would want to do where you go from genes to brain to behaviour. It's gonna be very hard. If each of those dna effects are so tiny, you're gonna. Definitely
to get away from a modular approach to neuroscience, where you think you know this gene does this and then that has that effect you know it's gonna, 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 Polly Genetic, that is every trade, is influenced by many many genes and that would include traits in the brain. You know neurotransmitter levels whatever, but the other word that's important is fire trophy every dna difference has many many effects. So you know your 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 thing. So this Polly Genetic 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 singer
Jeanne, hard, wired, deterministic perspective. Yes, there's a lot there so ill what's break apart. If you these concepts the other there's an analog point to make about the brain. There are very few parts of the brain, they only do one thing we can say this is the part of the brain that he no recognizes faces right in this. It does nothing Elsewhere the euro, even pisiform Cortex, does other things. So the real picture is you know of play a trophy where Any one. Gene in this case control too many trades and also in the support you making. The book are concept of disorders like schizophrenia, is itself misleading and it makes sense to talk more in terms of mentions for trades as opposed to these terminal. Disorders and in you, an analogy which really drive on the point with high,
in an enemy wanna talk about height and the the imaginary problem of giant ism. To clarify this concept. Ok, it is just a hypothetical example, but it does make the point that Suppose you decided, you got a new disorder here, giant ism, so people over sixty five inches their giants and everybody else is normal in height. And yet you find that all the genes there have been thousands that have been identified in the thousands of dna differences. 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. All of this is quite Tat of 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, so people who are higher than average are more likely to have that dna difference so Dna research, I think, puts the nail in the coffin of diagnoses. Now you might say: well, that's it
the stupid example. I mean. Why would anyone divide height which is so normally distributed into a dichotomy, but I think that's what we're doing with most other disorders. You know depression, no one thinks depression, you wake up one day and you depressed depressive symptoms are almost caught their quantitatively distributed and never find genes for a disorder. Any Jane you find is distributed through the population like more concretely, one of the first of these effects that were identified using these new approaches. Calgene on white association- was a dna difference that was associated with Body mass index. So this gene had an a t. Argue the four nucleotides basis of DNA, AC, teasing, J, r and d in the old in. Thousands of years ago we were all t t, but then some
got a mutation, that was an a and that a seem to have been adapted, the story used to be that it lousy to conserve fat and, in the end, the stone age, that would be a good thing, as you never knew when your next meal was coming, but now that that is makes you more likely to become obese in a fast food nation. So if you have to is your three pounds heavier than someone who has won a and If you have no ways what that that one eight makes you three pounds heavier than someone with no ways: Tt Tt, so six pound differences twenty dna. That's what we mean by an association, so that was found obesity initially, but then they found that that dna difference works quantitatively through the throughout the distribution. That is, if you're you and your sibling, you have an a and they don't. You are likely to be. If we get a lot of situation, siblings, like that three pounds heavier on average
but that only accounts for one percent of the variants of by mass index and when that was published in science in two thousand and seven people talk swell one percent, I mean: what's that turns out it's one of the biggest effects that we can find for complex disorder, complex traits in common disorders, so it is 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 door to try and understand it mechanistically, but you can put them altogether aggregate them in a Polly genetic score and put make pretty substantial predictions like we can predict twenty five percent of the variants in height and about ten percent of the variants in weight by putting all of these together. So for wait, this one dna difference. I was talking about accounts for one percent, but then these other dna differences account for nine percent. So altogether you can predict about ten percent of the various, but these Polly genetic scores are all necessarily perfectly normally distributed because it's it's the central limit, theorem of statistics. You know you flip a coin, and if the book hundred coins and you get this normal distribution of heads entails and that's it,
you're doing it, you're flipping LEO's. You know you either have one a or the other illegal or two of them. So these politics growth are perfectly normally distributed so that the genetic liability for everything any disorder, autism, schizophrenia, corner heart disease, it's perfectly normally distributed. So I think that is really, I think, ought to put the nail in the coffin of diagnosis because I really believe in psychiatry in psychology. These diagnoses have held us back tremendously and all of the DNA studies, these Genome White Association studies are chase control studies, so the whole game is defined these people who meet these. What I think are arbitrary diagnostic criteria and you call them cases likes, gets a frantic, and everybody else is a control wrote and that's really how us back, because it's just simply not true
yeah because everybody else is normal, so called normal, could be just like these six foot, three, and who's. Not class has a giant but still- as all of these increased height probability. Genes and it means that we all have thousands of genes for schizophrenia right. It's just quantitative and I you know. If you have a very high, we called polygenic score for schizophrenia, as Ed probably takes. We all have stresses that would freak us out and as you've mentioned several times in your podcast, that, if you did have a genetic propensity towards schizophrenia, probably ought to be careful about some of the psychedelics, for example. Red or some of the evidence suggests the Highty Hc sort of marijuana could also be dangerous in that situation is like alcoholism, you, if you have the genetic propensity, it doesn't mean you gonna become Elk Pollack, you necessarily gonna becomes gets a frantic you're, just more likely to be, and given the
stresses and strains of life. You are more likely to be tipped over the edge than someone else here, and it's These genes are very likely contributing to who you are in noticeable ways that are that put you on this spectrum, which has schizophrenia as its terminal so like that these genes for height? that would render a giant six five for beyond are also operative in you at the at the height of five ten. It's just you have a different compliment of in or not talking about many many genes for any one of these traits exactly right. The picture is, I think, the Fraser is it the abnormal is normal and they were all on every spectrum that that we could posit exists in the popular we're all somewhere on it and whether we have it symptom, ology that interest in or not
as the only difference right. So it's it gives us a a fine grained way of thinking about human difference end and the Foundries between what is considered, the normative or normal end pathway, logical Emmy, its common to I think, you're references in your ever Aristotle. The analogy between madness and genius has been Braun and ya. Think probably too much has been made of that, but this is susceptible to in the end, a genetic analysis and where we can look at the GINO type of what. If we want to call genius and the GINO type of what have we the call madness and just see what how much genetic real estate they share. No, that's really right. One implication I find quite interesting to is I'm basically saying there are no disorders, they're, just quantitative dimension threat, and one application of that, then, is if there's no disorder, there's nothing to cure. It's not like you,
yes or no, it's all quantitative, it's a matter of more or less were alleviating symptoms, rather than here being a disorder. It all has to do with psychology aping medical science is where a lot of this does work. If you have a simple cause of cause, if you'd like to continue listening to this podcast you'll need to subscribe, it Samharris, DOT, org you'll get access to all full length episode Megan, says podcast and two other subscriber only content, including bonus episodes amaze Conversations. I've been having the waking about making sense, podcast ad free and relies entirely unless their support and you can. Subscribe now sand Paris, dot org.
Transcript generated on 2020-07-23.