Episode 63: Brian Boutwell on Twin Studies and Heritability

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[00:00:12]  Blue: Welcome to the theory of anything podcast Today we have a guest On the show Brian bout about well. I say that right you got it. All right. We’ve got Peter here Also, how’s it? How’s it going Peter? Hey, Bruce? so, um, Brian and I started talking a while back and He he like a lot of us. He read David Deutsch and became very excited about a lot of the ideas But Brian is interesting because he actually works in the social sciences. He would be technically considered social sciences Or is it just adjacent to social sciences? probably Either or adjacent or in the social sciences behavioral sciences. I think any of those labels would be appropriate

[00:00:59]  Green: It just occurs to me that Brian and I are both Sort of heretics in the David Deutsch world and that I’m a public school teacher and he’s a Sociologist who studies or genetics

[00:01:14]  Blue: so Brian sent me two articles And one is called behavioral genetic methods and that’s by Willoughby polderman and Brian himself And the other one and that one is was in nature and then the other one was um meta -analysis of the heritability of human traits based on 50 years of twin studies by polderman And a whole bunch of other people whose names I can’t pronounce And I read through those papers and Not being in the field. I ended up with lots of questions, but they were very fascinating papers And as Peter just mentioned There’s definitely a a feeling amongst a lot of fans of David Deutsch that certain that I don’t know if I’d say that they dismiss the entire social sciences Some of them maybe do but I think some of them take parts of them seriously You might hear them mention psychology or something like that But definitely there seems to be some skepticism around a lot of these fields And these papers really kind of lay out What the twin studies were how those types of studies are done And I just found it super fascinating. So I wanted to invite Brian to the show And try to ask him questions about stuff so that I can understand this better And really kind of dig into it. And then Brian and I have also talked a lot about how do you apply poppers epistemology to

[00:02:44]  Blue: Social sciences, which is a really kind of a tough question And I don’t know if we’re going to be able to get to that subject I just asked Brian before the show Maybe we’ll need two episodes so we can do that that second subject as its own episode But this is what Brian and I have been talking about and he’s got some really interesting ideas on both of these subjects And so that’s why I invited him to the show and honestly, it’s kind of me just being selfish I wanted a chance to Say, hey Brian, can you like explain these things to me better? There’s a lot of things in here that are kind of technical I’m a layman I don’t understand them and I really wanted to ask Brian questions and try to understand these articles better so That was why I invited him to the show and I thought hey, let’s record this It can be a podcast episode and I suspect I’m not the only person who would be interested in this subject So with that introduction Brian why don’t you why don’t you tell us a little bit about yourself and how you discovered david deutch and Kind of your interest in both david deutch and in the field that you’re in

[00:03:45]  Red: Yeah certainly and it really is a Pleasure to to get a chance to join you guys and talk about these things Like you mentioned, I’ve uh I found deutch’s work within the the last handful of years and I sort of arrived at it uh just via the recommendation for like a better word of a colleague of mine And it it really did just Sort of provide a jolt to my intellectual life in a really wonderful way So I guess to I’ll just pause on that briefly to say so I’m Just in terms of professional affiliations. I’m associate professor of uh in the school of applied sciences at the university of mississippi also hold a secondary appointment as a professor of Population health in the johnty bower school of health at the university mississippi medical center I was a visiting scholar at cambridge university uh in 2022 um And I’ve been at the university of mississippi now for this will be four years Uh, and I’ve been in academia for oh gosh, this is when you start to feel old about 13 years um And the as bruce was describing the the the work that I do is sort of um broadly Uh devoted to trying to to understand aspects of human nature. Um, sometimes that involves kind of the more uh Regrettable aspects violence and aggression Uh, and then um, it can then you know spans over into fields like medicine. So I do work Uh on diabetes type two general aspects of health and wellness longevity health span um And then also, uh components of

[00:05:43]  Red: Psychiatry different forms of uh psychiatric problems and how they impact functioning and behavior And all of that is really done using the toolkit of behavioral genetics, which is how I think it’s a A productive way to think about uh behavior of genetics twin studies things that we’re going to discuss as In some ways they exist as a field unto itself But in many other ways, it’s simply one among many toolkits that try to Or rather that are available to researchers whether it’s medicine or economics Uh as a among other things a way to improve causal inference capacity when you uh, you can’t do a randomized experiment, which is uh Pretty common in terms of the types of questions. We study the unethical to do those things Which we’re getting all that but that’s a sort of a potted uh career bio So, okay.

[00:06:41]  Blue: Thank you And that was actually what I found so fascinating about these papers is um Let me see if I can kind of explain my own background on this A lot of my friends online that are fans of david deutch they seem very very skeptical of any sort of um Scientific theory if it if it doesn’t have a explanation that’s mechanical. So In past episodes, I don’t know if you’ve heard these episodes are not brian But in past episodes we talked about some of their stances on universality versus iq, let’s say um, and they have really big problems with iq because as a theory iq Doesn’t even attempt to explain why some people would be smarter than others, right?

[00:07:30]  Blue: It it simply makes the claim that some are uses maybe tries to measure g factor But it’s not like a highly explanatory theory if that makes any sense and so they’re very skeptical of any sort of theory that that doesn’t have That kind of deep mechanical explanation now i’ve used an example on the show of How that just isn’t really how I understand critical rationalism critical rationalism allows for there to be a hierarchy of explanations so If I say and this is the example i’ve used over and over again if I say um You know oranges stop scurvy that is an explanation even though there is no Mechanical explanation for why oranges stop scurvy now It’s not a deep explanation But it is an explanation and it’s a completely valid scientific explanation Because it can be tested Now if I were to improve that explanation to vitamin c stop scurvy I’m now starting to get more into the mechanism not very far, but a little bit more So that’s a more empirical theory than the first one and therefore is considered in critical rationalism the better explanation And then we could go even further We could get into vitamin c stop scurvy because it affects the connective tissue blah blah blah blah And we can come up with this really kind of deep explanation That’s way more testable than the other two And yet if you falsify it you falsify the other ones And so that they exist as a hierarchy Where the explanations get more and more intense and therefore more testable And that’s how I understood critical rationalism.

[00:09:04]  Blue: I didn’t see it as you can dismiss um A theory because it’s quote non -explanatory most theories have at least a little bit of explanation And therefore as long as they’re testable they’re there and i’ve argued this with a lot of people online and this seems to be fairly consistent that i am On the outside on this that most of my friends of david doge that consider themselves critical rationalists Disagree with me on this And yet I this is how when I read popper. This is what I understand popper to be saying like I I’m not sure where they’re coming up with this alternative view because it doesn’t seem to be what popper is saying to me in his books So and one of the reasons why I had some concerns with this is they will often say like i’ll i’ll mention a theory That is low explanation like let’s say iq theory And they’ll say not only does it not have an explanation, but you’re just doing correlations And i’ll say no i’m i’m not just doing correlations. We’re talking about causation You know and and they’ll say no, it’s just correlations. It’s no different than and they’ll use examples from the medieval times It’s no different than You know trying to look at Humors or whatever and trying to come up with explanations say no, this is like nothing like that, right? It’s this we’re talking about actual causal explanations Then i’ll usually cite judea pearl’s work and i’ll say we can test causation using randomly controlled tiles trials, right?

[00:10:32]  Blue: It’s the fact that i’m listing something as a correlation If it’s done within the right inquiry as part of the right experiments We can actually test whether something causes something else using randomly controlled trials And pearl lists out a whole theory of how we do that How you go about trying to cut the connections. It doesn’t require that I have a deep explanation of the mechanism I just have to know that this causes that and then I can through a randomly controlled trial Come up with an appropriate experiment to test if there is a causation there or not And again, I feel like i’m kind of on the outside on this that most of my friends who consider themselves critical rationalists Disagreed with me and again It seems to me like i’m just going with what popper wrote I I don’t think popper had any problem with what judea pearl would have said, right? It’s When you sent me these papers The thing that I found so fascinating was That they’re really about how do you test for causation when you can’t do a randomly controlled trial No, that’s right. So We’re kind of two steps in now. First, you’ve got those who are skeptical of randomly controlled trials, which i’m not like I totally get that you can test for causation using randomly controlled trials I the people who claim you don’t I don’t feel like they’re even taking a scientific attitude to to be honest Um, or they just don’t understand it. They need to go understand your day of pearls theory I’m not sure what it is.

[00:12:01]  Blue: They’re missing But I can see why there would be more skepticism Over if you couldn’t do a randomly controlled trial that is that’s harder for me to wrap my mind around Like I can easily wrap my mind around why a randomly controlled trial Tests causation where it’s much harder for me to wrap my mind around How you would do that if you can’t do a randomly controlled trial and that’s why I found your papers so fascinating But they were also very technical and as a layman I found them a little hard to understand and to get my mind entirely wrapped around them That’s kind of my background and why I found your papers so fascinating. Does that make sense?

[00:12:36]  Red: Oh, certainly and uh, it makes good sense and a a lot of interesting Um content in there to impact. So it’ll be fun to try and talk through, you know, some of these concepts and and see if They become compelling.

[00:12:50]  Blue: Okay. All right sounds good Well, let me just start with I’m going to quote from your papers and I’m going to in some cases I’m going to ask you interview type questions in some cases. I’m just asking for myself Can you explain this because I didn’t understand it and I’d like to understand it better So, um, I don’t think I always wrote down where I know when I’m quoting you from the articles But I’m not sure I remember always which of the two articles I’m quoting So I I will do my best to give the quote and if I need to I’ll try to figure out which paper it came from but When I was taking notes, I was just like jotting stuff down quickly because I was excited and I didn’t Maybe make it into great interview questions um To some degree this show people if you’re listening to the show you expect our show to be somewhat technical And to be about trying to figure these things out This isn’t Strictly like in many ways. This is not an interview of me to you This is me trying to understand these topics better and you’re here to help me do that If that makes any sense it

[00:13:53]  Red: does. Yeah, and hopefully I’m Up to the challenge or and and capable of providing something useful.

[00:14:00]  Blue: Okay So right at the beginning of one of the um, the the polderman Both articles are from polderman. If I say the polderman article, I really mean the one that you were to co -author on Gotcha, um It says the relative importance and specific nature of influence of genes and environment on human traits remains Controversial so up right up front. He’s saying this is a hotly debated topic. Maybe he also meant politically debated topic I don’t know he I didn’t get that from reading the article But um, could you talk about why this would be what would be controversial about this topic? So we’re kind of just up front putting the elephant out in the room Why is this a controversial topic? Why would scientists feel like they need this is a debatable topic Uh,

[00:14:47]  Red: it’s an interesting question. So I think in in the way that, um controversy is sort of invoked in that situation uh it captures a variety of of Things related to why behavior genetics can sometimes um, you know Spark some some debate and and sometimes heated debate. And so one aspect of that is uh Really related to I think some lingering misunderstandings about certain concepts for in particular the word heritability uh, and uh, sort of the uh, completely understandable, but Regrettable tendency to confuse that word with inherited And I’m sure we may may be playing talk about both of those so I won’t go into a ton of detail at this point But they they aren’t the same Even though they’re, you know, they’re certainly related When we’re talking about heritability We’re describing something different than when we talk about the inheritance of a particular trait Uh, and so we can we can talk about that distinction, but it is a really important distinction because You’re

[00:16:06]  Blue: right that I have some questions on that But why don’t you go ahead and now that you’ve brought it up? Why don’t you make the distinction and and help everybody understand the difference between heritability and and inherited?

[00:16:18]  Red: Oh, certainly. So, uh the Probably everybody can remember back to Yeah, being in a high school biology class or maybe a intro to bio class in college um, and you were uh working with Or learning about Mendel’s work with peas, right? So we remember doing those sort of punnett squares where you’re crossing uh a smooth P with a p that tends to be wrinkled and you sort of map out the disappearance and reemergence of uh traits like The smoothness of the p inside the pot kind of thing so A lot of time I think for a lot of folks that’s when we start to talk about genetic influences Those are the types of examples that come to mind because it you know, it sort of makes sense and Mendel’s work was obviously foundational especially when it was merged with um With darwin’s insights about natural selection and sort of made the two Uh mesh well and explain you mentioned sort of mechanism earlier. It helped better explain The transmission of traits from parents to offspring and and it helped uh Answer a variety of questions and and and you know was one of those great sort of scientific achievements in my opinion um and so The the trouble is When we talk about heritability It’s You know easy to imagine inherited But heritability is simply a statistic. It’s a One of three parameters in behavioral genetics Where we subdivide variants in some trait. So it’s it’s a way of Understanding along with two types of environmental effects that we’ll talk about Why members of the population differ from one another? So in other words, let’s imagine that We’ve got a you know, uh, we’ll keep the example very oversimplified at this point Uh, again

[00:18:27]  Red: the small group of individuals and we’re interested in how tall they are And you know, one of the obvious things we’ll notice is that they are different in how tall they are Some are relatively taller. Some are relatively shorter. There’s variation in height So what at at a basic level what twin studies do sort of the classic twin study? um As we refer to it is uh, it it partitions The reason for that variation into three factors Uh, the first is heritability The second is what we call shared environment The third is also a type of environmental effect. We call it the non -shared environment And so we can go through those in a moment, but the point about heritability is that it’s simply Uh, an an estimate of how much of that variation is the result or or is rather associated with genetic differences that exist between those individuals in our Example our height example And so some of those differences are going going to be linked to genetic differences Other differences are going to be linked to different environmental experiences Precisely,

[00:19:39]  Blue: that’s

[00:19:39]  Red: right. And so The twin studies, uh, just work to partition variance and heritability is one part of variance Partitioning but it the reason we don’t want to Confuse that with inherited is it it makes Sense logically and mathematically to talk about a trait or uh, some particular trait being having about 30 percent of variance Being heritable it does not make sense to say that 30 percent of the trait is inherited That that’s incorrect and really even sort of nonsensical

[00:20:18]  Blue: Okay, let me see if I can try to summarize what I think you just said Yeah, certain traits may be inherited like let’s the classic example of blue eyes I don’t even know if that’s actually true

[00:20:30]  Red: But well men men daily in traits is sort of how we would refer to it where there’s you know a single gene Kind of situation Exactly, that’s

[00:20:41]  Blue: right. Okay. So that’s what inherited is so the the classic example is blue eyes I don’t know if that’s actually true that blue eyes are inherited as a mendelian trait, but that’s the one they always use in school So, um, let’s pretend like it is in any case So if if blue eyes is determined by a single trait and then you either have it or you don’t and it’s recessive Then that would be an inherited trait Whereas the height is not strictly inherited because there’s a whole bunch of different factors. It’s really more a matter of heritability

[00:21:13]  Red: Right. And so there’s quite a few things wrapped up in that. Um When talking about something like a eye color or you know Again going just going back to the pea plant because it’s familiar to a lot of folks smoothness versus round or a wrinkled peas That is the proper place to use things like inherited,

[00:21:34]  Blue: okay

[00:21:35]  Red: part of the reason height becomes, you know inappropriate in a situation like that is It’s what we call a polygenic trait There are hundreds likely thousands of genetic variants that play some small role In explaining why some individuals are taller than others and they do that in conjunction with The types of environmental differences that you mentioned things like nutrition or deprivation Um and and sort of together It that helps us better Get a sense of if it’s height we’re interested in why some folks are taller than others in some population of people

[00:22:12]  Blue: Okay Now in the article it also says we showed that a majority of traits 69 The observed statistics are consistent with a simple parsimonious model where the observed variation is solely due to additive genetic variation Now that wasn’t a term I had really heard before I could probably guess as to what it means just by The choice of words being used there, but I would prefer not to guess

[00:22:38]  Red: So

[00:22:38]  Blue: what are additive genetic variations and how do they differ from non additive genetic variations?

[00:22:45]  Red: Yeah, so this is also It’s a good point to go back to that that word controversy because this is another form that Controversies can sometimes be too strong of a word where some very interesting and useful debate still occurs in in quantitative genetics behavioral genetics and it is this issue of additive versus non additive heritability so additive is Very much like what you might intuit it refers to, you know, if we have uh, some complex trait Maybe height and say there’s a you know a thousand genetic variants or you might hear me slip and use the word allele it just refers to different forms of a particular gene say That there are a thousand alleles linked to variation in height the effects of those alleles represent the sum of their individual influence so together with the environment they you know, they have independent and Individual effects on whatever outcome we’re interested in

[00:23:57]  Blue: okay

[00:23:58]  Red: non Refers to interactions between those alleles so that Maybe having one allele One allele magnifies the effect of another on the trait we’re interested in okay and so Really, I think that’s we can certainly go further into it if you like but I think that just understanding that is sufficient to sort of get the idea that When studies certainly uh are You know sensitive the idea that sometimes they’re they’re you know, there are important non additive effects to think about for genetic variant or Heritable variants and they can calculate those We called dominance effects dominance heritability And we can estimate if we just have reason to suspect that they’re present We can adjust the models and try and get a sense of that But there is a In return returning this idea of debate there has been a fair amount of work and we allude to it in the paper both using you know, just theoretical insights simulation models and then a variety of Evidence generated from twin studies over the years Where we you know, we can Be reasonably at least I’m reasonably Comfortable the idea that most of the heritable Variants we observe is from that that’s additive model where individual leels are all contributing their individual small effects So

[00:25:32]  Blue: it it seemed to me that the paper made a big deal out of the fact that the majority of traits were additive um Like since i’m not in this field, I didn’t necessarily understand why that was a big deal So so is it just because that means that the model is quite simple in most cases?

[00:25:53]  Red: That that’s I think fair to say part of it. Um There it’s certainly a nuanced debate a lot of it sort of hovers around methodological concerns that our models are you know, giving us Misspecified or incorrect results or biased estimates like maybe overestimating the effects of heritability or the effects of some type of environment because of these Non -additive effects these interactive effects that we’re not paying attention to So that’s part of the concern is that our our results are biased and that’s an important concern. There’s no doubt about it um and as I mentioned Uh, and we do have some tools to sort of investigate that and so the other concern is And it is connected to the first is that the sort of classic twin studies Give a vastly oversimplistic account of how genes influence these complex phenotypes and the argument is you know, there are Important interactions between genes and there are important interactions between genes and environment and and just a partition variance into heritability shared environment non -shared environment is to give a Such a misrepresented picture that it borders on, you know, um, just A caricature And again, even though I don’t necessarily agree with those arguments They have been very crucial in the development of the field and sort of testing the assumptions of the models And you know, again the more methodological side of things. So, uh, they’re certainly Nuggets of very important information in there. And so When folks have debated these issues, they’ve done the a bunch of fields Connected to behavior genetics a great service because those are very important issues

[00:27:49]  Green: Okay, so am I understanding your last comment correctly that you you feel that some people who are Tied into these these twin studies and things take the conclusions About a bit too far

[00:28:05]  Red: No, no, I would say that what

[00:28:07]  Green: you’re saying. Oh, okay.

[00:28:08]  Red: I would just say that some of the debate revolves around um, the idea that development of complex traits, whether that’s height or perhaps something like schizophrenia or major depressive disorder or you know, depression in general These are very complex um Types of things to study and what’s it what I think is also important to point out is When we’re a lot of times when we’re debating the importance of something like additive effects versus non additive The debate is not about Whether genes are important both sides agree that they’re important What they’re disagreeing about is the extent to which Things like comp these interactions between genes or interactions between genes in the environment are You know being missed in the basic approach of twin studies, but they’re you know Sometimes agreement can get lost in disagreement. There’s a agreement that that you know genetic effects are important and interesting for complicated outcomes Okay,

[00:29:15]  Blue: so let me just take this statement that we show that the majority of traits 69 Are due to additive genetic variation. Let me take that statement at face value So let’s let’s assume for the sake of argument that you know God comes down and tells us. Yes. That was exactly correct or something like that. So now know it to be correct Okay, what does it actually mean? So so Let me see if I can make my question more sharp here. Does that mean that they’re Those traits do not have interactions between genes in an environment And that the environment may influence it and genes may influence it But they’re not having some weird interaction between them that it’s actually There’s a thousand genes and if you have 500 of them, you’re going to be a certain height and there’s environment You need certain kinds of nutrition during development and that will affect your height But it’s not necessarily a complex interaction between genes and environment in in the case of these 69 of traits

[00:30:18]  Red: Yeah, so I think so correct me at any point if I misstate something you just said But so if you were to make the statement Uh that We can dismiss the importance of gene gene interaction or gene environment interaction for complex traits Uh because most of the variants in comp complex traits tend tends to be additive I would say that that is not a good through statement.

[00:30:47]  Blue: Okay

[00:30:48]  Red: interpretation. What I would say is The the assumption of additivity or of additive effects Is a good guiding assumption, but for any particular research topic or Area of study, let’s say, you know, just go back to schizophrenia We might have a theory might guide us and this is kind of part of the importance of good theory good explanation theory might guide us toward suspecting Uh and in, you know, some interaction between two uh alleles or three alleles or Okay, leels in the environment and we can we can and should investigate that So it certainly doesn’t take that off the table doesn’t take it make it less interesting or less important But it really in in some ways is sort of pragmatic It tells us that you know if additive genetic effects or are they sort of a guy if that assumption holds We’re going to get Estimates of heritability that are less likely to be Biased substantially if that makes sense.

[00:31:52]  Blue: Okay Now kind of related to that was the article said many genetic variants Contribute to the variation of complex traits and the effect sizes are typically small however The sum of the variants explained by the detected variants Is much smaller than the reported heritability of the trait This missing heritability That’s in quotes has led some investigators to conclude that non additive variations must be important Um, can you help me understand this concept of missing heritability?

[00:32:28]  Red: absolutely so uh twin studies have been around for uh relatively speaking longer amount of time than the more modern sort of um Technological advances that allow us to do something like a genome -wide association study

[00:32:46]  Blue: I I noticed that like they started back in like the 40s or 50s or something

[00:32:52]  Red: Yeah, they’ve been around have a long history and um Whereas to do things like uh study the Or even to just do simple genotyping With like polymerase chain reactions pcr Is it’s relatively new technology and you know going back to the human genome project in the early Which sort of was wrapping up in the early 2000s where we had mapped the genome um And that at that point we were able to especially as the technology became cheaper and cheaper and cheaper to use to genotype And measure the presence of certain genes certain genetic vary variations that folks might have Maybe you know which version of a dopamine related gene that they were carrying And and see if those were linked to these complex traits that twin studies were telling us were heritable Which again, even though heritability and inherited aren’t the same heritability does imply Uh genetic influence on a trait right and so we could then go out and try and investigate whether You know a certain dopamine gene Explained any part of why some individuals tend to be more Perhaps vulnerable to depressive episodes or major depressive disorder And we sort of we mentioned this in our paper and I think uh the meta analysis does as well um There was a flood of what we call candidate gene research And in general those were um and I say this is somebody who who published candidate gene research They were underpowered they were um Sort of ill -equipped to find real effects and as a result a lot of those findings didn’t replicate They were you know false positives or you know sort of Fault starts so to speak and and They were as a result.

[00:34:53]  Red: I I don’t do candidate gene studies anymore The amount of can’t you’ll still see some candidate gene work published But uh much there’s a much greater emphasis and uh use of these genome -wide association studies and what these studies allowed us to do well investigate possible associations between hundreds You know hundreds and thousands of places in the genome with complex traits and so we were able to Uh not only look at whether certain places in the genome certain alleles correlated with something like height We could also use those genetic variants themselves to calculate heritability So the the I mean the the way that that’s done is interesting and important, but it actually is not super Relevant in this case The long and short of it is you can calculate heritability estimates using Measured DNA so these looking at uh different alleles captured in these genome -wide studies and what When especially early on when folks were doing this what they were finding is that The heritability estimates they were getting from using measured, uh

[00:36:13]  Red: Snips so I’ll explain that term just briefly if if I use the word snip it refer it’s an abbreviation It refers to a single nucleotide polymorphism So uh the idea that at a certain point in the genome one might have a particular, you know base pair and a Or a t if we think back to basic biology, but That’s that’s enough to argue to just describe that it’s having a different version of a of a gene Which is I’ve been oversimplifying, but that’s all right So you can use that information to calculate heritability and what uh missing heritability as a term refers to is When folks did that what they found is they got heritability estimates that were considerably lower than what twin studies were providing so Okay, if

[00:37:00]  Red: a twins if you know if we conducted a twin study Calculate the variance in height uh that was heritable and found that uh 80 percent of the variance was uh attributable to the genetic variation We did the same thing using uh genome wide association data We found that we only explained five percent of the variance in height and so What I think a couple things are important there one the conclusion was not that genetic effects are irrelevant for height it was that Twin studies are sort of washing over these very complex networks of interactions between genes that That you know explain variance in height and and sort of goes back to the idea that maybe assuming that additive effects were um The rule rather than the exception was wrong And so one of the points we make in our paper is that you know with time And even at the time some folks were arguing that Look is missing heritability is is really not The confounding issue that you think it is uh because part of it could be the simple fact that The uh arrays that we were using to do these genotype uh the genotyping for these genome wide association studies We’re missing um what we call uh rare variants or just snips that occur at A relatively low rate in the population And so when you account for that you should be able to explain more variants that we thought was missing I see So in essence we moved the field moved from thinking that most of the heritability was non additive to Oh wow, actually most of these are additive well, I would say I think maybe the The useful way to think of it is That

[00:38:55]  Blue: On

[00:38:56]  Red: a couple fronts one so when we did we were able to do and we mentioned a couple of these studies in our paper You take something like height recent study That used that had the capability of sort of detecting presence of both common and rare Alleles uh explained I think it was around 68 percent So it had a gene -based heritability estimate of about 68 percent for height That’s still lower than what you will often get with twin studies But it’s getting much much closer. So that missing heritability as we say in the paper Starting

[00:39:30]  Blue: just there. Okay.

[00:39:31]  Red: Yeah, it’s getting filled in but going back to that second point The the idea of complex non additive types of interactions in some ways that is We can use additive effects as a good guiding assumption But for any particular trait we might be compelled again by theory or or some other piece of evidence That we want to investigate gene -genic interactions using something like GWAS and that’s that’s completely defensible and important So it doesn’t mean that you can’t look for non additive interactions. We we can and should

[00:40:05]  Green: Okay,

[00:40:05]  Blue: okay.

[00:40:06]  Green: Can I jump in real quick? Yes. Um, you I Sort of you’ve mentioned twin studies a lot. It occurs to me that it’s sort of the opposite of a twin study Which might seems to me might be more easier to to study Which aligns to kind of your experience is where non genetically related siblings are Raised together uh Right in or in a shared environment are are the conclusions of those kinds of studies as important as the twin studies

[00:40:38]  Red: so I did I want to make sure I’ve got uh Interpreting your question, right? So are you are you asking that? Is it possible to do sort of the classic design that we would normally do with? Identical and fraternal twins, but do it with just maybe full siblings and half siblings and

[00:40:57]  Green: Yeah, yeah, yeah like going

[00:40:59]  Blue: in that direction

[00:41:00]  Green: I mean, it seems to me that’s much more common than twins being Raised apart would just be the opposite non genetically related Siblings raised together right

[00:41:11]  Red: Yes, okay, so just uh So we are thorough in this answer you mentioned in your twins raised apart that is That is an important design. It’s relatively rare. There aren’t many of those folks We do you’re right. You’re correct that we classic twin designs rely heavily on The use of identical and fraternal and I guess at this point we can also Give a term and define it so monos. I got it dies. I got it The more you know sort of term you’ll see in the literature monos. I got it refers to identical twins twins that result from a single Egg splitting fertilized egg splitting

[00:41:49]  Green: Okay,

[00:41:49]  Red: and as a result Those individuals are essentially have carbon copies of the same genome

[00:41:56]  Green: Yeah

[00:41:57]  Red: clones of each other basically dies, I got it twins are The in some ways the same as full siblings They’re the result of two separate fertilized eggs And just like full siblings they share half of their Genome, but they also share prenatal environment obviously so Typically when we’re doing twin studies, uh, you’re going to see Identical and fraternal twins used in the study you can absolutely do Very similar types of analyses using Full siblings half siblings The important thing is that you have a sample comprised of siblings Uh with types that differ from each other and how related they are to each other. So full siblings share half of their You know dna, uh, just like dz twins All right dies. I got it twins. Uh, half siblings would share, you know, half of that And so as long as you know the genetic overlap between your sibling types you can conduct behavioral genetic types of analyses and What one of the so you talked about maybe the availability of twins or that sort of connected to one of the points you mentioned Over the years and and we it’s not in the paper, but it’s actually a resource. I’m pretty excited about it’s in our supplementary material, uh on, uh, the journals website we Wanted to offer anyone interested in behavior genetics a resource for how to find data And what’s pretty amazing is that When you when you sort of look at what’s available to anyone who wants to do these types of studies There’s a massive amount of data available large samples thousands of twin pairs And a lot of it’s freely available to download And folks can go out.

[00:43:52]  Red: So that’s a large part of what our paper was meant to be Was a resource for anybody who’s interested in in this stuff because there is really an abundance of twin data But yes to go back to your question We can use full siblings and half siblings. We’re a little bit limited in terms of the some of the inference capabilities Compared to say when we have identical and fraternal twins But um, it’s it that’s an option as well I see.

[00:44:20]  Green: Thank you.

[00:44:21]  Red: Oh, absolutely

[00:44:22]  Blue: So does the amount of heritability change? um Like let’s say let’s take an example of we were trying to measure How much height is heritable today versus say in the medieval ages where nutrition was bad With the amount of heritability Change

[00:44:41]  Red: Absolutely.

[00:44:42]  Blue: Okay.

[00:44:42]  Red: Yep. Absolutely that necessarily stable. It does depend on the actual environment That you’re correct. And it’s a very important point. It’s one of those sort of related to Not confusing heritability with inherited is the Heritability should not be mistaken to be some type of fixed number A trait can be heritable At one point in time like now, you know height right now is highly heritable But as you point out, you know, if we were to hop in a time machine and be capable of Observe, you know doing a twin study Uh in a prior human epoch We’re probably going to find that most of the reason People differed in their height was because of access to nutrition and not because of genetic differences When you have severe caloric restriction Common with parts of the population What the answer to the question of why are some people taller than others is going to have a lot to do with Well, some folks are not getting the requisite amount of Chloric intake in order to grow and so in that regard environment becomes a much more salient Explanation of why some folks are taller than others. So, yeah, you’re 100 right.

[00:45:58]  Blue: Okay, you know, I Way back. I did I did some episodes where we we talked about And we’ll do this a little bit in this episode too about some of david dutch’s criticisms of these sorts of studies in beginning of infinity And one of the things I pointed out Is that the criticism that he was bringing up for mental traits was really kind of also valid for physical traits because No, David dutch does not doubt that genes affect heights like that wouldn’t make sense. Everybody knows genes affect height, right? and yet They don’t really directly affect height It still depends on some sort of complex interaction with do we have nutrition or not and maybe other things I mean, I know about nutrition. I don’t know about other causal factors um and so You can’t really ever say this gene Directly except for the mandelian ones this gene directly caused this inheritance It’s still there’s always some sort of assumption of given a certain setting given a certain Culture background level of knowledge time period Etc We’re talking about the heritability within that setting. Is that correct or am I got that wrong?

[00:47:16]  Red: So there are multiple points in there where good points are being made, but I think they’re Ultimately leading to maybe uh, not the best conclusion regarding how to understand genetic influences on complex traits. And so I I do want to be careful here. I don’t I mean Deutsch is incredibly insightful and I don’t want to attribute Anything to an argument he would make that, you know, if he were to hear it, he might say well, that’s unfair That’s not what I think. So I’ll just talk in general terms about those issues and so on one hand the idea that You know for really complicated complex traits, uh, specifically There aren’t simple, you know uh easy to explain Mechanisms that get us from genetic variant to trait and that’s entirely correct We, uh, you know, we certainly When we show whether using genome wide association studies or twin studies That a trait is heritable. In fact, this is, you know, we we actually in the paper we talk about this We consider this to be a point Captured by the fourth law of behavior genetics, which deals with the idea that For complex traits, there are made probably thousands of genetic variants involved. They’re all having very small effects And the effects are not direct. They the effects are far upstream of the trait we’re interested in and so In some ways though, I don’t know that I think that’s a useful way of thinking even with Sort of Mendelian traits the pathways may be easier in some ways to trace But even then, you know, if it’s a, you know genes are

[00:49:10]  Red: Sort of the the old term that used to use are the central dogma of molecular genetics is that genes code for the production of proteins Those proteins then have to be assembled into, uh, you know, longer more complex entities And if it’s uh, you know From there, they may be proteins that build either structural components of our body or functional components of our body You know tissues, bones, tendon, all those things. They have to be assembled from the, uh, the products of what genes are doing. So really in many ways Any outgrowth of some genetic influence is complicated Right, so it’s not it’s not really a criticism of twin studies or jiwa studies to say that You know, uh, there’s no simple path from genetic effect to trait so that In a way that renders heritability uninteresting or unimportant and I think that really is, um An important aspect because it again is a more general point. For example, we may you know, if we’ve got a, um You know a drug trial and Well, actually Tylenol is a good example. So acetaminophen in somewhat, you know, if we were to we wouldn’t do this at this point But let’s say we ran a clinical trial Uh to figure out whether or not Tylenol is in it has the effect of relieving headaches more quickly than placebo, right?

[00:50:39]  Red: And let’s say that the clinical trial, uh With experimental design so that you’re randomly assigned to take Tylenol when you get a headache But you don’t know if you’re getting Tylenol Or you’re randomly assigned to take a sugar pill, but you don’t know And then we’re going to observe the results and what we find is that the folks who take Tylenol Even though they don’t know it their headaches go away Much faster. So we conclude that Tylenol has a causal effect on speed of headache remediation, right? That tells us nothing about the mechanism by which that happens,

[00:51:13]  Blue: right?

[00:51:14]  Red: We assume the mechanism is there Because you know, we infer that Nothing magical is happening between Tylenol administration and headache remediation

[00:51:26]  Blue: So

[00:51:26]  Red: if we assume there’s no magic, there’s a causal pathway playing out now We simply may not know it, but it is there and so I don’t think I think simple lack of insight about causal pathways is is it doesn’t really render The results of twin studies uninteresting or unuseful.

[00:51:46]  Blue: Okay, fair enough so, um in the polderman articles that’d be the one that Um, you’re not an author on it says the largest heritable estimates for traits classified under The ophthalmological domain i.e eyes followed by the ear nose and throat Dermatological and skeletal domains So that was in order of reducing amount of heritability Now that seems fairly straightforward that genes would affect a purely physiological trait like eyes, ears, skeleton, things like that But I can understand why there would be more skepticism around the idea of cognitive or personality traits being heritable So now in the nature paper, so this would your your paper It says the overarching conclusion at this point And in time is that all measured human traits are to some extent heritable and that many genetic variants With each exerting a small fact explain this heritability Now can we talk about what that means? That all measured human traits are to some extent heritable that that’s uh In context, I I think I would have assumed That you meant of the ones we’ve thought to measure at this point But but the way that stated just kind of me taking it out of context It it could be interpreted as meaning um literally all Traits all including personality traits are to some degree heritable um Help me understand how I should understand that statement

[00:53:30]  Red: Yeah, absolutely. So uh, I mentioned a second ago the fourth law of behavior genetics What you just described is the first law and keep in mind to uh When when I’m talking about laws here It absolutely am not trying to imply that us and behavior genetics have laws akin to Uh physical law that one might use in you know in astrophysics or something like that speed of light or whatever um what I mean is A much more something much more general But it has to do with the idea that we have found we have repeatedly found the same thing Over and over and over again that we functionally we might You know, we may as well treat that as a our version in the behavioral sciences Of as a law and so the first law of behavior genetics, uh, and these were this the by the way This idea was proposed in 2000 uh What would that be 14 15 years before the polterman meta analysis by a Psychologist named Eric Turkimer very important behavioral geneticist And the first law of behavior genetics being that all we should assume all complex traits are heritable And so why why would that be interesting? Well, it’s interesting for a variety of reasons But before we get there to your question That is I’m not gonna speak for anybody else, but me that is sort of the guiding assumption That Is inherent in my thinking whether we’ve done, you know done five studies on a trait or a hundred We should start with assuming that it’s at least partly heritable

[00:55:12]  Blue: Okay, here’s by the way a quote from your article So consistent were the results that behavioral genetic research has come about as close as possible for a field outside the physical sciences To producing laws then I had to look up what the laws were And here’s what I found Um, because I don’t think it actually stated them in the paper, but it said we we did it

[00:55:35]  Red: was in a box In the paper. Maybe I missed it. It was easy. That’s okay. It was Totally understandable, but go ahead.

[00:55:42]  Blue: Okay law number one all human behavioral traits are heritable Number two the influence of genes on human behavior is greater than the family environment Three the significant number of behavioral traits A significant number of behavioral traits may be explained neither by genes nor by family environment And for a typical human behavioral trait is associated with very many genetic variants Each of which accounts for a very small percentage of the behavioral variability

[00:56:14]  Red: You got it.

[00:56:15]  Blue: Okay. So those are the four laws

[00:56:18]  Red: Those are those are the four laws the fourth law was the most recent. It was uh proposed You know, I think around 2014 as well kind of in the wake of The polterman meta analysis now

[00:56:32]  Blue: for some reason it was called four laws and two corollaries I’m not even sure I caught what the two corollaries were.

[00:56:37]  Red: Yes. So the two corollaries are something that We in our article and then another individual sort of proposed can currently Two different versions by I’ll give them to you. I read them to you and then that might Take us in some interesting directions from from here regarding why the the laws are important in the first place so From our paper, I’ve got it in front of me as well Corollary one the first law of behavior genetics implies that trait level correlations between phenotypes Phenotype is anything we can observe or measure. So phenotype can be height phenotype Could be major depressive disorder. So it’s just the trait we’re interested in First law implies that trait level correlations between phenotypes may sometimes reflect overlapping genetic influences across those traits simply means that because complex traits are influenced by so many Genetic variants it stands the reason that for some traits They’re going to be influenced by Some of the same genetic variants. So it might be depression And some other type of comorbid disorder that’s common with depression. So that if you you know, if you get If an individual becomes depressed, they’re also maybe more likely to develop an anxiety disorder And so what the corollary one refers to is the idea that probably those two complex traits Are impacted by some of the same genetic variants

[00:58:10]  Blue: Okay

[00:58:11]  Red: corollary two I think is is If I had to rank order, maybe the more important of the two causal inference ability degrades to the degree That the implications of corollary one remain uncorrected in a particular study design So that I recognize that that is a bit cumbersome in terms of its language, but it basically The what it means is it’s something very practical and it’s that if we assume that Not only are two traits correlated. So maybe we find that people who have generalized anxiety disorder also tend to have depressive symptomology If we want to make the argument That generalized anxiety disorder causes The likelihood of depression to rise it causes depression We have to contend with the fact that there is likely genetic overlap between depression and generalized anxiety disorder Because if we don’t the what we make ourselves vulnerable to is something called confounding And it basically means, you know, we risk assuming that x causes y When in fact it doesn’t that there’s another variable. Maybe z That impacts both x and y and it forces Creates a correlation between the two But if we don’t know that it could lead us to a bad conclusion or a spurious conclusion and so Yeah, and so this is you know gets us to the point actually briefly I’ll make this point because I think it’s important Whether it’s an outwardly stated

[01:00:03]  Red: position or not This type of point is why Experimentation is still considered the gold standard of causation in science in terms of research design right When we randomize individuals to some treatment exposure So in other words, we create our experimental groups our treatment group and our control group With through randomization We level the different the idea is to make those groups essentially as identical to each other as we possibly can

[01:00:32]  Blue: Right

[01:00:32]  Red: so that at the end of the day the only difference between them is our treatment Right. So in the Tylenol example, the only difference between the two groups in the study was that one group got Tylenol The other group didn’t and so when when the Tylenol group gets rid of their headache faster the the Most defensible conclusion is that the Tylenol caused it. That’s the only thing that differed between the groups

[01:00:59]  Blue: Right.

[01:00:59]  Red: So when you can do experimental designs, you don’t have to worry about either corollary You don’t have to worry about the three law or the four laws of behavioral genetics Because the randomization deals with the two corollaries and it deals with any other possible thing that could Found your findings. So in

[01:01:19]  Blue: Judea Pearl’s book The book of why It talked about This quite a bit and he used the example of smoking Throughout it would be unethical. You could Do a causal study of smoking if you didn’t mind the fact that you pop possibly giving people lung cancer, right? So instead you have to use data that that wasn’t in a randomly controlled trial And so now there’s now you’ve opened yourself up to the possibility of a confounding factor And so this then and he he gives a history at least his history of Of how people tried to deal with the how scientists tried to deal with that problem And it it sounds like it was a very complicated problem that we’ve only fairly recently started figuring out how to deal with there There was apparently He talks about two people that were smoking and one of them was arguing that smoking does cause cancer And I forget who the two people were they were famous scientists and it was causing that that it didn’t and Or at least there would be no way to ever prove it And then he goes through some of the things that they eventually did that led to The theory that smoking causes cancer to become the better of the two theories Well, one of them was that they worked out the degree to which genetics would have to cause both smoking and cancer And it was like such a large factor that it was implausible

[01:02:49]  Red: Right

[01:02:50]  Blue: to explain it on its own And in fact, they eventually found that there was a genetic that caused both smoking and cancer But it had a much more plausible amount of effect And it was pretty minor by comparison to smoking itself being the causal factor

[01:03:04]  Red: correct Yeah, it’s uh, I should say too that Judea Pearl’s work has had a also a Tremendous impact on just my interest as a scientist and my the way I think about things It’s just foundational work in the book of why is just a wonderful book to read Accessible to anybody who’s interested in causation And you know, whether you’re interested or are more philosophical or more technical It’s just a fantastic book. I Enough But yes, and what’s interesting is the smoking example and lung cancer is a wonderful example to use Because it illustrates a variety of things one is The complexity of studying These important traits When you can’t do or rather the way that the challenge increases When you can’t do experimental manipulation. So indeed you plausibly could Assign some people randomly assigned some people to smoke cigarettes And then maybe devise some type of placebo device and have the other groups smoke those But to do so with the suspicion that it might cause one group to get lung cancer is beyond unethical, right? So we you’re not going to going to countenance that type of design So when you can’t do that or you shouldn’t do that You attack the problem in a different way, which is to say you attack it in a variety of ways One is, you know, you do in vitro studies exposing tissue to the carcinogens found in tobacco smoke or in You know chewing tobacco and you see if those things tend to induce the types of mutations that lead to cancer And and assuming they do and they do with smoking. That’s a piece of the evidence Another thing you can do is you can do sort of traditional

[01:05:11]  Red: observational methods where you maybe you sample A large sample of individuals living in a country say the United States You ask them about their smoking habits Maybe you follow when the study begins you follow them for 10 20 30 years and you You know at each time following up to see who in the sample Has developed some type of cancer and you use correlational methods to see if there’s a link between self -reported smoking And the development of lung cancer and let’s say we find that there is That’s another piece of evidence and this brings us to part of the reason. I think twin studies are so important one of the most powerful designs I would argue for causal inference outside of Experimental designs is the discordant. What’s known as the discordant twin design So to give you the sort of the most basic straight -ahead version We said earlier that identical twins have carbon copies of the same genome Now what’s interesting about that is And this also reflects The first law that complex traits are partially heritable, but not entirely heritable Identical twins differ from each other all the time in a variety of ways For a variety of reasons, but among those reasons Uh There cannot be the explanation that Identical twins differ from each other because of genetic differences Because right for all intents and purposes. They don’t have any genetic differences So when you have that situation, it’s a incredibly useful sort of natural experiment So one thing we can do and this was done, you know in terms of this smoking situation and with a variety of others Questions to this day We can

[01:07:13]  Red: Use data from twins who are Discordant for some outcome we’re interested in so imagine that we have a sample of identical twins Among that sample some Some number of those twins were smokers And their co -twin were not so they were discordant in their smoking habits One twin smoked their their sibling did not We can use that as a type of sort of Causal design to then investigate. Well, you know, does it seem to be the case that When twins were discordant for their smoking that the one the twin who smoked was more Often more typically developed lung cancer If we find that to be the case That is pretty compelling evidence of an environmental factor causing some outcome in this case smoking causing Exerting some type of causal effect on the cancer and notice I said it’s evidence of an environmental effect

[01:08:14]  Blue: Right because

[01:08:15]  Red: genetic differences can’t explain that effect Right

[01:08:18]  Blue: it can’t be so you’ve refuted the idea that it was a gene causing both at that point because

[01:08:23]  Red: You haven’t refuted it. What you’ve done though is is the same thing something similar to what randomization does You’ve held the effects of genes constant,

[01:08:32]  Blue: right? If that makes

[01:08:34]  Red: sense So it’s a little different than refuting it. It’s still possible that there might be genetic overlap between smoking habits and Vulnerability to cancer that’s sort of a separate issue. We can use twin studies to investigate that too But when we use a discordant design, what we’re saying is we’re not going to allow genetic effects To confound Some effect of an environment on some outcome.

[01:08:58]  Blue: Yeah, okay Yes Okay, let me read a bit more from the articles here um behavioral genetic designs can be applied in fields as diverse as economics political science psychology and medicine among others and then from The other paper by studying genetically identical twin pairs that differ in some key Attributor diagnosis the drawback of traditional case control studies can be largely surmounted Um a sample of about 300 twin pairs finding heritability estimates of 41 53 61 41 and 44 percent for the five dimensions of neuroticism and openness And conscientiousness respectively So the papers separately are taken together And the four laws you just mentioned There there is We are saying that personality traits are heritable

[01:09:54]  Red: Yes, there’s there’s good good evidence of that. They personality traits like other cognitive traits like other physiological traits Uh adhere to the four laws of behavior genetics

[01:10:05]  Blue: Okay Now with that in mind though, there are several things your paper said that I wasn’t quite sure I understood So one of them was this concept of quasi causation. Let me let me give you the quote By controlling for common causes twin studies Can test what what have been referred to as quasi causal hypotheses The use of phrases like quasi Causality and causal inference as opposed to straightforward causality highlights that twin studies like other Epidemiological approaches cannot typically demonstrate causality between two variables They cannot prove that x the exposure causes y the outcome

[01:10:46]  Red: Yeah, so we were actually quoting a study from 2021. There’s excellent paper That is much more sort of narrowly focused on the various twin designs Used for causal inference Fantastic paper that we cite in our article and and so folks who are interested Can look that up that’s a quote from that article and essentially what it What it’s asked it’s asking a type of rhetorical question in a way or hypothetical question and the question is this are Twin, you know the discordant twin studies like what we’ve been talking about as Powerful of an engine of causal inference as a randomized clinical trial or randomized experimental design And the answer is no they’re not These types of twin studies are vulnerable to certain types of confounding and there’s a Really helpful literature out there on that. It’s fairly It’s a fairly methodological point But the the the important takeaway is pretty straightforward And it’s that just because you’re doing a discordant twin study With identical twins does not mean that you have not down Proof which I don’t even like the word proof anymore For reasons, you know, we can we can talk about too It doesn’t mean you have not down evidence that x causes y just because you did a twin study You absolutely do not what you have is a valuable piece of evidence That is You know, if it’s the initial finding if you’re sort of the first to do that study It has to be weighted Very lightly until there have been efforts to replicate it.

[01:12:28]  Red: So in other words, it needs to keep showing up if that’s if my you know Trust in the finding is going to increase But the the point that sort of we were trying to draw attention to is that discordant twin studies are exceedingly useful But they’re one among other options in a toolkit Including some options and actually pearl does a really nice job and in his book Talking about some of these options that don’t require twin data And yet can still give you if you satisfy certain assumptions can give you pretty potent causal insights And so we what we’re trying to do is is avoid the You know, I’m obviously enthusiastic about these designs But I don’t want ever want to convey that they’re a panacea for you know, the problems of causal inference

[01:13:19]  Blue: It’s interesting that you used the term weighted there in reference to evidence. So in beginning infinity, David Deutch talks about possible problems with the concept of weight of evidence In in context, he’s not talking about what you’re talking about. It’s a different concept of weight What you just Suggested really was we weight the evidence less because it has yet to be replicated which which makes perfect sense to me That and that’s even consistent with critical rationalism that we don’t really consider an observation an observation until really basically You can anyone can do the experiment and can get the same result

[01:14:01]  Red: And that’s right

[01:14:02]  Blue: now become a Something that we have to contend with that everybody gets the same result when they do this experiment

[01:14:07]  Red: yes, so

[01:14:08]  Blue: that’s actually a I would argue correct and fair way of understanding the concept of weight of evidence within a critical rationalist Frameworks. I just wanted to kind of call that out. I know some people may say well, wait, didn’t David Deutch say that you We don’t weight evidence

[01:14:23]  Red: Yeah, it’s a great point And it’s one of those things where as the word left my mouth I I sort of anticipated that it might register with you all for that reason um, some of its force of habit because As I mentioned, uh, I was heavily persuaded uh by popper and deutch sort of collectively and others as well that um You know, it’s not useful to think in terms of Something like science verifying truths So it’s not not how I think about the work that I’ve mentioned either But yes, and I do very much just mean it in a the I guess parochial Yeah, so you know Let’s let’s not get too excited until other folks start to find the same thing right right

[01:15:11]  Blue: And that makes sense a study comes out And the media does what they do and they say this you know challenges this belief or this theory or whatever and a scientist knows We have to wait to see it replicated But you can’t really say that it’s not evidence either right I mean like you now have this effect It’s been found in a legitimate study and now the criticism of the study begins and we have to see if people can replicate it So I think that the metaphor of weight makes sense in that case that we’re giving it less weight until it gets replicated That’s my sense. Okay.

[01:15:52]  Red: Absolutely because I you know, and I know I can’t call it to memory. So I won’t say for sure, but I If if I’m remembering correctly, I think deutch has addressed us in a couple articles if not in the books That it’s certainly possible that you A particular experiment or a particular study arrived at some type of result that’s erroneous because of a weak or inadequate research design It might be that your instrument In your physics lab was poorly calibrated Right, and we we find that out after the fact and that this is why we we treat a finding provisionally because we we may well find out next week That no our instrument was not calibrated, right? So we can’t trust the the results

[01:16:40]  Blue: Right cosmological observation.

[01:16:42]  Red: Yeah, and so that that’s really the same spirit in which I used a point too is that Or with any finding especially those that tend to get sort of splashed in the headlines Is that well It could be that you know the the sample was 20 people And statistically that creates problems, right? You know could yeah any number

[01:17:03]  Blue: and and this is another so I have an episode That we recorded two weeks ago. I don’t know if it’ll come out before or after this episode where I actually argued that there are definitely certain senses where saying weighted evidence makes sense and another one would be like p -values, right or

[01:17:20]  Red: yeah Absolutely

[01:17:21]  Blue: that some some things that we call evidence They just have a much better p -value because maybe the sample size was larger or something like that So you you were fishing with the finer net as Debra mail would put it I don’t see any way around that certain pieces of evidence if they’re statistical which in your field they would be Some of are going to be weighted more than others because they were literally a better study that used a finer net to try to catch to try to Find severely test the the hypothesis So it makes sense to use the metaphor of weight in that case or at least as a layman I’m going to use the metaphor of weight. It makes sense to me, too but if you look back at what dutch actually said he was actually talking in context of um, you know politics and things like that. I think that there are many cases where we talk about weighted evidence That it doesn’t make sense and I think dutch was talking about cases where it did not make sense

[01:18:18]  Red: Totally agree and I think part of that, you know, again, we can say this for a future discussion, but I think part of what was wrapped up in his various discussions of that was this idea of almost Being careful not to turn science into an authority Was, you know, something we hopefully would have projected During as part of the enlightenment. So yeah

[01:18:43]  Blue: My next question is about temporary heritability. Let me let me Talk quote from the article here the data show a decrease in mono zygotic and dizygotic twin resemblance after adolescence So does this mean that heritability traits? Significantly drop as we become adults Um, sort of become our own man so to speak and how significant is this drop It is the drop only drop only for personality and cognitive traits or or does it actually also drop for Other types of traits and then here’s the thing before you answer that those are my questions But there’s some other statements from The article that I want to take into consideration as you’re answering the question For example, ranging between 57 and 73 percent depending on measure Such as indicators of spatial and verbal development Interestingly these estimates were found to be much lower in children as opposed to older participants That’s like the opposite of what I just quoted often hovering around 45 percent That seems very high still Even as talking about older I just had noticed that it was the opposite of the first quote from the other article And then it seems then it also says very early in life heritability estimates can be as low as 20 percent Which typically rise to around 40 percent in middle Childhood and then often balloon as high as 80 percent in adulthood again. That seems the opposite of the the first quote So maybe uh, you can shed some light on this this concept of temporary heritability based on age

[01:20:22]  Red: Yeah, so, uh, it’s a really interesting Sort of topic to discuss To answer part of your question Uh Not only can heritability estimates change across the life force for certain traits But in in sort of in lockstep with that It implies that the environmental variance components also change, right? So is as heritability Okay, as heritability estimates go down Uh either estimates of the shared environment or the non -shared environment have to go up because those three Components sum to one or a hundred percent and so we again, um Here I guess the more general statement is that Heritability and environmental sources of variance can and do change across the life force It really depends on the trait that we’re interested in Um And that that sort of informs how those different estimates change for certain sort of cognitive traits as you as we talk about in the paper Uh, the heritability estimates tend to rise with age and and remember Part of understanding what what this is saying Uh means that we need to think back In terms of what heritability means and at its core it it is a Sort of an answer to the question of what explains differences between folks in a population and so All that we’re saying it is not saying that genes matter in childhood and they don’t matter at all in adulthood Or environment doesn’t matter at all in childhood and matters adult a lot in adulthood. That’s not the proper interpretation Rather what it’s sort of Showing is that over time with age

[01:22:07]  Red: The the reasons the explanation for Differences in a population become increasingly more attributable to genetic variation than environmental variation And it that’s in again thinking about certain cognitive traits and um, it’s a different sort of a different story for personality traits now It doesn’t necessarily those types of general rules are in many important ways Depending on the trait that we’re interested in not all, you know, if we’re talking about heritability of a some complex trait across The life course of a human those heritability estimates might be relatively static. They may not change very much, you know Whether we calculate them at age 10 20 30 50, whatever the case might be Or they might change with time And there are various ways to to think about Explanations for why and how that happens mechanisms for how it happens what explains it And those are all we cite a lot of those papers in in our paper And so folks who interested can can track those down as well, but the the You know, this is sort of the idea of heritability is not a fixed construct It’s not a snapshot measure of how, you know, genes causing a trait that never changes It is a part of an explanation For individual differences and the environment is also part of that explanation

[01:23:35]  Blue: So no one of the articles said the data show a decrease In resemblance after adolescence, but then the other article Seems to have twice said that the heritability increases as you go into adulthood And that might be different for cognitive traits versus personality traits

[01:23:54]  Red: Yeah, we we so again speaking in very just very broad terms. We you don’t tend to see uh, so rather you you see the effects on Our heritability estimates for more cognitive based traits indicators of intelligence. So spatial analytical abilities memory certain aspects of recall and memory and processing speed and Language ability those types of things sort of more indicators broad indicators of intelligence The heritability of those things Has been seen to increase Over time The same is not doesn’t seem to be the case with what we would think of as more Classic personality traits and so we take sort of the the highly influential model of the big five or ocean So openness conscientiousness extroversion agreeableness and eroticism All are sort of have typically show small to moderate heritability estimates And they they don’t seem to get those estimates don’t seem to go up with time. In fact, uh, in some cases non -shared environmental Effects seem to go up across the life course It’s not to say that they’re you know heritability estimates drop to zero But they they can change with age

[01:25:22]  Blue: Um, that actually makes sense to me. Um, okay, so let’s talk about, um David Deutch’s criticisms of some of these studies that are in beginning of infinity So obviously we all know that correlation isn’t causation So deutch gives a series of arguments to the idea that we we That we to the idea that we can currently know how much genes really by themselves cause inheritance or uh personality of personality or cognitive traits. So the example he uses is um slavery in the 19th century Uh, if we were to do a study we would find that it is highly heritable Um, he also gave an example of attractiveness being heritable, which I would assume it is But suggest the possibility that culturally we may change what we count as attractive in the future And therefore, um the heritability even though it is heritable It may not be in the future Um, can you maybe talk a little bit about that particularly the example of slavery? Um, because that that does seem like it’s kind of relevant to what we’re talking about Slavery would have been a heritable trait in a study For the obvious reasons that there’s an explanation for Why certain racial groups were in slavery and others weren’t

[01:26:49]  Red: Yeah, so In regards to to deutch’s points, I don’t Take issue with any of them, uh, except to say that I I think it it would be in you know In my I would argue that they don’t nest while the points are are valid points to make They’re not at odds with I don’t think anything we’ve talked about and I don’t know that The best conclusion is the one that he reaches in terms of Sort of the information provided in a twin study is is not something we should really be concerned about

[01:27:27]  Blue: right, okay

[01:27:29]  Red: And so what I’ll to maybe unpack that a little more I’ll start with we talked about earlier that heritability estimates in terms of particular You know moments in time Are very much likely to be different Sort of the classic example that’s been replicated Quite a few times concerns the heritability Of cognitive functioning depending on socioeconomic status and so what This again, it’s been replicated A number of times at this point and the general idea is that the heritability of the sort of cognitive functioning May actually be highest in higher SES stratus in other words as income rises as socioeconomic status Which is a broad term you’ll see in the social sciences simply refers to a number of things beyond just income and dollars But in some ways captures The functionality of an environment safety of a neighborhood You know again social status measured in a variety of ways including income as those things go up We might expect that the heritability of cognitive traits would also go up and whereas in as In lower SES strata where there’s more socioeconomic disruption where there’s a more economic Struggle, we might expect that heritability estimates would be lower. Why would that be? Well, again, this is not unlike our example of nutrition, right when when we’re asking the question why are individuals

[01:29:19]  Red: different in a population Part of that In this case with heritability It may well be that the far more salient reason that individuals differ in their cognitive abilities at lower SES levels is because Because of environmental disruptions Because there’s a lack of resources because there’s a you know, whether that’s quality education Um access or access to proper nutrition any number of things in an environment that might disrupt the development of cognitive and executive function Whereas at as those SES levels increase What happens is they start to lack the ability to explain those differences, right? And so that’s when we we might see heritability estimates rise and I’ve I’ve I’ve used words like might and expect intentionally here Because even though the the I believe there was a fairly recent meta -analysis these effects showing that they they replicate well I like think of all All of this stuff is provisional and so But at least at the moment When you see something like heritability estimates differing As a result of socioeconomic status It it it’s not, you know It is actually Indicative of something interesting and something we might expect and also keep in mind The classical twin study which gives us heritability shared environment non -shared environment just by itself In some ways it’s sort of a cause It it the interpretation is differences in the population are associated with either environmental differences or genetic differences You can take additional steps to sort of investigate causality more But I think we should sort of resist the idea with the classical twin study anyway to say, you know that Genes are causing some outcome or the environment is causing some outcome We can certainly use twin studies as a jumping off point.

[01:31:24]  Red: For example, we so let’s say we show Pick also, you know dementia certain forms of dementia or maybe Alzheimer’s disease in particular Those are are moderately the relatively highly heritable traits But It’s only recently when we’ve been able to do more powerful types of genome analysis where we’ve had large samples like A sample called the uk biobank those types of things where we can start to investigate whether Certain genetic variants seem to truly have causal effects on the, you know, whether it’s by impacting brain structure Or function in some way that you know in ways that Sort of maybe create the prototypical plaques and tangles that we see in uh Alzheimer’s patients Things that disrupt cognitive functioning in a physiological way right by impacting neural functioning Potentially and so I think while I wouldn’t Necessarily equiple with the points that George was making I would simply add. I don’t I don’t know that it would lead you to To sort of have a dim view of of the ability of twin studies to to help understand causation or explanation

[01:32:40]  Green: Can I interject with a quick question?

[01:32:42]  Red: Yes,

[01:32:43]  Green: I I think for myself I know that as my sort of world view has sort of I don’t want to say evolved but sort of shifted from being, you know, very tied into I Judith rich Harris and Steven Pinker those those books and really That were sort of like I said before sort of almost like an explosion in my brain kind of a thing like wow The genetics is just it influences everything You know, you look at the the family down the street and you assume that the the the parents are so So uh responsible and the the kids are so good. It’s just They they think it’s it’s really all about genetics, you know, I but Maybe I was a little extreme in that direction I don’t know but as I sort of moved into being more influenced by Deutsch and just getting more into philosophy in a way I’ve started to look at things more In terms of epistemology, I guess in turn rather than just biology like Just seeing human beings as more of our Our our minds rather than brains That if that makes any sense So it’s almost like our minds are saw as I understand it software That’s running on on hardware and you know software I think can always be rewritten and you know might not be easy to do But you can always always always Change your software What what do you think maybe if sorry if this is just getting out too too much on the tangent But are are we are our minds or our brains?

[01:34:28]  Red: so I that is uh I love that question and Part of the I’ve come to love it even more in recent years as my my work is sort of expanded to include interest in Cognition cognitive science consciousness Both from a philosophical standpoint and a sort of more mechanical standpoint In terms of like even how would you build an artificial mind? That would be essentially human and it’s phenomenal awareness and those types of things so All of those are are tied in interesting ways to the question you just asked and I think I think it’s there’s a number of ways to answer it The idea that just because you know We you know, we start to we might start to get a better understanding of The way that structures in the brain Differences in those structures either, you know Calls one to be more likely or less likely to say develop some form of dementia And then we through additional work over the years. We link those differences in brain structure

[01:35:46]  Red: To as being a product in part Of differences in certain genetic variants that one might carry or might not carry I don’t know that that does anything to our ability to think more broadly about you know solving Really pressing medical and social problems like Alzheimer’s disease and dementia they in some ways the Again, this was one of the sort of I think Really wonderful points that dutch makes in a variety of places Is that the idea that problems are Solvable that unless there’s some physical law demanding that, you know, it You know something is off limits It’s not in terms of it doesn’t make the problem easy It doesn’t matter if the problem is understanding psychiatric outcomes or personality disorder outcomes or medical outcomes and solving Problems that may arise in those contexts but Again when we’re if we’re just thinking in terms of cause and effect just because Something may have Maybe in part caused by Some genetic influences It does not there’s nothing written in that that says You know change is impossible in there Disorders of vision or are heritable people we correct those every day with environmental intervention vulnerability to migraine Is you know, I don’t I couldn’t call the heritability estimate to mine, but probably low to moderate Correctable every day with And new medications become available all the time actually you just you see commercials pretty frequently for different

[01:37:41]  Red: migraine Interventions that are you know, whether you Once a month or When you have a migraine on set or whatever the point is just because the problem is is hard to solve Uh, it does not then translate to it’s impossible to solve and just because Certain causal effects impact some outcome does not imply that uh, it is beyond the reach of change and I’ll I’ll stop rambling in a second. I think the A last point I would add though is we do I think there is um a temptation To when we start to make distinctions between genetic effects and environmental effects is to presume that the genetic effects are the hard ones to you know to wrestle with Not the environmental ones and I think that’s uh Quite often can be mistaken and so one example that I like to you know Uh, especially with students when I talk about these things in in doctoral seminars or whatever is the example of Language as it relates to the accent that one speaks with So all children assuming, you know, there are no type of Um Acquired injury or some type of problem preventing it Accepting those cases All children learn language.

[01:39:10]  Red: That’s a capacity that’s universal in humans happens all over the world every day It’s incredible to watch whether you have kids or you have nieces and nephews or it doesn’t matter It’s it’s it’s wonderful to watch that sort of explosion of language in kids and What’s interesting is that Certainly, they’re you know, we have the biological hardware Necessary and we understand more today about the read neural regions associated with language functioning in various ways but the the language that we acquire and the regional accents that we acquire Are completely rather differences in those things are completely environmental in nature I I have a you know, at least I’m told a bit of a southern accent Had it my entire life If I were to move to the northeast or the west coast that accent not going anywhere. It’s gonna I’m gonna take it right with me and The inverse of that is pinker talks a lot about this in the blank slate Judy Harris talks a lot about it in her book as well in the nurture assumption the you know When linguists study Children of say folks who have immigrated to a new country What they find is that though while at home they may hear their parents speak in the native the language of the country where they They moved from so let’s say someone You know moves from the United States to England and their parents speak with American accent in English Their children who are exposed to their parents at home, but their peers say at school will speak with an English accent wholly environmental Now that’s interesting in its own right, but

[01:40:57]  Red: Imagine how easy it might be if someone whatever accent that you speak with you were told I Can’t speak with that accent anymore. You got to you got to speak with an entirely different accent It’s possible actors do it. It can be you certainly change your accent. I would argue it’s probably not particularly easy to do Nor is it easy as we age to learn a new language From scratch We’re young children human children do it. I mean Without you know any great difficulty I can remember taking Spanish in high school and struggling Midally to try and and get a sense of the

[01:41:35]  Blue: same here.

[01:41:36]  Red: Yeah, and so what’s interesting is the you know We the language we acquire as a result of geography and environmental effects where we’re born That in no way makes it easy to change your language or to acquire new language with age So just my my only point is simply because something may be Very much influenced by the environment doesn’t necessarily guarantee that it’s easy to change but all of that said you know, there’s no reason None of none of what we’ve talked about today In my opinion councils any type of despair in terms of the changeability of some outcome

[01:42:17]  Blue: So let me try to make a steelman version of How I think I understand Dwight’s criticism.

[01:42:24]  Red: Sure. Absolutely

[01:42:25]  Blue: So let’s let’s actually use the example of accent that you just used If I so you by explanation you just explained why it is that Accent actually a hundred percent environment

[01:42:39]  Red: Difference is an accent. But yes.

[01:42:41]  Blue: Yeah, but let’s say that I set up an experiment Let’s say I didn’t know that for whatever reason I don’t have that explanation. So I set up an experiment I I’m probably going to find that there is Some sort of heritability If the experiment doesn’t take the right things into consideration the right confounding factors I would almost assuredly find that there is a heritability to accent Because it does in fact match up with with genes quite well So the the issue here would be how can you really know That when you say 30 % of accent is explained by heritability that that’s even a meaningful statement And that it wasn’t just the confounding factors that you don’t understand or know about at this point and that you’re not taking into consideration

[01:43:30]  Red: Yeah, so it’s it’s a good question. There are a couple of things Going on there that I think we should probably point out first One is that we wouldn’t want to say that 30 % of accent is The result of genes what we would want to say is and and I’m not trying to pick on any, you know Pick on you unnecessarily, but the verbiage really is important What we want to say is that 30 % of the variance in accent might be the result of genetic variants or heritability, right?

[01:44:03]  Blue: So you say the result of but let me let me be clear. I have definitely heard it said explained by So so they do use the term explained by instead of result of in a lot of cases And I think that’s what some people are taking exception to but continue from there

[01:44:18]  Red: No, I totally totally worth pointing out And I’m I’m I’m certain guilty of it as well and using sort of just Common words like explained by as opposed to associated with but so it’s fair point Well, what I would say then is To to get those if what we’re after is a heritability estimate, we’re not going to calculate that with a true experimental design What you would be showing with that design is you would be holding everything Presumably if you’re doing randomized trial, you’re going to be holding everything else constant including genetic factors In order to investigate whether some treatment or exposure that you’re interested in has a causal effect on accent You could certainly do that. But if we’re after a heritability estimate Or in theory, you could do it. I don’t know that it necessarily be ethical depending on the treatment But if we’re going to calculate a heritability estimate, we’re going to do a twin study and what you’re going to find Based on sort of the the math of how these Heritability estimates and environmental estimates are calculated Very likely that the heritability of accent is is zero At or near zero based on and again, we take we take advantage of relatedness to to get to that

[01:45:38]  Blue: Well, no, that makes sense. So so we’re not talking about necessarily you could do a random controlled trial with accent I don’t doubt that but let’s say we’re not for whatever reason. Okay You could still do a causal study of accent even without a random controlled trial by simply setting up the right kind of Natural experiment and taking the right kind of data with twin studies or something like that And then you would very quickly discover That accents actually just determined by environment not by Genetics and in fact, you would even though you didn’t do a random controlled trial You would get the right result. You would find zero heritability to accent if you’re doing a twin twin study Okay, I’m with you. Okay so Let’s talk about then so we’ve kind of danced around this and this might even just be too technical for me But when I read your papers It is very it gives a very technical explanation of how they work out causality when you don’t have a um random controlled trial

[01:46:46]  Red: Yep,

[01:46:46]  Blue: and I admit I just cannot make sense of what the paper saying it is too technical It is stuff that i’m just not familiar enough with is it possible for you to try to Give me some reasonable examples to help me understand How it is that you can determine? Accent is caused by environment not heritability or slavery is caused by environment Not heritability and how you would work that out in trials if you can’t do a randomly controlled trial

[01:47:18]  Red: absolutely, so I think the the A useful way to think about this might be um with a specific example, so I’ll take one. Let’s see Take maybe a more Psychological or medical example, but let’s let’s say that We are well, we’ll go back to smoking and lung cancer because I think that’s a useful one. Um The way that suppose we have uh, we have an explanation of lung cancer that involves exposure to cigarette smoke right and we we think that you know, there are a number of lab studies showing that uh the carcinogens in that we know to be present in um nicotine smoke Are capable of inducing, you know, uh mutations in dna that then Uh, you know typically form tumors and so we have that little we have that piece of evidence In our mind as we’re thinking about explanations for wine lung cancer tends to happen And we know of course that we’re not going to take healthy humans um Randomly assign them the smoke or not smoke because that’s just it’s off the table and should be And so we start to think okay What are what are some of the things I can capitalize on? that will let me um Do a better job at at Making the argument that smoking causes lung cancer or not maybe that’s not even the best way to phrase it Because maybe we don’t we’re not trying to push an argument But we’re trying to be as harsh as we can on our explanation that smoking causes lung cancer We’re trying to

[01:49:04]  Blue: test it right

[01:49:05]  Red: exactly. So we’re going to do our level best outside of an experiment to To subject our explanation to criticism and maybe refuted in in some general sense, right?

[01:49:20]  Blue: Right.

[01:49:20]  Red: So one of the ways we go about that is We have a large sample of twins And what we’re going to find is that in that sample Some of those twins whether they belong to an identical twin pair or a fraternal twin pair Some of those individuals are going to be smokers and their sibling Won’t be Right. So the term we used earlier when we’re talking about this is uh discordance. There’ll be Something present in one twin something not present in the other and so What we can do and there are different ways to do this, but I like this example specifically because it sort of cuts right to the heart of it Which what we’ve done when we’ve made the argument that smoking causes lung cancer Or we’ve explained lung cancer as being a product of cigarette smoking We’ve made an uh, we’ve invoked some element in the environment That is acting as a treatment of a sort and causing some particular outcome in this case the The exposure or treatment Is smoking the outcome is cancer? So what we want to do And what experimentation allows us to do in other cases is we want to rule out any other possibility That something else might explain the association between smoking and lung cancer We want to we want to Hold everything else constant is the language you’ll hear sort of researchers use and When we especially Um, let’s say that we’re not and this actually is a good opportunity to make another point because it’s a it’s a theme in our our paper

[01:51:04]  Red: There are reasons to use twin studies that have nothing to do with being interested in genes You can adopt a discordant twin design and not care one bit about genetic effects And and that’s completely defensible in fact in some cases heritability estimates Just aren’t interesting particularly because we sort of expect to find them and in those cases Those heritable factors represent a nuisance that we need to control for just like anything in the environment might represent a nuisance so what the identical twin design allows is Of the things that we’re going to hold constant We’re going to do ideally when we use this design, we’re going to rule out the possibility that genetics Or shared environment have any or family environment early, you know Shared environmental experience have anything to do with our outcome of interest because twins share both their genome And their environment identical twins 100 genetic overlap 100 environmental overlap So what we’re doing in this case is in a most most basic sense is we’re Trying to see if it is the differences in smoking That might be causing the differences in lung cancer and let’s say we do our twin study and that’s what we find that We you know calculate these effects in the data. We show that There’s a considerable increase in cancer Rates for twins who smoke Versus twins who don’t it’s not a guarantee because in some cases maybe, uh, you know One twin smokes the other doesn’t but both develop lung cancer that suggests that Cancer is partly heritable to some extent, right? We may not know what that means mechanistically, but that’s what it would imply but Using this design showing this, you know continued discordance between smokers and non smokers for their cancer

[01:53:06]  Red: occurrences should Should be interpreted assuming we meet other assumptions as as pretty compelling evidence that the smoking is causing Cancer, right? No, that makes

[01:53:16]  Blue: sense Okay, would the following statement then be true? So let’s take the example of slavery being heritable The only would the following statement be true that the only way we would actually find a study that slavery in the 19th century Was heritable is if we did the experiment wrong to begin with and that if we did the experiment, right If we set it up correctly, we would find that it is not heritable even back in the 19th century

[01:53:40]  Red: well so I think the more The more general way of thinking about this is to One not to necessarily invoke language about experiments versus remember when we’re doing a twin study We’re not doing an experiment. That’s true.

[01:53:59]  Blue: The experiment may be the wrong word, but I

[01:54:02]  Red: think it may maybe this might be a helpful way to think of it just in general Right, and it goes back to the idea that heritability estimates are not fixed constructs they’re their variance components that can change over time and it So thinking about when I see a heritability estimate or an environment and this holds for shared and non -shared environment estimates as well Is that that by itself? Does not tell me that gene, you know, there are strong causal genetic effects on a trait Nor does it guarantee that there are strong environmental causes of some trait All what that tells me In and of itself is that in that sample at that time This variation or variance in this trait that i’m interested in is partly explained by genetic differences Or partly associated with genetic differences partly associated with environmental differences That is that’s the extent of what I can say if I want to probe that Further investigating various causal effects I’m going to need to do something else in my research design. That might be a genome -wide association study That might be a discordant twin study and I’m not talking necessarily I’m not talking specifically about dutch’s example of about slavery, but I’m talking as a general principle I think this is a useful way to think is that it If we just simply looking at the results of a twin study showing that some trait is partly heritable It tells you something useful, but that that whatever That thing that’s useful has pretty strong limits on it If you want to start to pursue other questions, you’re going to need to do some additional things So

[01:55:47]  Blue: let’s talk about a genome -wide association study because that comes up and then the other one was a polygenetic score And I didn’t really understand what those were. I’ve got some quotes about them Yeah, yeah, maybe go

[01:55:58]  Red: ahead with the quotes and we can talk through what those maybe mean

[01:56:02]  Blue: Okay, so one common use of model comparison used to test a full a c e model against a trimmed a e model In which the c parameter is dropped a meaning heritable c meaning common environment e meaning showed environment This method evaluates each model in terms of parsimony does dropping c lead to improved or diminished goodness of fit mz twins discordant for some variable Can be used to evaluate environmental effects with greater specificity cross lag lodge logitunnel discordant twin design Which makes this particular design desirable a point which may have Been already intuited by readers is that it improves the ability to test whether Changes in one trait cause changes in another over time So that does seem like so you’re saying that first of all maybe help explain What a gwas genome -wide association study is And does it actually allow me to work out without an experiment causation? Or can it or how would it?

[01:57:10]  Red: um The the short okay, so one thing to clarify The the quotes you read Were dealing with applications of twin and sibling designs. Okay a genome -wide association study Does not necessarily they can they do not by definition have to include siblings so Like we say in our we’ve got a brief A little quote in the paper um, and this refers to using gwas studies to calculate heritability estimates, but we say, you know gwas has helped generate new methods for estimating heritability without the need for siblings We can use it with or we can do it with genetic data alone. So what is a gwas study? the genome -wide association study Is sort of followed in the wake of what we talked about as candidate gene studies where maybe we were We would take a cheek swab from a sample of a hundred or thousand participants in a study We would do some genetic analysis maybe we’re interested in a particular dopamine gene or a serotonin gene to see if that Those things increase vulnerability to depression or anxiety So we we do a cheek swab collect some buccal cells. We do probably PCR and That way that we can we’re collecting data about individuals in our sample and let’s say that this serotonin Relevant gene that we’re interested in comes in one of four varieties. And so what our candidate gene data will tell us Uh, is which one of those four varieties each person in our sample carries, right version one two three or four Okay, uh, and then two copies of both. So Whether they’re homozygous or heterozygous and so

[01:59:02]  Red: What that study would then do is try and correlate To see if there’s a correlation between the genes that individuals carry in the outcome that they’re interested in maybe anxiety a gwas study those studies as we talk about in the paper quite a bit of problematic issues with them small samples just things that made it very difficult to have to put a lot of You know much of any stock in the in the findings so with moving forward in time and You with the advent of new technologies and as those technologies became cheaper It was possible to Instead of looking at one or two places in the genome We could look at hundreds of thousands of variants in the genome And so and and then use use that information both to Uh, you can it can be used to estimate its own type of heritability estimate Or it can be used to construct What you ask about which is a polygenic Score And so What a polygenic score and there is much more sort of technical treatment in the paper And I I’m going to oversimplify here But I would anybody interested more in the the technical aspects of it certainly that that’s available And hopefully we made them accessible as we could in the paper But the idea is basically we’re sort of We’re taking the results of GWAS and sort of trying to calculate the collective presence of A genetic propensity for some outcome. So it might be a polygenic risk score For schizophrenia.

[02:00:42]  Red: So we’re you know any part of the genome of the may say we looked at a thousand places in the genome and you know, we found A bunch that seemed correlated with Schizophrenia So then we would create a new variable and that would be the polygenic score and it would basically capture the level of genetic risk That folks in the sample carried and so that would differ as well Maybe I would have higher scores on the polygenic risk measure, meaning I would have potentially higher genetic propensity for some trait others would have lower scores on the polygenic risk scale Meaning they would have a less Apparent genetic risk for some trait and then we would have a sample full of information like that We could then use that polygenic score to investigate it further to say, you know, see if it has direct effects on some type of brain structure or anxiety traits themselves That alone does not that’s not a guarantee of causal effects. There are other things that can explain that association but You what’s interesting is and there’s some really cool recent papers that have done this and even if we don’t have time to Really get to them this time.

[02:01:59]  Red: I can I can send them your way and potentially talk about them next time What what I think is particularly important about not only GWAS studies, but also sibling studies twin designs These these data can be combined You can use information from GWAS Derived from GWAS studies something like a polygenic score and put them in a sibling design And so in that case You can investigate Say you use just fraternal twins dz twins They might differ in their polygenic risk because they differ from each they only share half of their dna The other half is different from the sibling So it these types of data can be combined Including with sibling data and that does start to give you some some fairly interesting Ways to investigate possible causal routes But just simply doing a GWAS study what you’ve done is potentially reveal associations between Some genetic variant and some complex trait if you want to talk more about causation especially if you want to begin to understand And How that causal effect plays out there are There’s it’s certainly, you know, there it’s plausible to do and there are other very Interesting fascinating designs that then start to allow you to investigate. All right There seem to be these genetic variants associated with say something like Schizophrenia How would that be possible? Well, we might start to Take more granular looks at things and what we find is that The these this particular set of genes seems to be Very much enriched in this particular type of neural tissue, right that influences an area of the brain related to language functioning or it disrupts you know Language functioning in some way.

[02:03:54]  Red: So that starts to give us it starts to give us a picture of Mechanism right and pathway. So that that is I I know that’s a very long answer I apologize for rambling, but it it it It sort of echoes that point earlier of In isolation Showing a trait to be heritable finding GWAS correlate or hits with Genetic variants in a GWAS study in some trait that alone is not Dispositive for really anything except the finding in that study It has to be, you know, you need to continue to put the pieces of the puzzle together And actually the other thing I would add is Uh It’s strong to me It makes a very strong case for the need of guiding theory or explanation if you want to use more gorgeous terms Uh, you need to be working with good x good hard to vary explanations that guide you in terms of where to look what pathways Um and that kind of thing.

[02:04:54]  Blue: Let’s go back to the 19th century slavery example Let’s pretend like obviously in this case part of the reason why he’s using this as an example is because we already know what the explanation is But let’s let’s pretend like we didn’t right or we’re living in the 19th century We’re aliens observing the humans or something and and we’re missing a lot of things that the humans would understand And we’re trying to figure out if slavery, you know, to what degree it is heritable Um, but they’re smart aliens. They’re good scientists They they know how to set up a good natural situation like this to try to study it How would these aliens go about trying to look at the heritability of slavery? And what would they find would they find that it is or isn’t heritable?

[02:05:40]  Red: So, I mean it’s it’s a sort of a Reflexing way to to think about the issue. Well, again, what I would say is the one Experimentation is something different, right and trying to

[02:05:56]  Blue: Yeah, I try to drop the word experiment this time. You’re looking it’s it’s and maybe a natural experiment would be as far as we can go Yeah,

[02:06:04]  Red: okay, and in regards to heritability You know, I Know I know it’s a tricky thing to speculate about but let’s say that um I think Deutsch Says that, you know in his thought experiment, which will just take on face that you you happen to arrive at some non -zero heritability estimate I mean the obvious implication is that it would be a mistake to think that that tells you anything about the causes of slavery And I think but again, this is this is kind of why I said earlier that I don’t necessarily take issue with the those points on their face because the same is true for showing that You know, there are correlations between genes in a GWAS study and some other complex trait. That’s not enough Or showing that a trait is heritable You know if were you to take from that and infer that You know the environment is sort of irrelevant that is a genetically determined trait. That’s an erroneous conclusion For you know for all of the things we talked about and and so that’s why Heritability estimates just represent a piece of the puzzle in the same way that in You know environmental sources of variance represent another and then to build more insightful

[02:07:29]  Red: Types of explanation it requires A variety of things other moving parts that are that go much beyond a single type of study design Uh, and I think that that’s the the what makes sort of I think behavioral genetics A tricky field to contemplate in some ways is that all of the points that we’ve talked about apply in studies that You know just normal social science studies that you see every day Right, maybe you might find a correlation between Someone’s level of agreeableness and their job success just to pick a personality example, right? So agreeableness is a broad personality trait And let’s say we do a study. We’ve got a thousand individuals. Nobody’s related to anybody else. It’s a sample of just individuals Drawn from the population got a sample of a thousand of them. We asked, you know, we measure their level of agreeableness We somehow measure their Occupational success over time, right and we find that more agreeable people tend to do better in their chosen occupation, right so There are so many reasons why We can’t Just based on those correlations inferred very much at all about causal effects genetic effects environmental effects. They’re all wrapped up in one package that’s Impossible in that setting to pull apart If you could do an experiment where you randomly manipulated someone’s or individual’s level of Agreeableness, which is impossible, but just for the matter of a thought experiment, imagine we could do that Uh, we let’s say we could just turn dials and randomly set people at various places of agreeable or disagreeable on that personality trait Then we you know, that would be a much stronger step in the direction of saying that agreeableness

[02:09:23]  Red: Causes occupational success now if we thought about that obviously we can’t do that Thought about it in terms of the discordant twin design we’ve been discussing what we might look at is differences in agreeableness that emerge between identical twins because that’s certainly plausible One twin may be more agreeable than the other Twin identical twins don’t correlate perfectly for their personality styles And so and obviously this is kind of easily observable for anyone who knows twins. They they can often be Quite different from each other in terms of Their personalities. They’re similar, but there are also differences And so in identical twins that the more agreeable twin on average tends to have better occupational success That’s a I would argue a stronger piece of evidence than the First example where we just use the a thousand unrelated individuals But it’s a you know as these things start to accumulate that’s when we start to Understand our phenomena of interest, but just sort of overly simplistic reliance on something like a heritability estimate Deutsch rightly rejects that and I think in general we should reject any type of you know, lazy conclusions about heritability

[02:10:41]  Blue: Could we do something similar with the 19th century slavery example though? Like could we come up with a way of collecting the data using discordant twins or something like that? That would allow these aliens who don’t understand to realize this is not actually a heritable trait

[02:10:59]  Red: um I mean Perhaps if I sat down and thought about it long enough it because you would have I would need to think through The design honestly, it’s not it sort of fits in the category one of those examples I prefer not to you know Speculate too far about because then it then it you run the risk that People might think you’re actually serious about contemplating a Explanation of that particular outcome.

[02:11:26]  Blue: Well, in this case, I’m assuming that it’s that that isn’t the explanation that heritability isn’t Explanation, I’m just wondering how the aliens could figure this out that that isn’t the explanation

[02:11:37]  Red: Yeah, so no it’s I it’s a Completely reasonable question in in the sense of how do we just a broader sense of how do we avoid erroneous conclusions?

[02:11:47]  Blue: right

[02:11:48]  Red: and in some ways As we’ve already said that just calculating heritability and environmental estimates on its face is not enough on

[02:11:57]  Blue: its own right But could they even reasonably? Figure out that it’s not really heritable or does heritability as a concept Mean nothing more than correlation

[02:12:11]  Red: well, so let’s go back to the example of that we used for Cognitive the heritability of cognitive traits, right? And the the finding in in sort of that’s emerged several times in the past that certain cognitive traits become more heritable as socioeconomic status increases, right? And so in a case like that we let’s imagine we just we conducted the first twin study of You know some cognitive trait and we find that it’s about 40 percent of the variance is heritable variance And about 60 percent of the rest of the variance is explained by the non -shared environment Just looking at that again That that alone tells me some interesting things But those interesting things have limits So let’s say that I one of the ways that we might expect that we might you know sort of conjecture and refute certain ideas to go back poppers vernacular is let’s say, all right Think about what these estimates are telling us these are telling us about Uh, where what we can attribute variance in this sample too But again that goes back to some of the differences are seen linked to genetic differences other Other aspects of these differences seem to be a product of the environment. In fact 60 percent of the variance in this case was explained by environmental variation So that might prompt us to think because we know some other things about cognitive traits That we’ve amassed knowledge. We’ve amassed over time one of which is Uh, you know cognitive development in general is vulnerable to environmental disruption lack of calories You know, uh environmental adversity of different kinds discrimination Racism a whole bunch of environmental Things that vary in the population that can impede Cognitive growth in human beings.

[02:14:10]  Blue: Yes,

[02:14:10]  Red: that would lead us to then Expect all right Let’s look at because we we also know that heritability heritability estimates are not fixed constructs They can and do change in set certain settings. So now that could get us to the point of thinking. All right, let’s look of let’s specifically investigate heritability These heritability estimates across different strata of socio -economic environment uh, and then You know, we sort of arrive at the finding that’s that’s emerged several times which they do change those heritability estimates vary depending on socioeconomic uh effects and Again, I I don’t want to harp on this too much in the sense of there might be a study that comes out tomorrow that finds relatively stable heritability across these strata or it replicates the original finding again That’s in this case sort of secondary the point is um We have to do some additional work and also remember sort of the basic tenets that we talked about earlier that these These things aren’t you know, sort of concrete Irrefutable pieces qualities of whatever trait we’re studying Uh, there are many more moving pieces to the puzzle

[02:15:23]  Blue: right. Okay

[02:15:26]  Green: We’ve kept brian a long time Can I is it do you have another uh question bruce or or can I ask a quick one? Oh, no go ahead? um Sorry if this takes us on a little different path, but I think I think it’s related I You know, I on the podcast last week I was kind of mentioning how you know, my field is is education and you know oftentimes when I see sociological studies There or studies about education or kinds of related soft science fields my bs detector just goes crazy I don’t know. I can’t help it. I oftentimes I think I think that it might be because they they are making assumptions about humans whether related to behaviorism or Marxism or other political kinds of things that just kind of just does not ring true for me and then after that Just the conclusions just don’t really go anywhere um And as I’ve gotten more into popper and things I think I’ve I might have amplified that in a way um, I’m not going to I’m not certainly not saying anything that you’ve said here or in your papers or your excellent collet articles. I mean That I would encourage everyone to go and read. I think you’ve written about 10 for collet, which are just great um, but you know just to sort of Play devil’s advocate. I just wonder if it’s just possible that there are assumptions in here about in this kinds of research that just um Maybe maybe aren’t aren’t completely valid um, if I may just read something I wrote on Facebook Um, it’s not Didn’t get too many likes.

[02:17:24]  Green: Maybe it’s not as clever as I thought but let me let me just read it and see what you think Person one. Hello friend. Here’s a thousand books and a thousand movies that you must experience Also, I’m going to keep you in my house for two decades and explain to you in a in minute detail My philosophy on life until the thought of me speaking to you makes you grown Person two Sounds good.

[02:17:47]  Red: Nothing else going going on Person one.

[02:17:50]  Green: Oh But scientific studies indicate I don’t actually have any influence over you. That comes from nature Person two WTF Okay, so the idea is that I think you just on a on a human level You know, I mean, how does it even make sense to say that parents don’t Influence our children or keep him in our house for 20 years We’re like interacting with them and the most like Intimate way pretty much you can interact with another person. I mean is it even Does it even make sense that you can parse out? You know nature and nurture and and the influence of genes and all this Do you see where I’m going with this?

[02:18:35]  Red: Oh, certainly. Absolutely. It’s a great question.

[02:18:37]  Green: I would just love your thoughts

[02:18:39]  Red: Yeah, so um yeah, well, I think first of all, I’ll start by agreeing in some ways to the idea that it’s It’s not intuitive at all that you know, something like uh shared family environments might not matter In terms of and I put matter and sort of air quotes We’ll get back to what that means in a second, but you know, may not be as impactful on human development as we presume them to be But I think that in and of itself sort of implies something That I think is pretty widely appreciated in science certainly by you all and probably anybody listening is that Uh, you know, the nature of reality can often be pretty severely at odds with our intuitions About the world. Uh, sometimes they align and other times they don’t And in this case, you know, if we’re going to sort of scrutinize those intuitions, there are different ways we can do it Uh, and by different ways, I mean different research designs One way is the twin method. We’ve been talking about another way is uh, sort of the classic type of method that’s often Reference with twin studies and those are studies of monos. I got it twins separated at birth and raised apart That’s another way to sort of scrutinize this particular Uh idea about parenting effects Another way is adoption studies So to look at adopted siblings in this case siblings who are unrelated to each other and unrelated to their Adoptive parents but are raised together in the same home To see how similar they are to each other and so we can sort of start with that in general what you find is that

[02:20:24]  Red: While there might be some some degree of similarity in terms of their personalities their interests political Orientations those types of things there might be some superficial similarity early in life Most of it’s gone by the time they’re in adolescence or adulthood So any if we presume any effects of the parenting environment That function to make those adopted kids similar to each other those effects have Pretty much dissipated at with age Another again going back to the mz twins reared apart what we tend to find is that we might expect Those exposures to sometimes vastly different homes not always but quite often very different experiences um would create a quite a bit of difference in fact if we think especially In terms of parenting effects being you know sort of the foundational things that shape human development We would expect those individuals to be quite different because they don’t share any parents don’t share any Formative years in the same environment what we find is that they’re remarkably similar personality traits cognitive traits educational attainment All the way down to sort of more superficial things like hobbies and Extracurricular interests those types of things that incredibly similar and then you can combine that then the findings of twin studies where The shared environmental component is where we would expect sort of parenting effects that Make kids similar to each other. That’s where those effects would live And you know, as we mentioned with the laws of pg behavior genetics and then just sort of repeated findings those shared environmental effects Can sometimes show up in childhood Maybe small to moderate effects, but for for quite a few traits.

[02:22:15]  Red: They’re gone by adulthood Uh, and then for other traits, they’re never really there in in strong effect Uh at all there are a few exceptions to this but this is sort of a general rule and then That’s you know, so we sort of piece together this puzzle in a variety of ways and I think there are a couple of things that That create the consternation that that folks feel when they’re sort of coming into this literature for the first time one is that There are all of these studies showing correlations between what parents are doing and and some outcome in the kid Well, what you have to one thing to remember there is unless we’re using some type of twin or sibling design It’s just it’s as likely that the reasons parents outcomes correlate with child outcomes Is because of genetic overlap parents also share genes with their kids And so we need to account for the correlations that might be that might exist between parents and children that are linked to genetic correlations genetic overlap that they have so when we Twin studies sibling studies Allow us to account for that adoption designs allow us to to account account for that in a certain way And we just don’t find these strong parenting effects and it sort of has Led to the the general conclusion at least the argument I would endorse is that most of the reason The biological children who are raised with their biological parents tend to be similar to each other Is because they share genes with each other The the additional shared home environments not contributing much more on top of that Now the second reason this can prove frustrating

[02:24:04]  Red: I think uh has to do with forgetting that most of the time heritability estimates Uh and shared environmental estimates are Often much smaller than non -shared environmental estimates So we forget that this is not saying that biology is all it matters and quite the contrary in fact it’s saying most of the time The environment explains most of the differences between humans. It’s just not the family environment It’s the non -shared environment all of the things that happen to us that make us different from our siblings So it could be anything from one sibling finds themselves in a particular peer group at school and the other one doesn’t One peer peer influence. Yeah, exactly. And so The other thing I would add to that though is there is a completely defensible plausible mechanism by which Uh the way parenting effects could manifest themselves Uh and that’s through the non -shared environment and and I think in this case Um Imagine that you know and maybe folks who have kids might imagine this too It it’s completely plausible that parents can act in ways that that treat their children differently And that can create Differences between the children and so in that case parenting would be an environmental effect, but it would be a non -shared effect Um, I’m not saying there’s a ton of evidence for that. I’m just saying it’s completely plausible that parenting Would could function to increase differences between kids Although one thing that needs to be kept in mind there is that in in in many cases Parents, uh the

[02:25:42]  Red: differential treatment that can emerge across kids is more a result of the differences sort of pre -existing in the child that the parents are reacting to versus The differential treatment causing the differences in the two siblings, but that aside um It is You know, it’s sort of there are varieties of pieces of evidence that sort of arrive us at the idea that Developmentally speaking personality speaking those types of things the the shared environment Effects are not as large frequently as either genes or non -shared environment now The the final thing that creates consternation is people I don’t want to say that too accusatory. There can be a temptation to conflate What I’ve just talked about with the idea that parents Don’t matter and I emphasize that word and in that regard.

[02:26:40]  Red: I think that is just a very That would be a conclusion that would that would make me fairly despondent because We were talking about earlier before we started recording, you know Fortunate to have a wonderful family so many good memories with my parents mom and dad brother But my brother and I happened to be adopted we so we fit within that framework of an adoption design We’re not biologically related to each other or to our parents and we’re very different from each other Our personalities are exceedingly different Uh, we’re we’re different people, but that doesn’t mean that we don’t you know Both have wonderful, you know lasting memories that we can call up of, you know Fun times with parents or them helping us get through difficult times in our life and just well spring of of Good things that we can call to mind and those things absolutely matter and the converse is also true Uh, it’s completely implausible that that you know and happens. Sadly a fair amount Parents do terrible things to their children and and uh put them in psychological or physiological uh Path of harm

[02:27:58]  Green: It seems like that’s the

[02:27:59]  Red: caveat and

[02:27:59]  Green: a lot of these studies is Trauma is is kind of like you want to like isolate that right the trauma trauma. Yeah

[02:28:06]  Red: Certainly we’ll see so all right This actually has a methodological component to it. It’s the idea of restricted range Most of what parents what what it’s also capturing is what parents do in sort of a normal range variation Yeah, too far out in that curve to where you’re talking about Abuse neglect maltreatment. That’s that does not apply to what we’ve said those are Sort of qualitatively different in terms of parenting effects and there is good evidence that those matter for different outcomes in in child development And so um, the other point I like to make this actually I wish I had thought of it Judith Harris and pinker both Provided the different versions of it. I think Judy’s conception might have been first. I think it was because blank slate came later from pinker, but this idea of We we imagine That part of the moral obligation parents have to kids is that they are playing a causal role In shaping various components of their development, you know, their psychological development their moral development The nature of their character Those types of things, right? So we we assume that that’s part of the moral obligation but The first point to make there is even if Those effects are not as strong as we think it doesn’t damage the moral obligation at all Uh, there’s still a moral obligation of one human to another To to not cause grievous harm and to provide especially when you have parents and children, right?

[02:29:48]  Red: because It would also probably be a mistake and I don’t know it would be one a lot of folks make To assume that say one spouse Who let’s say they met when they were in their 20s met at college or whatever, uh, you know Have a long term get married at a long term relationship. Whatever it would probably be a bit Mistaken to think I’m going to cause significant personality change In my spouse over time. I’m going to remold them into the person. I want them to be That’s probably a mistake that you don’t make many times in relationships What’s what you find is that you know part of the reason that attracted you to the person was the nature of who they were already and so I don’t think we would ever be tempted to conclude that just because we don’t have strong causal effects on their personality development That we can treat them any way we can or want to or that our relationship doesn’t matter because i’m not causing You know, they’re cognitive traits to develop. I mean, that’s that’s a recipe for uh Disappointing and disastrous relationships.

[02:30:56]  Green: That’s an excellent perspective.

[02:30:58]  Blue: So I wanted to actually ask about I I read a book and I want to say it was pinker, but it may not have been pinker Where they made the case that while when we when we talk about parental influence what they’re trying to measure is What your actions In the environment you’re creating as a parent how it impacts the child But that isn’t actually the main influence of a parent the main influence of parent is who the parent is So for example, and this is what the book claimed at least. I don’t know if it’s true or not that like if the parent has a high education or is wealthier or Something along those lines that the very fact that you were born into that environment Will have an influence on that child compared if they weren’t born into that environment even if it’s not specifically What you as a parent is doing that is you know, you decide you’re going to read them Good night moon every night may have no impact at all on them but whether that you were, you know The very fact that they were born um in a marriage or in a more wealthy environment or They know that you have a higher education that those things Do in fact have an impact is that true or false and I wish I could remember well enough which book I

[02:32:19]  Red: I didn’t find Much disagreeable about that at all. I mean again, this goes back to the idea that the no one certainly People might make this argument I Would always like to be on record as not making the argument that Biology is all that matters. I mean the evidence is far to the contrary The environment definitely matters that twin studies provide some of the best evidence of that but yet and yes, it can include things like what you talk about in terms of Some things that that we might even equate with just good luck The idea that you know, we have good health because we were born Not in a time before modern medicine really took hold Absolutely and then the examples you give of yes, you know the I mean even within the The course of a lifetime of a child so maybe uh, you know Two parents have decide to have children later in life when their finances are more settled as opposed to early in life when You know, there are you know, things are much more economically unsettled and I don’t would it rule out the possibility? That could certainly change a number of things in terms of the experiences of the kids Um, so yeah, it’s uh all of that to say. Yeah, I think it’s what you say is is plausible certainly If

[02:33:46]  Blue: I recall correctly the book was claiming That there is absolutely an influence of parents on children But it has more to do with who the parent is not what actions the parent chooses to make That was the point the book was trying to make and I wish I could remember which book it was I

[02:34:05]  Red: think in in some ways that that could be seen as a version of sort of what I said earlier is that most of the uh similarities or correlations that we see emerge between biological parents and and their biological offspring when they’re all raised in the same home Is is more the result of the genetic overlap? That that exists between parents and offspring So in other words part of sort of who they are in that regard that the additional things that happen in the shared environment Don’t do much to alter, you know, make things more similar between kids if that makes sense

[02:34:42]  Blue: Yeah, okay.

[02:34:44]  Green: I think this perspective can really make people a better parent really, uh, you know, that’s how When I got really got into this, uh, these these twin studies and and read the books we mentioned. I um It felt kind of liberating in a way because I I really I Didn’t feel like I was molding my children into Perfect humans. I just felt like I could just Do what made sense to me and just enjoy my children really and you know, I read to them every every day uh, not because I think I’m it’s terribly influential to them It’s just because I love to read to my children and you know, I just try to think about what what I enjoy To and you know, just enjoying life together and not like, you know, children change Us too and I think it’s just uh

[02:35:43]  Red: It’s I don’t want to cut your off. It’s funny. You mentioned that though. It’s because it has a more Your it’s a very interesting good nuance point It goes by the name often in sort of the developmental litter literature as child driven effects But it is what part of what you described that children impact their parents. Yeah.

[02:36:02]  Green: Yeah

[02:36:03]  Red: Sometimes in unexpected ways. I mean, oh, yeah I think we my wife and I don’t have kids yet We hope to one day but I so I but I can still imagine the idea that You know, the experience of parents vastly changes whenever they have, you know, another human being that they become Uh, completely responsible for so. Yes. Yeah, I have no doubt that that’s fairly landmark change in a person’s life

[02:36:29]  Blue: The other thing I wanted to ask concerning this though was like, let’s let’s say we took religion as a factor Okay. Now undoubtedly there is a genetic factor to religiosity. I don’t doubt that

[02:36:40]  Red: Um,

[02:36:41]  Blue: but what religion you are is definitely not random Right. It’s if you do go on to be a religious person There’s a very good chance. It’s the religion of your parents Because that’s the one you’re familiar with and that you know and that you grew up with So it would be hard to say that that wasn’t an influence of your parents, right? If that makes any sense, but that may not be like a trait that These sorts of studies would even be interested in necessarily

[02:37:11]  Red: No, it’s a very good example and it would fit in the category of something I might you give a general exception to um, depending on What precisely we were talking about so you used an interesting term first and that was religiosity so if we think of religiosity as sort of the um The the general combination of personality styles and traits that lead one to be sort of inclined To seek out spiritual experiences religious experiences those types of things That it does show sort of small to moderate heritability estimates not surprising like every other trait huge environmental effects But if what we’re talking about instead if we you know Be a little careful with the language and we say maybe denomination So one might be bad. It’s methodist. Whatever the case might be. Uh, yeah Chris versus hindu or sure certainly one absolutely Uh lord, yes, uh, depending on where much like accent depending on place of birth and and and elements of family culture and those types in broader national culture Uh time period in which one was born Yeah, no doubt about it. That that’s uh, I would say very much akin to accent that we were talking about and language that one speaks Yeah

[02:38:32]  Blue: I guess what i’m trying to say though is that that would be a case where you would expect a very high influence From parents as

[02:38:41]  Red: potentially. Yeah, so if you did uh, let’s say you did a twin study of religious affiliation Uh somehow, you know, uh and quantified it not not as um, this would prove methodologically tricky just the nature of how you would measure it, but let’s imagine We could do it you would yes, I would imagine Large insignificant shared environmental effects nothing really in terms of heritability, right? Yeah

[02:39:08]  Blue: I guess my point is is that that’s probably not a trait You’d be interested in looking at scientifically to begin with if for no other reason then because you already have a really good Explanation as to what that it’s going to be a shared environment trait I

[02:39:22]  Red: don’t know that I would go that far because We we shouldn’t necessarily forget about the non -shared environment and there are studies not a ton of them But there are several studies happy to share those with you too uh looking at It’s a type of When difference design looking at differences in religiosity Uh predicting differences in overt delinquent behaviors and at least some Uh some number of studies have found some evidence suggesting that higher religiosity Uh Corresponded to less delinquent involvement. So more pro -social behavior. So that that’s yeah It’s still interesting in a certainly in a social science framework of the effects of religion exposure to religion in various ways And how that manifests as behavior twin studies are quite useful for that

[02:40:12]  Blue: No, I could see that I was thinking more about the denomination or sure

[02:40:16]  Red: Yes, that that in that regard just pure denomination. Yeah, you’re I think your intuition’s pretty good I I would at least speaking for me and if I’m what I want to focus on or behavioral outcomes or whatever I’m gonna it’s more the religiosity type of thing I would be interested in

[02:40:33]  Blue: what I’m suggesting though is as an answer to Peter’s question It may be the types of things that parents do in fact influence children on Happen to fall often into a category where we wouldn’t be that interested in asking about them scientifically to begin with Um, so they that wouldn’t be what the study would be about the study would want to study religiosity not which denomination you’re in

[02:40:56]  Red: Yeah, I think that’s fair in a lot of cases. Maybe if we sat here long enough We might think of some exceptions to its other examples, but I’m yeah, that makes sense

[02:41:05]  Blue: Okay, let’s wrap this up. Uh, I guess peter. Do you have any final questions before we? Call it quits for today

[02:41:13]  Green: Keep going for six hours, but you know, I think we’ve kept brian Long enough and I’ve truly enjoyed it’s just a especially for someone who is more of a lay person who doesn’t you know I mean, I’m not in the in the world of academia or anything and just to be able to talk to someone As smart as you are brian is just a it’s a thrill. I have to pinch myself. It’s a low low amplitude event in the multiverse

[02:41:43]  Red: You both are being too generous and in time with your compliments. I I enjoyed it. I had a blast I’m looking forward to part two Down the road. Um, but no it was a pleasure and and I you know, I apologize for my inadequacy at explaining things I know I’m there are other folks who could have given you better Examples and in clarity than I than I could but I still very much appreciate the chance to come on and talk about this stuff

[02:42:11]  Green: All right. Thank you. Thank you so much.

[02:42:14]  Red: Absolutely

[02:42:17]  Blue: The theory of anything podcast could use your help We have a small but loyal audience and we’d like to get the word out about the podcast to others So others can enjoy it as well to the best of our knowledge We’re the only podcast that covers all four strands of david oich’s philosophy as well as other interesting subjects If you’re enjoying this podcast, please give us a five star rating on apple podcast This can usually be done right inside your podcast player Or you can google the theory of anything podcast apple or something like that Some players have their own rating system and giving us a five star rating on any rating system would be helpful If you enjoy a particular episode, please consider tweeting about us or linking to us on facebook Or other social media to help get the word out If you are interested in financially supporting the podcast, we have two ways to do that The first is via our podcast host site anchor. Just go to anchor dot fm slash four dash strands f o u r dash s t r a n d s There’s a support button available that allows you to do reoccurring donations If you want to make a one -time donation go to our blog, which is four strands dot org There is a donation button there that uses paypal. Thank you

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