Scientists often try to quantify nature-vs-nurture, bandying about the results of experiments as yielding a numeric breakdown. “In our data, tufted fluffy western bandicoot distress cry length was determined 17% by environment and 83% by genetic factors.” This sort of statement is echoed and simplified by the Press: “Bandicoot Distress Cry Length 83% Genetic!”
The problem with this is that such a number is relative to a particular environment, and can change dramatically in a different setting. Let me give a toy example: let's say there is some wild animal, a species of rodent called gedankels, which are about 20cm long as adults. If you look at variability in length, it's 20±5cm. These gedankels all eat well, and about the same things, and so variability in length among this population is 95% genetic. Now, it turns out there is a plant, the inhibiweed, that constitutes a substantial portion of the diet of these wild gedankels, and inhibiweed contains a substance that inhibits gedankel growth. So you go in and raise some gedankels under different conditions, where half of them eat no inhibiweed, and those inhibiweed-restricted-diet gedankels grow to 50±5cm. In this new population, length has gone from 95% genetic to 95% environmental!
The point is that what proportion of variability in some trait is genetic vs environmental depends completely on not just the genetics of the population, but also the environment. And this same thing can hold for other traits. Let's say there's some gene that makes people insightful but rebellious and easily bored. In one sort of environment (public schools in Texas, say) this gene might be negatively correlated with achievement, while in another (home schooling by biology professor parents, say) this gene might be positively correlated with achievement.
This is not just a theoretical concern. To give possibly the most familiar example, the gene for sickle cell anemia is positively correlated with health in some environments (ones with malaria) and negatively in others.
So even if we find some population that seems to score poorly on some standardized test of intelligence, and this seems caused by some particular genetic factor ... it does not follow that we should just give up. On the contrary: it may well be possible to change the environment to eliminate or even reverse the effect, and knowing the particular genes may well give us a handle on how to do so. This is the true promise of understanding our own genetics as a species, and it is the exact opposite of the implicit impression given by credulous press reports of some trait being controlled only x% by environmental factors in some sample, as if that's a death knell to any hope of changing it more than x% by environmental manipulation.
I don't mean to spam but I've seen a previous post of yours suggesting you're open to some amount of self-advertising.
You said, "We are not assuming that genes are in Hardy-Weinberg equilibrium, whatever that is."
I was thinking of writing a post for a while on "whatever that is" and that's below. Hoping people interested in a post explaining the basics of heritability would also be interested in a post attempting a clear and precise explanation of Hardy-Weinberg Equilibrium:
Thanks! For anyone else reading this, I don't just tolerate but encourage self-promotion for anything that's topic or spiritually related. (This is both.)
I don't have any opinion about the general heritability debates that I feel comfortable sharing in public (yet). :) But I will say that after starting from a baseline of thinking everything is highly heritable, I learned a lot from reading Gusev, e.g. about some of the weaknesses of existing twin studies. So I think he provides some useful skepticism.
Sorry to question the hypothetical when you specifically said not to, but I'm curious and know nothing about this field: does the simplifying assumption of asexual reproduction really not matter at all? Seems like it should!
Maybe you could also do it by assuming the gene is on the y-chromosome, near-starvation is determined by fathers, and only manifests for baby boys. But... still seems like a distraction!
Oh, it certainly matters, because with sexual reproduction you can't think about people as having "tall" or "short" genes, but you have to consider lots of cases: Each parent and the baby can basically be SS, ST, TS or TT, so there are 4^3=64 cases to worry about instead of just four.
You can create an example where the same issue manifests while reflecting all that, but I wasn't able to figure out a way to do it without making everything much more complex. (At least, not other than my other fix of perfect assortative mating.)
The copy article on your site has a duplicate question for
> Say there’s an island where neither genes nor the environment influence height. Except, some people have a gene that makes them inject their babies with human growth hormone, which makes them 5 cm taller. How heritable is height?
Yes, similarly the table on short and tall genes registers correctly on the main website but not this substack post. Here it's like:
Baby genes Parent genes Food Height Short Short Lots 165 cm Short Tall Semi-starvation Less than 165 cm Tall Short Lots More than 165 cm Tall Tall Semi-starvation 165 cm
But all-in-all thanks Dynomight for this article! I love to see this kind of stuff.
Thank you! I have classical Ehlers Danlos Syndrome, and it's always been described as heritable. The definition I was working with was "present at birth" which is clearly not accurate. This makes a lot more sense. In all but one of the types of EDS, a mutation happens to one of the collagen genes, which makes connective tissue, like tendons, skin, and other soft tissue weak. I've always held the belief that there's little you can do to change or strengthen the collagen. If you have the mutation, and even if you're born in Asia, to parents who are deaf, or are adopted by parents without EDS; even if you take ballet classes as a child, are educated in 4 different languages, or grow up next to a nuclear power plant; even if you have surgery to fix a tendon, take collagen supplements, or do aquatic therapy every day, the 👏🏻 collagen 👏🏻 will 👏🏻 still 👏🏻 be 👏🏻 defective because the environment change doesn't matter. There are things we can do about the *symptoms* the weak collagen and connective tissue cause, like pain, hypermobile joints, GI troubles, etc. But unless we edit the gene, the condition will exist.
Sorry to hear about that! I don't know much about EDS, but what I do know is consistent with what you said, treatment is supportive and can reduce symptoms.
In the context of this essay, the only point I would make is that it doesn't follow simply from the technical definition of heritability that lifestyle changes can't improve things. Even if something is >99% heritable, that only means that *normal* lifestyle changes probably don't have much impact. But it doesn't prohibit the possibility that more unusual lifestyle changes could do something.
Anyway, we know lots about the causal mechanisms of EDS, and lots of interventions have been studied. So I think there's no reason to rely on the very crude measure of statistical heritability. It basically adds nothing when we already have studies of interventions.
Also, it's quite possible that when people say it's "heritable" they're using the normal English "heritable" rather than the technical ratio-based "heritable". That collision causes endless unnecessary confusion and is what I was complaining about here: https://dynomight.net/heritable/#:~:text=egregious
Hmm. Here is a true story. I was adopted at birth by young nitwits who successfully hid all the details of my birth until I was old enough to ask questions. The birth mother went into the hospital with the adoptive mother's name, so my birth certificate was phony. From a very young age, I "knew" that I was in the wrong tribe despite the superficial similarities in appearance [same skin color etc]. I knew how to read well before formal schooling began without being taught. The tribe didn't value that and refused requests to go to the public library after I had read most of what was available in the school library. The tribe's motto, "People like us don't...fill in the blank". I heard this often about so many things: read books, magazines, watch the news, go to college, talk about 'things', ask questions, learn to speak other languages, and on and on. Eventually, compassionate public school teachers tried to get me into college at age 15, but the tribe refused to cooperate because people like us...don't. Finally a tribal member told me the story of the illegal adoption, and I understood-of course I didn't fit in this tribe. It was like the egg of a swimming bird had been put in a chicken's nest. The chicken would never understand why one of the chicks was able to swim-heritability. I wasn't from them, didn't have to struggle to be one of them. I swam away. Later in a college genetics class, I understood more but was still tribeless. From this personal experience/small sample size, I think that heritability is everything. The environment is not nothing, but the math doesn't work.
Thank fuck, I was gonna write a post on this but now I can just link this. Wonderful. Mainly for the reason of pointing out that high heritability doesn’t imply that traits can’t be intervened on.
A good way of doing this is just pointing out muscle mass and strength have really high heritability, but going through the actual definitions is ideal!
Ah, perhaps I should have used that as an example! I'd guess that some non-negligible fraction of the heritability of muscle mass is driven by personality differences, which are in turn driven by genes. Genes that drive you towards exercise or a physical work will tend to make you stronger even though those are choices. So if you're choosing if you want to exercise it's completely irrelevant.
I’ve read that the tendency to be an active adult (where active = regular participation in sport/gym attendance/etc) has strong heritability, and results in about 25% of adults engaging in said activities, and the rest being notably less inclined to do so - but perhaps still responsive to other factors, like the fun and sociability of team sports, and/or local cultural value of same. I often ponder this when I see advertising which encourages adults to be active - will pulling that environmental lever make a difference for the 75%?
(Written years ago in response to the New York Times Sunday Opinion piece “How Genetics Is Changing Our Understanding of ‘Race’” by geneticist David Reich, 23-Mar-2018, https://www.nytimes.com/2018/03/23/opinion/sunday/genetics-race.html)
Scientists often try to quantify nature-vs-nurture, bandying about the results of experiments as yielding a numeric breakdown. “In our data, tufted fluffy western bandicoot distress cry length was determined 17% by environment and 83% by genetic factors.” This sort of statement is echoed and simplified by the Press: “Bandicoot Distress Cry Length 83% Genetic!”
The problem with this is that such a number is relative to a particular environment, and can change dramatically in a different setting. Let me give a toy example: let's say there is some wild animal, a species of rodent called gedankels, which are about 20cm long as adults. If you look at variability in length, it's 20±5cm. These gedankels all eat well, and about the same things, and so variability in length among this population is 95% genetic. Now, it turns out there is a plant, the inhibiweed, that constitutes a substantial portion of the diet of these wild gedankels, and inhibiweed contains a substance that inhibits gedankel growth. So you go in and raise some gedankels under different conditions, where half of them eat no inhibiweed, and those inhibiweed-restricted-diet gedankels grow to 50±5cm. In this new population, length has gone from 95% genetic to 95% environmental!
The point is that what proportion of variability in some trait is genetic vs environmental depends completely on not just the genetics of the population, but also the environment. And this same thing can hold for other traits. Let's say there's some gene that makes people insightful but rebellious and easily bored. In one sort of environment (public schools in Texas, say) this gene might be negatively correlated with achievement, while in another (home schooling by biology professor parents, say) this gene might be positively correlated with achievement.
This is not just a theoretical concern. To give possibly the most familiar example, the gene for sickle cell anemia is positively correlated with health in some environments (ones with malaria) and negatively in others.
So even if we find some population that seems to score poorly on some standardized test of intelligence, and this seems caused by some particular genetic factor ... it does not follow that we should just give up. On the contrary: it may well be possible to change the environment to eliminate or even reverse the effect, and knowing the particular genes may well give us a handle on how to do so. This is the true promise of understanding our own genetics as a species, and it is the exact opposite of the implicit impression given by credulous press reports of some trait being controlled only x% by environmental factors in some sample, as if that's a death knell to any hope of changing it more than x% by environmental manipulation.
I don't mean to spam but I've seen a previous post of yours suggesting you're open to some amount of self-advertising.
You said, "We are not assuming that genes are in Hardy-Weinberg equilibrium, whatever that is."
I was thinking of writing a post for a while on "whatever that is" and that's below. Hoping people interested in a post explaining the basics of heritability would also be interested in a post attempting a clear and precise explanation of Hardy-Weinberg Equilibrium:
https://nickpbailey.substack.com/p/what-hardy-weinberg-equilibrium-is
Thanks! For anyone else reading this, I don't just tolerate but encourage self-promotion for anything that's topic or spiritually related. (This is both.)
Did you mean to add the exponent 2 to the cm label when discussing the variance of height?
Yup, variance has units of the base quantity squared!
Thanks. Obviously statistics and probabilities are not my strong suit
Thanks for this.
Since you've mentioned Gusev, where do you stand on the recent missing hertability debates?
Are you planning another post on that (I sure hope so)?
I don't have any opinion about the general heritability debates that I feel comfortable sharing in public (yet). :) But I will say that after starting from a baseline of thinking everything is highly heritable, I learned a lot from reading Gusev, e.g. about some of the weaknesses of existing twin studies. So I think he provides some useful skepticism.
Sorry to question the hypothetical when you specifically said not to, but I'm curious and know nothing about this field: does the simplifying assumption of asexual reproduction really not matter at all? Seems like it should!
Maybe you could also do it by assuming the gene is on the y-chromosome, near-starvation is determined by fathers, and only manifests for baby boys. But... still seems like a distraction!
Oh, it certainly matters, because with sexual reproduction you can't think about people as having "tall" or "short" genes, but you have to consider lots of cases: Each parent and the baby can basically be SS, ST, TS or TT, so there are 4^3=64 cases to worry about instead of just four.
You can create an example where the same issue manifests while reflecting all that, but I wasn't able to figure out a way to do it without making everything much more complex. (At least, not other than my other fix of perfect assortative mating.)
Interesting, are the pairs symmetric? Like does it matter which come from which side?
The copy article on your site has a duplicate question for
> Say there’s an island where neither genes nor the environment influence height. Except, some people have a gene that makes them inject their babies with human growth hormone, which makes them 5 cm taller. How heritable is height?
Thanks, fixed! (I think I was moving this around and debating the right order.)
Yes, similarly the table on short and tall genes registers correctly on the main website but not this substack post. Here it's like:
Baby genes Parent genes Food Height Short Short Lots 165 cm Short Tall Semi-starvation Less than 165 cm Tall Short Lots More than 165 cm Tall Tall Semi-starvation 165 cm
But all-in-all thanks Dynomight for this article! I love to see this kind of stuff.
Thanks fixed. (Substack somehow still doesn't support tables, so I need to copy-paste them as images, which I apparently often fail to do correctly.)
Thank you! I have classical Ehlers Danlos Syndrome, and it's always been described as heritable. The definition I was working with was "present at birth" which is clearly not accurate. This makes a lot more sense. In all but one of the types of EDS, a mutation happens to one of the collagen genes, which makes connective tissue, like tendons, skin, and other soft tissue weak. I've always held the belief that there's little you can do to change or strengthen the collagen. If you have the mutation, and even if you're born in Asia, to parents who are deaf, or are adopted by parents without EDS; even if you take ballet classes as a child, are educated in 4 different languages, or grow up next to a nuclear power plant; even if you have surgery to fix a tendon, take collagen supplements, or do aquatic therapy every day, the 👏🏻 collagen 👏🏻 will 👏🏻 still 👏🏻 be 👏🏻 defective because the environment change doesn't matter. There are things we can do about the *symptoms* the weak collagen and connective tissue cause, like pain, hypermobile joints, GI troubles, etc. But unless we edit the gene, the condition will exist.
Did I explain that correctly?
Sorry to hear about that! I don't know much about EDS, but what I do know is consistent with what you said, treatment is supportive and can reduce symptoms.
In the context of this essay, the only point I would make is that it doesn't follow simply from the technical definition of heritability that lifestyle changes can't improve things. Even if something is >99% heritable, that only means that *normal* lifestyle changes probably don't have much impact. But it doesn't prohibit the possibility that more unusual lifestyle changes could do something.
Anyway, we know lots about the causal mechanisms of EDS, and lots of interventions have been studied. So I think there's no reason to rely on the very crude measure of statistical heritability. It basically adds nothing when we already have studies of interventions.
Also, it's quite possible that when people say it's "heritable" they're using the normal English "heritable" rather than the technical ratio-based "heritable". That collision causes endless unnecessary confusion and is what I was complaining about here: https://dynomight.net/heritable/#:~:text=egregious
Hmm. Here is a true story. I was adopted at birth by young nitwits who successfully hid all the details of my birth until I was old enough to ask questions. The birth mother went into the hospital with the adoptive mother's name, so my birth certificate was phony. From a very young age, I "knew" that I was in the wrong tribe despite the superficial similarities in appearance [same skin color etc]. I knew how to read well before formal schooling began without being taught. The tribe didn't value that and refused requests to go to the public library after I had read most of what was available in the school library. The tribe's motto, "People like us don't...fill in the blank". I heard this often about so many things: read books, magazines, watch the news, go to college, talk about 'things', ask questions, learn to speak other languages, and on and on. Eventually, compassionate public school teachers tried to get me into college at age 15, but the tribe refused to cooperate because people like us...don't. Finally a tribal member told me the story of the illegal adoption, and I understood-of course I didn't fit in this tribe. It was like the egg of a swimming bird had been put in a chicken's nest. The chicken would never understand why one of the chicks was able to swim-heritability. I wasn't from them, didn't have to struggle to be one of them. I swam away. Later in a college genetics class, I understood more but was still tribeless. From this personal experience/small sample size, I think that heritability is everything. The environment is not nothing, but the math doesn't work.
Thank fuck, I was gonna write a post on this but now I can just link this. Wonderful. Mainly for the reason of pointing out that high heritability doesn’t imply that traits can’t be intervened on.
A good way of doing this is just pointing out muscle mass and strength have really high heritability, but going through the actual definitions is ideal!
Ah, perhaps I should have used that as an example! I'd guess that some non-negligible fraction of the heritability of muscle mass is driven by personality differences, which are in turn driven by genes. Genes that drive you towards exercise or a physical work will tend to make you stronger even though those are choices. So if you're choosing if you want to exercise it's completely irrelevant.
Agreed, I wonder if there has been research on that specifically? Heritability of inclination to exercise. Probably somewhere
I’ve read that the tendency to be an active adult (where active = regular participation in sport/gym attendance/etc) has strong heritability, and results in about 25% of adults engaging in said activities, and the rest being notably less inclined to do so - but perhaps still responsive to other factors, like the fun and sociability of team sports, and/or local cultural value of same. I often ponder this when I see advertising which encourages adults to be active - will pulling that environmental lever make a difference for the 75%?
heritability from twin studies seems to be around .5 at the highest, often lower
Excellent breakdown.
Shame that genetic variances in height are so controversial that it takes real bravery to talk about it in polite society.