One quick piece of semantic and linguistic housekeeping for the commenters…
Heritable != Molecular / Genetic Mechanism
There is a conflation of these terms in popular discourse that does a disservice to the field of statistical genetics, imo. There are mechanisms of inheritance that operate various length / time scales other than that of biological macromolecules. For example, if you tell me what language your parents natively speak I can tell you your primary language with >90% accuracy.
So before we start getting 3 replies deep into any thead, please remember that retrospective observational data measured with unqualified instruments is notoriously confounded and that we can barely infer causal structure in controlled functional genomics experiments (much less a GWAS of phewas). So let’s all please keep an open mind and not be so certain about our beliefs.
> For example, if you tell me what language your parents natively speak I can tell you your primary language with >90% accuracy.
According to the link above, the heritability of the primary language is zero, whereas the heritability of what language(s) a person speaks in general (whether primary or secondary) is not necessarily zero and varies by language.
This comment reads as if it were dropped into a generic "genetics of lifespan" thread,. The Dynomight article is already making a much more sophisticated version of some of these same points. The article's central argument is precisely that heritability is a contingent observational statistic, not a Platonic form. This particular article isn't conflating heritability with genetic mechanism at all. It's interrogating a simulation model and its assumptions. The warning about "unqualified instruments" and "retrospective observational data" feels off as this paper isn't a straightforward observational study. it's a parametric simulation fitted to twin registry data.
This comment might be very useful in a Reddit thread full of people saying "50% of lifespan is in your DNA," but it's a bit off-target as a response to this particular article.
The accurate version of the result would be something like: “if you model lifespan as aging + i.i.d. noise and dial the noise to zero, heritability of the aging component is ~40-50% in our model.” Which is barely a finding, since by construction reducing i.i.d. noise has to increase heritability of whatever non-noise remains.
This would require an accurate definition of ageing. What is ageing? How is it related to life span? Because in theory, there can be definitions of ageing that are not tied to life span. For instance, do bacteria age? Does this affect life span? What is the life span of a bacterium anyway? Does hydra age? (For those who don't know much about biology: literally everything ages, if you define ageing as functional decline over time. Even viruses would age, if you define it as functional infections possible plotted over time. Does DNA and RNA age? The definitions become blurry; almost no molecule is immune to changes and modifications, so just about anything would age. So it really depends on the definition, and we need to read the definition before we can accept assumptions based on it. Thus: what is ageing and how does it relate to lifespan, as definition?)
I believe that your example of "what language your parents natively speak" is incorrect.
Some ways of measuring heritability would have trouble detecting this as environmental, but that is considered a deficiency in those measures, not part of the definition of heritability. Any serious study into heritability of language would quickly find it is largely due to the common environment.
Heritability has a very specific meaning in quantitative genetics [1], which in many ways is not what your intuition would suggest [2]. It is this usage that the article talks about that.
That said, there are plenty of critiques of this definition of heritability, and not just because it is different from what a layperson would expect it to mean.
For example, the way it is used also usually has a big problem in that the standard formula assumes that Cov(G, E) = 0 (or at least is negligible), whereas in practice that is not actually true [3, 4].
This definition of heritability is also mathematically flawed in that it assumes (without evidence) that P = G + E, or at least can be reasonably approximated this way. Given that human development is the result of a feedback loop involving genetic and environmental factors, one would expect a model closer to something like a Markov chain. Proposed justifications of a simple additive model as an approximation (e.g. via the central limit theorem for highly polygenic traits) have to my knowledge never been tested.
More recent genome-wide association studies [5] have actually shown a considerable gap between heritability estimates from genotype data and heritability estimates from twin studies, known as the "missing heritability problem".
OP has another post on the definition of heritability, which I really liked: https://dynomight.net/heritable/ . I'm a layman, though, so since you seem knowledgeable, I would love to hear your thoughts on that article!
For instance, OP's definition H = Var[G] / Var[P] seems to bypass the issues you mentioned:
> For example, the way it is used also usually has a big problem in that the standard formula assumes that Cov(G, E) = 0 (or at least is negligible), whereas in practice that is not actually true [3, 4].
> This definition of heritability is also mathematically flawed in that it assumes (without evidence) that P = G + E, or at least can be reasonably approximated this way.
> Heritability has a very specific meaning in quantitative genetics [1]
Literally the first paragraph of that page is
> Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"
That matches what I assumed it meant, and it seems like OP and the post are arguing that that is some kind of surprising interpretation.
> OK, but check this out: Say I redefine “hair color” to mean “hair color except ignoring epigenetic and embryonic stuff and pretending that no one ever goes gray or dyes their hair et cetera”. Now, hair color is 100% heritable. Amazing, right?
Uhm, no. That is exactly what I (and I think most people) would expect the answer to be.
> That matches what I assumed it meant, and it seems like OP and the post are arguing that that is some kind of surprising interpretation.
The unintuitive part is that in quantitative genetics, heritability is defined in terms of variance in traits at the population level, not as the passing of traits from parents to offspring (that would be heredity [1]). Of course, I may have misinterpreted what you said in your OP when you cited the wiktionary definition of "[g]enetically transmissible from parent to offspring", and if so, I apologize, but at the time it seemed to me that you were talking about heredity.
> Uhm, no. That is exactly what I (and I think most people) would expect the answer to be.
What the article is talking about is that if you fix Var(E) = 0, then Var(P) = Var(G) in the standard heritability model, i.e. all phenotypic variance is explained entirely by genotypic variance (because in that model, Var(P) = Var(G) + Var(E)).
Fun fact (even if only tangentially unrelated): In Western countries, wearing glasses is a highly heritable trait, because wearing glasses is a strong proxy variable for refractive error [2], such as nearsightedness, which is highly heritable. It is often brought up as another example of how the quantitative genetics definition does not match conventional use of the word.
The heritability statistic that occurs in the literature is the ratio of genetic variance to phenotypic variance.
Two corrollaries:
* When discussing heritability results from the literature, we are discussing that statistic, not your intuitive understanding of what the word should mean.
* In the scientific literature, your conception of heritability doesn't operate. In the scientific sense, the number of hands you have has low heritability, despite being genetically determined.
I think you're going to find "let's check Wiktionary" is not the decisive move in these kinds of discussions that it is elsewhere.
Another great example of the unintuitiveness of heritability is the fact that earrings are highly heritable. Earrings are highly correlated to a specific genetics (being female), so they're very "heritable", even though that correlation is an arbitrary cultural fashion.
I heared the same distinction as OP, but it is the other way around, it's the degree to what a trait is inherited from you parents which cannot be explained by the enviroment or Random Chance.
There is a genetic component to alcohol use disorder, for example. But if one is in an environment where there is no access to alcohol whatsoever, then that person, despite their genes, will not develop an alcohol use disorder. The disorder can still be passed from parent to child, but it's more complicated than just genes.
What you're expecting heritability to mean is essentially "are genes responsible for expressing this trait", which is very different from "can I get this trait from my parents?" which does not impose any particular method for passing on the trait.
If the study doesn't use sequenced genes of parents and children as input into the model, it can't make the distinction between genetic or non genetic influence by parents.
That is exactly wrong. The measure of heritability used in the scientific literature is very much tied to genetics, just not in a very direct way. That is, heritability is a measure of how much of the variance in a trait is explained by genetics vs environment. In this sense, wealth will have a relatively low heritability, because it is weekly tied to genetics, even though it is very much a trait most people inherit from their parents. Skin color will have a high heritability, because the variance in skin color is almost entirely explained by genetics.
The unintuitive part is that traits with almost no genetic variance at all, such as the number of arms, have very low heritability - since, in a population study, almost the entire variance in the number of arms will be explained by environmental factors (very very few families have 1 or 3 arms as a recurring trait - and there are way more people who lose their arms during life).
"Welcome to science hell, professor. This is IshKebab, he once saw something on the internet about your field of expertise and is going to spend eternity lecturing you on it."[1]
"How heritable is hair color? Well, if you’re a redhead and you have an identical twin, they will definitely also be a redhead."
So, red hair is primarily caused, in most cases, by a defective enzyme involved in pigmentation. Wikipedia mentions it: https://en.wikipedia.org/wiki/Red_hair - you can read up on pubmed for that https://pubmed.ncbi.nlm.nih.gov/10326071/ and more recent articles. Now why is the claim "identical twins" must be redhaired? First it assumes that identical twins are fully identical on the genetic level. This is not the case, there are many differences. Statistically these are, of course, much less than when you compare many different people to one another usually. So it can be assumed that in most cases the "identical" twins (a better term would be monozygotic; note that even wikipedia here https://en.wikipedia.org/wiki/Twin defines the word incorrectly. Monozygotic does not say ANYTHING about "identical". Mono means one; zygotic means "from the zygote" or "derived from the zygote"). Of course in most cases the genes, if compared 1:1, will be identical. But this is not always the case, and it also depends a lot on the mutation at hand (or rescue mutations - see genetic cosuppression). So it COULD be that identical twins are NOT both redheads. One possibility is a simple spontaneous mutation at a nucleotide position that could restore functionality of at the least one enzyme mentioning above with regard to pigmentation. During DNA replication errors can also happen. The rate of error creation may be low for many reasons, but it is above zero, so it could happen.
That problem in the article could have been avoided if he would have chosen something else other than "they will definitely also be a redhead". Other users here on Hackernews also pointed out other incorrect or incomplete statements or assumptions made. This also ties into "definitions". Ultimately there is a much easier definition first: define max age span and average age span of cohorts. Then you need to define heritability with this regard. The claim of "more or less life span" when heritability is redefined, means that someone did a very poor, sloppy job beforehand already.
> Almost all human traits are partly genetic and partly due to the environment and/or random. If you could change the world and reduce the amount of randomness, then of course heritability would go up.
There has been a lot of effort to determine systematic environmental factors that would influence things like intelligence and while it's easy to do harm (lead exposure) it's all but impossible to do any good.
It implies that the only environment that matters is either purely random (truly random accidents, circumstances) or non-systematic (results from non-linear interaction of environment and genes).
When stated that way it almost feels like a tautology because this is what genes exist to do in the first place. To control the interactions of their vessel and environment to the maximum degree. And from the perspective of an individual gene, all the other genes are part of the environment too.
> There is no such thing as “true” heritability, independent of the contingent facts of our world.
It's uncomputable (need to run Monte Carlo simulations on a human life). All efforts are to approximate it.
What you're saying is completely accurate, but I'd add that it's all relative. Are you falling towards the ground, or is the ground falling towards you? For instance malnutrition lowers IQ, in both directions. There is an inverse correlation between IQ and BMI, but what's most interesting is that that correlation has maintained just as strong even as obesity rates skyrocketed, which is suggestive that there's probably something causal, in some direction, somewhere in there.
And so in modern times if it turns out that eating less than most people apparently want to contributes to IQ, are you doing something good by eating less, or are they doing something bad by eating more? I think it's basically the same thing, just looked at in different ways.
Or are smarter people better able to regulate their food intake? (Either innately, or because society gives them other privileges which makes them less likely to overeat)
I would say, that on the whole, this has to do with habituated impulse control and self-restraint.
Classical writers speak of this as well, things like how inordinate and undisciplined appetites (not just for food, mind you; sex, too, and undue acquisitiveness of all sorts, for instance) darken the mind. What is inordinate and undisciplined is not proportioned or directed by reason. So, such character traits are rooted in fidelity to reason which means that not only do they avoid the aforementioned darkening of the mind by moderation of appetite, but the very character strength of being able to do so enables rational existence in other things.
Innate intelligence doesn't secure discipline. Indeed, it gives the person a bigger footgun and allows for more elaborate rationalizations of vice.
Which then begs the question, what is IQ actually measuring - something more like innate intelligence, or a fairly big slice of learned, habituated test-taking ability?
Regardless of what underlying trait it's actually measuring, the habituation factory is a big component of its supposed bias - that is, has your background taught you the kind of problem-solving habits that will help you to post the best possible score?
> Which then begs the question, what is IQ actually measuring - something more like innate intelligence, or a fairly big slice of learned, habituated test-taking ability?
> "It is a variable that summarizes positive correlations among different cognitive tasks, reflecting the assertion that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks."
In other words people who are good at these tests are also good at real world tasks. Meaning IQ measures much more than one's ability to pass an IQ test. There are of course many examples of poorly structured IQ tests (including people re-taking the same IQ test and doing better at it the second time around). However a well-structured IQ test presenting novel questions (absent popular culture references and trivia) provides a very good approximation of the g factor in almost all cases. This means high IQ is highly correlated with things like income, unemployment, crime, homelessness, addiction, divorce, and many other objectively measurable life outcomes.
There is room for a philosophical debate about what g factor is, but it is beyond contest at this stage that g factor is real, and IQ almost always does a very good job of measuring it.
> which is suggestive that there's probably something causal, in some direction, somewhere in there.
Perhaps suggestive, but far from conclusive (I know you know this too). To me, it is suggestive that there is likely some other factor that may explain the relationship better, but then again, I am wrong more often than right, so what do I know? ;)
For example, compare that to growing wealth inequality, and I wouldn't be surprised if that is a potential factor. Less income = less access to care, less access to healthier food options, perhaps less time to for self-care, etc., and if wealth/career potential is gatekept by academic achievement, economic utility, or intelligence, then I can see the two, intelligence and BMI, being correlated, but not directly causal. Though, no study would give people large sums of money to improve their lives, so I doubt we will know for certain.
The point is not that it is something hard to compute that we can only approximate. The point is that there is no well-defined heritability independent of the environmental distribution.
> while it's easy to do harm (lead exposure) it's all but impossible to do any good.
That's just a meaningless statement no different from "while it's easy to subtract negative numbers, it's all but impossible to add positive numbers."
> or non-systematic (results from non-linear interaction of environment and genes).
Non-linear interaction does not mean non-systematic. Computer programs are fully deterministic (and therefore "systematic") while being non-linear (and therefore generally unpredictable). It is true to say that when things are non-linear it's hard to tell with certainty what effect some policy will have, but given that most human systems are non-linear, this is true for just about everything.
This is demonstrably untrue. IQ has increased consistently for decades, far faster than genetic factors can explain. Environmental factors like education, nutrition, and medical care are the obvious explanation.
This also assumes that IQ testing has remained static. It has not. IQ tests continue to evolve and there are >1 of them and they do not all agree. I.E. the tests themselves might be responsible for some of the variance.
> At the elite level, marathon performance is defined by energy availability as much as physiology.
> Maintaining a pace of 2:50 per kilometer requires a constant supply of fuel. Even small disruptions in energy delivery can result in significant time loss.
coppsilgold is the one who made a hard-line, clear-cut dichotomy when they said "it's easy to do harm [but] it's all but impossible to do any good". bglazer referenced several interventions that are known to increase IQ which challenge this dichotomy. Saying that it is difficult to separate "doing good" and "stop doing harm" is agreeing with the point that coppsilgold created a distinction without a difference.
it's hard to separate IQ decreasing and return to mean with IQ stabilizing
in 20th century most of the world moved past famine and toxins - did any factor of similar scale happen in 21st century as well to start looking for opposite processes?
The standard biology formula for heritability is h = Var(genetic) / Var(phenotypic)
Which I bet is very useful for some kind of technical work, but it's amusingly confusing to lay people.
The author goes on to critique its misuses but the textbook example to make clear "heritability" is not as obvious as it sounds is that by this definition human bipedalism heritability is near zero because there's near zero variance.
It's at odds with "heritable or not", the interesting question to us peasants. If there's a disease that gives you spots, we want to know if you can get it from your ma and pa. We don't want to know that nearly everybody hides the spots with makeup.
Then there's the matter of whether there's just a small population with the genes for it, and whether it's polygenic, or mitochondrial, or otherwise non-mendelian, and all that gets factored into this heritability value along with cultural things like the use of concealer and the probability of having your face torn off by a bear. It kind of reminds me of inflation, as a useful measure.
You can see why this is so frustrating for laypersons, but the point isn't that you can't use a colloquial meaning of the word when shooting the shit with your friends or whatever. It's just important to keep the rigorous definition separated from the informal definition when citing the literature, or you end up in weird places.
thinking about how to communicate it in a clear way. “the control knobs of what actually makes us different from one another” — you don’t expect one of your kids to be quadripedal. otoh this doesn’t really capture the precise notion either.
This is an example of how twins give us information when one variable is fixed - genetics. Can reciprocal information be found when observing the opposite: adoptees who share no genetic base but had the same upbringing in the same environment?
> Heritability of human lifespan is about 50% when extrinsic mortality is adjusted to be closer to modern levels.
I think by “accounting for confounding factors” they mean setting extrinsic mortality to the equivalent of zero contribution. So you’d expect it to be the asymptote left side.
0: especially enjoyed talking about typos and then writing “doing to go”. I like little jokes like that.
The original paper and this post basically seem to agree on one point: in a scientific sense, the term heritability is hopelessly overloaded and as a result having a coherent discussion about the genetic and environment influences on phenotype/organism characteristics, including lifespan, is impossible with current terminology.
Identical twins have the same DNA. Any differences between the 2 of them is not genetic. Studies of twins are very important when you try to separate "nature vs nurture".
An evolutionary biology professor of mine—a renowned and outspoken if often inscrutable guy—liked to say, facetiously, "everything is 50% heritable." I think he was getting at something along these lines.
The Dutch have been both the shortest and tallest population in Western Europe in the past 300 years. I've never found a satisfactory explanation for how this can be, if heritability figures for human height (and weight, and IQ, and-) are correct.
My intuition is that the average genetic human potential, for traits that are ostensibly hierarchical, is higher and narrower than is usually accepted - which is uncomfortable for those whose ambitions require, either directly or by incidence, that most people don't reach that potential. Or, that they're not actually hierarchical traits at all; value depends on context (and is generally made up).
Oddly, the former is probably preferable to most, since, "There is no inherent value in dying old versus young," probably doesn't track for most people.
The belabored point of the article is that heritability isn't fixed. In the past there were highly variable rates of malnutrition which created a major environmental factor for height, as well as many other traits, which would reduce their heritability. But as malnutrition faded and most environmental factors that significantly affect height faded, differences in populations became increasingly determined by genetics, and so its heritability increased.
You don't find better nutrition and sexual selection for height satisfactory?
> value depends on context (and is generally made up).
Value is not relative. It is objective, ontological, and teleological. Context only shifts situational value relevance, but the value itself remains as is.
>You don't find better nutrition and sexual selection for height satisfactory?
A few centuries aren't long enough for such marked selective pressure on a polygenic trait.
>Value is not relative. It is objective, ontological, and teleological.
I am conflating objective measurements (value) with subjective situational qualifications of the relevance of those measurements (also "value", kinda) because most people understand that I mean the latter. I acknowledge your pedantic correction of this conflation; please feel good about yourself and move on with your day.
"A few centuries aren't long enough for such marked selective pressure on a polygenic trait."
Are you sure? In extremis, if blue-eyed people (a polygenic trait) are considered absolutely unfuckable, I would expect them to disappear from the population in 10-15 generations, or at least become very, very rare.
Seems like the author is doing some redefining here like he's accusing the paper's author.
Perhaps the statement was meant to mean "fulfillment of hereditary characteristics change when society changes" but it wouldn't be that hard to say it if that's what it was supposed to be...
Heritability is the proportion of variance in a trait that can be ascribed to genetics. So if you increase or decrease the total variance in the population u change heritability by definition. Eg. Split the pop in half and give one half less food - that half will be smaller (eg shorter in humans) and variance will increase thus the heritability will necessarily decrease.
Yeah, it's not immediately obvious, but if we created perfect utopia where conditions are ideal, perfectly matched for given individual, heritability would be 0%.
> OK, but check this out: Say I redefine “hair color” to mean “hair color except ignoring epigenetic and embryonic stuff and pretending that no one ever goes gray or dyes their hair et cetera”. Now, hair color is 100% heritable. Amazing, right?
It seems incredibly disingenuous to lump together epigentics and hair dye when talking about heritability of hair color. We all know when we talk about inheriting hair color we're talking about natural hair color.
> his paper built a mathematical model that tries to simulate how long people would live in a hypothetical world in which no one dies from any non-aging related cause, meaning no car accidents, no drug overdoses, no suicides, no murders, and no (non-age-related) infectious disease.
Which is exactly what everyone means by lifespan in this context. No one on earth is trying to figure out how much genetics contributes to the odds of being hit by a bus.
> veryone seems to be interpreting this paper as follows:
>> Aha! We thought the heritability of lifespan was 23-35%. But it turns out that it’s around 50%. Now we know!
Which is the correct interpretation. Proper elimination of confounding factors is good science. The previous estimates were low because they weren't properly measuring what we are all referring to when we talk about lifespan.
This misses half the problem, which is that there aren't many intrinsic traits people care about. Your height is as biological a thing as anything else, but it's tied to your environment in the same sense as hair color. That's the point the author is making: that's it's difficult to deconfound these things, and that when we discuss "heritability", as a statistic that appears in the literature, we've always talking about confounded measures.
> Your height is as biological a thing as anything else, but it's tied to your environment in the same sense as hair color.
And you wouldn't draw a distinction between the person who is short because of poor diet and the person who is short because they lost their legs in a car accident? Both are "environmental factors" which affect the distance between the top of your head and the ground, but that's not what we are referring to by height.
> we've always talking about confounded measures.
No, we haven't. It doesn't matter that confounding factors exist in the data, we can and near exclusively do talk about abstract concepts. We live in a world where there are no perfect circles, but we can talk about things having diameters. We live in a world where people die from unnatural causes, but we can still talk about people having natural lifespans. That removing confounding factors is hard doesn't change the fact we routinely make our best effort to do just that because it is necessary for discussing the abstract concept we all refer to.
One quick piece of semantic and linguistic housekeeping for the commenters…
Heritable != Molecular / Genetic Mechanism
There is a conflation of these terms in popular discourse that does a disservice to the field of statistical genetics, imo. There are mechanisms of inheritance that operate various length / time scales other than that of biological macromolecules. For example, if you tell me what language your parents natively speak I can tell you your primary language with >90% accuracy.
So before we start getting 3 replies deep into any thead, please remember that retrospective observational data measured with unqualified instruments is notoriously confounded and that we can barely infer causal structure in controlled functional genomics experiments (much less a GWAS of phewas). So let’s all please keep an open mind and not be so certain about our beliefs.
OP has another post on the definition of heritability, which I really liked: https://dynomight.net/heritable/
> For example, if you tell me what language your parents natively speak I can tell you your primary language with >90% accuracy.
According to the link above, the heritability of the primary language is zero, whereas the heritability of what language(s) a person speaks in general (whether primary or secondary) is not necessarily zero and varies by language.
This comment reads as if it were dropped into a generic "genetics of lifespan" thread,. The Dynomight article is already making a much more sophisticated version of some of these same points. The article's central argument is precisely that heritability is a contingent observational statistic, not a Platonic form. This particular article isn't conflating heritability with genetic mechanism at all. It's interrogating a simulation model and its assumptions. The warning about "unqualified instruments" and "retrospective observational data" feels off as this paper isn't a straightforward observational study. it's a parametric simulation fitted to twin registry data.
This comment might be very useful in a Reddit thread full of people saying "50% of lifespan is in your DNA," but it's a bit off-target as a response to this particular article.
I think the comment is speaking to the thread, not responding to the author.
The accurate version of the result would be something like: “if you model lifespan as aging + i.i.d. noise and dial the noise to zero, heritability of the aging component is ~40-50% in our model.” Which is barely a finding, since by construction reducing i.i.d. noise has to increase heritability of whatever non-noise remains.
This would require an accurate definition of ageing. What is ageing? How is it related to life span? Because in theory, there can be definitions of ageing that are not tied to life span. For instance, do bacteria age? Does this affect life span? What is the life span of a bacterium anyway? Does hydra age? (For those who don't know much about biology: literally everything ages, if you define ageing as functional decline over time. Even viruses would age, if you define it as functional infections possible plotted over time. Does DNA and RNA age? The definitions become blurry; almost no molecule is immune to changes and modifications, so just about anything would age. So it really depends on the definition, and we need to read the definition before we can accept assumptions based on it. Thus: what is ageing and how does it relate to lifespan, as definition?)
I believe that your example of "what language your parents natively speak" is incorrect.
Some ways of measuring heritability would have trouble detecting this as environmental, but that is considered a deficiency in those measures, not part of the definition of heritability. Any serious study into heritability of language would quickly find it is largely due to the common environment.
> Heritable != Molecular / Genetic Mechanism
Hmm let me just check Wiktionary for "heritable"
> Genetically transmissible from parent to offspring
Ok then. Maybe it has some specific meaning in biology? A search for "heritable meaning in biology" let me to this page: https://www.cancer.gov/publications/dictionaries/cancer-term...
> In medicine, describes a characteristic or trait that can be passed from a parent to a child through the genes.
IMO this post is dumb and the paper is perfectly clear to non-pedants.
Heritability has a very specific meaning in quantitative genetics [1], which in many ways is not what your intuition would suggest [2]. It is this usage that the article talks about that.
That said, there are plenty of critiques of this definition of heritability, and not just because it is different from what a layperson would expect it to mean.
For example, the way it is used also usually has a big problem in that the standard formula assumes that Cov(G, E) = 0 (or at least is negligible), whereas in practice that is not actually true [3, 4].
This definition of heritability is also mathematically flawed in that it assumes (without evidence) that P = G + E, or at least can be reasonably approximated this way. Given that human development is the result of a feedback loop involving genetic and environmental factors, one would expect a model closer to something like a Markov chain. Proposed justifications of a simple additive model as an approximation (e.g. via the central limit theorem for highly polygenic traits) have to my knowledge never been tested.
More recent genome-wide association studies [5] have actually shown a considerable gap between heritability estimates from genotype data and heritability estimates from twin studies, known as the "missing heritability problem".
[1] https://en.wikipedia.org/wiki/Heritability
[2] https://en.wikipedia.org/wiki/Genetic_variance
[3] https://en.wikipedia.org/wiki/Gene%E2%80%93environment_inter...
[4] https://en.wikipedia.org/wiki/Gene%E2%80%93environment_corre...
[5] https://en.wikipedia.org/wiki/Genome-wide_association_study
OP has another post on the definition of heritability, which I really liked: https://dynomight.net/heritable/ . I'm a layman, though, so since you seem knowledgeable, I would love to hear your thoughts on that article!
For instance, OP's definition H = Var[G] / Var[P] seems to bypass the issues you mentioned:
> For example, the way it is used also usually has a big problem in that the standard formula assumes that Cov(G, E) = 0 (or at least is negligible), whereas in practice that is not actually true [3, 4].
> This definition of heritability is also mathematically flawed in that it assumes (without evidence) that P = G + E, or at least can be reasonably approximated this way.
> Heritability has a very specific meaning in quantitative genetics [1]
Literally the first paragraph of that page is
> Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"
That matches what I assumed it meant, and it seems like OP and the post are arguing that that is some kind of surprising interpretation.
> OK, but check this out: Say I redefine “hair color” to mean “hair color except ignoring epigenetic and embryonic stuff and pretending that no one ever goes gray or dyes their hair et cetera”. Now, hair color is 100% heritable. Amazing, right?
Uhm, no. That is exactly what I (and I think most people) would expect the answer to be.
> That matches what I assumed it meant, and it seems like OP and the post are arguing that that is some kind of surprising interpretation.
The unintuitive part is that in quantitative genetics, heritability is defined in terms of variance in traits at the population level, not as the passing of traits from parents to offspring (that would be heredity [1]). Of course, I may have misinterpreted what you said in your OP when you cited the wiktionary definition of "[g]enetically transmissible from parent to offspring", and if so, I apologize, but at the time it seemed to me that you were talking about heredity.
> Uhm, no. That is exactly what I (and I think most people) would expect the answer to be.
What the article is talking about is that if you fix Var(E) = 0, then Var(P) = Var(G) in the standard heritability model, i.e. all phenotypic variance is explained entirely by genotypic variance (because in that model, Var(P) = Var(G) + Var(E)).
Fun fact (even if only tangentially unrelated): In Western countries, wearing glasses is a highly heritable trait, because wearing glasses is a strong proxy variable for refractive error [2], such as nearsightedness, which is highly heritable. It is often brought up as another example of how the quantitative genetics definition does not match conventional use of the word.
[1] https://en.wikipedia.org/wiki/Heredity
[2] https://en.wikipedia.org/wiki/Refractive_error
The heritability statistic that occurs in the literature is the ratio of genetic variance to phenotypic variance.
Two corrollaries:
* When discussing heritability results from the literature, we are discussing that statistic, not your intuitive understanding of what the word should mean.
* In the scientific literature, your conception of heritability doesn't operate. In the scientific sense, the number of hands you have has low heritability, despite being genetically determined.
I think you're going to find "let's check Wiktionary" is not the decisive move in these kinds of discussions that it is elsewhere.
Another great example of the unintuitiveness of heritability is the fact that earrings are highly heritable. Earrings are highly correlated to a specific genetics (being female), so they're very "heritable", even though that correlation is an arbitrary cultural fashion.
I heared the same distinction as OP, but it is the other way around, it's the degree to what a trait is inherited from you parents which cannot be explained by the enviroment or Random Chance.
There is a genetic component to alcohol use disorder, for example. But if one is in an environment where there is no access to alcohol whatsoever, then that person, despite their genes, will not develop an alcohol use disorder. The disorder can still be passed from parent to child, but it's more complicated than just genes.
What you're expecting heritability to mean is essentially "are genes responsible for expressing this trait", which is very different from "can I get this trait from my parents?" which does not impose any particular method for passing on the trait.
If the study doesn't use sequenced genes of parents and children as input into the model, it can't make the distinction between genetic or non genetic influence by parents.
That is exactly wrong. The measure of heritability used in the scientific literature is very much tied to genetics, just not in a very direct way. That is, heritability is a measure of how much of the variance in a trait is explained by genetics vs environment. In this sense, wealth will have a relatively low heritability, because it is weekly tied to genetics, even though it is very much a trait most people inherit from their parents. Skin color will have a high heritability, because the variance in skin color is almost entirely explained by genetics.
The unintuitive part is that traits with almost no genetic variance at all, such as the number of arms, have very low heritability - since, in a population study, almost the entire variance in the number of arms will be explained by environmental factors (very very few families have 1 or 3 arms as a recurring trait - and there are way more people who lose their arms during life).
"Welcome to science hell, professor. This is IshKebab, he once saw something on the internet about your field of expertise and is going to spend eternity lecturing you on it."[1]
[1] https://www.tomgauld.com/shop/science-hell-print
the value of this number is different when you redefine how the number is calculated
Yep, checks out.
The article is not good, sorry.
For instance, it begins via:
"How heritable is hair color? Well, if you’re a redhead and you have an identical twin, they will definitely also be a redhead."
So, red hair is primarily caused, in most cases, by a defective enzyme involved in pigmentation. Wikipedia mentions it: https://en.wikipedia.org/wiki/Red_hair - you can read up on pubmed for that https://pubmed.ncbi.nlm.nih.gov/10326071/ and more recent articles. Now why is the claim "identical twins" must be redhaired? First it assumes that identical twins are fully identical on the genetic level. This is not the case, there are many differences. Statistically these are, of course, much less than when you compare many different people to one another usually. So it can be assumed that in most cases the "identical" twins (a better term would be monozygotic; note that even wikipedia here https://en.wikipedia.org/wiki/Twin defines the word incorrectly. Monozygotic does not say ANYTHING about "identical". Mono means one; zygotic means "from the zygote" or "derived from the zygote"). Of course in most cases the genes, if compared 1:1, will be identical. But this is not always the case, and it also depends a lot on the mutation at hand (or rescue mutations - see genetic cosuppression). So it COULD be that identical twins are NOT both redheads. One possibility is a simple spontaneous mutation at a nucleotide position that could restore functionality of at the least one enzyme mentioning above with regard to pigmentation. During DNA replication errors can also happen. The rate of error creation may be low for many reasons, but it is above zero, so it could happen.
That problem in the article could have been avoided if he would have chosen something else other than "they will definitely also be a redhead". Other users here on Hackernews also pointed out other incorrect or incomplete statements or assumptions made. This also ties into "definitions". Ultimately there is a much easier definition first: define max age span and average age span of cohorts. Then you need to define heritability with this regard. The claim of "more or less life span" when heritability is redefined, means that someone did a very poor, sloppy job beforehand already.
It implies that the only environment that matters is either purely random (truly random accidents, circumstances) or non-systematic (results from non-linear interaction of environment and genes).
When stated that way it almost feels like a tautology because this is what genes exist to do in the first place. To control the interactions of their vessel and environment to the maximum degree. And from the perspective of an individual gene, all the other genes are part of the environment too.
It's uncomputable (need to run Monte Carlo simulations on a human life). All efforts are to approximate it.What you're saying is completely accurate, but I'd add that it's all relative. Are you falling towards the ground, or is the ground falling towards you? For instance malnutrition lowers IQ, in both directions. There is an inverse correlation between IQ and BMI, but what's most interesting is that that correlation has maintained just as strong even as obesity rates skyrocketed, which is suggestive that there's probably something causal, in some direction, somewhere in there.
And so in modern times if it turns out that eating less than most people apparently want to contributes to IQ, are you doing something good by eating less, or are they doing something bad by eating more? I think it's basically the same thing, just looked at in different ways.
Or are smarter people better able to regulate their food intake? (Either innately, or because society gives them other privileges which makes them less likely to overeat)
I would say, that on the whole, this has to do with habituated impulse control and self-restraint.
Classical writers speak of this as well, things like how inordinate and undisciplined appetites (not just for food, mind you; sex, too, and undue acquisitiveness of all sorts, for instance) darken the mind. What is inordinate and undisciplined is not proportioned or directed by reason. So, such character traits are rooted in fidelity to reason which means that not only do they avoid the aforementioned darkening of the mind by moderation of appetite, but the very character strength of being able to do so enables rational existence in other things.
Innate intelligence doesn't secure discipline. Indeed, it gives the person a bigger footgun and allows for more elaborate rationalizations of vice.
Which then begs the question, what is IQ actually measuring - something more like innate intelligence, or a fairly big slice of learned, habituated test-taking ability?
Regardless of what underlying trait it's actually measuring, the habituation factory is a big component of its supposed bias - that is, has your background taught you the kind of problem-solving habits that will help you to post the best possible score?
> Which then begs the question, what is IQ actually measuring - something more like innate intelligence, or a fairly big slice of learned, habituated test-taking ability?
This question was asked and answered many decades ago in sociology. Researchers moved onto more interesting topics and fields. IQ tests measure g factor (https://en.wikipedia.org/wiki/G_factor_(psychometrics)).
> "It is a variable that summarizes positive correlations among different cognitive tasks, reflecting the assertion that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks."
In other words people who are good at these tests are also good at real world tasks. Meaning IQ measures much more than one's ability to pass an IQ test. There are of course many examples of poorly structured IQ tests (including people re-taking the same IQ test and doing better at it the second time around). However a well-structured IQ test presenting novel questions (absent popular culture references and trivia) provides a very good approximation of the g factor in almost all cases. This means high IQ is highly correlated with things like income, unemployment, crime, homelessness, addiction, divorce, and many other objectively measurable life outcomes.
There is room for a philosophical debate about what g factor is, but it is beyond contest at this stage that g factor is real, and IQ almost always does a very good job of measuring it.
> which is suggestive that there's probably something causal, in some direction, somewhere in there.
Perhaps suggestive, but far from conclusive (I know you know this too). To me, it is suggestive that there is likely some other factor that may explain the relationship better, but then again, I am wrong more often than right, so what do I know? ;)
For example, compare that to growing wealth inequality, and I wouldn't be surprised if that is a potential factor. Less income = less access to care, less access to healthier food options, perhaps less time to for self-care, etc., and if wealth/career potential is gatekept by academic achievement, economic utility, or intelligence, then I can see the two, intelligence and BMI, being correlated, but not directly causal. Though, no study would give people large sums of money to improve their lives, so I doubt we will know for certain.
The point is not that it is something hard to compute that we can only approximate. The point is that there is no well-defined heritability independent of the environmental distribution.
There's no well defined "a rock too heavy for a person to lift" too, but we manage. So, what's the point?
> while it's easy to do harm (lead exposure) it's all but impossible to do any good.
That's just a meaningless statement no different from "while it's easy to subtract negative numbers, it's all but impossible to add positive numbers."
> or non-systematic (results from non-linear interaction of environment and genes).
Non-linear interaction does not mean non-systematic. Computer programs are fully deterministic (and therefore "systematic") while being non-linear (and therefore generally unpredictable). It is true to say that when things are non-linear it's hard to tell with certainty what effect some policy will have, but given that most human systems are non-linear, this is true for just about everything.
This is demonstrably untrue. IQ has increased consistently for decades, far faster than genetic factors can explain. Environmental factors like education, nutrition, and medical care are the obvious explanation.
This also assumes that IQ testing has remained static. It has not. IQ tests continue to evolve and there are >1 of them and they do not all agree. I.E. the tests themselves might be responsible for some of the variance.
how does one separate "doing good" and "stop doing harm"?
I'd personally count nutrition squarely in the second category
The recent marathon world records are apparently due to improved nutrition.
Here's the producer of the hydrogels talking about the exact process of getting the maximum carbohydrates into the runner:
https://maurten.no/blogs/m-magazine/how-sabastian-sawe-fuele...
> At the elite level, marathon performance is defined by energy availability as much as physiology.
> Maintaining a pace of 2:50 per kilometer requires a constant supply of fuel. Even small disruptions in energy delivery can result in significant time loss.
coppsilgold is the one who made a hard-line, clear-cut dichotomy when they said "it's easy to do harm [but] it's all but impossible to do any good". bglazer referenced several interventions that are known to increase IQ which challenge this dichotomy. Saying that it is difficult to separate "doing good" and "stop doing harm" is agreeing with the point that coppsilgold created a distinction without a difference.
Also we are past that. Now IQ started decreasing.
it's hard to separate IQ decreasing and return to mean with IQ stabilizing
in 20th century most of the world moved past famine and toxins - did any factor of similar scale happen in 21st century as well to start looking for opposite processes?
Generally that statistic refers to populations in isolation, not the entire world in aggregate.
It is fairly well agreed upon that American kids across the nation are currently testing lower than they were in 2010.
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The standard biology formula for heritability is h = Var(genetic) / Var(phenotypic)
Which I bet is very useful for some kind of technical work, but it's amusingly confusing to lay people.
The author goes on to critique its misuses but the textbook example to make clear "heritability" is not as obvious as it sounds is that by this definition human bipedalism heritability is near zero because there's near zero variance.
It's at odds with "heritable or not", the interesting question to us peasants. If there's a disease that gives you spots, we want to know if you can get it from your ma and pa. We don't want to know that nearly everybody hides the spots with makeup.
Then there's the matter of whether there's just a small population with the genes for it, and whether it's polygenic, or mitochondrial, or otherwise non-mendelian, and all that gets factored into this heritability value along with cultural things like the use of concealer and the probability of having your face torn off by a bear. It kind of reminds me of inflation, as a useful measure.
You can see why this is so frustrating for laypersons, but the point isn't that you can't use a colloquial meaning of the word when shooting the shit with your friends or whatever. It's just important to keep the rigorous definition separated from the informal definition when citing the literature, or you end up in weird places.
thinking about how to communicate it in a clear way. “the control knobs of what actually makes us different from one another” — you don’t expect one of your kids to be quadripedal. otoh this doesn’t really capture the precise notion either.
This is an example of how twins give us information when one variable is fixed - genetics. Can reciprocal information be found when observing the opposite: adoptees who share no genetic base but had the same upbringing in the same environment?
Funny[0]. And cool. But I don’t think they mean:
> Heritability of human lifespan is about 50% when extrinsic mortality is adjusted to be closer to modern levels.
I think by “accounting for confounding factors” they mean setting extrinsic mortality to the equivalent of zero contribution. So you’d expect it to be the asymptote left side.
0: especially enjoyed talking about typos and then writing “doing to go”. I like little jokes like that.
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The original paper and this post basically seem to agree on one point: in a scientific sense, the term heritability is hopelessly overloaded and as a result having a coherent discussion about the genetic and environment influences on phenotype/organism characteristics, including lifespan, is impossible with current terminology.
I did not understand what is meant by heritability
Why is it applied to twins if genes are inherited from parent to child?
How readhedness is 100%? I understand Mendel study in school is simplification, but you can get all sorts of gene mixes in kids
> Why is it applied to twins
Identical twins have the same DNA. Any differences between the 2 of them is not genetic. Studies of twins are very important when you try to separate "nature vs nurture".
I highly recommend the author's other post https://dynomight.net/heritable/
An evolutionary biology professor of mine—a renowned and outspoken if often inscrutable guy—liked to say, facetiously, "everything is 50% heritable." I think he was getting at something along these lines.
A reminder to be cautious as semantics can be used to cherry pick the data. Which already happens in many aspects of day to day life.
The world is only understood by nuance, and we're not great at that.
h() for hazard, probably.
https://en.wikipedia.org/wiki/Gompertz_distribution
In an other news, someone is always 100% right, when being right is redefined aptly.
The Dutch have been both the shortest and tallest population in Western Europe in the past 300 years. I've never found a satisfactory explanation for how this can be, if heritability figures for human height (and weight, and IQ, and-) are correct.
My intuition is that the average genetic human potential, for traits that are ostensibly hierarchical, is higher and narrower than is usually accepted - which is uncomfortable for those whose ambitions require, either directly or by incidence, that most people don't reach that potential. Or, that they're not actually hierarchical traits at all; value depends on context (and is generally made up).
Oddly, the former is probably preferable to most, since, "There is no inherent value in dying old versus young," probably doesn't track for most people.
The belabored point of the article is that heritability isn't fixed. In the past there were highly variable rates of malnutrition which created a major environmental factor for height, as well as many other traits, which would reduce their heritability. But as malnutrition faded and most environmental factors that significantly affect height faded, differences in populations became increasingly determined by genetics, and so its heritability increased.
> I've never found a satisfactory explanation
You don't find better nutrition and sexual selection for height satisfactory?
> value depends on context (and is generally made up).
Value is not relative. It is objective, ontological, and teleological. Context only shifts situational value relevance, but the value itself remains as is.
>You don't find better nutrition and sexual selection for height satisfactory?
A few centuries aren't long enough for such marked selective pressure on a polygenic trait.
>Value is not relative. It is objective, ontological, and teleological.
I am conflating objective measurements (value) with subjective situational qualifications of the relevance of those measurements (also "value", kinda) because most people understand that I mean the latter. I acknowledge your pedantic correction of this conflation; please feel good about yourself and move on with your day.
"A few centuries aren't long enough for such marked selective pressure on a polygenic trait."
Are you sure? In extremis, if blue-eyed people (a polygenic trait) are considered absolutely unfuckable, I would expect them to disappear from the population in 10-15 generations, or at least become very, very rare.
"heritability depends on society"
Seems like the author is doing some redefining here like he's accusing the paper's author.
Perhaps the statement was meant to mean "fulfillment of hereditary characteristics change when society changes" but it wouldn't be that hard to say it if that's what it was supposed to be...
Heritability is the proportion of variance in a trait that can be ascribed to genetics. So if you increase or decrease the total variance in the population u change heritability by definition. Eg. Split the pop in half and give one half less food - that half will be smaller (eg shorter in humans) and variance will increase thus the heritability will necessarily decrease.
Yeah, it's not immediately obvious, but if we created perfect utopia where conditions are ideal, perfectly matched for given individual, heritability would be 0%.
> OK, but check this out: Say I redefine “hair color” to mean “hair color except ignoring epigenetic and embryonic stuff and pretending that no one ever goes gray or dyes their hair et cetera”. Now, hair color is 100% heritable. Amazing, right?
It seems incredibly disingenuous to lump together epigentics and hair dye when talking about heritability of hair color. We all know when we talk about inheriting hair color we're talking about natural hair color.
> his paper built a mathematical model that tries to simulate how long people would live in a hypothetical world in which no one dies from any non-aging related cause, meaning no car accidents, no drug overdoses, no suicides, no murders, and no (non-age-related) infectious disease.
Which is exactly what everyone means by lifespan in this context. No one on earth is trying to figure out how much genetics contributes to the odds of being hit by a bus.
> veryone seems to be interpreting this paper as follows:
>> Aha! We thought the heritability of lifespan was 23-35%. But it turns out that it’s around 50%. Now we know!
Which is the correct interpretation. Proper elimination of confounding factors is good science. The previous estimates were low because they weren't properly measuring what we are all referring to when we talk about lifespan.
This misses half the problem, which is that there aren't many intrinsic traits people care about. Your height is as biological a thing as anything else, but it's tied to your environment in the same sense as hair color. That's the point the author is making: that's it's difficult to deconfound these things, and that when we discuss "heritability", as a statistic that appears in the literature, we've always talking about confounded measures.
> Your height is as biological a thing as anything else, but it's tied to your environment in the same sense as hair color.
And you wouldn't draw a distinction between the person who is short because of poor diet and the person who is short because they lost their legs in a car accident? Both are "environmental factors" which affect the distance between the top of your head and the ground, but that's not what we are referring to by height.
> we've always talking about confounded measures.
No, we haven't. It doesn't matter that confounding factors exist in the data, we can and near exclusively do talk about abstract concepts. We live in a world where there are no perfect circles, but we can talk about things having diameters. We live in a world where people die from unnatural causes, but we can still talk about people having natural lifespans. That removing confounding factors is hard doesn't change the fact we routinely make our best effort to do just that because it is necessary for discussing the abstract concept we all refer to.