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 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.
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.
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.
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
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.
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.
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.
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.
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.
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).
> 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.
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.
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.
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.
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?
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.
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.
I'd personally count nutrition squarely in the second category
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.
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?
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.
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.
> 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.
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
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".
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.
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.
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.
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...
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.
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.