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.
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.
> 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.
> 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.
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 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.
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.
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.
> 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.
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.
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.
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.
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.
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 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.
h() for hazard, probably.
https://en.wikipedia.org/wiki/Gompertz_distribution
The world is only understood by nuance, and we're not great at that.
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.
"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.
> 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.