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.
> 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 seeing 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.
> 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 exists but is 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.
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.
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.
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.
> 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 seeing 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.
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 exists but is uncomputable (need to run Monte Carlo simulations on a human life). All efforts are to approximate it.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.
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.
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...