You seem to be making some very sweeping claims about heritability here. In what sense is ‘heritability not what I think’?
Do you seriously think that moderate heritability doesn’t say anything at all about how much genes matter, versus how much ‘non-agentic things can influence a trait’?
Heritability is not equivalent to “how much genes impact traits.” Kaj Sotala says it well here:
Caution: heritability, as in the statistical concept, is defined in a way that has some rather counter-intuitive implications. One might think that if happiness is 50% heritable, then happiness must be 50% “hardwired”. This is incorrect, and in fact the concept of heritability is theoretically incapable of making such a claim.
The definition of heritability is straightforward enough: the amount of genetic variance in a trait, divided by the overall variance in the trait. Now, nearly all humans are born with two feet, so you might expect the trait of “having two feet” to have 100% heritability. In fact, it has close to 0% heritability! This is because the vast majority of people who have lost their feet have done so because of accidents or other environmental factors, not due to a gene for one-footedness. So nearly all of the variance in the amount of feet in humans is caused by environmental factors, making the heritability zero.
Another example is that if we have a trait that is strongly affected by the environment, but we manage to make the environment more uniform, then the heritability of the trait goes up. For instance, both childhood nutrition and genetics have a strong effect on a person’s height. In today’s society, we have relatively good social security nets helping give most kids at least a basic level of nutrition, a basic level which may not have been available for everyone in the past. So in the past there was more environmental variance involved in determining a person’s height. Therefore the trait “height” may have been less hereditary in the past than now.
The heritability of some trait is always defined in relation to some specific population in some specific environment. There’s no such thing as an “overall” heritability, valid in any environment. The heritability of a trait does not tell us whether that trait can be affected by outside interventions.
Similarly, one hypothesis that can explain high heritability yet not result in the post’s implications being right is that the studies aren’t properly controlled. From habryka:
Most estimates for heritability would still be significant even in a genetically identical population (since cultural factors are heritable due to shared family environments). You can try to control for his with twin adoption studies, which controls for shared family environment, but still leaves a lot of different aspects of the environment the same. You could also adjust for all other kinds of things and so get closer to something like the ”real effect of genes”.
I am not fully sure what Donald Hobson meant by “effect of genes” but more generally heritability is an upper bound on the effect of genes on individuals, and we should expect the real effect to be lower (how much lower is a debate with lots of complicated philosophical arguments and people being confused about how causality works).
From Wikipedia:
In other words, heritability is a mathematical estimate that indicates an upper bound on how much of a trait’s variation within that population can be attributed to genes.
I think a problem here is regulation systems. There has been strong natural selection for having exactly 2 feet, meaning that many innate mechanisms have developed to keep that number consistent. This is what suppresses the heritability of number of feet; but these sorts of mechanisms are clearly much less active on many of the traits that geoffreymiller mentioned, as those traits have a lot more variance.
However, thinking about it, I suppose the regulation systems point could also be made with respect to culture: In many ways, culture acts to regulate people’s values; if someone misbehaves, then they will receive corrections so as to make them more aligned with the culture’s values. And I suppose that would, by the same logic, be expected to increase the heritability.
tailcalled—these issues of variance, canalization, quality control, etc are very interesting.
For example, it’s very difficult to understand why so many human mental disorders are common, heritable, and harmful—why wouldn’t the genetic variants that cause schizophrenia or major depression already have been eliminated by selection? Our BBS target article in 2006 addressed this.
Conversely, it’s a bit puzzling that the coefficient of additive genetic variation in human brain size is lower than might be expected, according to our 2007 meta-analysis.
In general, animal behavior researchers have found that even traits quite closely related to fitness (reproductive success) are still quite heritable, and still show significant genetic variance, even in ancestrally typical wild environments. So, the (initially plausible) view that evolution should always minimize genetic and phenotypic variance in important traits seems often incorrect—apart from situations like number of feet, where we do find extremely strong canalization on the biomechanically optimal design.
For example, it’s very difficult to understand why so many human mental disorders are common, heritable, and harmful—why wouldn’t the genetic variants that cause schizophrenia or major depression already have been eliminated by selection? Our BBS target article in 2006 addressed this.
I’ve read various discussions on this, e.g. Marco Del Giudice’s book. Just quickly skimming your article, you seem to be raising some of the same points that I saw in his book.
One question: isn’t the liability-scale heritability estimate the wrong value to use? Or at least, not straightforwardly the right one. I believe the effective heritability for the purposes of selection would roughly speaking be the prevalence times the liability-scale heritability, is that correct? So if e.g. schizophrenia has a liability heritability of 80% but a prevalence of 0.32%, that would lead to an effective heritability (for the purpose of selection) of 0.26%?
Conversely, it’s a bit puzzling that the coefficient of additive genetic variation in human brain size is lower than might be expected, according to our 2007 meta-analysis.
I’m not sure why this puzzle isn’t solved by births being a constraint?
In general, animal behavior researchers have found that even traits quite closely related to fitness (reproductive success) are still quite heritable, and still show significant genetic variance, even in ancestrally typical wild environments.
Two questions:
Could it be because they have not reached a local optimum with regards to reproductive success?
Could it be a collider/tradeoff thing? E.g. you can have a lot of offspring or you can invest a lot into the offspring you do have? So if you count the number of offspring, you don’t just get the fitness axis, but also for lack of a better word, the r-K axis.
It’s hard to know how to respond to this comment, which reveals some fundamental misunderstandings of heritability and of behavior genetics methods. The LessWrong protocol is ‘If you disagree, try getting curious about what your partner is thinking’. But in some cases, people unfamiliar with a field have the same old misconceptions about the field, repeated over and over. So I’m honestly having trouble arousing my curiosity....
The quote from habryka doesn’t make sense to me, and doesn’t seem to understand how behavior genetic studies estimate heritabilities, shared family environment effects, and non-shared effects.
It’s simply not true that ‘heritability would still be significant even in a genetically identical population (since cultural factors are heritable due to shared family environments).’ Cultural factors are not ‘heritable’, by definition. (Here habryka seems to be using some non-scientific notion of ‘heritability’ to mean roughly ‘passed down through families’?)
Also, heritabilities are not ‘upper bounds’ on the effect of genes. Nope. If there is any measurement error in assessing a trait (as there usually is for psychological traits), then an estimated heritability will often be a lower bound on effects of genes. This is why behavior genetics studies will sometimes report a ‘raw heritability’ but also a ‘heritability corrected for measurement error’, which is typically higher.
My point is not to shift your beliefs about genetics, but to show that your conclusions cannot be shown from heritability, since the statistic is incapable of making the claims you want to make.
That doesn’t mean the claims are necessarily wrong (they may be rescued), but that more work is necessary to make the claims that you want to make.
You seem to be making some very sweeping claims about heritability here. In what sense is ‘heritability not what I think’?
Do you seriously think that moderate heritability doesn’t say anything at all about how much genes matter, versus how much ‘non-agentic things can influence a trait’?
Yes, or close to it.
Heritability is not equivalent to “how much genes impact traits.” Kaj Sotala says it well here:
Similarly, one hypothesis that can explain high heritability yet not result in the post’s implications being right is that the studies aren’t properly controlled. From habryka:
I think a problem here is regulation systems. There has been strong natural selection for having exactly 2 feet, meaning that many innate mechanisms have developed to keep that number consistent. This is what suppresses the heritability of number of feet; but these sorts of mechanisms are clearly much less active on many of the traits that geoffreymiller mentioned, as those traits have a lot more variance.
However, thinking about it, I suppose the regulation systems point could also be made with respect to culture: In many ways, culture acts to regulate people’s values; if someone misbehaves, then they will receive corrections so as to make them more aligned with the culture’s values. And I suppose that would, by the same logic, be expected to increase the heritability.
tailcalled—these issues of variance, canalization, quality control, etc are very interesting.
For example, it’s very difficult to understand why so many human mental disorders are common, heritable, and harmful—why wouldn’t the genetic variants that cause schizophrenia or major depression already have been eliminated by selection? Our BBS target article in 2006 addressed this.
Conversely, it’s a bit puzzling that the coefficient of additive genetic variation in human brain size is lower than might be expected, according to our 2007 meta-analysis.
In general, animal behavior researchers have found that even traits quite closely related to fitness (reproductive success) are still quite heritable, and still show significant genetic variance, even in ancestrally typical wild environments. So, the (initially plausible) view that evolution should always minimize genetic and phenotypic variance in important traits seems often incorrect—apart from situations like number of feet, where we do find extremely strong canalization on the biomechanically optimal design.
I’ve read various discussions on this, e.g. Marco Del Giudice’s book. Just quickly skimming your article, you seem to be raising some of the same points that I saw in his book.
One question: isn’t the liability-scale heritability estimate the wrong value to use? Or at least, not straightforwardly the right one. I believe the effective heritability for the purposes of selection would roughly speaking be the prevalence times the liability-scale heritability, is that correct? So if e.g. schizophrenia has a liability heritability of 80% but a prevalence of 0.32%, that would lead to an effective heritability (for the purpose of selection) of 0.26%?
I’m not sure why this puzzle isn’t solved by births being a constraint?
Two questions:
Could it be because they have not reached a local optimum with regards to reproductive success?
Could it be a collider/tradeoff thing? E.g. you can have a lot of offspring or you can invest a lot into the offspring you do have? So if you count the number of offspring, you don’t just get the fitness axis, but also for lack of a better word, the r-K axis.
It’s hard to know how to respond to this comment, which reveals some fundamental misunderstandings of heritability and of behavior genetics methods. The LessWrong protocol is ‘If you disagree, try getting curious about what your partner is thinking’. But in some cases, people unfamiliar with a field have the same old misconceptions about the field, repeated over and over. So I’m honestly having trouble arousing my curiosity....
The quote from habryka doesn’t make sense to me, and doesn’t seem to understand how behavior genetic studies estimate heritabilities, shared family environment effects, and non-shared effects.
It’s simply not true that ‘heritability would still be significant even in a genetically identical population (since cultural factors are heritable due to shared family environments).’ Cultural factors are not ‘heritable’, by definition. (Here habryka seems to be using some non-scientific notion of ‘heritability’ to mean roughly ‘passed down through families’?)
Also, heritabilities are not ‘upper bounds’ on the effect of genes. Nope. If there is any measurement error in assessing a trait (as there usually is for psychological traits), then an estimated heritability will often be a lower bound on effects of genes. This is why behavior genetics studies will sometimes report a ‘raw heritability’ but also a ‘heritability corrected for measurement error’, which is typically higher.
My point is not to shift your beliefs about genetics, but to show that your conclusions cannot be shown from heritability, since the statistic is incapable of making the claims you want to make.
That doesn’t mean the claims are necessarily wrong (they may be rescued), but that more work is necessary to make the claims that you want to make.