Heritability, Changeability, and Cultural Shifts – A Quickie
My previous post – “Squid Ink” – has spawned a little discussion about the role of the “environment.” However, I’d argue what all the discussion is about – what it is always ever about when people invoke “environment” – is changeability. This is what people really want to know about that, and they see heredity – rightly or wrongly – as an impediment to that. So, spurred by some tweets by “Misdreavus”, I’m going to leave a few bits here that touch on that matter.
In reality, a thorough discussion on this matter deserves a longer post – perhaps something even longer than a post. I refer people to my previous posts Environmental Hereditarianism and Why HBD for some of my earlier thoughts on the matter.
First, Elijah Armstrong has responded to my previous post with a post of his own (What racial differences are wholly environmental? ). See the discussion over there. But I wanted to especially highlight a comment by Meng Hu:
Every debate of nature-nurture is fruitless, purposeless, time-wasting, if the discussants do not include malleability in the equation. In fact, the nature-nurture question is not relevant at all. Those who have read The Bell Curve probably know what I’m talking about. Let’s cite the authors then :
For practical purposes, environments are heritable too. The child who grows up in a punishing environment and thereby is intellectually stunted takes that deficit to the parenting of his children. The learning environment he encountered and the learning environment he provides for his children tend to be similar. The correlation between parents and children is just that: a statistical tendency for these things to be passed down, despite society’s attempts to change them, without any necessary genetic component. In trying to break these intergenerational links, even adoption at birth has its limits. Poor prenatal nutrition can stunt cognitive potential in ways that cannot be remedied after birth. Prenatal drug and alcohol abuse can stunt cognitive potential. These traits also run in families and communities and persist for generations, for reasons that have proved difficult to affect.
Recently, Richwine in “IQ and immigration policy” made the same kind of argument. They are both right. You also have another insightful comment from Sesardic (2005) Making Sense of Heritability :
… when we say that Alzheimer’s disease is incurable, we mean, roughly, that no current medical intervention can stop the degenerative process in the brain that leads to death in about seven to ten years. What strengthens the claim of incurability is that there have been intensive attempts to find a cure, which have produced no results so far. So, the existing environmental variation includes the measures that were deliberately introduced in the hope that they might be effective. It is precisely the fact that these measures were unsuccessful that justifies the modal claim that the disease is incurable (i.e., that it cannot be cured, rather than that it is just not cured).
… But as explained above, the expression “local modifiability” gains on strength and relevance if “existing environments” involve many attempts to influence the trait in question. If these attempts are unsuccessful and if the heritability remains high, then we will know not only that redistribution of existing environments will have little effect on phenotypic differences but also that all the concerted efforts undertaken so far to influence the phenotype have failed. In that case, “locally non-modifiable” would move closer to what common sense understands as “nonmodifiable.”
To let you see, let’s examine those studies :
Haworth et al. (2009). A Twin Study of the Genetics of High Cognitive Ability Selected from 11,000 Twin Pairs in Six Studies from Four Countries.
Brant et al. (2013). The Nature and Nurture of High IQ: An Extended Sensitive Period for Intellectual Development.
You see that heritability is lower among high IQ people. But everyone knows that it is easier to boost low IQs, and there are empirical proofs to that. The relevant question is how much you can boost IQ. If, in advanced countries, every attempts so far have failed to produce meaningful and sustainable gains among low IQs, it does not matter whether h2/e2=0.60/0.40 or h2/e2=0.00/1.00. When low IQs [cannot] be improved sustainably, it is more than justified to place environmental effects on the genetic side of the ledger.
Heritability is irrelevant. Environment is irrelevant. GE correlation is irrelevant. All what matters is malleability.
To which I responded:
While I get the spirit of your argument, and broadly I think it is correct that malleability, in many arenas at least, trumps heritability, we have to be rather careful with that criterion.
Let me give two examples: height and BMI. Both of these are just as heritable as IQ. In both cases, however, we have a certain degree of “malleability.”
In the case of height, we’ve seen secular changes, primarily an increase in the mean in the 20th century (which followed an apparent decrease in the U.S. in the 19th century). Much of this change appears to have been environmentally mediated. This would mean that height is technically “malleable.” However, height isn’t really malleable “after the fact”, say in adults, regardless of your environmental intervention. This means that it is apparently some intervention that occurs at some point in early development – likely childhood – that makes the difference. But how malleable is that, then?
The problems with the malleability criterion becomes even more acute when one considers BMI. There has been a great secular increase in BMI in the last few decades across much of the world, one that is apparently wholly environmental in origin. And indeed, the “malleability” of BMI is the focus of a secular religion in modern society, because some environmental interventions can change it, especially on the short term. But, it appears to be rather stubbornly resistant to change on the longer term. So what I’m asking with this is how malleable is it, really then? How do we call that one?
But BMI especially demonstrates a problem in conventional language when we talk about heredity, because people often assume heritability (inversely) = degree of malleability, when that is not the case. This is why you have foolish people going about how BMI cannot be “due to genes” when it is in fact incredibly heritable.
I get your point, that from practical point of view, at the end of the day, heritability is secondary to degree of malleability – because it doesn’t make a difference if a phenotype is wholly environmental if we are unable to change it. The single best example of that is probably homosexuality. This is mostly environmental in origin. But is essentially unchangeable once established.
However, I think homosexuality also serves to demonstrate the importance of decomposing the “heritable” from the “environmental” source of trait variance: it tells you where to target if you want to “change” the trait. In the case of homosexuality, for example, attacking the pathogen, perhaps with a vaccine, is your likely best course. In the case of IQ however, likely only changing the genes, with some form of eugenics, is your best shot if that’s your goal (various adverse environments in the developing world and their potential impacts notwithstanding).
And yes, I agree that “malleability” in this fashion is a function of technological limitations. It is not necessarily outside the realm of possibility that future interventions might be able to alter these currently less malleable traits. But, since we don’t know if and when that will happen, it makes more sense to exclude that from our discussion for now.
I will add that the BMI example shows the limitations of understanding that there is an environmental component – because in that case, we still don’t know what that is and hence, how to modify the trait of interest. This is despite a lot of searching for these factors.
I often regard this matter as “an advanced” topic, as in rather difficult to properly understand even for those versed in this topic. I’d expect it would be even more confusing for lay people. However, it is supremely important, in that this is a topic where making the fine distinctions is quite often warranted in discussion.
Now, add Misdreavus’s recent tweets to the matter:
And the KEY point:
I’m hoping that this post clears up – at least somewhat – the situation with genes, environment, and change, both evolutionary and non-evolutionary. It might not; this is a somewhat complicated topic. Or I guess, more accurately, it’s not that it’s that complicated, it’s just that it requires laying aside a lot of priors in order to understand (kind of like free will). As we know all too well, people have a hard time doing that.
Feel free to share your thoughts in the comments. I know they’ll be many.