The heritability debate, again

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Like the level of selection debate, the debate about what heritability means has a life of its own. The latest shot comes from Scott Barry Kaufman who argues (among other things) that:

The heritability of a trait can vary from 0.00 to 1.00, depending on the environments from which research participants are sampled. Because we know that genes play some role in the development of any trait, the precise heritability estimate doesn’t matter in a practical sense.

Heritability depends on the amount of variability in the environmental factors that contribute to a trait. The problem is that our understanding of the factors that contribute to the development of human traits in general — and to IQ in particular — is currently so deficient that we typically do not know if the environmental factors important in the development of a particular trait are stable across testing situations, vary somewhat across those situations, or vary wildly across those situations.

In his conclusion he states:

At the very least, heritability tells us how much of the variation in IQ can be accounted for by variation in genetic factors when development occurs in an exquisitely specific range of environments. However, David S. Moore has argued that even this is not significant when we realize that the magnitude of any heritability statistic reflects the extent of variation in unidentified non-genetic factors that contribute to the development of the trait in question.

(HT: Bryan Caplan)

Through his post, Kaufman constructs a series of paper tigers, tears them down and implies that because the extreme case does not hold, we should be wary of heritability estimates. I did not find much to disagree with in his examples, but the I differed on the conclusions we should draw.

So, where I do not agree – first, the heritability estimate does matter. While I don’t think it is hugely important whether the heritability of IQ in a specific sample is 0.5 or 0.6, it is important whether the measured heritability is 0 or 0.6. As Caplan notes in his post:

My money says, for example, that the average adult IQ heritability estimate published in 2020 will exceed .5.

I think that Caplan is right (although I might have stated some conditions about the relevant sample), and Kaufman’s argument overstates how finely tuned the environment needs to be to get a meaningful heritability estimate. Heritability estimates of a sample of children growing up in extreme poverty might be much lower (or zero) but as is found again and again, once the basic requirements of a child are met, heritability estimates for IQ are consistently above 0.4. We can construct arguments that in each study there are different gene-environment interactions and so on, but if genes weren’t important in variation in IQ and the gene-environment interactions weren’t consistent to some degree, why would such consistent heritability results (and correlation between parent and child IQ) be found?

Further, these results matter. They suggest that poverty is affecting the IQ of some children, and policies could be tailored to cut this disadvantage. For children not subject to deficient environments, the high heritability of IQ should influence policies such as those for education. Children are different and the education system should take this into account.

Implicit in Kaufman’s post was the “its all too complex” argument. Social and biological sciences are complex (which is why I find them interesting). However, if we fully accepted Kaufman’s argument that “our understanding of the factors that contribute to the development of human traits … is currently so deficient that we typically do not know if the environmental factors important in the development of a particular trait are stable across testing situations”, it would put into question most of the data analysis in economics, sociology and biology. Econometrics operates on the idea of all other things being equal.

Fortunately, Kaufman has not taken the Gladwell-esque approach of suggesting that we forget about genetic factors. Kaufman suggests further research into how nature and nurture are intertwined. If it is all too complex, we should start unwinding the complexity. However, I believe that, in the meantime, this complexity does not mean that we should throw out all the results that have previously been obtained.

**This is a cross-post from my blog Evolving Economics.

6 Comments

  1. It wouldn’t be necessary to do so many heritability studies if psychologists and sociologists would stop operating under the assumption that their trait of interest is determined by the environment.

    Even when they say, like Kaufman, that genes matter, they don’t take it fully into account in their hypothesis generation. The heritability research forces them to.

  2. I don’t read the Huffington Post that often, but I did notice this article, and it irritated me.

    Aside from the obvious political agenda (minimizing the connection between heredity and IQ is always popular!), it seems very misleading to make a blanket assertion that heritability can vary between 0.00 and 1.00. My blue eyes were 100% determined by my genes, and short of gouging my eyes out at birth nothing in the environment was going to change that. I’m sure there are plenty of other traits like this, as well as traits where heritability can be pushed down from 1.00, but never anywhere close to 0.00.

  3. OT: Natural selection at work in Sweden,

    http://www.dn.se/nyheter/sverige/krav-pa-nya-kostrad

    Google translate will give you a pretty good idea what’s going on.

  4. The more we attempt to engineer environmental egalitarianism, the more we push up heritability. You cannot win. The facts are the facts, and I wish that politics could be put aside for the interest of science.

  5. My blue eyes were 100% determined by my genes,

    Were they, really? My understanding is that we can’t yet determine whether a given person will have blue eyes even if we know which alleles of the relevant genes they’ve inherited.

  6. Kaufmann also waded into whether there are hereditary differences between different ethnic groups and nationalities.

    http://www.iqscorner.com/2010/08/flynn-effect-and-iq-disparities-among.html

    This prompted a response here.

    http://www.iqscorner.com/2010/09/williams-comments-on-scott-barry.html

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