Nature vs nurture vs inequality: an end to the cognitive dissonance

Ages ago, I listened to a Freakonomics podcast outlining economist Steven Levitt’s argument that, so long as parents aren’t abusive, it doesn’t really matter what parents do, because it won’t affect how their kids turn out. His very persuasive argument was how similarly adopted twins turned out despite being raised by different families. The adopted twins were far more similar to each other and to their biological parents than to their adopted parents. Most controversially, if you know something about how IQ scores differ through society, the evidence suggested that, within non-abused families in developed countries, environment has virtually no impact on IQ. I couldn’t see any counter-argument to twin studies, but I also didn’t know how to square this with wild differences of IQ according to environment (e.g. socio-economic status, rural vs urban) and all the research showing how environment affects all manner of outcomes, including IQ, and just the sheer implausibility (not to mention weird caste-like justification of inequality) that IQ and other characteristics within developed countries are more or less set in stone by genetics. It’s nagged at me ever since.

Finally, today I came across the answer in the wonderful book Mindware: Tools for Smarting Thinking by Richard E Nesbitt (should be the basis of the National Curriculum — it’s basically a bible for critical thinking):

Levitt asserts that family environment has relatively little effect on children’s intellectual skills. He bases this conclusion on studies of adoptive children. Studies have shown that a child’s academic abilities are far more influenced by the IQs of his biological parents than the IQs of his adoptive parents. But correlations are the wrong data to look at to reach an estimate of the importance of family environment. We need to look instead at the results of the natural experiment of adoption of a child versus leaving the child with the birth parents, who typically are of much lower socio-economic status. The environments created by adoptive parents are substantially more favourable in many respects than those of families in general. And in fact the school performance of adoptive children is half a standard deviation higher than that of siblings who were not adopted; the IQs of adopted children are more than a standard deviation higher than non-adopted siblings; and the higher the social class of the adoptive parents — and therefore the more favourable the intellectual environment on average — the higher the IQ of the adopted child. The effects of family environment on intellectual skills are actually very great.

In Levitt’s, he didn’t come up with his mistaken conclusions about the effect of adoptive environments on his own. Behavioural scientists and geneticists have been using the correlational data to reach wrong conclusions about environmental effects on intellectual ability for decades.

Elsewhere, Levitt emphasises the critical importance of childhood education and family environment in tackling inequality, the success of Scandinavian states in doing so, and the fundamental importance of basing such interventions on robust experiment-supported research, rather than our presuppositions on what will work, however intuitive they might seem to us. What a guy ❤.