Book Review: The Nurture Assumption, by Judith Rich Harris.

The Nurture Assumption isn’t quite the book I expected. Amazon tells me that customers who bought it also bought The Blank Slate, by Steven Pinker, and The Bell Curve, by Charles Murray, which is what I expected. Based on that, you might expect it’s a book about how human nature is influenced by genes rather than the environment, possibly with a racist chapter or two thrown in there. But Harris is less interested in the relative influences of nature and nurture than in changing how we look at the idea of “nurture.” As Steven Pinker says in the introduction, “We all take it for granted that what doesn’t come from the genes must come from the parents.” This book is about why that assumption is wrong.

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The Dickens-Flynn model of IQ, part 4: Implications.

What are the implications of the Dickens-Flynn model – for analysis of race, education, inequality, and other aspects of human nature?

The most important thing, it seems to me, is that the Dickens-Flynn model makes it easy to explain racial IQ differences without suggesting that blacks are genetically less able. This was never impossible, but under the Jensen model it was difficult to imagine how the circumstances of black families could be so consistently awful as to explain the size of the IQ gap. So the preferred solution to this problem was to shun IQ researchers, call them racists, and deny mountains of research showing that IQ is important. That’s actually still the most common solution, but thanks to Flynn’s model (and probably also thanks to haranguing by Fredrik deBoer and Scott Alexander), a few liberal outlets – especially Vox – are gingerly dipping their toes in the waters of “maybe not being IQ denialists.” Flynn proved that liberalism’s commitment to racial equality is fully compatible with its commitment to empiricism, which is a really big deal.

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The Dickens-Flynn model of IQ, part 3: The social multiplier, and race.

We’ve established than a one-time intervention for a single person can’t permanently change their IQ, because once their environment returns to normal, so will their IQ.


But what if the “normal” environment changes? That’s what Flynn believes has happened over time – average levels of education have increased, more jobs require abstract reasoning, and so on. The sum of all these changes adds up to something vastly more powerful than a one-time intervention, which Flynn calls the “social multiplier.” This is his explanation for the effect that bears his name; it’s why average IQ scores have increased all over the world. And it’s an effect that builds on itself – the more time you spend around people who have developed their ability to reason abstractly, the better you get at reasoning abstractly – and then you become part of the social environment that raises other peoples’ IQs.

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The Dickens-Flynn model of IQ, part 1: Background.

This was originally going to be a review of What is Intelligence?: Beyond the Flynn Effect, by James R. Flynn.  However, like so many of my reviews, it quickly became something else – I realized that I couldn’t fully address what I found important about Flynn’s ideas without drawing also on his earlier work, Race, IQ, and Jensen.  Also, his more recent theories are summarized very well in the article “Heritability estimates versus large environmental effects: The IQ paradox resolved”, which is much shorter than his later book. I will also reference some things Thomas Sowell has written, for reasons I’ll explain later.

(Incidentally, for purposes of this post, I will be assuming that the reader correctly understands the concept of heritability.)

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