The Dickens-Flynn model of IQ, part 2: The model.

So what does Flynn’s theory – the opposite of the Jensenist theory, which I will call the “environmentalist” theory even though that name means something else in most contexts – actually say about intelligence?

  1. IQ tests measure a real aspect of intelligence, but that aspect is not necessarily the central aspect of intelligence; in fact, intelligence is probably not a unified trait, but a collection of loosely-related traits.  Different IQ tests might measure different aspects, and there is no reason to prefer “g-loaded” IQ tests – those designed to measure the “g factor” specifically – over other IQ tests.
  2. Gains in IQ over time measure, not an improvement in overall intelligence, but improvement in certain, narrow kinds of abstract thinking that our society has come to value more than it used to; society now devotes more effort to developing these kinds of thinking than it used to, so children today outperform previous generations.
  3. Relatively small, innate differences in intelligence exist between individuals, and the social environment – the “individual multiplier” – tends to magnify these differences over the course of an individual’s life.
  4. If any innate differences in IQ between races exist, they are very small – small enough to ignore for purposes of social analysis.  The relatively large differences between races that we actually measure are caused mostly by differences in social environment – and notably, Flynn seems to think that cultural segregation, rather than direct discrimination, is the main culprit.

The first two points get at the question of what IQ actually is. Different measures of mental ability tend to be highly correlated, and some people think that’s because they’re really all measuring the same underlying thing – a measure of pure brainpower, if you will.

The alternative view – what Flynn believes – is that different measures of mental ability tend to be highly correlated for the same reason that different measures of athletic ability tend to be correlated – not because they’re measuring exactly the same thing, but because they’re measuring a system of interrelated abilities that tend to hang together in society. Flynn likes sportsball analogies, so here’s an example: If you looked at a typical American high school, you’d probably find that skill in football, basketball, and baseball are highly correlated – in part because they all rely on some common skills, but also because the people who practice hard at one sport might tend to practice hard at all three.

Now, you could probably still design tests that separately measured skills for football, basketball, and baseball, and attempts to do that for intelligence haven’t been tremendously successful. On the other hand, the Flynn-effect changes over time have not affected all submeasures of intelligence equally, which argues that different aspects of intelligence are separable.

It seems to me that, for purposes of social analysis, it doesn’t matter too much whether intelligence is a unified thing or not. Whether it is or it isn’t, we’re still confronted with the same questions – what things influence intelligence, how malleable is it, and what does it mean for society that people who excel at one mental ability tend to excel at all mental abilities?

I should note, though, that Flynn’s position, though it represents the “left-ish” end of a spectrum within intelligence research, would still probably unwelcome in the Huffington Post. Flynn is clear that IQ tests do a reasonably good job of measuring what people ordinarily think of as “intelligence”, and that people that score highly on IQ tests really do perform better on a wide variety of real-world tasks. To borrow an analogy from economics – the unemployment rate is not one unified thing; it can be defined in terms of U1, U2, U6, and so on. But “high unemployment” and “low unemployment” are still real things, with real implications for society.

The third point – the “individual multiplier” – is probably the most confusing part of Flynn’s theory.  To explain it, Flynn turns once more to sportsball: children who have some natural talent for basketball tend to enjoy basketball more, practice it more, and receive more attention and training than children who have less natural talent, and over the course of a lifetime, these environmental feedback effects magnify differences in basketball skill until they vastly larger than the difference in natural talents.

When I first read this, I thought he was describing a “snowball effect”, where small differences in early childhood talent and environment build on each other to set a child’s IQ trajectory. But that’s exactly what doesn’t happen – what Flynn is trying to explain here is why programs like Head Start can raise a child’s IQ in the short term, but those effects quickly fade; and why IQ in adulthood is much more heritable than childhood IQ.
Flynn has a formal, mathematical model for how the individual multiplier works, and studying that eventually helped me understand what he was saying, but I would rather explain it in very general terms, even if those terms don’t quite match the model:

  • Someone’s IQ at any point in time is influenced quite a bit by their current environment, and also somewhat by the average effects of the environments they have experienced in the past.
  • A child who lives with their parents and goes to school has very little control over their environment, so they’re often in environments that raise or lower their IQs relative to what you might expect from their genes. These effects lower the heritability of childhood IQ.
  • As children grow older and become adults, they have much more control over their lives, and they tend to make choices that sort them into environments that are matched to their innate cognitive abilities – people who are cognitively talented go to college, spend time around other people with college degrees, and take jobs that require abstract reasoning; people who are less cognitively talented don’t go to college, spend time around other people without college degrees, and take jobs that require concrete reasoning. These environments magnify their innate genetic differences, and so adult IQ is more heritable than you might expect. It also means that the heritability estimates from twin studies in some sense exaggerates the “pure” genetic component of IQ.

At the risk of sounding trite, this model says learning is a lifelong process, and there’s nothing special about early childhood. Someone’s IQ is a product of an entire lifetime of influences, and there’s no single intervention that can change someone’s trajectory. Even the most drastic intervention – adoption – has very little effect on adult IQ.

But even though “interventions” don’t work, large-scale social change does. Which brings us to part 3.

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