The new consensus on IQ

The relationships among intelligence, race, human development, and genetics are among the most important topics for students of inequality. These topics are also sites for recurring ideological battles, most recently involving Jason Richwine’s research on Hispanic immigration to the US.

There has been a persistent argument that intelligence is more or less impervious to environmental intervention, but this is not the consensus of recent research. So if the last time you paid attention to psychological research on intelligence, you need to catch up. Here’s a quick way to do it.
This is the abstract from a superb recent summary article by leading psychologists Richard Nisbett and Eric Turkheimer and several other noted social scientists.

We review new findings and new theoretical developments in the field of intelligence. New findings include the following: (a) Heritability of IQ varies significantly by social class. (b) Almost no genetic polymorphisms have been discovered that are consistently associated with variation in IQ in the normal range. (c) Much has been learned about the biological underpinnings of intelligence. (d) “Crystallized” and “fluid” IQ are quite different aspects of intelligence at both the behavioral and biological levels. (e) The importance of the environment for IQ is established by the 12-point to 18-point increase in IQ when children are adopted from working-class to middle-class homes. (f) Even when improvements in IQ produced by the most effective early childhood interventions fail to persist, there can be very marked effects on academic achievement and life outcomes. (g) In most developed countries studied, gains on IQ tests have continued, and they are beginning in the developing world. (h) Sex differences in aspects of intelligence are due partly to identifiable biological factors and partly to socialization factors. (i) The IQ gap between Blacks and Whites has been reduced by 0.33 SD in recent years. We report theorizing concerning (a) the relationship between working memory and intelligence, (b) the apparent contradiction between strong heritability effects on IQ and strong secular effects on IQ, (c) whether a general intelligence factor could arise from initially largely independent cognitive skills, (d) the relation between self-regulation and cognitive skills, and (e) the effects of stress on intelligence.


About Bill Gardner

A health care researcher and a child and quantitative psychologist by training. I am an American living in Canada and am Professor of Paediatrics, Obstetrics & Gynaecology, and Community Health & Epidemiology at Dalhousie University; and Professor of Pediatrics, Psychology, and Psychiatry at The Ohio State University. I also blog at The Incidental Economist ( and you can follow me @Bill_Gardner on Twitter.
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9 Responses to The new consensus on IQ

  1. sao says:

    But Hispanics aren’t a race. Their origins span 4 continents, N. America, S. America, Africa and Europe in any combination from 100% of one to a mix of all 4. You can’t draw any conclusions about genetic adaptations or maladaptations by looking at such a genetically heterogenous group, no matter how careful your research.

  2. Bill Gardner says:

    Sao, I agree with you. Your point was an important criticism of Jason Richwine’s dissertation. I referenced Richwine just to provide context; I don’t have any comment to make about Hispanic ethnicity or genetics.

  3. orerb says:

    This article summarizes the opinions of a few leading psychologists. But it is hardly a “consensus” view of the literature. Nisbett, in particular, is well known for promoting the “environmentalist” view of intelligence far beyond what the literature allows us to say. See this review of his 2009 book:

  4. Bill Gardner says:

    Thanks for the link. I’ve skimmed it and am impressed. I am at least persuaded that you are right that “consensus” may be too strong a word. I will acknowledge that I am perhaps too inclined to assume that an APA panel and American Psychologist publication represents consensus. In addition, I am probably biased by my a) interest in epigenetics, b) my policy commitments to early intervention, and c) long term friendship with Eric Turkheimer. I’ll give it close read.

  5. I am just an eager observer from the field of animal breeding and genetics.Just like JR Flynn founder of the Flynn Effect. Comparing with animal genetics , IQ as a trait a with very high heritability can effectiively be improved by selection. Education is an environmental/non genetic intervention and does not change IQ genetically nor phenotypically. It turn out (my finding) to be a continuous selection for high IQ. Only thoes with high IQ can pass all the Exams every students have to go through from high school to the Graduate school ( Doctorate/ PhD ). By mating selected animals with high breeding/genetic value we can produce a new generation of animals with an average genetic performance. Drawing an analogy in the human population, the observed secular continuous improvement of average IQ scores in modern advanced and developing countries applying education as a tool for a general improvement we found the IQ /Flynn Effect puzling /paradoxal. Not so !! In human populatios we donot have to do planned mating … and it turned out that what our younger advanced educated generation regulate themselves by picking their mates among their equelly high educated classmates or across class mates the so called assortative mating . That is how it all happened. The only factor hampering the IQ improvenment seems to be the urge to limit the number of children per family in those educated couples and the negative effects of higher numbers of children per family in low educated population. That is what I can comment on the point b) among the theories. Your comment please.

  6. This is to add some words to my former reply. When I said that when mating is done among selected animals with higher breeding / genetic values (e.g each bull wlth several cows) the resulted group of calves will form a new generation of cattle with an average productivity higher than the average of the parent generation. Further selection for higher productivity in this new generation will result in furthe genetic improvement. I hope this will make things clear. Thank you !

  7. mesolithica says:

    Hmm.. they haven’t found specific genes for a lot of things, but we know they have a genetic cause.

    IQ in adults is estimated now at about 70% to 80% genetic. It has a .33 correlation to gross brain size.

    The heritability of IQ varies with age (Wilson effect), which is why people stuck on environment as the cause of IQ difference insist on referencing studies of children, which is very much evidenced here. The heritability in children is LOW, which is relevant to the class differences in heritability of IQ. No-one has found that level of class difference in adults, although I expect there is some. It will probably down to substance abuse and poor eating habits in infancy or before birth, not schooling or post infancy social environment

    You should take a look at Nancy Segal’s work on virtual twins. Unrelated infants raised together, they show some relation to each other when young, but by the late teens the shared environment has very little effect.

    • lagergeld says:

      I agree. I’ve noticed they focus on children and don’t deal with the Wilson Effect. They also tend ignore not only that intelligence runs in families but also attempt to attack decades of international identical twin studies.

      Nisbett is pretty open about his agenda and bias in his work.

  8. lagergeld says:

    This isn’t a new consensus; it’s a debunked claim. Nisbett’s methods and conclusions are shaky at best and he’s been unable to respond to critics of his work.

    Refer to:

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