Genes and IQ

Richard E Nisbett, an important cognitive psychologist, has published a book on heredity and environmental contributions to intelligence, Intelligence and How to Get ItThe NY Times has a review of it that gives us a  useful, though partial, update on the state of the debate.

Nisbett emphasizes the importance of a cognitively rich environment for children, and the very unfortunate fact that it tends to be associated with other sorts of privilege, such as social and economic class.  Environment does seem to make a different to one’s IQ score, which in turn is also closely correlated with a different in future economic status.  This is the clear perpetuation of privilege.

The review also relays a vivid example  of the fact that even if differences among individuals were wholly hereditary, it does not follow that differences among groups must be:

 The classic example is corn seed planted on two plots of land, one with rich soil and the other with poor soil. Within each plot, differences in the height of the corn plants are completely genetic. Yet the average difference between the two plots is entirely environmental.

16 thoughts on “Genes and IQ

  1. The whole business of genes versus environment is silly. We don’t need to do research to know that children who are malnourished will be developmentally retarded. The question has always been, is our environment set up to get the most out of our genes? Not, is there a link between environment and development?

  2. Carl, I’m not sure it is silly. Even when it’s clear there’s a big environmental component behind something we regard as bad (or good), knowing what portion is genetic can at least sometimes make a big difference in treatment or remediation.

    I don’t know if that will turn out to be true of intelligence, and I think people like Nesbitt, who certainly wants to stress the importance of environment, may well be addressing the question of heredity because of some pretty poisonous views that are too prevalent still.

  3. I have more sympathy with Carl here. Philosophers of biology need to step up when we people start making claims of this sort. When we talk about genetic versus environmental influences, it is almost always a population level claim and tells us very little about individuals. Further, when we do look at the development or evolution of traits, we are always looking at the genetics within a particular (or set of particular) environment(s). In my experience when people make claims about the proportion of something that can be explained by genetics or environment, they almost always get these two things wrong.

    Richard Lewontin’s Biology as Ideology speaks well to these sorts of issues. Another great source is John Dupre’s book Human Nature and the Limits of Science. Both are easy reads and provide arguments that are of use to feminist philosophers and activists. Both speak to problems with sociobiology and evolutionary psychology and John’s book directly addresses gender issues.

  4. alpha feminist, I’m not sure I’m following you. I do think the kind of account Dupre gives us should make us wary of thinking of intelligence as some pure physical, a-cultural and a-social phenomenon, and that’s the kind of thing that led me to give a conditional response to Carl. But I want to resist the idea that we can be sure it is simply silly to think something about it could be genetically grounded. When we look at something like Dehaene’s work on “the number sense” we do get a pretty clear picture in which physical structure is really important, so eventually we might profit from knowing how and in what stages these structures develop. Mind you, as far as I can see, what we’re learning is how important the environment is, including one without physical insults to the brain.

  5. What I was defending was the notion that ‘genes versus environment’ is not a well grounded way to frame these sorts of questions since there will always be both kinds of causes. Talk of these kinds of causes often gets muddled (I am not saying that you were doing this muddling, but just that there is lots of it out there and I have to admit that it bugs me) because when researchers say things like 70% of philosophical ability is environmental, they are talking about a population and not saying that 70% of my philosophical ability is environmental. Perhaps this is an overly obvious point.

    I agree that knowing more about the mechanisms involved and the functioning of different kinds of causes can aid in developing interventions. But I worry about what it means to say that something is genetically grounded, given phenotypic plasticity and the limited number of environments in which many of these kinds of claims are tested. Also, even though we might be very careful about this, ‘genetically grounded’, in alot of practice and as interpreted by some readers can quickly turn into ‘genetically determined.’

    I also worry that focusing on either genetic or environmental causes can reify the genes versus environment dichotomy. I am teaching a philosophy of biology class right now focusing on evolutionary psychology and even though most of the researchers involved say that they are cognizant of the problems with the dichotomy, they often go on to argue in ways that are based on that very assumption and the results are troubling to say the least. I am starting to think about this as such a deep assumption that it is almost like a gender schema–even if we don’t explicitly endorse it, we implicitly act in accordance with it. I think the resulting problems with uptake may diagnose some of the dysfunction in much of this science.

    That being said I wholeheartedly endorse efforts to give our children the most rich and nurturing environment that we can.

  6. General cognitive ability (IQ-type intelligence) is one of the most strongly heritable of all mental traits, it is heritable to about the same degree as height or body build. About 60 to 80% of variation in IQ is due to genetic differences, and the remaining 20 to 40% of variation is not due to the family environment (the shared environment) but rather is due to poorly understood influences from random chance events or peer groups. Richard Nisbett is really a rather minor figure in the intelligence science field and he unfortunately is strongly bonded to the outdated environmentalist view that was once championed by darlings of the left such as Richard Lewontin and the late Stephen Jay Gould. Most of the modern major players in the field of intelligence science (people like Arthur Jensen, Phil Rushton, Ian Deary, Dorret Boomsma, Danielle Posthuma, Wendy Johnson, Matt McGue, Thomas Bouchard, Sandra Scarr, Nancy Segal, Robert Plomin, Stephen Petrill, Linda Gottfredson, David Lubinski, Roberto Colom, Nick Martin et al.) have accepted the fact that IQ is strongly genetically determined. Many of these experts are excited about the prospect of soon understanding the genetics and the neurobiology of human intelligence.

    It is funny that most upscale liberal high IQ parents relish the fact that they are able to pass on to their own children their high IQ gene alleles and so therefore their biological children grow up to be high achievers and go on to graduate and professional schools (just like their mommy and daddy did), but these same parents wring their hands and fret about the fact that lower class low IQ parents usually have children that are low IQ and low academic achievers. The liberal parents claim that they fervently wish that the lower class low IQ children could be just as smart as their own children. But they usually are careful to move to upscale neighborhoods and suburbs or to get their children into special gifted classes or elite private schools so that their children will not have to associate very much with the lower class lower IQ children.

    Sandra Scarr did an experiment in which black toddlers were adopted into upper middle class white homes in Minnesota (the famous Minnesota Adoption Study). But despite being raised in the nurturing higher class white environment, the adopted black children grew up to have an average IQ of only 83.7 when they were 17 years old–the same as the average IQ of black 17 year olds who were raised in the supposedly debilitating black home environment!!

    Sorry, my dear liberal friends, but when it comes to IQ (whether you are talking about individual differences or ethnic/racial differences) all the emerging scientific evidence is pointing toward the fact that GENES TOTALLY RULE and the environmental effects are VERY WEAK!

    Before accepting Nisbett’s mostly falacious environmentalist views on IQ, you may wish to learn more about the hereditarian view, here are some good links-
    Linda Gottfredson’s website with various publications, especially interesting is the link on her website to her online debate with IQ-race environmentalist Eric Turkheimer at the Cato Institute website:

    A good review of the hereditarian view on race and IQ by Jensen and Rushton:

    Click to access PPPL1.pdf

  7. Richard E. Nisbett is one of the founders of cognitive psychology, and his work starts a number of very important lines of thought.
    Of course, there are people who disagree with him and have argued vigorously for the dominance of “nature” over nurture. Many more people have challenged this research and its assuption. The challenges are rigorously scientific and address both the methodological assumptions and the empirical implications.

    It would be nice if high IQ parents could be assumed to have high IQ children but, as many of us are aware, genetic transmission, even if it is significant, doesn’t work that way.

  8. There is a lot of misunderstanding about heredity figures, which are, as Galtonian says, population figures (of a particular population, too). Indeed, the variation in tested western populations that is due to genes is 60-80% (and if you stratify the population, the heredity figure is highest with 50 year olds, but it’s still not 100%, so genes don’t “totally rule”).
    This says absolutely nothing about individuals. It is not true that 60-80% of your IQ is determined by that of your parents, so the notion of passing on high IQ alleles and begetting high achievers is a misinterpretation of what heredity figures actually are.
    There are quite some methodological issues with adoption and twin studies. For instance regarding the mentioned Minnesota adoption study, is it reasonable to assume that the children that were given up for adoption are likely to be of average IQ? I don’t think so.
    Also, research on IQ testing has shown that if you test a class full of people, the composition of the class matters. Girls do worse in maths tests when there are boys in the room. Likewise, black people score worse on IQ tests if there are white people in the room.

    A note on “very weak environmental” effects when it comes to intelligence. There are quite some nongenetical congenital syndromes that affect IQ that are distinctly environmental by nature, for instance fetal alcohol syndrome.
    And of course, diet is of vital importance to the development of IQ (take for instance iodine deficiency).

    So, Galtonian, it seems that we completely and utterly disagree on the conclusions to be drawn from the research.

  9. In addition, IQ is on the rise – 3 points a generation, I believe. Hardly a sign of its being hereditary.

  10. yes, i think that’s the flynn effect that gladwell wrote about in the new yorker last year. but then, he also wrote that because iq’s raise 3 points a year, the tests have to be recentered (kind of like when they changed the sat tests and i got dumber) – which might skew its effectiveness as a measure.
    that is just to say, i have strong reservations about these sort of neat dichotomies, and especially the use to which they are put, of the sort that alphafeminist expressed (and which i think galtonian demonstrates to a certain degree). i have heard research like this used as an excuse to give up on poor kids, because they just will never have a rich enough environment to develop “properly.”

  11. Philosophers of biology have written quite a lot on genes and what’s wrong with genetic determinism — the view that genes (or genetic traits more generally) determine phenotypic traits. When alphafeminist says that philosophers of biology need to `step up when we people start making claims of this sort’, I think the problem is not as much with the philosophers, and more with the science journalists and popular science writers, who still write about `the’ gene that `programs’ for this or that trait.

    For people with access to academic journals, David Moore has a nice article in Philosophical Psychology (21:3, June 2008, pp 331-48) that surveys some basic misperceptions about genes and phenotypic traits that lead people to believe in genetic determinism. Here is a direct link.

  12. i think that you’re right noumena to point out that one shouldn’t paint with too broad a brush here. but i can’t completely let philosophers off the hook because i have seen/heard them (though they may or may not have been philosophers of science/biology, i don’t know) argue that i shouldn’t be in philosophy because as a woman i don’t have the right genetic material!

  13. Noumena,

    When I said that philosophers of biology, like me, need to step up, I did not mean that we need to do the research, that is already being done and I think done well. What I meant is that we have the tools to understand the science and the social and ethical implications of the science. The science journalists may not be engaging this material the way we would like, but we have not been engaging the public, or the scientists, the way I would like. Kristin Schrader-Frechette is an interesting role model. She does hard ass philosophy of biology, and uses that expertise to address environmental harms at the level of public policy and writes for academic and non academic audiences. When I say ‘step up’ I mean engage in relevant and timely social issues. Simply put, use our powers for good–for the public good in a public forum.

  14. There are a number of biological correlates with IQ, such as myelination and cortical thickness in the prefrontal cortex. Here is a discussion of a recent study by Thompson at UCLA:

    “The UCLA researchers took the study a step further by comparing the white matter architecture of identical twins, who share almost all their DNA, and fraternal twins, who share only half. Results showed that the quality of the white matter is highly genetically determined, although the influence of genetics varies by brain area. According to the findings, about 85 percent of the variation in white matter in the parietal lobe, which is involved in mathematics, logic, and visual-spatial skills, can be attributed to genetics. But only about 45 percent of the variation in the temporal lobe, which plays a central role in learning and memory, appears to be inherited.”

    “In healthy adults, greater intelligence is associated with larger intracranial gray matter and to a lesser extent with white matter. Variations in prefrontal and posterior temporal cortical thickness are particularly linked with intellectual ability”

    ‘Relationships between IQ and Regional Cortical Gray Matter Thickness in Healthy Adults’ Narr et al Cerebral Cortex 2007 17(9):2163-2171

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