IQ, Class and Genes

After reading the NYTimes series on class, and my post about it, a reader emailed me to suggest that the discussion of inherited position within a "meritocracy" was ducking the question of genes and IQ.  For example, one of the strongest predictors of how well kids do in school is their mother’s level of education.  Is this because well-educated mothers read to their kids a lot and use more extensive vocabularies, or because they continued in school because they were good at it, and they passed those genes onto their kids?

It’s a fair question, and the truth is almost certainly a bit of both.  A paper by Erik Turkheimer et al. a few years ago found that among very poor families, the environmental conditions were more important than genes in predicting IQ, while among middle- and upper-income families, genetic factors were dominant.   The published article is pretty technical, but there’s a nice layperson’s discussion of it and interview with Turkheimer available from Connect for Kids.

This research suggests that there’s a threshold level below which children aren’t able to develop to their full genetic potential.  But above that level, what parents do isn’t as critical (at least with regard to IQ) as we often think.  As Turkheimer says in the interview:

“In the range where a lot of people spend their time…you know, ‘Should I hang the black and white mobile over my kids’ crib?’ kind of thing, it probably does not matter.”

6 Responses to “IQ, Class and Genes”

  1. Jennifer Says:

    That’s interesting research. I have seen it described by analogy with height. Everyone probably knows that people 200 years ago were much shorter than they are today, because of poor nutrition. So there are environmental factors that stop you from living up to your full genetic potential, but once you’ve got the right environment, then your genes control the outcome.
    But from your original posters question, I would have thought that a mother’s level of education was only a limited indicator of the child’s genetic inheritance. Seems more likely to be a class indicator to me.
    An example from my own experience. I’ve found that (gross generalisation, but here goes) smart first generation immigrant women from non english speaking backgrounds are likely to only have high school education, whereas a woman who’s just as smart but from a longstanding Australian family is likely to have a degree.

  2. jen Says:

    I’m not sure what to think about the twin forces of IQ and class. Clearly they can work together to reinforce the concept of “inherited meritocracy”.
    My bigger fear is just that it muddies the waters. Leveling the playing field would be much easier if there weren’t two forces at work.
    I do think it’s compelling, and a good sign, that we as a country never question the concept of merit. We expect people to earn their status, and we as Americans work hard to make inherited privilege look like earned privilege.

  3. RussellBC Says:

    I love the NY Times series on Class. As someone who teaches on issues of oppression, it was nice to see some current information on this silent/hidden issue in the popular media. I have always been a “nurture” rather than “nature” person – believing that one’s environment was the main causal factor to life success. But being a new parent and seeing some things emerging in my son that (annecdotally I grant you) I would have attributed to nurture issues is altering my thinking. This concept of environment affecting genetic potential is intriging.

  4. Jackie Says:

    I think nature and nurture are forces that work in tandem and must both be considered to get a full picture of any person/condition/etc. I think it’s setting up a false dichotomy to say it must be once or the other, you know?
    It’s kind of like those studies about breastfeeding and IQ as well– does it really increase IQ, or is it that more educated women are more likely to be able to breastfeed longer due to more flexible or accomodating work?

  5. dave s Says:

    When Hitler was plundering all the conquered nations to keep Germans fed and happy he took basically all the food out of Netherlands, and the winter of 44 was a time of near starvation there. After the war, the Dutch thought, well, we should try and get something out of this suffering, and they looked at the kids who had been so hungry in this time in terms of IQ – would it depress the IQ, would it matter how old the kid was in the period, maternal starvation in utero.
    They found almost no effect of starvation on IQ. What they did find was a significant effect of having been the oldest child – oldest (and only) children had higher scores. If anything, this suggests that the threshold level Turkheimer was talking about wasnt all that high.

  6. Chi Says:

    Some interesting propaganda here. Turkheimer’s study doesn’t show much because the children were aged 7 or under. This is well before the shared environment factor vanishes.
    Also, note that East Asians average above whites even when raised in white homes. This is the case even where there has been severe malnourishment.
    “Contrary to “culture” theory, the ethnic academic gaps are almost identical for transracially adopted children, and to the extent they are different they go in the opposite direction predicted by culture theory. The gap between whites and Asians fluctuated from 19 to .09 in the NAEP data while the gap in the adoption data is from 1/3 to 3 times larger. This is consistent with the Sue and Okazaki paper above which showed that contrary to popular anecdotes, the values that lead to higher academic grades are actually found more often in white homes. In other words Asian-Americans perform highly despite their Asian home cultural environment not because of it. And though the sample is meager, I find it interesting that the gap between the black and white adopted children was virtually identical (within just 4-6 points) to the gap between whites and blacks in the general population, just like in the Scarr adoption study.”
    http://www.gnxp.com/MT2/archives/004064.html
    Some problems with the Turkheimer study:
    1 – The study included only young children and does not make any attempt to extrapolate that all other findings of significant increases in h^2 by age 17 are in any way invalid. The effects of the shared environment vanish at around age 12.
    2 – Turkheimer began his paper by recognizing that the heritability of cognitive ability in childhood is well established.
    3 – Turkheimer made no attempt whatsoever to determine what components of SES he was measuring. There are three obvious items to consider: macro environmental, micro environmental, and genetic. All work to date indicates that the first of these can be found in children, but that it is absent in late adolescents; by late adolescence, all of the environmental component is of the second type; and that genetic intelligence is the largest determinant of SES.
    4 – Turkheimer says that the effect he observed was related to the homes in which the children were raised. This is interesting, since it relates to the adoption studies which show that after childhood there is no adult IQ correlation between biologically unrelated children who were reared together in the same home.
    5 – Turkheimer discusses in some detail that SES is not strictly an environmental variable, since it is known to be (statistically) caused by the intelligence of the parents. He points out that the models he used “cannot determine which aspect of SES is responsible for the interactions” observed.

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