Don’t forget parents share genes with their offspring

By Razib Khan | April 12, 2013 4:11 am

In 2002 I read The Blank Slate. With all due respect to Steven Pinker one of the most fascinating aspects of this book was actually a review of the work of another psychologist, Judith Richard Harris. Harris’ own views are explicated crisply in The Nurture Assumption. In it she reviews and expands on a major insight from behavior genetics: over the long term parental influence seems to be a relatively marginal predictor in terms of many behavioral traits. To be explicit, one can imagine a personality trait which varies in the population. The variation of genes may explain 40% of the variation of the trait. The variation in parental child-rearing techniques, “shared home environment,” may explain 10% of the variation of the trait. The remaining 50% of the variation may be “non-shared environment.” That basically means we don’t have a definitive explanation of what the 50% remainder is, though Harris posits that this consists to a great extent of peer groups.*

However you quibble with the details of Harris’ line of reasoning, the key takeaway is that people often neglect that parents and offspring share genes when considering the influence parents have upon their children. I think it is important to keep this reality in mind when reading pieces like in The New York Times, The Power of Talking to Your Baby. Basically, higher socioeconomic status parents talk to their infants and toddlers more, resulting in a larger vocabulary and presumably giving their offspring a head start. This is a really big deal, and I’ve started hearing about this nugget of wisdom a lot from friends. Providence, Rhode Island, is even spending $5 million dollars to shrink the “word gap.”

Social environment and enrichment matters. The Providence project is exactly the kind of local experiment that Jim Manzi recommends in Uncontrolled. But one of Manzi’s points is that there is no silver bullet in many social science domains. Rather, there are lots of small incremental angles of improvement. And, it seems likely from the behavior genetic data that there are only going to be limited gains in terms of closing presumed intellectual gaps. A plausible, if unpalatable, possibility is that lower socioeconomic status families where there is little complex vocabulary exposure for children are this way simply because these families are disproportionately less intelligent. Adoption studies suggest that I.Q. can increase, at least up to adolescence, by switching a child from a lower (biological) to a higher socioeconomic status (adoptive). But the gap between the adoptive and biological children is not closed. The “word gap” is not going to magically transform the social landscape, though it may have an influence on the margins.

Finally, I have to also be a killjoy and point out that these early life interventions often have a track record of diminishing returns. I am aware of the Perry Preschool Project, and I hope that that pans out, but looking into it it seems that the hopes of many rest on only a few cases. The reason that early gains are often extinguished is that people mature into unstable environments where their initial dispositions may lead them toward choices which prevent them from flourishing. If we’re serious about intervention in the lives of the lower socioeconomic segments of the population we need to get serious in a Nordic fashion: cradle to grave. It seems to me that these periodic enthusiasms for a particular didactic technique reflect the reality that we’re looking for a magical return-on-investment solution. There may be no such thing.

* I am aware that this component may mask epistatic genetic effects.

CATEGORIZED UNDER: Behavior Genetics
MORE ABOUT: Behavior Genetics
  • Robert Ford

    Poor people don’t have good grammar so would it matter if they spoke more? If they did, poor kids would grow up immersed in discussions on Mountain Dew Theory and the nuances of NASCAR.
    Also, how legit is Cochran’s theory about deaf kids? They should show this same “word gap” but probably don’t (?)
    Word gap, achievement gap…Gap gap.

  • marcel proust

    Some questions about the fn, in particular, the phrase, “epistatic genetic effects”.

    When people talk about non-linear effects or terms (e.g., in the box labeled “General model for quantitative phenotype” here), are they referring to the same thing as the phrase, “epistatic genetic effects”?

    If so,
    a) are they synonyms?
    b) if not synonyms, is one a proper subset of the other?

    Please, more than “yes/no” responses.

    • razibkhan

      epistasis is a subset technically. gene-to-gene. but i don’t think it really covers many-gene-to-many-gene interactions. so non-linear is probably a bigger space in theory. also, some environmental effects are probably non-linear.

  • Charles Nydorf

    addressing social equality by getting serious in a Nordic fashion is precisely what we liberals have always advocated

  • JonFrum

    I’d be careful when playing the Nordic card. I have Swedish relatives, and have met them here and in Sweden. The Nordic system worked in Sweden because Swedes were taking care of Swedes. Now that Sweden is filling with immigrants from very different cultures, the Nordic system is breaking down. And here in the United States, we have sub-cultures that divide us that the Nordic countries didn’t deal with until now. When Swedes say ‘we,’ they mean ethnic Swedes. In America, there is no such ‘we’ allowed. Diversity denies it.

    • razibkhan

      yeah. i’m not stupid, i’m aware of this argument. the bigger point is even if it isn’t possible, cradle-to-grave is really the best bet if you want to minimize inequality. short-term boosts diminish.

      • Emil Kirkegaard

        Even in Scandinavia, differences between groups grow with time, not fade away. For instance, in healthy, the upper class now lives 10 years longer than the poor class.

        I think liberal eugenics is the way to go for seriously improving mankind before we become cyborgs in the more distant future.

  • T. Greer

    Robert Putnam’s Bowling Alone presents heaps upon heaps of evidence that the generation of the 30s/40s was not able to “pass on” the attitudes and practices that made them so civically involved, socially responsible, and trusting in general. He suggests that WWII exp. is what forged their exceptional civic virtue, suggesting that social experiences might be a big factor in that that unknown 50%.

    “That basically means we don’t have a definitive explanation of what the 50% remainder is, though Harris posits that this consists to a great extent of peer groups.”

    I think 2nd/3rd generation immigrant studies might bear this out – my personal observation has been that 2nd/3rd gen immigrants adopt the norms/behaviors/culture of the television and the school room , not their parents. (Trying to find data to verify this has been difficult. Lots of research has been done on language acquisition, which mirrors this assessment. Richard Nisbett’s Geography of Thought presents evidence that Asian Americans can “switch” between Asian and Western cognitive traits, but he is ambivalent on which tis their norm. The Pew Survey Rise of the Asian Americans has the interesting data point that 2nd gen attitude and actions regarding pre-marital sex and pre-marital child rearing are more similar to other Americans than their parents, so that might support the point as well.)

    But assuming this is true, I’ve got to ask: is this a universal find or the trait of one generation (in one country)? I suppose a conservative could argue that the home has lost much of the influence that it once had, that children and parents are less connected to each other (Putnam – hardly a conservative – would agree with this ) and spend less time in the home in general, that television and other types of mass media are a new influence on child development, and that universal education has done some strange things to child development as has normally occurred in agrarian civilization’s 6,000 years. Is it possible that the parents of 1900 ha greater influence on their children than the parents of 2000?

    • Karl Zimmerman

      Mass media undoubtedly has more effect on assimilation than we give it credit for. For example, many localized, non-Anglophone minorities in the U.S. (non-Amish German-speakers in Pennsylvania, Spanish Speakers in New Mexico, Cajun French in Louisiana) started losing their mother tongue only once radio broadcasting exposed them to the wider world. The only U.S. minorities which have been good at keeping their home languages are ones like the Amish, and the Hasidim, who almost totally shut themselves off from the outside world. Indeed, a lot of the Amish’s supposed Luddite bent is not because they are anti-technology per-se, but because they recognize by accepting “English” technology like cell phones, their distinctive culture will die out.

      That said, keeping segregated educational systems is also important, since, (as Judith Rich Harris notes), school is where we learn to assimilate to the group norm. Still, looking at groups like young evangelicals (who seem to be less reflexively anti-gay than their parents) it seems separate schooling isn’t enough if you have some tenuous connections to the wider cultural zeitgeist.

    • Sandgroper

      Definitely not in just one country. In my observation (not trivial) it’s a universal.

      • Sandgroper

        Sorry…with the exceptions such as Karl has mentioned, which also applies to European children in Chinese-speaking societies.

  • Karl Zimmerman

    I’ve often considered a hypothetical society which was “communist” until you enter the workforce, “libertarian” after you do. If ensuring absolute equality of opportunity is the most important societal value, one could imagine a society where every effort is made to ensure a childhood and young adulthood which maximizes potential. Everyone is given access to the same educational system, and potentially even raised collectively by the state, to minimize differences in nurture. Assessment tests determine peoples initial talents and interests, and mold them to maximize these potentials. Once they reach whatever the pinnacle of education is for someone of their aptitude level, they’re left on their own. I’m not sure it would be workable, but it shows that in order to actually eliminate any environmental variance, we’d need to at least have child-rearing involve essentially totalitarian levels of government influence, which people coming from a liberal (in the classic sense) political tradition would abhor.

    As an aside, Judith Rich Harris’s other book, No Two Alike, was such a let down. Most of the book was essentially an update and elaboration of arguments from her first book. I thought she was actually going to elaborate on her hypothesis on how group socialization causes differences between personalities (say making the claim that if one is a “leader,” “follower,” or “outcast” it has varying effects on the different Big 5 traits), but she just ended the book suddenly with a “this is my hypothesis, people should test it!”

  • TheBrett

    Pre-school is probably too late to get some of the best early childhood intervention. Kevin Drum has mentioned that the most effective interventions happen when you get to the kids between 0-3 years old.

    • razibkhan

      i think early intervention is going to have positive results. just not the ones implied here.

    • Your Lying Eyes

      Yeah, it’s kind of amusing watching the CW shift on this so rapidly. Just a few months ago, when Obama gave his State of the Union, we were all so sure universal Pre-K would do the trick. But now we all know it must truly be before even pre-school where interventions are necessary, because the gap is already there at 3. And, since the gap isn’t fair, and unfair things are wrong, clearly then it must be fixable.

  • razibkhan


    • marcel proust

      cat got your tongue? 😉

      Thanks for the response to my question earlier. I’ll have to read some more to understand your answer (it too is a bit terse given my understanding).

      – I don’t understand the sentence fragment reference, “gene-to-gene.”

      – Also, I realize that I’ve long assumed, perhaps reasonably (or correctly) perhaps not, that most environmental effects are non-linear. When thinking about environmental poisons, for very small quantities, the body can respond and perfectly repair insults up to a very low threshold. Above that threshold, there may be a linear response, the body’s being able to repair less and less, until some higher threshhold, where the body just becomes too weak and sick to respond effectively at all.

      But I think you were talking in the OP about “environment” largely in terms of behavioral interventions, by parents, schools and other institutions. I’m not sure how you would measure the size of the intervention here to determine linearity. Hours in pre-school?

  • Your Lying Eyes

    What are heritable non-genetic effects? Is that another term for shared environment?

    • GenghisTemujin

      Yes, but only if you include all the Rumsfeldian unknown unknowns, like specific eccentricities of the ancestral environments (both close and distant) of all the independent agents being acted on (e.g. any specific genetically/chromosomally/otherwise-localized worldlines involved. Also: organisms, ambiguously-owned connections to uteri, anything falling on one or more of the contradictory spectra of parasitesymbiote, etc.).

  • Karl Zimmerman

    As a leftist (hell, an actual socialist) I see nothing disagreeable with the statement that the poor are less intelligent.

    Certainly there can be debate about the degree to which it is true. Many wealthy people can be duller than you would expect by their economic status, and many individual poor people will be intelligent, but for one reason or another (bad luck, bad policy, or having other traits which make success difficult, like low consciousnesses) didn’t make it out of poverty.

    But to argue that there is no difference in intelligence as you go up the economic scale, you have to do one of two things.

    1. Be such an extreme blank slater that you think there is no hereditary component to intelligence at all. Which does not fit the preponderance of data.

    2. Conclude that the modern West has zero meritocracy. That is to say, all of the meritocratic functions in both governance and the private market do not result in a society any more fair than the most rigid sort of feudalism would. This is ridiculous. We might argue they don’t go far enough, but minus some backsliding over the last 30 years modern western society is self-evidently more meritocratic than at any other time in global history.

  • Street Anthropologist

    Do you think intelligence is related to the acquisition of information that develop babies’ five senses and kids’ comprehension, thinking and reasoning?

    Growing up in a ghetto-where colors are mostly black and gray, usual sounds are gunshot and rap music, textures are dust and dirt, tastes are from canned goods and 99 cents store, and smells are from garbage and crack-of course babies will grow up dumb because of those limited information. Ghetto kids hang out at basketball courts and on gang-infested streets. What new information can they get from those same, familiar places where they grow up?

    I’m interested to read stuff on acquisition of information and brain development. Any recommendation?

  • pnard

    Well, has anyone come up with some model of evolution where offspring (in any species) can end up similar to their parents but the primary reason is not genes?


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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