Judith Rich Harris & nurture & nature

Since Bradlaugh & Heather have mentioned Judith Rich Harris, I would recommend both of her books, The Nurture Assumption & No Two Alike to any reader who wishes be introduced to behavior genetics.   You can also check out my interview of Harris from a few years back. For the more politically inclined, a summary of a discussion in The Corner about Ms. Harris’ ideas.

The core of Judith Rich Harris’ reason for offering her thesis is simple; for decades behavioral geneticists have found that on a wide range of traits human population level variation is predicted by the following components:

50% genetic variation
10% shared environment variation
40% other environment variation

You can dispute the details about the specific number, but, the short of it is that “shared environment,” the environment we experience growing up as children within the family, seems to have a much smaller longer term predictive effect than genetic variation and other environmental variation.  The “other environmental variation” is somewhat squirrely.  It could for example be reducible down to biological components, such as gene-gene interactions, or developmental noise.  Judith Rich Harris argues that that other 40% are our peers, or, specifically peer culture.

When I say that 50% of the variation in the population can be accounted for by genes, I do not mean that the trait is “50% genetic.”  I mean that if you look at genetic variation, from that you can already predict 50% of the variation of the distribution of the trait across the population.  To make it more concrete, consider that genetics accounts for 80-90% of the variation in height in developed nations, but less in developing nations.  How to interpret this?  In developed nations nutritional inputs are maximized so that variation in height is not predicted by what you eat, because everyone receives a sufficient amount of calories for optimal development. In contrast in many developing nations there is variation in caloric intake so that some people are short simply due to a lack of nutritional inputs.  So more of the variation can be predicted by environmental variation in a society where there is more environmental variation. In developed nations there is very little operational nurtitional variation when it comes to inputs which determine height; beyond a certain number of calories humans increase in size horizontally as opposed to vertically. Naturally the only variance that remains is genetic, ergo, height is more heritable in developed nations.

What does this have to do with personality and behavior?  In a society which is fragmented into various subcultures one assumes that predicting from genes to trait value will be dicier because all things are not controlled. In other words, cultural framework matters, but within that framework variance still remains.  Judith Rich Harris makes the provocative argument that selection of peers are more efficacious in affecting life outcomes in offspring than direct parental modelling.  Perhaps being from a broken home is less important than your peers being from broken homes.  Within families this naturally results in much of the variance in sibling outcomes being due to their varied genetic endowments because they likely share peer environment.

How does this affect politics and public policy? I believe it makes the model of human psychological and social development more complex.  It also suggests that there will be limits on what environment can do to eliminate inequality or variation.  It also implies that a certain level of goodness or badness may be “baked in the cake,” so to speak.

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4 Responses to Judith Rich Harris & nurture & nature

  1. Ron Guhname says:

    According to sociological research, peers are very important, but it’s very difficult to choose friends for your kids. The best strategy seems to be to choose the best environments for your kids, school being foremost, and to try to break off bad friendships before they get started. Once they’re formed, pack it in–you’re done.

    Or pray (good term for this forum) that your kid prefers the company of adults.

    The friendship dilemma is obviously one that the government is not going to fix. Not even Obama.

  2. Jason Malloy says:

    I think Harris was wrong; the research actually shows that parents are more important than peers. Even when there is no genetic relationship parents have a meaningful effect on behaviors like smoking and drinking.

    Meanwhile, people seek out their own best-matched peers, so simply moving to a better neighborhood doesn’t seem to have much effect on behaviors. If lil’ Timmy liked rollin’ with the Gs when he lived in the hood, he’ll probably be able to locate a similar crowd (with a little more effort) when the family packs up for Vermont.

  3. Jason Malloy says:

    Adding that both influences are relatively small.

  4. ◄Dave► says:

    I tried three times to post this comment on the following No Two Alike thread; but it just disappears. Since the subject is the same, I’ll try part of it here…

    Stephen Pinker has written eloquently on this topic in his book, “Blank Slate.” From the Preface:

    The idea that nature and nurture interact to shape some part of the mind might turn out to be wrong, but it is not wishy-washy or unexceptionable, even in the twenty-first century, thousands of years after the issue was framed. When it comes to explaining human thought and behavior, the possibility that heredity plays any role at all still has the power to shock. To acknowledge human nature, many think, is to endorse racism, sexism, war, greed, genocide, nihilism, reactionary politics, and neglect of children and the disadvantaged. Any claim that the mind has an innate organization strikes people not as a hypothesis that might be incorrect but as a thought it is immoral to think.
    The taboo on human nature has not just put blinkers on researchers but turned any discussion of it into a heresy that must be stamped out. Many writers are so desperate to discredit any suggestion of an innate human constitution that they have thrown logic and civility out the window. Elementary distinctions — “some” versus “all,” “probable” versus “always,” “is” versus “ought” — are eagerly flouted to paint human nature as an extremist doctrine and thereby steer readers away from it. The analysis of ideas is commonly replaced by political smears and personal attacks. This poisoning of the intellectual atmosphere has left us unequipped to analyze pressing issues about human nature just as new scientific discoveries are making them acute.
    An honest discussion of human nature has never been more timely. Throughout the twentieth century, many intellectuals tried to rest principles of decency on fragile factual claims such as that human beings are biologically indistinguishable, harbor no ignoble motives, and are utterly free in their ability to make choices. These claims are now being called into question by discoveries in the sciences of mind, brain, genes, and evolution. If nothing else, the completion of the Human Genome Project, with its promise of an unprecedented understanding of the genetic roots of the intellect and the emotions, should serve as a wake-up call. The new scientific challenge to the denial of human nature leaves us with a challenge. If we are not to abandon values such as peace and equality, or our commitments to science and truth, then we must pry these values away from claims about our psychological makeup that are vulnerable to being proven false.

    Exploring the nature of mind and consciousness being an avocation of mine, I have come to really appreciate Pinker’s work. ◄Dave►

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