Gene Expression

Over the past week I’ve been asked via email and on message boards about about David Shenk’s new book, The Genius in All of Us: Why Everything You’ve Been Told About Genetics, Talent, and IQ Is Wrong. Since I haven’t read the book I can’t really comment, but I did finally listen to Will Wilkinson’s interview with Shenk on bloggingheads.tv. It seems to me that Will exhibited more clarity and precision in one sentence in relation to the term heritability than Shenk did in 10 minutes. It is true there are many people who don’t understand that 80% heritable does not mean that a trait is “80% genetic.” In fact, I really don’t know what a trait being “80% genetic” means in a precise sense, but I also know that long time readers of this weblog do fall into this trap.

Instead of reading Shenk’s book I strongly suspect that people might gain some more genuine insight about heritability and the genetics of complex traits by looking at what we know about height. We don’t know much in terms of the underlying genes; height seems to be controlled by many genes of small effect. But, we do know that in the developed world, where nutritional intakes have saturated, height is about ~80% heritable. That is, most of the variation in the population can be accounted for by variation in genes. There are probably gene-environment interactions in regards to the trait of height. For example, there may be individuals whose genotypes are more sensitive to nutritional deprivation than others, so that changing uniform nutritional intakes across a population may not change just the median of the distribution, but also the general shape. But those interaction effects are obviously not as important today in the developed world where malnutrition is very rare.

At least judging by the conversation with Wilkinson, and the title of the book, Shenk seems to want to spotlight people who are many standard deviations from the norm. For example, Mozart and Michael Jordan are arguably not 1 in 100, or even 1 in 1,000, in regards to their domains of virtuosity. I think that focusing this far out to the tails is interesting, and makes for good narrative as one can populate it with illustrative anecdotes, but on any given quantitative trait most people are going to be much closer to the median. Variation on the margins of the normal are very significant, and all too often ignored. In here that I think that the simplest models have the most utility. So you want to complexify, just focus on the outliers….

Note: Using Amazon’s search inside feature I see that Shenk mentions gene-environment interaction quite a bit, but not gene-environment correlation.

Comments

  1. #1 Chris
    March 16, 2010

    I had not known there were two different terms for gene/environment relationships. Good to know.

  2. #2 OneSTDV
    March 16, 2010

    I respond to a number of interviews and essays from Shenk:

    http://onestdv.blogspot.com/2010/03/responding-to-david-shenks-genuis-in.html

  3. #3 zlz
    March 16, 2010

    But variation on the margins of the normal are very significant.

    Do you mean “are not very significant”?

  4. #4 razib
    March 16, 2010

    Do you mean “are not very significant”?

    no, i meant significant. if you are 6’1 inch as an american white male you’re about 1 standard deviation above the norm. you’re taller than average (top 15% or so), but not very tall. nevertheless, this height makes a huge difference in dating and aspiring toward a management position in an organization. if you’re 7’1 you’re 5 standard deviations above the norm, and you’re at a height where your chances of playing pro basketball are pretty good. 7+ footers who have never played often are encouraged to because their height is enough. but these people are so rare that we need to weight down their significance. and also, i assume if you’re freakishly tall or short a simple additive & independent model of genetics is going to be a problem. but not so much if you’re 6’1.

  5. #5 zlz
    March 16, 2010

    Ah. I see. I had been wondering if you were making a “these are so freakishly rare and exceptional that they don’t invalidate the use of a simple theory that works nearly always” sort of argument. But, it seems you weren’t.

  6. #6 Meng Bomin
    March 17, 2010

    In addition to the overuse of outliers to illustrate what should have been points with regard to the general population, I was struck during the diavlog at how much he used gene-environment interaction to essentially downplay the existence of a genetic component to variation. A lot of what he said in the early parts of the interview were pretty generic, but toward the end he balked when Wilkinson suggested that genetics may have played a role in Jordan’s success in addition to the amount of practice that he was rather enthusiastically citing.

    The whole interview seemed like an act of obfuscation. Now, it may be that Shenk was just a little to trigger-happy and wanted to shoot down any sort of na├»ve hereditarian explanation of the topic, but the lack of clarity in his explanations in an interview suggests to me that his book isn’t particularly worth reading.

  7. #7 razib
    March 17, 2010

    as i told will in email, note that jordan was 5’11 inches as a sophomore. he gained at least 4 inches in high school, and another few inches in college. jordan surely had a strong work ethic, but he reached adult size a bit later than the typical male (not uncommon with basketball players, david robinson gained many inches in college too).

  8. #8 DavidB
    March 21, 2010

    There is a perennial market for books arguing that anyone (or anyone’s children) can be a genius. I haven’t read Shenk’s book, but I did read a book a few years ago by a British psychologist called Howe (now dead, I think), and it was rubbish. Howe’s main argument (and from what I’ve seen Shenk is similar) is that ‘genius’ (Mozart, Einstein), etc, involves a great deal of hard work, training, and discipline, and THEREFORE it is the product of nurture not nature. I think it would be quite a good informal IQ test for people to ask them to identify the fallacies in this ‘argument’.

  9. #9 DavidB
    March 23, 2010

    This is a review (not by me) of the Howe book I mentioned. The argument seems very similar to Shenk. I wonder if Shenk gives credit to Howe?
    http://dannyreviews.com/h/Genius_Explained.html

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