Turkheimer Contra Cochran
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July 07, 2018, 10:34 AM
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Professor Eric Turkheimer writes:


Posted at 12:38h in Eric Turkheimer – Gloomy Prospect Blog by Eric Turkheimer

… What about groups? I agree with Cochran: if someone found a well-understood genetic mechanism that had a deterministic effect on behavior within a close range, some IQ equivalent of webbed paws, and groups turned out to differ in that mechanism, the race-hereditarians would have what they want. But it hasn’t turned out that way. What a well-intentioned hereditarian ought to be doing is searching for a mechanism of that kind, and some of them are; more power to them. I don’t think they will be successful but I have no fundamental problem with the effort. That’s science. What hereditarians shouldn’t be doing is trying to twist basic data about polygenic heritability into false intuitions that genetically-based group differences in behavior are somehow inevitable. They aren’t. As I have said many times, if different groups of people were genetically “tuned” (Sam Harris’ term) to behave in certain ways, wouldn’t you think we would have some examples by now? Maybe not for IQ, for which moral-panicking liberals like me are holding back the inevitable progress of science, but for some other polygenic behavioral trait, innocent and uncontroversial? “Oh yes, we know that the Japanese tendency to be introverted is based in their genome, but Latin American love of salsa dancing turns out to be environmental.” But there is nothing, not one single thing.

Uh … It seems like we do have many examples. Danes have a more milk-drinking culture than do Vietnamese. Sherpas are more likely to be employed as a Himalaya guides than lowlanders. Kenyans are more likely to be in the distance running business than Hindus or Senegalese. In South Central Los Angeles, African Americans are more likely to get basketball scholarships than their Mexican American neighbors. Mexican American high school baseball players are less likely to be pitchers than their white American teammates due to their shorter average stature. Budapest Jews have a more literate lifestyle than do Budapest Gypsies. Germans are more into tanning and nudism than are Arabs. There hasn’t been a non-black starting cornerback in the NFL since 2003.

I could go on for hours like this. Now, no doubt some of my examples are wrong, yet as Sam Spade counts off his reasons for why he “won’t play the sap:”

“But look at the number of them.”

Turkheimer also makes an argument much like one I’ve often used about how the existence of average differences betweens races is not all that much different from the existence of individual differences within extended families. As I’ve several times said, even identical twins are not identical. Turkheimer says:

Say the heritability of IQ is .5. What does the distribution of differences between identical twins look like? This is a concrete way of estimating the quantity we actually want to know: how much can IQ vary, conditional on a fixed genotype? There are complications, like measurement error which reduces heritability, and restriction of environmental variance and gene-environmental correlation, which inflate heritability—call it a wash. With a heritability of .5, the standard deviation of the non-genetic variance in IQ, the distribution of IQ within identical twin pairs is sqrt(.5*225)=10.58. …

Very large IQ differences are plausible for IQ with a heritability of .5. We don’t really want to know the mean of this distribution (it’s just a transformation of the variance), we want the plausible range. The very upper tail would be pairs in which one member got hit on the head by a brick or something, so let’s take the 90th percentile as an estimate of things that might plausibly happen in the real world. The 90th percentile is 26 points. A 26 point difference for a heritable trait in people with exactly the same genome. Golden retriever swimming ability isn’t going to come out like that. Sure, you could play around with the parameters, but it is almost impossible to get it down to anything resembling the 12-15 point difference that tends to be of interest, and this is between identical twins.

Of course, an obvious difference in differences between identical twins and between members of different races is that you can’t really predict which direction the difference between identical twins will run. It’s quite random or at least fairly mysterious. In contrast, race is not determinative but informative in, say, predicting which athlete might become an NFL starting cornerback.

Simple take away: human behavior is very malleable conditional on genotype.

But “malleable” isn’t the ideal word since it implies that we know how to social engineer consistent differences, whereas much of the difference tends to be random or at least obscure.

As I wrote in my review of Carl Zimmer’s book:

A subtle problem with Lewontin’s observation is that its proponents want you to believe it’s absolutely true, but it actually only works relativistically.

Lewontin’s 15 to 85 ratio for racial groups compared to the whole human race is similar to the genetic diversity ratios found within families compared to their racial group.

On average, two people of the same racial group are about as genetically similar to each other compared to the rest of the world as an uncle and nephew are to each other versus the rest of their racial group.

As you’ve noticed, there is both genetic diversity and similarity within families. For example, the author tends to portray his brother as possessing quite a different personality from him, which no doubt he does in many ways. Yet, in other fashions, the two brothers aren’t really all that different: Carl Zimmer is a genetics journalist for The New York Times, and his brother Ben Zimmer is a linguistics journalist for The Wall Street Journal.

Half full and half empty, heredity and environment, nature and nurture, similarity and diversity, lumping and splitting, absolute and relative … These concepts may seem like warring dichotomies that can’t be reconciled, but they are better understood as useful complements.

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