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March 08, 2005

Reading Books is Hard!

Looking again at my old Psych 101 textbook earlier today, I found this passage:

Consider, first, not people but tomatoes. (This "thought experiment," illustrated in Figure 6.5 on the next page, is based on Lewontin, 1970.) Suppose you have a bag of tomato seeds that vary genetically; all things being equal, some will produce tomatoes that are puny and tasteless, and some will produce tomatoes that are plump and delicious. Now you take a bunch of these seeds in your left hand and another bunch in your right hand. Though one seed differs genetically from another, there is no average difference between the seeds in your left hand and those in your right. You plant the left hand's seeds in pot A, with some soil that you have doctored with nitrogen and other nutrients, and you plant the right hand's seeds in pot B, with soil from which you have extracted nutrients. When the tomato plants grow, they will vary within each pot in terms of height, the number of tomatoes produced, and the size of the tomatoes, purely because of genetic differences. But there will also be an average difference between the plants in pot A and those in pot B: The plants in pot A will be healthier and bear more tomatoes. This difference between pots is due entirely to the different soils -- even though the heritability of the within-pot differences is 100 percent.


For example, in the much-discussed book The Bell Curve: Intelligence and Class Structure in American Life (1994), the late psychologist Richard Herrnstein and conservative political theorist Charles Murray cited heritability studies done mostly with whites to imply that the gap in IQ scores between the average white and the average black child can never be closed. Wade & Tavris, Invitation to Psychology, 1999, pg. 212

Compare that with this:

As we discussed in Chapter 4, scholars accept that IQ is substantially heritable, somewhere between 40 and 80 percent, meaning that much of the observed variation in IQ is genetic. And yet this tells us nothing for sure about the origin of the differences between races in measured intelligence. This point is so basic, and so commonly misunderstood, that it deserves emphasis: That a trait is genetically transmitted in individuals does not mean that group differences in that trait are also genetic in origin. Anyone who doubts this assertion may take two handfuls of genetically identical seed corn and plant one handful in Iowa, the other in the Mojave Desert, and let nature (i.e., the environment) take its course. The seeds will grow in Iowa, not in the Mojave, and the result will have nothing to do with genetic differences. Herrnstein & Murray, The Bell Curve, 1994, pg. 298

Oopsie. Isn't there also a discussion, on page 313, of how heritable group differences are not necessarily any more or less immutable than environmental differences?

Its shocking to me -- shocking -- that the authors of a textbook couldn't be bothered to actually read their sources and/or report them accurately.

Posted by God Fearing Atheist at 06:18 PM