I mentioned below that Berkeley economist Brad DeLong had issued on his "reality-based" blog a self-satisfied mathematical proof that the distribution of genes around the world must be homogenous, even thought as you know and I know, but Brad doesn't know, they aren't. A lively argument then broke out in his Comments section.
What's interesting is that the eminent professor has now gone through his Comments section and deleted many posts that undermine his worldview. Where does he find the time? Unfortunately, he forgets to delete the responses by his supporters attempting to answer the now-deleted heresies, making the experience rather like looking at those pictures from the Bolshevik Revolution pictures where Stalin had Trotsky airbrushed out from Lenin's side.
Physicist Steve Hsu sends me the following section from DeLong's comments, in which DeLong left the original comment by his supporter and then deleted the responses by Gregory Cochran and Hsu. This first commented passed muster with DeLong:
Posted by: bambi vs godzilla | Sep 13, 2005 8:58:15 PM
Defined as genetically distinct groups, races don't exist. That’s what I learned, anyway, and nothing anyone has written here suggests I wasn’t paying attention to the teacher. Yes, some groups differ genetically from others; but how you divide groups depends on which genes you decide to examine. That means that if you are prepared to look obsessively you can find genetic markers to distinguish Poles from Swedes. For example, Swedes might have more wrinkly foreskins. Thus, Poles and Swedes are “different.” Great!
AFAIK (admittedly not very much) genetic diversity is irreducible. But if in fact there is a way to divide groups genetically that isn’t arbitrary, then fine, what is it? If in fact someone has devised a method to place an individual into one and only one racial group, what is that method?
But Cochran's and Hsu's were too horrible to be allowed to remain:
Posted by: gcochran | Sep 13, 2005 9:52:37 PM
As for your teacher, and the other people who said this kind of thing - well, mistakes were made. The key is that a given allele that is especially common in Swedes is correlated with _other_ alleles that are especially common in Swedes. Do principal component analysis on the covariance matrix for many loci (or cluster analysis) and !presto! - Bob's your uncle.
When someone like Jared Diamond talks this talk, you'd almost think that he doesn't know any population genetics.
Posted by: steve [Hsu] | Sep 13, 2005 11:17:21 PM
"Do principal component analysis on the covariance matrix for many loci (or cluster analysis) and !presto! - Bob's your uncle."
This gets right to the point (see an earlier post by gcochran for a less terse explanation). Too bad that very few readers here will understand (or even try to understand) what it means. Bambi vs Godzilla had the insight to ask the question properly. Will he or she make the effort to understand the answer?
Imagine each individual's genetic code as a point in a space of *very high* dimension. Then look at clusters of points. (Define a cluster as a group of points whose distance from each other is less than some radius; distinct clusters are separated by distances larger than this radius.) These clusters map directly onto traditional groupings of ethnicity. In fact, a recent study by Neil Risch at UCSF showed that self-reported "race" correlates very well with the clustering results. (Mixed race people are obviously an exception, but as discussed they are a small fraction of the total population, and will continue to be for some time.)
People (especially professors of social science) who confidently state to their students that "there is no genetic basis for race" should think through the analysis described above and look at the data carefully if they want to retain their credentials as scientists.
From the conclusions of the Risch paper (Am. J. Hum. Genet. 76:268–275, 2005):
Attention has recently focused on genetic structure in the human population. Some have argued that the amount of genetic variation within populations dwarfs the variation between populations, suggesting that discrete genetic categories are not useful (Lewontin 1972; Cooper et al. 2003; Haga and Venter 2003). On the other hand, several studies have shown that individuals tend to cluster genetically with others of the same ancestral geographic origins (Mountain and Cavalli-Sforza 1997; Stephens et al. 2001; Bamshad et al. 2003). Prior studies have generally been performed on a relatively small number of individuals and/or markers. A recent study (Rosenberg et al. 2002) examined 377 autosomal micro-satellite markers in 1,056 individuals from a global sample of 52 populations and found significant evidence of genetic clustering, largely along geographic (continental) lines. Consistent with prior studies, the major genetic clusters consisted of Europeans/West Asians (whites), sub-Saharan Africans, East Asians, Pacific Islanders, and Native Americans. ethnic groups living in the United States, with a discrepancy rate of only 0.14%.
You know, I'm all for that First Amendment thing, but you've got to draw the line somewhere. I mean, we just can't have physicists going around in public saying things like:
"Imagine each individual's genetic code as a point in a space of *very high* dimension. Then look at clusters of points. (Define a cluster as a group of points whose distance from each other is less than some radius; distinct clusters are separated by distances larger than this radius.) These clusters map directly onto traditional groupings of ethnicity."
Think of the children!