I was shocked to discover that Professor DeLong actively and surreptitiously censors comments on his blog. You can read about it here. I can't explain his actions without assuming his goal is obfuscation, rather than truth seeking.
I've copied three of my comments below, originally posted to this discussion of human evolution. The third was removed without explanation.
Posted by: steve | Sep 12, 2005 7:55:47 PM
As mentioned, Brad's calculation neglects the possibility that mutations which might be adaptive in one environment are not necessarily adaptive in another.
According to the recent Lahn research (linked to by Anne, above), certain alleles of genes with direct effects on brain function have been subject to strong selection over the last tens of thousands of years. In certain populations (e.g., in Eurasia), the new alleles have rapidly replaced their predecessors, so they were clearly adaptive in those environments. In other populations (sub-Saharan Africa), the new alleles are rare, so they were probably less adaptive.
I don't know what will happen in the future, but current research shows that geographically isolated populations can have very different distributions of certain alleles, and not just those related to superficial features like skin or hair color.
Most fascinating is the possibility that relatively recent mutations had something to do with the rapid advancement of human civilization over the last 5000 years. (The ASPM variant may have emerged about that long ago.)
Posted by: steve | Sep 13, 2005 10:07:14 AM
As already noted, it will take hundreds of years (at minimum) for mixing to eliminate the correlations between genes and "race" (or ancestral geographic lineage) that we currently have. That is a very long time from the perspective of social policy, although not in evolutionary terms.
I am by no means a fan of Sullivan, but I think he is correct to say that most liberals (I am one myself) have, due to wishful thinking, gratefully accepted the "there is no scientific basis for race" line. Anne's post of the NYTimes op-ed by LeRoi gives the history of this facile, but now doomed, position. (Cochran's explanation above is very clear - better than LeRoi's.) I don't think most people appreciate that we are now on a Moore's Law growth curve for genomic information. Google "hapmap" and have a look for yourself at the state of the art.
Rather than rely on the scientifically unsupported claim that "we are all equal," it would be better to teach our students that we all have inalienable human rights regardless of our abilities or genetic make up. Continuing to rely on the false equality premise only undermines the liberal position on race issues.
Posted by: steve | 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%.