A late convert

Cavalli-Sforza with Kistler Prize (2002). The paths of Glory lead …

Human Biology has interviewed Luigi Luca Cavalli-Sforza, probably the best-known human geneticist (Manni, 2010). His worry? The growing rift between anthropology and biology:

Unfortunately, at least in the United States, anthropology is in decline: The cultural moiety is separating from the rest and loves to declare that it is not science—what is it, instead? The rest of the U.S. anthropology departments (variable according to places, but mostly a mixture of physical anthropology, primatology, archaeology, linguistics) fortunately seem to resist this trend, but anthropology seems to be losing ground. There is a need for a new anthropology capable of keeping unity, and to develop human science curricula that may promote an original, fresh outlook.

Why this retreat from biology? Ask almost any anthropologist. You’ll be told that there is much more genetic variation within human populations than between them. With culture, we see the reverse: the differences are primarily between populations. So how can genetic differences explain cultural differences? Such explanations are inevitably wrong and, needless to say, dangerous.

And you’ll be told that this view is endorsed by all credible geneticists, including Cavalli-Sforza. Just read the same interview:

Don’t you feel that results pointing to intracontinental genetic differences can reinforce racist theories, as some pharmacogenomic studies recently did?

LLCS: The between-population genetic variation observed with 650,000 SNPs on the 52 populations of the HGDP is 11% (Li et al. 2008) with a very small standard error. It becomes 16% for the X chromosome, as is expected if nearly all the genetic variation is due to drift—that is, the role of natural selection is very limited. The ca. 30-year-old estimate by Lewontin (1972) of this quantity (15%) was based on other markers and populations and was a reason to encourage banning the use of the word race in humans. In any case the new value is even more supportive of dropping the word race. What we really need to ban is racism, and this is not a socially easy-to-do program. Charles Darwin, already, was skeptical about the usefulness of the race concept in humans, having noted that human variation is geographically almost continuous for most traits.

Man has been studied more carefully than any other animal, and yet there is the greatest possible diversity amongst capable judges whether he should be classed as a single species or race, or as two (Virey), as three (Jacquinot), as four (Kant), five (Blumenbach), six (Buffon), seven (Hunter), eight (Agassiz), eleven (Pickering), fifteen (Bory St. Vincent), sixteen (Desmoulins), twenty-two (Morton), sixty (Crawfurd), or as sixty-three, according to Burke. This diversity of judgment does not prove that the races ought not to be ranked as species, but it shows that they graduate into each other, and that it is hardly possible to discover clear distinctive characters between them. (Darwin 1871: 226)

Well, no. Darwin was not “skeptical about the usefulness of the race concept in humans” In the above quote, he was denying that humans had diverged into different species. But he did not deny the reality of human races, as he stated a few pages previously:

There is, however, no doubt that the various races, when carefully compared and measured, differ much from each other,—as in the texture of the hair, the relative proportions of all parts of the body, the capacity of the lungs, the form and capacity of the skull, and even in the convolutions of the brain. But it would be an endless task to specify the numerous points of difference.

[…] If a naturalist, who had never before seen a Negro, Hottentot, Australian, or Mongolian, were to compare them, he would at once perceive that they differed in a multitude of characters, some of slight and some of considerable importance. On enquiry he would find that they were adapted to live under widely different climates, and that they differed somewhat in bodily constitution and mental disposition. If he were then told that hundreds of similar specimens could be brought from the same countries, he would assuredly declare that they were as good species as many to which he had been in the habit of affixing specific names.

But why bother quoting Darwin? It’s more fun to quote Cavalli-Sforza!

The differences that exist between the major racial groups are such that races could be called subspecies if we adopted for man a criterion suggested by Mayr (1963) for systematic zoology. Mayr’s criterion is that two or more groups become subspecies when 75 percent or more of all the individuals constituting the groups can be unequivocally classified as belonging to a particular group. As a matter of fact, when human races are defined fairly broadly, we could achieve a much lower error of classification than 25 percent, implying, according to Mayr, the existence of human subspecies. (Cavalli-Sforza & Bodmer, 1977)

Well, that was Cavalli-Sforza back in 1977. Perhaps he was still unaware of Richard Lewontin’s finding that genes vary much more within human populations than between them. Was not this “a reason to encourage banning the use of the word race in humans”?

Except that Lewontin had published that reason in 1972. Five years later, Cavalli-Sforza was apparently still unimpressed. And he continued to use the race concept much later, as in this journal article from the late 1980s:

The first split in the phylo-genetic tree separates Africans from non-Africans, and the second separates two major clusters, one corresponding to Caucasoids, East Asians, Arctic populations, and American natives, and the other to Southeast Asians, (mainland and insular), Pacific islanders, and New Guineans and Australians (Cavalli-Sforza et al., 1988).

Cavalli-Sforza did not convert to race denialism until the mid-1990s, with his opus The History and Geography of Human Genes.

What motivated his conversion? Had Lewontin’s 1972 paper been further bolstered by new data and arguments? Not really. In fact, the 1980s and 1990s saw growing evidence that the same genetic overlap that Lewontin found between human populations also occurs between many species that are nonetheless distinct in anatomy, physiology, and behavior (see previous post).

As one anthropologist told me: “I don't think our perception of the general patterns of genetic variation changed much from '76 to '94, but the intellectual climate that geneticists operate in sure did.”

References

Cavalli-Sforza, L.L., P. Menozzi, and A. Piazza. (1994). The History and Geography of Human Genes. Princeton: Princeton University Press.

Cavalli-Sforza, L.L., A. Piazza, P. Menozzi, and J. Mountain. (1988). Reconstruction of human evolution: Bringing together genetic, archaeological, and linguistic data. Proc. Natl. Acad. Sci. USA, 85, 6002-6006.

Cavalli-Sforza, L.L. and W.F. Bodmer. (1977). The Genetics of Human Populations, San Francisco: W.H. Freeman and Co.

Darwin, C. R. (1871). The Descent of Man, and Selection in Relation to Sex. London: John Murray.

Lewontin, R.C. (1972). The apportionment of human diversity. Evolutionary Biology, 6,
381-398.

Manni, F. (2010). Interview with Luigi Luca Cavalli-Sforza: Past research and directions for future investigations in human population genetics, Human Biology, 82, 245–266.