In a previous post, I noted certain discrepancies between Luca Cavalli-Sforza’s current stand on the race concept and his earlier one. This reversal seems to have occurred between his 1976 book Genetics, Evolution, and Man and his 1994 opus The History and Geography of Human Genes (whose cover map is curiously at odds with his statement that human genetic variation does not cluster into racial groups).
Such a change of heart is all the more puzzling because the case against the race concept had already been made in 1972, when Richard Lewontin showed that genetic differences within human races greatly exceed genetic differences between human races. That was—and still is—the main argument for race denialism. If this argument failed to convince Cavalli-Sforza in 1976, what happened to make it more convincing in 1994?
This is all the more puzzling because several authors since 1972 have challenged Lewontin’s argument. Mitton (1977) and (1978) showed that within-race variation exceeds between-race variation only if one gene is examined at a time. The pattern reverses if several genes are examined at the same time. Another flaw in Lewontin's argument is that he used genetic data from genes that code for enzymes, blood groups, and various building blocks of human tissue. Yet these ‘structural’ genes appear to have been marginal to human evolutionary change. As Stephen J. Gould (1977, p. 406) noted:
Such a change of heart is all the more puzzling because the case against the race concept had already been made in 1972, when Richard Lewontin showed that genetic differences within human races greatly exceed genetic differences between human races. That was—and still is—the main argument for race denialism. If this argument failed to convince Cavalli-Sforza in 1976, what happened to make it more convincing in 1994?
This is all the more puzzling because several authors since 1972 have challenged Lewontin’s argument. Mitton (1977) and (1978) showed that within-race variation exceeds between-race variation only if one gene is examined at a time. The pattern reverses if several genes are examined at the same time. Another flaw in Lewontin's argument is that he used genetic data from genes that code for enzymes, blood groups, and various building blocks of human tissue. Yet these ‘structural’ genes appear to have been marginal to human evolutionary change. As Stephen J. Gould (1977, p. 406) noted:
The most important event in evolutionary biology during the past decade has been the development of electrophoretic techniques for the routine measurement of genetic variation in natural populations. Yet this imposing edifice of new data and interpretation rests upon the shaky foundation of its concentration on structural genes alone. (faute de mieux, to be sure; it is notoriously difficult to measure differences in genes that vary only in the timing and amount of their products in ontogeny, while genes that code for stable proteins are easily assessed).
Indeed, if we look at differences in structural genes we see a high degree of overlap not only between human populations but also between morphologically distinct species (see previous post).
So why did Cavalli-Sforza change his mind? A cynical answer was provided to me by one anthropologist: “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.”
Some light has been shed on this question by Sesardic (2010). Aside from being an excellent rebuttal of race denialism, this paper also quotes an unpublished manuscript by one of Cavalli-Sforza’s collaborators A.W.F. Edwards. The manuscript describes the following episode:
When in the 1960s I started working on the problem of reconstructing the course of human evolution from data on the frequencies of blood-group genes my colleague Luca Cavalli-Sforza and I sometimes unconsciously used the word ‘race’ interchangeably with ‘population’ in our publications. In one popular account, I wrote naturally of ‘the present races of man’. Quite recently I quoted the passage in an Italian publication, so it needed translating. Sensitive to the modern misgivings over the use of the word ‘race’, Cavalli-Sforza suggested I change it to ‘population’. At first I was reluctant to do so on the grounds that quotations should be accurate and not altered to meet contemporary sensibilities. But he pointed out that, as the original author, I was the only person who could possibly object.
References
Bodmer, W.F. & L.L. Cavalli-Sforza. (1976). Genetics, Evolution, and Man. WH Freeman and Company, San Francisco. pp 563-572.
Cavalli-Sforza, L.L., Menozzi, P. & Piazza, A. (1994). The History and Geography of Human Genes. Princeton: Princeton University Press.
Gould, S.J. (1977). Ontogeny and Phylogeny, Belknap Press: Cambridge (Mass.).
Lewontin, R.C. (1972). The apportionment of human diversity. Evolutionary Biology, 6, 381-398.
Mitton, J.B. (1977). Genetic differentiation of races of man as judged by single-locus and multilocus analyses, American Naturalist, 111, 203-212.
Mitton, J.B. (1978). Measurement of differentiation: reply to Lewontin, Powell, and Taylor, American Naturalist, 112, 1142-1144.
Sesardic, N. (2010). Race: a social destruction of a biological concept, Biol. Philos. early view.