The evolution of Cavalli-Sforza. Part VI

A composite map of human genetic variation appeared on the cover of Cavalli-Sforza’s tome The History and Geography of Human Genes (1994).

With the sudden end to his work on gene-culture co-evolution, Cavalli-Sforza returned to population genetics. Actually, he had never left it. He had always been looking for new population data and adding it to his global map of human genetic variation.

For any one gene, the map typically showed much more variation within than between human populations, just as Lewontin had found back in 1972. The pattern changed, however, when several gene maps were superimposed on each other. With data coming in from more and more genes, there emerged a distinct pattern of continental populations—the same ones that Cavalli-Sforza himself had once called “races.” This composite map would eventually appear on his tome The History and Geography of Human Genes (1994).

In 1991, he announced a new phase of his research: the Human Genome Diversity Project (HGDP), a program to collect and analyze DNA from all human populations. It would be the crowning achievement of his career. Among other things, it would “produce a mine of data to comprehensively explore human prehistory, determine the genetic relationships between the earth’s populations, and provide valuable information on human genetic diseases” (Stone & Lurquin 2005, p. 160).

Cavalli-Sforza did not expect controversy. After all, he had been pursuing this kind of research for the past twenty-five years. He had also done all the right things, including not saying anything about links between genetics and behavior. There was of course his Inuit study, but it had been aborted at the last minute. Finally, the project had support from a broad range of scientists, including his old colleague Walter Bodmer. It could not possibly go wrong.

It did go wrong. In fact, he had stuck his hand in a hornet’s nest. For the first time in his life, people were denouncing him as a racist and the HGDP as a “vampire project.” He was flabbergasted by what seemed to be a big misunderstanding.

Yet there had been no misunderstanding. The new project violated principles that Cavalli-Sforza himself had earlier acquiesced to. This point was made by two opponents, Joseph Alper and Jon Beckwith, who denied that the HGDP would contribute anything worthwhile to the study of the human genome:

First, […] human beings share more than 99% of their DNA. Second, most of the total genetic variation in the human population occurs within any single group. Intragroup genetic variance is much larger than intergroup variance. Sampling U.S. residents alone with their enormous range of ethnic and racial backgrounds would probably encompass the vast bulk of human variation. It would be hard to justify the cost of the HGDP if its goal were merely to obtain the remaining small amount of genetic variance not accounted for by sampling only U.S. and/or European residents.
(Alper & Beckwith 1999)

This is the same argument that Richard Lewontin had made in 1972 (1). Genes vary much more within human populations than between them. In fact, over 85% of human genetic variation cannot be linked to populations of any kind. It exists only among individuals that belong to the same population (Lewontin 1972). Because this argument met with little or no opposition from other geneticists, including Cavalli-Sforza, it steadily won over more and more people, eventually becoming conventional wisdom by the 1990s.

At worst, however, Lewontin’s finding simply meant that Cavalli-Sforza was wasting his time. Why make a fuss? Since when is it racist to waste your time?

I remember putting a similar question to an anthropology professor. Why were sociobiologists “racists” when most of them never said anything about race or race-related issues? He looked at me thoughtfully, as if the usual answers wouldn’t work with me. He finally replied that sociobiologists were engaging in “unnecessary debates.” He paused and then added: “Besides, you never know where this stuff will lead to.”

There was nothing racist in the HGDP by itself. It did, however, draw attention to the existence of human populations and could therefore frame questions about the ways people differ from each other:

[…] we argue that because the aim of the HGDP is to define genetic differences and similarities among peoples, the potential for racism is inherent in the study design of the project.
(Alper & Beckwith 1999)

What most concerns us is not competition for research funds, although this is an issue in a lightly funded discipline. Rather, what most concerns us is the construct of human variation that the project might embody and reify, and the type of training and socialization that the project will provide for young physical anthropologists. (Goodman & Armelagos 1996, p. 182)

In the face of these attacks on the HGDP, the only successful counterattack would have been to demolish Lewontin’s argument. Cavalli-Sforza could have pointed out that genetic variation between populations differs qualitatively from genetic variation within populations. He could have likewise pointed out that genes vary much more within than between certain species that are nonetheless distinct from each other anatomically, physiologically, and behaviorally.

Instead, he chose the path of least resistance. He began to cite Lewontin’s 1972 paper after having ignored it for two decades. He also began to argue that the HGDP provided further proof for Lewontin’s conclusions:

Last year the Human Genome Diversity Project used 1990s genetics to extend Lewontin’s analysis. Its conclusion: genetic variation from one individual to another of the same “race” swamps the average differences between racial groupings. The more we learn about humankind’s genetic differences, says geneticist Luca Cavalli-Sforza of Stanford University, who chairs the committee that directs the biodiversity project, the more we see that they have almost nothing to do with what we call race.
(Begley 1995, p. 67)

Yet all of this was beside the point. If Lewontin was right, the HGDP was wrong—or at least not needed, as two of its opponents noted:

Perhaps, in the right hands, the data will prove once and for all that races are abstractions, that, as Marie-Claire King (1993) says, we will find so much within group variation that the project will be a key to a non-racial science. But, we have known for at least twenty years that within group variation is so much greater than between group variation (Lewontin 1972). We do not need a very expensive data collection exercise to show this. The data are already at hand.
(Goodman & Armelagos 1996, pp. 181-182)

Cavalli-Sforza failed to see the substantive nature of attacks on the HGDP (2). The attacks were fueled not by a horrible misunderstanding, but rather by a sincere belief that very little genetic variation actually exists between human populations. The project was therefore at best unnecessary and at worst mischievous.

He could have met that belief head on by explaining why it was mistaken. Instead, he embraced it as a gesture of good faith.

Perhaps he did see what was going on. Perhaps he thought he could outfox his opponents—by appearing to give them everything they wanted while keeping the essential. Such a double jeu can work if one’s opponents are easily fooled.

But these ones weren’t. The funding dried up and many researchers who had initially been interested began to shy away. Contrary to what Cavalli-Sforza states in his autobiography, the HGDP remains uncompleted to this day, at least in its originally intended form.

Notes

1. Richard Lewontin did not specifically criticize Cavalli-Sforza’s project, but he did attack HUGO (the Human Genome Project). He was in fact one of the first, if not the first, to denounce human genome studies:

[…] simple internal forces, the genes, are now held responsible not only for human health in its normal medical sense but for a variety of social problems, among them alcoholism, criminality, drug addiction, and mental disorders. […] The current manifestation of that belief in the importance of our inheritance in determining health and disease is the human genome sequencing project, a multibillion-dollar program of American and European biologists that is meant to take the place of space programs as the current great consumer of public money in the interest of conquering nature.
(Lewontin 1991, p. 46)

It is unclear what role Lewontin played in mobilizing subsequent opposition to the HGDP. The usual view is that this opposition was spontaneous and broad-based, being largely made up of critics from post-colonial, non-Western societies. This view ignores the role of a vanguard of Western academics, like Lewontin, who had earlier identified such research as a target to be attacked.

2. In his autobiography, Cavalli-Sforza mentions only the opposition from a private Canadian foundation, RAFI (Rural Advancement Foundation International):

I think they were simply short of money. Being in contact with many indigenous groups in the Americas and Oceania, they sought to advertise their merits by criticizing our project. They spread the rumor that we wanted to patent DNA to enrich ourselves and to exploit the indigenous peoples, as many biotech companies had already done by patenting plant hybrids. In addition, we would be able to spread discriminatory information about these peoples or even prepare biological bombs against certain ethnic groups. These rumors were totally unfounded, but they found receptive listeners and enabled the foundation RAFI that propagated them to survive another eight or nine years. (Cavalli-Sforza & Cavalli-Sforza 2008, p. 233).

References

Alper, J.S. and J. Beckwith. (1999). Racism: A central problem for the Human Genome Diversity Project, Politics and the Life Sciences, 18, 285-288.

Begley, S. (1995). Three is not enough. Surprising new lessons from the controversial science of race, Newsweek, February 13, pp. 67-69.

Cavalli-Sforza, L.L. and F. Cavalli-Sforza (2008). La génétique des populations : histoire d'une découverte, Paris: Odile Jacob. (translation of Perché la scienza : L’aventura di un ricercatore).

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

Goodman, A.H. and G.J. Armelagos (1996). The resurrection of race: The concept of race in physical anthropology in the 1990s, in L.T. Reynolds and L. Lieberman (eds), Race and Other Misadventures: Essays in Honor of Ashley Montagu in his Ninetieth Year, General Hall: Dix Hills (NY), pp. 174-185.

Lewontin, R. (1991). Biology as Ideology. The Doctrine of DNA, Toronto: House of Anansi.

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

Stone, L. and P.F. Lurquin. (2005). A Genetic and Cultural Odyssey. The Life and Work of L. Luca Cavalli-Sforza. New York: Columbia University Press.

The evolution of Cavalli-Sforza. Part V

Inuit man making a soapstone carving.

The 1970s saw L.L. Cavalli-Sforza become a renowned human geneticist. His meteoric rise was made possible by two textbooks co-authored with Walter Bodmer: The Genetics of Human Populations (1971) and Genetics, Evolution, and Man (1976), as well as several joint articles in leading journals.

Nonetheless, his collaboration with Bodmer came to an end in the late 1970s (1). Why? No answer is given in his autobiography or in Stone and Lurquin’s biography. In fact, the autobiography has only three mentions of Bodmer. Two are single sentences. The one lengthy mention gives the impression of “damning with faint praise” (2).

To understand how this collaboration ended, one must understand how it began … in a triangular relationship that brought together not only Cavalli-Sforza and Walter Bodmer but also Joshua Lederberg, the leading geneticist at Stanford. It was the latter who helped him during the difficult postwar years, who invited him to Stanford in 1968, and who got him a permanent position there in 1972. It was also Lederberg and one of his protégés, Bodmer, who showed him the ins and outs of American academia, especially textbook publishing. Cavalli-Sforza naturally felt indebted to the two of them.

By the late 1970s, he had a long list of publications and felt reasonably secure. Perhaps he began to feel hindered by his collaboration with Bodmer. Or perhaps Bodmer seemed to be taking more out of it than he was putting in. Or perhaps …

One thing is clear. Cavalli-Sforza was planning to study how our species had evolved genetically under the influence of history and culture. Such plans could not include Bodmer, who knew little about human genetics and even less about the other two.

Cavalli-Sforza wanted to bring all three elements together to show that the natural environment has not been the main driving force of natural selection in our species. We have instead undergone selection by human culture—oral and written language, social organization, technology, means of subsistence, and so forth. In short, we have been created by our own creations.

This point was already being raised in the late 1970s as an argument against genetic determinism. Unlike other animals, we do not adapt to our environment through changes to our genes. We instead change our environment to make it better adapted to us. Therefore, it is our environment that does the changing, not our genes.

Cavalli-Sforza realized that this argument was overstated. Clearly, humans have changed genetically in order to inhabit a wide range of natural environments from the equator to the arctic. A Dinka and an Inuit differ anatomically and physiologically in many obvious ways.

But the critics of genetic determinism had missed another point. If our environment is now dominated by our cultural creations, it follows that these creations also dominate our adaptive landscape—we adapt primarily to our cultural environment and only secondarily to our natural environment. Thus, genetic change has come about primarily to make us better adapted to ourselves and our creations.

This in turn leads to two conclusions:

1. Human genetic evolution has accelerated in response to the quickening pace of human cultural evolution.

2. Each human culture has created its own adaptive landscape. Genetic differences between human populations have been primarily responses to cultural differences.

This line of reasoning has a name: gene-culture co-evolution. It can be traced back to Darwin, but there was a resurgence in the early 1980s with the writings of Robert Boyd and Peter Richerson, particularly Culture and the Evolutionary Process (1985). I had always assumed that it all began with that book, but the ground zero actually seems to have been a cultural evolution class that Cavalli-Sforza taught to Boyd and Richerson in 1978-79 (Stone & Lurquin 2005, p. 108).

Cavalli-Sforza wished to prove the existence of gene-culture co-evolution. In the mid-1980s, he organized a project with several professors from Queen’s University (Kingston, Ontario) and Université Laval (Quebec City) (3). The aim was to determine whether natural selection favors different mental toolkits in hunting and gathering societies versus agricultural societies. This rationale was later described by one of his project associates, John Berry, a psychologist at Queen’s University:

Hunters, by this way of thinking, require good visual acuity, keen disembedding skills and a well- developed sense of spatial orientation. To hunt successfully, the hunter must be able to discern the object of the quest (which is often embedded in a complex visual landscape), then disembed the object, and finally return to home base. In contrast, agriculturalists need not develop these particular skills, but rather they need to invest in other areas of development, such as conservation (in both the economic and the Piagetian senses) and close social interactions. (Berry 2008, p. 3)

In this joint project, Cavalli-Sforza wished to study Inuit artists to see whether their talent came from a genetic predisposition or from socio-cultural learning. This aim is spelled out in an unpublished report he wrote with Berry:

One of the most remarkable phenomena in the contemporary Canadian Arctic is the presence of highly-acclaimed art forms — carving in stone and ivory, and printing on paper. The question we ask is: how can we account for the wide-spread distribution of such talent in a small dispersed population?

[…] Is it possible that artistic talent is transmitted culturally (from parents to offspring, from others in society to the artist, and from peers to artist)? How can we assess these types of transmission?

Is it possible that artistic talent is transmitted genetically (from parents to offspring)? How can we assess such transmission?
(Berry & Cavalli-Sforza 1986, p. 2)

The Inuit population lends itself to such a study for several reasons:

With most individuals having had a reasonably fair chance and stimulation to become artists, one is in a better condition to study possible genetic factors contributing to artistic talent, if any. Another great advantage of carrying out this study among the Inuit is the frequency with which adoptions (also early ones, at birth) occur in this population. Frequencies of adoptions reported during the meeting varied from 15% to 30%. Adoptions allow one to distinguish cultural from biological inheritance by studying correlations of adopted children with foster relatives on one hand and biological relatives on the other.

The general strategy will be to select artists in specific communities (to be discussed later), and to study artistic talent in particular. Also to be studied are their biological and foster relatives (if any), including parents, brothers, sisters, children, and more remote relatives (when this is feasible and convenient). “Controls”, i.e. individuals who lay no claim to artistic talent, in spite of adequately trying, may also have to be selected and studied in a similar fashion.

[…] The study of traits other than artistic talent per se, that may be correlated with it (and indeed may be components of it) will also be of interest. Given enough information one can hope to separately estimate two quantities, called respectively cultural and genetic heritability (see examples in analysis of IQ).
(Berry & Cavalli-Sforza 1986, p. 5)

The project fell through. At Laval, we assumed there had been a problem with funding. At Queen’s, Cavalli-Sforza explained that he could no longer continue because of illness.

In their biography, Stone and Lurquin (2005) make no mention of illness during this period, the only bouts of ill health being an operation for bladder cancer in 1976 and a heart attack in 1991. In any case, ill health would have been a reason for postponing the project, not for canceling it.

Even more curious, this project is not mentioned in any of his publications, be they books, journal articles, conference proceedings, or poster sessions. The paper trail is limited to his one unpublished report (Berry & Cavalli-Sforza 1986). A similar blank appears in his writings on gene-culture co-evolution. Although he has written abundantly on this concept, there is surprisingly little on one key element: the impact of cultural evolution on genetic evolution. When he does give examples, he limits himself to the usual suspects: lactose tolerance in cattle-raising societies, and malaria resistance in tropical agriculturalists (Cavalli-Sforza & Cavalli-Sforza 2008, p. 264). There is no trace anywhere in his published writings of a belief that natural selection has favored different mental traits in different cultural environments (4).

And yet he held such a belief back in the mid-1980s—a time when he almost became his own man.

Notes

1. Google Scholar lists 26 joint publications by Cavalli-Sforza and Bodmer from 1970 to 1976. From 1977 to 2010, there are only 10 joint publications, 6 of which are re-editions or translations of textbooks from the 1970-1976 period. The remaining 4 are multiple-author articles where Cavalli-Sforza and Bodmer appear amid a long list of contributors.

2. Does Cavalli-Sforza make an oblique criticism of Bodmer in his autobiography?

“[…] unfortunately, [ambition] often makes you lose sight of the essential virtues, like honesty, moderation, and altruism. It can blind you. Some of my colleagues distinguish themselves more by their ambition than by their genius. I know others—these are the most dangerous or the most ridiculous—whose ambition is much greater than their intelligence.” (Cavalli-Sforza & Cavalli-Sforza 2008, p. 303)

3. This was the only time I met him. He sat in on my thesis committee meeting and looked on good-naturedly. Of the three other professors present, only one seemed to know just how important he was. Afterwards, that one professor was dumbfounded by our ignorance: “You think Claude Lévi-Strauss is important? This man is the Lévi-Strauss of human genetics!”

4. In fact, Cavalli-Sforza has denied having such a belief during the period in question. In his interviews with Stone and Lurquin, he stated that his interest in culture was motivated by the very opposite belief:

“Yet another source of his interest in culture was the idea that the concept of human cultural learning was a valid weapon against racist arguments that differences between people (for example, different IQ scores among ethnic groups) were due to biologically determined “racial” differences." (Stone & Lurquin, 2005, p. 86)

References

Berry, J.W. (2008). Models of Ecocultural Adaptation and Cultural Transmission: The Example of Inuit Art, paper presented at the conference Adaptation et socialisation des minoritiés culturelles en région, June 3-4, Quebec City.

Berry, J.W., and L.L. Cavalli-Sforza. (1986). Cultural and genetic influences on Inuit art. Report to Social Sciences and Humanities Research Council of Canada, Ottawa.

Bodmer, W.R. and L.L. Cavalli-Sforza. (1976). Genetics, Evolution, and Man, San Francisco: W.H. Freeman.

Boyd, R. and P.J. Richerson. (1985). Culture and the Evolutionary Process, Chicago: Chicago University Press.

Cavalli-Sforza, L.L. and W.F. Bodmer. (1971). The Genetics of Human Populations, San Francisco: W.H. Freeman and Co.

Cavalli-Sforza, L.L. and F. Cavalli-Sforza (2008). La génétique des populations : histoire d'une découverte, Paris: Odile Jacob. (translation of Perché la scienza : L’aventura di un ricercatore).

Stone, L. and P.F. Lurquin. (2005). A Genetic and Cultural Odyssey. The Life and Work of L. Luca Cavalli-Sforza. New York: Columbia University Press.

The evolution of Cavalli-Sforza. Part IV

Walter Bodmer and Richard Lewontin at a conference, December 1965.
American Philosophical Society collection

The early 1970s saw two papers move the goalposts on race, first in academia and then throughout society. One was by Walter Bodmer and L.L. Cavalli-Sforza. The other was by a third geneticist, Richard Lewontin.

Bodmer and Cavalli-Sforza (1970) conceded that human races exist while denying that they differ statistically in intellectual capacity, at least on the basis of current evidence. Lewontin (1972) took a different tact: human races don’t exist. Period. No races, no race differences.

He came to this conclusion after analyzing the way various genes vary among human populations, specifically genes whose variants (‘alleles’) produce different blood groups, serum proteins, or red blood cell enzymes. Surprisingly, only 6.3% of this variation was accounted for by large continental races (i.e., ‘Caucasoids’, ‘Mongoloids’, and ‘Negroids’). Another 8.3% was accounted for by sub-racial populations. The rest—over 85% of human genetic variation—existed only among individuals of the same population.

This pattern had been known for some time with respect to blood groups. But researchers had assumed that some kind of balanced polymorphism was inflating within-population variation, perhaps one that hinders the spread of contagious diseases (1). By the early 1970s, however, the same pattern was appearing with other ‘structural’ proteins. The building blocks of flesh and blood were turning out to be remarkably the same in all humans. As Lewontin concluded:

It is clear that our perception of relatively large differences between human races and subgroups, as compared to the variation within these groups, is indeed a biased perception and that, based on randomly chosen genetic differences, human races and populations are remarkably similar to teach other, with the largest part by far of human variation being accounted for by the differences between individuals.

Human racial classification is of no social value and is positively destructive of social and human relations. Since such racial classification is now seen to be of virtually no genetic or taxonomic significance either, no justification can be offered for its
continuance.(Lewontin 1972, p. 397)

How did Cavalli-Sforza react? According to a recent interview, he saw this paper as a turning point in human genetics:

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.(Manni 2010).

Yet back in the 1970s, and even long after, his reaction was …. silence. From 1972 to 1989, Google Scholar lists 426 publications for which Cavalli-Sforza was an author or co-author (2). None of them cited Lewontin’s 1972 paper. He first commented on it in 1993, some twenty years after the fact (3).

Why the two-decade silence? If Lewontin’s paper had been so important in human genetics, why did Cavalli-Sforza take so long to acknowledge this importance?

It is hard to enter a silent person’s mind. A better approach would be to ask whether any thinking person had reasons for rejecting Lewontin’s finding, or rather the way he spun it. Such reasons fall under three headings:

1. A small genetic difference can make a big cultural difference
Even if human populations differ only slightly in certain genetic predispositions, these slight differences can have big effects.

For instance, the historical economist Gregory Clark has argued that the slow but steady demographic expansion of the English middle class from the 12th century onward gradually raised the population mean for predispositions to non-violence, deferment of pleasure, and other future-oriented behavior. Although the embryonic middle class was initially a small minority in medieval England, its descendants grew in number and gradually replaced the lower class through downward mobility. By the 1800s, its lineages accounted for most of the English population (Clark 2007, pp. 124-129, 182-183; Clark 2009).

The 1800s also saw the triumph of Victorian morality in England. This triumph was due not to a massive change in the gene pool, but rather to a slow incremental change that had finally reached a critical mass. The English middle class could now impose its behavioral norms on the whole population, thereby abandoning the ‘two-tier morality’ of other class-stratified societies.

2. Lewontin’s finding is true only if you look at one gene at a time
Genes vary much more within than between human populations only if we take one gene at a time. This pattern reverses if we aggregate variation at several gene loci. The more we aggregate, the more this genetic variation will exist between populations and not within them.

This fact was known to Cavalli-Sforza back in 1966 when he was constructing his first phylogenies of human populations: “it is desired that the number of genes considered be as high as possible in order to increase the reliability of the conclusions.” (Cavalli-Sforza 1966). When he and another colleague later aggregated data from 75 gene loci of 144 individuals belonging to 12 human groups in Africa, Asia, Europe, and Oceania, he found very little genetic overlap among the groups. Most individuals clustered with other members of their regional group (Mountain & Cavalli-Sforza 1997). This point has also been made by Mitton (1977, 1978), Edwards (2003), and Sesardic (2010).

Clearly, two groups are easier to tell apart with several criteria than with one. With enough criteria, any overlap will shrink to zero and all individuals can be unambiguously assigned to either group. This is basic logic. But all this proves is that human populations are identifiable. It doesn’t prove that the differences between them are greater than the differences within them.

3. The way a gene varies within and between populations will itself vary as a function of the gene’s selective value
When genes vary between populations, they do so usually because the population boundary separates different environments with different sets of selection pressures. Genes that differ across this boundary are necessarily genes that make a difference, i.e., that have high selective value.

In contrast, selective value is necessarily low for genes that differ within a population despite similar selection pressures (unless the different variants form a balanced polymorphism).

The two kinds of genetic variation are therefore not comparable.

And this leads to another problem. Yes, we have a lot of data on the way genes differ between populations, but that data comes largely from genes with little or no selective value—the ones that are most likely to differ within populations! When population geneticists look for a gene worth studying, they tend to choose one that responds weakly to natural selection. This choice is deliberate. They want the gene to be as close to selective neutrality as possible so that it changes at a predictable rate (i.e., only through random mutations). It thus provides a reliable ‘clock’ of population history.

Population geneticists also prefer to study genes whose protein products are easy to find and measure in body tissues. Such ‘structural proteins’ are similar in different species or even different genera. Humans and chimps, for instance, look very much alike if we compare the protein building blocks of their body tissues. These two species have diverged from each other largely through evolutionary changes at a higher level, particularly regulatory genes that control the pace and timing of development.

This point was grasped by Stephen J. Gould (1977, 406). He explained how such genes provide a misleading picture of genetic variation:

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).

I remember telling a geneticist that Lewontin’s finding applied only to genes with low selective value. He laconically replied that there was no evidence that things would be any different for genes with higher selective value.

Actually, there is real-world evidence. 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).

And Cavalli-Sforza in all this?

He was certainly aware that culture can amplify slight genetic differences. This was, in fact, part of his dual transmission theory—now known as gene-culture co-evolution (Stone & Lurquin 2005, p. 104-108).

He had also been aware since the mid-1960s that the genetic overlap among human populations is a function of the number of genes under consideration. In addition to his 1997 article with Joanna Mountain, this principle has been implicit in most of his work on human populations.

When questioned directly on this subject, with reference to Edwards’ reply to Lewontin (Edwards 2003; Khan 2006a), he diplomatically answered that both were right:

Edwards and Lewontin are both right. Lewontin said that the between populations fraction of variance is very small in humans, and this is true, as it should be on the basis of present knowledge from archeology and genetics alike, that the human species is very young. It has in fact been shown later that it is one of the smallest among mammals. Lewontin probably hoped, for political reasons, that it is TRIVIALLY small, and he has never shown to my knowledge any interest for evolutionary trees, at least of humans, so he did not care about their reconstruction. In essence, Edwards has objected that it is NOT trivially small, because it is enough for reconstructing the tree of human evolution, as we did, and he is obviously right.(Khan 2006b)

What about the third counter-argument? Was Cavalli-Sforza aware that genetic variation within populations is not comparable to genetic variation between populations? We see some awareness in his 1971 textbook, where he argues that most polymorphic genes have little selective advantage. Only in two cases are they subject to strong selection pressures. One case involves balanced polymorphisms. The other involves “transient polymorphisms”—genes quickly moving to fixation in those populations where they are advantageous (Cavalli-Sforza & Bodmer 1971, pp. 732-735). Such genes are thus more likely to vary between than within populations.

So perhaps he was aware. Or perhaps not. Even less clear is what he was thinking during his long silence on Lewontin’s 1972 paper. This paper was, after all, in Cavalli-Sforza’s own field of study. It was also widely commented on by other human geneticists. So why the silence?

One reason was his tenuous professorship at Stanford. It was this position that had propelled him to academic stardom, and he may have decided that discretion is the better part of valor. His pragmatism is recounted by a former colleague, Anthony Edwards:

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.(Sesardic 2010).

And the others in all this?

Lewontin’s paper met with either enthusiasm or silence. Two attempts at rebuttal were published in 1977 and 1978 by Jeffrey Mitton, a zoologist at a second-tier university. Another one was made much later, in 2003, by Anthony Edwards, a geneticist who no longer held an academic position. All three papers used the second counter-argument, i.e., within-population diversity exceeds between-population diversity only if you consider one gene at a time. Although I know several zoologists who are aware of the third counter-argument, none of them has ever written it up for publication.

Why did Lewontin’s paper meet with so little opposition? First, there was the wave of attacks on “racist” professors during the early 1970s, and the chill that subsequently spread through academic life. Many felt it best to be prudent. Second, there was the tenure-track system, which compelled untenured professors to ingratiate themselves with key members of academia. This system had always existed but was now being manipulated to advance an ideological agenda.

Thus began the soft totalitarianism of the late 20th century, not with a bang but with a whimper—or rather a silent acquiescence.

Notes

1. If your surface proteins differ from your neighbors’, you are less likely to be infected by contagious pathogens. There is thus selection for variability in surface proteins within each population.

2. In some cases, several references actually refer to a single paper (because of errors or variations in transcription). This overcount would not lead to an undercount of references to Lewontin’s 1972 paper.

3. He first cited Lewontin’s 1972 paper in 1990. His first substantive comments came three years later, when he cited it to show that genetic variation occurs mainly within human populations whereas cultural variation occurs mainly between them (Cavalli-Sforza 1993). This seems to be the only one of his publications that discusses the implications of Lewontin’s 1972 paper. All in all, he cited it three times in the 1990s and once in the 2000s.

References
Bodmer, W.F. and L.L. Cavalli-Sforza. (1970). Intelligence and race, Scientific American, 223(4), 19-29.

Cavalli-Sforza, L.L. (1966). Population Structure and Human Evolution, Proceedings of the Royal Society of London. Series B, Biological Sciences, 164, 362-379.

Cavalli-Sforza, L.L. (1993). “How are values transmitted?” in M. Hechter, L. Nadel, and R.E. Michod (eds), The Origin of Values, New York: Aldine de Gruyter, pp. 305-317.

Cavalli-Sforza, L.L. and W.F. Bodmer. (1971). The Genetics of Human Populations, San Francisco: W.H. Freeman and Co.

Cavalli-Sforza, L.L. and F. Cavalli-Sforza (2008). La génétique des populations : histoire d'une découverte, Paris: Odile Jacob. (translation of Perché la scienza : L’aventura di un ricercatore).

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World, Princeton University Press, Princeton and Oxford.

Clark, G. (n.d.). The indicted and the wealthy: surnames, reproductive success, genetic selection and social class in pre-industrial England,

http://www.econ.ucdavis.edu/faculty/gclark/Farewell%20to%20Alms/Clark%20-Surnames.pdf

Edwards, A.W.F. (2003). Human genetic diversity: Lewontin’s fallacy. BioEssays, 25, 798-801.

Gould, S.J. (1977). Ontogeny and Phylogeny. Belknap Press: Cambridge (Mass.)

Khan, R. (2006a). 10 questions for A.W.F. Edwards, Gene Expression, August 28, 2006.
http://www.gnxp.com/blog/2006/08/10-questions-for-awf-edwards.php

Khan, R. (2006b). 10 questions for Luigi Luca Cavalli-Sforza, Gene Expression, August 24, 2006.
http://www.gnxp.com/blog/2006/08/10-questions-for-luigi-luca-cavalli.php

Lewontin, R. (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.

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.

Mountain, J.L. and L.L. Cavalli-Sforza (1997). Multilocus genotypes, a tree of individuals, and human evolutionary history, American Journal of Human Genetics, 61, 705-718.

Sesardic, N. (2010). Race: a social destruction of a biological concept, Biology and Philosophy, 25, 143-162.

Stone, L. and P.F. Lurquin. (2005). A Genetic and Cultural Odyssey. The Life and Work of L. Luca Cavalli-Sforza. New York: Columbia University Press.