Did human evolution accelerate?

Modern humans changed little when they initially spread out of Africa and into the Middle East. Real change occurred farther north, when they entered seasonally varying environments that differed much more even in summer.

Three years ago, a research team led by John Hawks found that the rate of genetic change accelerated once ancestral humans had spread from Africa to the other continents. Over the past 40,000 years, natural selection seems to have altered at least 7% of our genome. And this process speeded up even more as agriculture replaced hunting and gathering over the past 10,000 years. The rate of genetic change then increased more than a hundred-fold (Hawks et al. 2007).

This finding, however, seems to be at odds with a recent Scientific American article by Jonathan Pritchard:

As early Homo sapiens spread out from Africa starting around 60,000 years ago, they encountered environmental challenges that they could not overcome with prehistoric technology.

Many scientists thus expected that surveys of our genomes would reveal considerable evidence of novel genetic mutations that have recently spread quickly through different populations by natural selection […]

But it turns out that although the genome contains some examples of very strong, rapid natural selection, most of the detectable natural selection appears to have occurred at a far slower pace than researchers had envisioned.
(Pritchard 2010)

Is there a fundamental disagreement here between Jonathan Pritchard and John Hawks? Perhaps not. Pritchard doesn’t actually deny that genetic change accelerated in ancestral humans. He simply states that its pace has been far slower than the one envisioned by “researchers.”

Curiously, he makes no reference to John Hawks. This is all the more curious because no one else matches the unnamed “many scientists” and “researchers.” Until three years ago, and even today, the conventional view has been that cultural evolution replaced genetic evolution in our species. Culture provided us with faster ways to adapt. Instead of changing our genes, we changed our environment by means of new technologies, modes of subsistence, forms of shelter, and so on.

That’s what I learned as an undergrad. If Pritchard wishes to argue against Hawks’ position, why not mention him by name? Why create a fictitious ‘conventional view’ that needs to be put in its place?

I see other weaknesses in this Scientific American article, particularly in the methodology behind its conclusion that human genetic evolution has been relatively slow. One is recognized by Pritchard himself. What matters is not the degree of change at a single gene, but rather the total change at all genes that influence a single trait:

A series of papers published in 2008, for example, identified more than 50 different genes that influence human height, and certainly many more remain to be found. For each of these, one allele increases average height by just three to five millimeters compared with the other allele.

When natural selection targets human height […] it may operate in large part by tweaking the allele frequencies of hundreds of different genes. If the “short” version of every height gene became just 10 percent more common, then most people in the population would quickly come to have more “short” alleles, and the population would be shorter overall.
(Pritchard 2010)

Another weakness is the impossibility of measuring the rate of genetic change directly:

It would be great if in our efforts to understand recent human evolution, we could obtain DNA samples from ancient remains and actually track the changes of favored alleles over time. (Pritchard 2010)

Because this approach is still in its infancy, Pritchard falls back on assumptions about when and where human populations have come into being. He assumes that Homo sapiens began to spread out of Africa some 60,000 years ago and then split into Europeans and East Asians some 20,000 to 30,000 years ago. These are the baselines he uses to calculate the rate of genetic change.

But these are high-end estimates. The ‘Out of Africa’ event is probably closer to 45,000 BP (1) and the best dating for the European/East Asian split is 20,000 BP (Laval et al. 2010) (2). Moreover, natural selection has not changed non-African humans at a constant rate since their ancestors left Africa. Those who remained within the tropical zone, such as Australian Aborigines, Papua-New Guineans, and Andaman Islanders, have changed surprisingly little. There has been much more evolution among those who spread out of the tropical zone and into temperate and arctic environments, beginning around 30,000 BP. Evolutionarily speaking, the key event was not when humans began to spread out of Africa. It was when they began to spread out of the Tropics (3).

So for many if not most traits, Pritchard is underestimating the rate of genetic change by a factor of two. Another source of error is his unspoken assumption that genetic change in Eurasia has never flowed back into Africa. By using Africa as a baseline for genetic change, he is excluding new Eurasian alleles that have displaced older ones even in Africa. Evidently, this error would lead to underestimation of the rate of genetic change both within and outside Africa.

Notes

1. Uranium dating suggests that modern humans entered the Middle East c. 46,500 BP (Schwarcz et al. 1979).

2. Maps of human prehistory typically show two lines of advance out of Africa: one turning left and into Europe and another turning right and into South Asia, Southeast Asia, and East Asia. The second line of advance did exist, but was not ancestral to present-day East Asians. It was instead ancestral to relic groups like the Andaman Islanders and the Semang, as well as Papua-New Guineans and Australian Aborigines.

East Asians, like the Inuit and Amerindians, have their origins in North Asia, as seen by their ‘Arctic’ physiognomy. These early North Asians in turn came from early Europeans, specifically the reindeer-hunting nomads who spread eastward through the steppe-tundra belt of northern Eurasia. In other words, Europeans and East Asians are not siblings who parted company in the Middle East some 45,000 years ago. The latter are instead ‘offspring’ of the former, the two groups having become reproductively isolated from each other at the height of the last ice age, c. 20,000 BP.

3. In sum, the ‘Out of Africa’ event did not occur when modern humans first ventured across the present-day Suez Canal. This is an arbitrary line based on current geopolitical realities. Ecologically speaking, the Middle East is part of Africa. Real adaptive change did not begin until modern humans had spread farther north and into environments with wide seasonal variations in temperature, vegetation, wildlife, and other resources.

References

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007).

Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA), 104, 20753-20758.

Laval, G., E. Patin, L.B. Barreiro, and L-Quintana-Murci. (2010). Formulating a historical and demographic model of recent human evolution based on resequencing data from noncoding regions, PloS ONE, 5(4), e10284

Pritchard, J.K. (2010). How we are evolving, Scientific American, October, pp. 41-47.

Schwarcz, H.P., B. Blackwell, P. Goldberg, and A.E. Marks. (1979). Uranium series dating of travertine from archaeological sites, Nahal Zin, Israel, Nature, 277, 558-560.

Ich bin Mittel-Ostländer?

Spread of farming in Europe. Der Spiegel

New research has revealed that agriculture came to Europe amid a wave of immigration from the Middle East during the Neolithic period. The newcomers won out over the locals because of their sophisticated culture, mastery of agriculture -- and their miracle food, milk.
(Schulz 2010)

This recent Der Spiegel article has stirred up comment in the blogosphere (Hawks 2010, Khan 2010, Sailer 2010). It argues that Europeans do not descend from the reindeer hunters who once roamed the continent during the last ice age. Nor do they descend from the more recent hunter-fisher-gatherers of the Mesolithic. All of those people went extinct. They were replaced by the real ancestors of present-day Europeans—farmers who began to spread out of the Middle East only 9,000 years ago and who reached northern Europe two millennia later—almost at the dawn of history!

If you have any doubts, this finding is based on “a barrage of articles in professional journals like Nature and BMC Evolutionary Biology, [whose authors] have turned many of the prevailing views upside down over the course of the last three years.”

There is nothing wrong with the above journal articles. A lot is wrong, however, with the Der Spiegel article. It neatly confuses two separate findings, only one of which supports the ‘population replacement’ hypothesis.

1. Origins of the European allele for adult digestion of lactose

Unlike most humans, Europeans can digest milk sugar (lactose) as adults. This is made possible by an allele that allows adults to produce an enzyme, lactase, that breaks down milk sugar. So where did this allele come from? Did it originate in Europe or in some place outside Europe?

According to Der Spiegel:

But where did the first milk drinker live? Which early man was the first to feast on cow's milk without suffering the consequences?

In a bid to solve the mystery, molecular biologists have sawed into and analyzed countless Neolithic bones. The breakthrough came last year, when scientists discovered that the first milk drinkers lived in the territory of present-day Austria,
Hungary and Slovakia.

The reader is left with the impression that the new allele had been brought to Europe from the Middle East. That impression is false. In fact, the above molecular biologists found no trace of this allele in DNA retrieved from the earliest European farmers. It apparently arose later as a mutation and then spread among Europeans through natural selection.

[…] the absence of the 13.910*T allele in our Neolithic samples indicates that the early farmers in Europe were not yet adapted to the consumption of unprocessed milk. Dairying is unlikely to have spread uniformly over Europe, and the use of milk in the Early Neolithic may have been rare. Although our data are consistent with strong selection for LP [lactose persistence] beginning with the introduction of cattle to Europe ≈8800 B.P., it is unlikely that fresh milk consumption was widespread in Europe before frequencies of the 13.910*T allele had risen appreciably during the millennia after the onset of farming.
(Burger et al. 2007)

Consequently, this area of research argues against the Der Spiegel article. Europeans did change genetically, but the change occurred through natural selection, not through population replacement (1).

2. Genetic divide between late hunter-fisher-gatherers and early farmers

Researchers have also retrieved mitochondrial DNA from Europe’s late hunter-fisher-gatherers and early farmers. Comparison shows a sharp genetic divide between the two groups. In particular, the first group had high incidences of haplogroup U—a genetic lineage that was rare among early farmers and still is among present-day Europeans.

The past year, however, has brought evidence of genetic continuity. After studying 92 Danish human remains that range in time from the Mesolithic to the Middle Ages, Melchior et al. (2010) found that high incidences of haplogroup U persisted among the earliest farmers and declined only in later groups.

Thus, the sharp genetic divide was not between late hunter-fisher-gatherers and early farmers. It seems to have been between the earliest farmers and groups that had been farming for at least a millennium or so. Once again, the evidence points to natural selection, and not to population replacement.

But isn’t mtDNA unresponsive to natural selection? That’s what I and others used to think. There is growing evidence, however, that some mtDNA loci can change in response to natural selection. In particular, some haplogroups seem to reflect a tradeoff between thermogenesis and ATP synthesis (Balloux et al 2009). If true, the decline of U-type haplogroups among early farmers may reflect the differences in physical activity (leading to overheating or underheating) that exist between hunting/fishing/gathering and farming.

Conclusion

The jury is still out. The evidence, however, seems to be tilting toward natural selection and away from population replacement as the best way to explain these genetic changes among ancestral Europeans. In short, the Der Spiegel article is bad science.

And bad journalism.

Note

1. Towards the end, the Der Spiegel article seems to acknowledge that the allele for adult digestion of lactose must have arisen after farming had spread to Europe:

Some [farmers] had genetic mutations that enabled them to drink milk without getting sick. They were the true progenitors of the movement.

As a result of "accelerated evolution," says Burger, lactose tolerance was selected for on a large scale within the population in the space of about 100 generations. Europe became the land of the eternal infant as people began drinking milk their whole lives
(Schulz 2010)

References

Balloux F., L.J. Handley, T. Jombart, H. Liu, and A. Manica (2009). Climate shaped the worldwide distribution of human mitochondrial DNA sequence variation. Proceedings. Biological Sciences, 276 (1672), 3447–55.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817182/?tool=pmcentrez

Burger, J., M. Kirchner, B. Bramanti, W. Haak, and M.G. Thomas. (2007). Absence of the lactase-persistence-associated allele in early Neolithic Europeans, Proceedings of the National Academy of Science, 104(10), 3736-3741.
http://www.pnas.org/content/104/10/3736.full

Hawks, J. (2010). Neolithic milk fog, John Hawks weblog, October 17.
http://johnhawks.net/weblog/topics/demography/neolithic/spiegel-volkerwanderung-2010.html

Khan, R. (2010). Völkerwanderung back with a vengeance, Discover, October 17.
http://blogs.discovermagazine.com/gnxp/2010/10/volkerwanderung-back-with-a-vengeance/
Melchior, L., N. Lynnerup, H.R. Siegismund, T. Kivisild, J. Dissing. (2010). Genetic diversity among ancient Nordic populations, PLoS ONE, 5(7), e11898.
doi:10.1371/journal.pone.0011898

Sailer, S. (2010). Are Europeans all Middle Easterners? October 17.
http://isteve.blogspot.com/2010/10/are-europeans-all-middle-easterners.html

Schulz, M. (2010). How Middle Eastern Milk Drinkers Conquered Europe, Spiegel Online International, October 15.
http://www.spiegel.de/international/zeitgeist/0,1518,723310,00.html

The evolution of Cavalli-Sforza. Part VII

Bird in a gilded cage

Cavalli-Sforza’s last big project was the publication of The History and Geography of Human Genes, which came out in 1994. Since then, he has kept himself busy tying up loose ends.

Advancing age is only one reason why he has lowered his sights. In fact, he had originally planned to work on two major projects until the end of his life. One was on gene-culture co-evolution. It would have involved studying the Inuit to see how their hunting lifestyle had selected for a keen sense of spatial orientation, specifically the ability to disembed an object from a larger visual landscape, to store it as a spatio-temporal model in the mind, and then to convert it back into a real-world object (e.g., a soapstone carving). Adopted and non-adopted Inuit would have been studied to find out how much of this ability was innate and how much learned. The project would have then served as a springboard for comparative studies of mental traits in other hunter-gatherer groups and, later, in agricultural populations.

That project suddenly aborted, for nebulous reasons. Its place was then taken by the Human Genome Diversity Project. This would have been a continuation of work that Cavalli-Sforza had been pursuing off and on since the mid-1960s, the main aim being to reconstruct how ancestral humans had split up as they spread out of Africa to the other continents. That project too came to a sudden end—in the face of violent accusations of racism. Funding dried up and researchers shied away. Today, research is still ongoing unofficially, the unspoken premise being that an unofficial project is less likely to catch flak than an official one. And the less Cavalli-Sforza has to do with it, the better.

So what should he do in his twilight years? One possibility would be a second edition of The History and Geography of Human Genes. This massive tome is based on data collected up to 1986, so it is now a quarter of a century out of date (Cavalli-Sforza & Cavalli-Sforza 2008, p. 281). An update is sorely needed and Razib Khan (2010) has shown how some of the gene charts could be redone. Such reediting would not be difficult. Most of the work could be delegated to other people, with Cavalli-Sforza keeping overall editorial control. His opus would thus gain a new lease on life and earn itself a place in university classrooms for another quarter-century. This is something he can and should do.

Yet something tells me he won’t. He seems content, or perhaps obliged, to rest on his laurels … and be buried with them. Until then, he will certainly not suffer from lack of recognition. His eventual departure from life will be met with eulogies of praise, such as befits a great man of science, and probably a state funeral in his home country.

And then his works will fade into obscurity. THGHG will be the first to go. Ironically, his earliest works will retain attention the longest. In twenty years, he will be remembered as we now ‘remember’ great anthropologists like William Sumner and Lewis Morgan.

But who knows? These are the shadows of what might be, not what must be. Cavalli-Sforza may still surprise us. Let me give him the last word of this unauthorized biography:

Why does one fear the unknown, the future, that which is new? Some stability is necessary for everyone’s life and well-being. It is normal to fear sudden changes that could upset this equilibrium.

[…] In all the cases where we feel powerless before the unknown, we should simply keep our eyes wide open and face the situation, if possible, with a certain fatalism, as befits the old saying, “whoever will live will see.”
(Cavalli-Sforza & Cavalli-Sforza 2008, pp. 326-327)

References

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.

Khan, R. (2010). A generation of human genetics & genomics. Discover Magazine. October 8.
http://blogs.discovermagazine.com/gnxp/2010/10/a-generation-of-human-genetics-genomics/#more-6985

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.