Be Fruitful and Multiply

Darwin 200 / by TJ Kelleher /

Agriculture and civilization have sped up the evolution of humanity. From this simple thesis grows an argument aimed at the heart of how we think about history.

The 10,000 Year Explosion would be important even if it were only about population genetics and evolutionary biology, but Gregory Cochran and Henry Harpending, a physicist turned biologist and a biological anthropologist, respectively, at the University of Utah, have written something more. This book is a manifesto for and an example of a new kind of history, a biological history, and not just of the prehistoric era. Covering broad ground over human history and prehistory, the authors argue for the singular importance of genes in human history, not just as markers of it but also as makers.

10,000 year explosion The 10,000 Year Explosion: How Civilization Accelerated Human Evolution By Gregory Cochran and Henry Harpending; Basic Books | Buy

The first four of the book’s seven chapters serve as something of a preamble to the final three. Cochran and Harpending first present the evidence for recent, accelerated human evolution after the invention of agriculture. In its own right that argument is a fairly revolutionary proposition, but one with clear data, both skeletal and genetic, to back it up; investigations of the human genome undertaken as part of the International Hap Map Project and elsewhere have clearly demonstrated that selection has been ongoing and has accelerated over time. This has been a landmark finding in human biology, and Cochran and Harpending, building on their own work and that of others, including John Hawks of the University of Wisconsin-Madison, convincingly tie the advent of agriculture — and the stresses resulting from the new diets, new modes of habitation, new animal neighbors, and new modes of living that agriculture made possible — to this accelerating evolution. It is work destined to launch a thousand careers. But Cochran and Harpending have bigger aims than just changing how biological anthropologists think about evolution or population genetics. Their argument’s most important implication is that because evolution is ongoing, history has not taken place with a cast of roughly fungible actors. Rather, the dynamic relationship between cultural and biological evolution means that history, especially macrohistory, has taken its shape because of the inherent genetic diversity of its actors, both individuals and groups.

About halfway through the book, Cochran and Harpending pause to consider two different ways of looking at the information found in gene variants. The more common view is to see them merely as markers of human migration, ignoring function — in fact, assuming a neutral function for genes. In this view, one variety of a gene, say, on a Y chromosome, is just as good as another; the alleles are neutral in their effects relative to one another, and so selection is not a concern of the analysis. This is not to say that such a neutral analysis is not interesting: It has helped researchers to ascertain which populations in Asia are ancestral to Native Americans, and whether modern Europeans are descendants of Paleolithic Europeans or of migrating farmers with origins in the Middle East. A more recent example is a study finding that Christian and Muslim men in Lebanon have specific Y-chromosome haplotypes that depend on their natal religion rather than their natal region. Such work has a long pedigree, at least as a fraction of the short history of biological anthropology; Luigi Luca Cavalli-Sforza is the endeavor’s grand old man, and Spencer Wells, of the National Geographic Society’s Genographic Project, is one of its leading practitioners today.

Cochran and Harpending also find value in such work, but they argue for a fuller appreciation of the geographic distributions of genes, and in doing so, they herald a new era not only in biological anthropology, but also for history. They do not stop with what information about human history can be found in the genes, precisely because many gene variants are not neutral. Where the usual geographical analysis treats the distribution of genes as an effect of history, in Cochran and Harpending’s view, the genes themselves are a cause: Two variants in the same gene do not necessarily have the same effect, and the relative selective advantages and disadvantages of them will — not surprisingly, to anyone versed in evolutionary biology — influence the movements of genes through populations over both space and time.

From that platform the authors undertake discussions of everything from the origins of the Arthurian romances in Britain to the Spanish conquest of the New World. Much of this was attempted before, in Jared Diamond’s Guns, Germs, and Steel, a book whose influence is clear in The 10,000 Year Explosion. But Cochran and Harpending do one better than Diamond. Where he was content with environmental determinism and sought to write around and even against human biology, Cochran and Harpending embrace it. That discussion of gene flow becomes the lynchpin in the argument for biology as central to history, and the backdrop for the book’s two biggest set pieces.

The first of those set pieces seeks to resolve a longstanding argument in historical linguistics by making a strong case for the Kurgan model for the origins of the Indo-European language group. The Kurgan model holds that the eponymous group, which spoke what we would call Indo-European, originated in the lands between the Black and Caspian seas before spreading their language elsewhere by conquest. Cochran and Harpending find herein the telltale signs of a specific kind of agriculture, dairy farming, and a complementary evolutionary novelty: the ability to digest lactose in adulthood. With a mobile food source, those milk-drinking warriors would have been able to terrorize and conquer their plant-tending neighbors; indeed, Cochran and Harpending find such a pattern repeating itself throughout history. Drinking milk, whether from cows, horses, or camels, is a behavior common to many of history’s greatest conquering peoples, whether Kurgans, Scythians, Arabs, or Mongols. Without ongoing evolution, the ability to digest milk would have never arisen; instead, it has done so multiple times, in multiple ways, in multiple places, and the human story has been unequivocally shaped by it. Indeed, the authors’ argument makes it difficult but interesting to imagine the language in which this book would have been written, and much else besides, if it were not for the ability to digest milk.

10000 year explosion Illustration by Tez Humphries

The second set piece, which takes up the entire final chapter, is even more audacious: It is an attempt to explain why Ashkenazi Jews have an average IQ so much higher than that of people at large. Much of this argument was published in the academic press in a 2005 paper, to wide media coverage and a storm of criticism and praise. Cochran and Harpending’s impatience to get to the core of their argument drives them to quickly dismiss most of their critics — too quickly, given the long and rancorous debate, especially in the United States, about the genetic heritability of intelligence. It would have benefited the book to consider those criticisms at greater length. Despite that weakness, this chapter is an important achievement: a consistent, thorough, biological history — or perhaps, better, a consistent biological hypothesis of a specific history, and a falsifiable one to boot.

The argument may, in the end, prove to be wrong, but it is not the clumsy racializing of bigots who hang pictures of Francis Galton on the wall. Many readers (or, more likely, nonreaders) may dismiss it as such anyway, but it nevertheless heralds a new era for biological anthropologists, one in which the explanatory power of their work doesn’t end with the advent of writing and the great civilizations of the ancient Middle East. As Cochran and Harpending have made this effort, some historians have similarly begun to incorporate biology in their own work. Daniel Lord Smail, a professor of history at Harvard University, has argued in his 2008 book On Deep History and the Brain that history does not begin with the advent of writing, and that historians ignore what he calls “deep history,” which includes prehistory and the evolutionary history of the human brain, at their peril. One can imagine the fruit that extended collaborations between such historians and anthropologists might bear.

The book is not flawless. There are passages, especially concerning findings outside human population genetics, that could have benefited from more thorough citation; in a book this bold, one would prefer to never simply take the authors’ word for something. Given how closely argued their set pieces are, some of their more minor propositions veer too far into the “just so” formulation habitually decried by critics of the evolutionary analysis of human affairs. For instance, the claim that the relatively recent invention of agriculture in the New World is responsible for the past decade’s discontent with economic liberalism in South America felt far too pat. And there are times when the pronoun “us” could conceivably mean the authors, Americans, or white people; especially in a book like this one, certain to suffer the scorn of many in the academic and popular left, such linguistic vagueness is an unwelcome distraction.

The strength and sheer number of the book’s best sections, however, more than overshadow the wanness and paucity of its worst. Even with its flaws, Cochran and Harpending’s book has provided the best example to date of what E.O. Wilson would recognize as consilient history: not history done just with science in mind or even done scientifically, but history done with human biology treated as an essential cause and effect of the stories that history tells, and as a key without which history cannot make sense. — TJ Kelleher is a senior editor at Seed.

    Darwin 200More From Our Darwin 200 Celebration.

Originally published February 12, 2009

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