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Thursday, May 7, 2009

Reading List: The 10,000 Year Explosion

Cochran, Gregory and Henry Harpending. The 10,000 Year Explosion. New York: Basic Books, 2009. ISBN 978-0-465-00221-4.
“Only an intellectual could believe something so stupid” most definitely applies to the conventional wisdom among anthropologists and social scientists that human evolution somehow came to an end around 40,000 years ago with the emergence of modern humans and that differences among human population groups today are only “skin deep”: the basic physical, genetic, and cognitive toolkit of humans around the globe is essentially identical, with only historical contingency and cultural inheritance responsible for different outcomes.

To anybody acquainted with evolutionary theory, this should have been dismissed as ideologically motivated nonsensical propaganda on the face of it. Evolution is driven by changes and new challenges faced by a species as it moves into new niches and environments, adapts to environmental change, migrates and encounters new competition, and is afflicted by new diseases which select for those with immunity. Modern humans, in their expansion from Africa to almost every habitable part of the globe, have endured changes and challenges which dwarf those of almost any other metazoan species. It stands to reason, then, that the pace of human evolution, far from coming to a halt, would in fact accelerate dramatically, as natural selection was driven by the coming and going of ice ages, the development of agriculture and domestication of animals, spread of humans into environments inhospitable to their ancestors, trade and conquest resulting in the mixing of genes among populations, and numerous other factors.

Fortunately, we're lucky to live in an age in which we need no longer speculate upon such matters. The ability to sequence the human genome and compare the lineage of genes in various populations has created the field of genetic anthropology, which is in the process of transforming what was once a “soft science” into a thoroughly quantitative discipline where theories can be readily falsified by evidence in the genome. This book has the potential of creating a phase transition in anthropology: it is a manifesto for the genomic revolution, and a few years from now anthropologists who ignore the kind of evidence presented here will be increasingly forgotten, publishing papers nobody reads because they neglect the irrefutable evidence of human history we carry in our genes.

The authors are very ambitious in their claims, and I'm sure that some years from now they will be seen to have overreached in some of them. But the central message will, I am confident, stand: human evolution has dramatically accelerated since the emergence of modern humans, and is being driven at an ever faster pace by the cultural and environmental changes humans are incessantly confronting. Further, human history cannot be understood without first acknowledging that the human populations which were the actors in it were fundamentally different. The conquest of the Americas by Europeans may well not have happened had not Europeans carried genes which protected them against the infectuous diseases they also carried on their voyages of exploration and conquest. (By some estimates, indigenous populations in the Americas fell to 10% of their pre-contact levels, precipitating societal collapse.) Why do about half of all humans on Earth speak languages of the Indo-European group? Well, it may be because the obscure cattle herders from the steppes who spoke the ur-language happened to evolve a gene which made them lactose tolerant throughout adulthood, and hence were able to raise cattle for dairy products, which is five times as productive (measured by calories per unit area) as raising cattle for meat. While Europeans' immunity to disease served them well in their conquest of the Americas, their lack of immunity to diseases endemic in sub-Saharan Africa (in particular, falciparum malaria) rendered initial attempts colonise that region disastrous.

The authors do not hesitate to speculate on possible genetic influences on events in human history, but their conjectures are based upon published genetic evidence, cited from primary sources in the extensive end notes. A number of these discussions may lead to the sound of skulls exploding among those wedded to the dominant academic dogma. The authors suggest that some of the genes which allowed modern humans emerging from Africa to prosper in northern climes were the result of cross-breeding with Neanderthals; that just as domestication of animals results in neoteny, domestication of humans in agricultural and the consequent state societies has induced neotenous changes in “domesticated humans” which result in populations with a long history of living in agricultural societies adapting better to modern civilisation than those without that selection in their genetic heritage, and that the unique experience of selection for success in intellectually demanding professions and lack of interbreeding resulted in the emergence of the Ashkenazi Jews as a population whose mean intelligence exceeds that of all other human populations (as well as a prevalence of genetic diseases which appear linked to biochemical factors related to brain function).

There's an odd kind of doublethink present among many champions of evolutionary theory. While invoking evolution to explain even those aspects of the history of life on Earth where doing so involves what can only be called a “leap of faith”, they dismiss the self-evident consequences of natural selection on populations of their own species. Certainly, all humans constitute a single species: we can interbreed, and that's the definition. But all dogs and wolves can interbreed, yet nobody would say that there is no difference between a Great Dane and a Dachshund. Largely isolated human populations have been subjected to unique selective pressures from their environment, diet, diseases, conflict, culture, and competition, and it's nonsense to argue that these challenges did not drive selection of adaptive alleles among the population.

This book is a welcome shot across the bow of the “we're all the same” anthropological dogma, and provides a guide to the discoveries to be made as comparative genetics lays a firm scientific foundation for anthropology.

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