The 10000 Year Explosion: How Civilization Accelerated Human Evolution [Paperback]

I read *The 10,000 Year Explosion* in one sitting. It's an incredibly dense 300 pages, synthesizing population genetics, classical history, archaeology and paleontology (to name a few fields). But the prose is straightforward and clear. The relatively abstruse nature of some of the intellectual framework means that many readers may encounter population genetics for the first time in their life, but for those who are less than enchanted by algebra these excursions are optional and one can safely "hum through" them and get to the meat.

And there is quite a bit of meat. Many books on human evolution have one main narrative arc; e.g., the Out-of-Africa migration, or the discovery of the Hobbits of Flores. In contrast, works which focus on world events tend to take a broad "peoples & places" vantage point, with little concern for non-human dynamics. As the authors note, *The 10,000 Year Explosion* is actually a work of genetic history, so naturally its purview is broader and its foundation more varied than is normally the case with narratives which attempt to sketch out the shape of human history. In fact, it is fundamentally different than other popular works of genetic history, such as *The Journey of Man* or *The Seven Daughters of Eve*. While those books attempt to infer prehistoric population movements from the patterns of particular genes today, *The 10,000 Year Explosion* aims to give full treatment to the evolutionary power of natural selection in shaping human history. Human migrations may shape genetics, but *The 10,000 Year Explosion* shows how genetics may shape human migrations, how culture may shape genetics, and how genetics may shape culture!

The abstract models which serve as the theory are fleshed out with specific case studies and familiar dynamics. For example, how did the Indo-European language family get to be so geographically expansive? There might be a genetic reason for this having to due with a particular adaptation. *The 10,000 Year Explosion* outlines the possibilities in detail. In a more general vein, the authors offer that agriculture might have sped up evolution, not resulted in its end. This seemingly counterintuitive claim on the face of it is eminently logical upon further inspection, and in fact has some empirical support. Finally, *The 10,000 Year Explosion* puts the spotlight on even relatively recent events. For example, the peculiarities of the genetic history of the Ashkenazi Jews over the past 1,000 years, and the impact of this upon the occupational profiles of the Ashkenazi Jews today.

*The 10,000 Year Explosion* is bursting with ideas big & small. Some of them require a bit of algebra for clarity, but much of it is amenable to common sense aided with illustration. Many of the ideas will have a "Why, that makes total sense!" quality to them, while other claims are of a type that many may find troubling if true. This is a book which will enlighten even if it infuriates.

The human species, according to Cochran and Harpending, is more interesting and more varied than would be imagined. They point out that the pace of human evolution accelerates linearly with population size (more people means more mutations), and that man has domesticated himself in many of the same ways that he has domesticated his plants and animals. The last 10,000 years really have seen an explosion of evolutionary change. There is the story of how lactose tolerant Indo-Europeans spread milk-drinking with blood and fire, why the Ashkenazi suffer from crippling genetic diseases at an unexpectedly high rate while winning 25% of Nobel Prizes in the last century, and how the Spanish really brought down the Aztecs and the Incas. This book is really the anti-"Guns, Germs, and Steel." The real accidents of history are matters of gene flow and chance mutation. This book compresses an astounding number of ideas into a few short chapters. As with the other reviewer, I was caught up by the active and engaging prose style, causing me to breeze through the book in 2-3 hours.

Despite the complexity of the subject, "The 10,000 Year Explosion" is clearly written and compellingly argued. The book is devoted to refuting the idea that human evolution stopped 10,000 or 50,000 years ago, as some have argued. Rather, humans are constantly adapting to diseases, cultural innovations, and myriad other changes in the environment. As Cochran and Harpending point out in the Overview to their book, "humans have changed significantly in body and mind over recorded history. Sargon and Imhotep were different from you genetically as well as culturally."

At some level, the idea is plainly correct. Sickle cell anemia, for example, results from an adaptation to malaria. Those who had the gene were more likely to live long enough to have offspring, so the genes that code for malaria resistance are much more frequent in populations originating from areas where malaria has been historically common.

The same principle explains why the New World's inhabitants were almost completely wiped out by diseases imported from the Old World--by some estimates, mortality approached 90% of the pre-1492 population of North America and South America. The denizens of the Old World had been pastoralists and farmers much longer than their New World counterparts, and so had been exposed to a host of nasty diseases that originate from domesticated animals (e.g., smallpox). The farmers who were lucky enough to have a genetic adaptation that could resist the diseases passed the adaptation along to their offspring, and over hundreds or thousands of years the genetic defense swept through the whole population. By the time Columbus reached the New World, he and has compatriots had evolved to resist the Old World's diseases. In the New World, the Native American population had turned to agriculture relatively recently and didn't have the same suite of domesticated animals as the inhabitants of the Old World. Native Americans had evolved no genetic defenses against the diseases brought by the Europeans, and millions died in the space of a few decades. (The tables were turned on the Europeans who ventured into Africa, who were genetically ill-equipped to deal with tropical diseases like malaria.)

Cochran and Harpending's discussion of the Ashkenazim is bound to be more controverial and disturbing. The authors argue that, during the Middle Ages, the Ashkenazi Jews were, for various cultural reasons, a genetically isolated population that could make a living only in certain demanding careers, such as money lending and asset management. All of these occupations rewarded great intellectual ability, so over a period of hundreds of years, the Ashkenazi Jews became smarter on average than other Europeans. (According to the authors, the average IQ of the Ashkenazi Jews is 112, about three quarters of a standard deviation above the European mean.) This pushed the normal distribution of IQ scores among the Ashkenazi to the right, so the Ashkenazi were rewarded with a disproportionate number of geniuses relative to the size of their population. As further support for their hypothesis, the authors point out that the genetic diseases like Tay-Sachs that are associated with the Ashkenazi population seem to be errant expressions of genes that enhance the performance of the brain and central nervous system.

Of course, many of us become very uncomfortable when genetics seems to suggest that one human population might, on average, be more intelligent than another. Arguments about the alleged superiority of one group over another have been used to horrible effect in human history. But the authors are optimists, not racists. Pointing out that there is a unique genetic adaptation among the inhabitants of the village of Limone sul Garda that greatly reduces the risk of coronary disease, the authors argue that "some of the results of history's experiments may even aid us in more ambitious efforts aimed at increasing human life spans and cognitive abilities." Fine up to a point, but we must always be wary of the enthusiasms of those who would twist such hopeful conclusions into an argument for a new form of eugenics.

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