The 10,000 Year Explosion: How Civilization Accelerated Human Evolution

We all know (or should know) the story. All humans shared common ancestors 100,000 years ago or so. Some migrated out of Africa more recently. All modern people are closely related, with within ethnic group genetic variations that are similar to global human genetic variations. There are, obviously, differences in physical appearance that have evolved, such as changes in complexion and eye and hair color. Also body shape differences; most skeletons can be typed by race, even though some claim race doesn't exist. Immunological differences make the news: different ethnic groups have different resistances to certain infectious diseases, different susceptibilities to certain genetic diseases, and, in some cases, genetic diseases based on resistance to specific infectious diseases. The authors of this book take the final step. They suggest we should really believe in evolution, really look at the genetic evidence of evolution, and accept that it occurs constantly and, therefore, even in modern humans. People spanning out over the planet encountered differing environments, differing pathogens, and different potential food sources. They adapted. And rapid expansion into different environments led to higher than normal rates of adaptation. This is, in a way, a book about human adaptability. Whatever people encountered, they found ways to adapt to; and this included genetic adaptation, not just cultural adaptation. When people encountered different climates, levels of sunlight, food sources, diseases, or whatever, some genetic forms (or alleles) were favored, and spread through populations. And if the environment itself could be transported, it gave a population an advantage that allowed it to spread, even if that meant replacing an existing human population. Suppose, for example, that early grain growers not only learned to grow grain, they also evolved to digest it more efficiently. That would give them a competitive advantage over another group of people who hadn't so evolved. While it might be possible to learn to grow grain in a generation, an advantage in digesting it would still favor the first population over the second. The authors posit that the adaptation allowing adults to digest milk significantly favored groups that developed it, because cows (and sheep and goats) are quite mobile, and provide a substantial nutritional advantage as milk sources rather than meat sources. (You can only eat a cow once, but you can milk it every day.) Probably the most controversial section is where the authors address the observed facts that Ashkenazi Jews both suffer from an unusually high incidence of genetic illness, and also score unusually highly, in a mean sense, on intelligence tests. (The authors explain why a modest difference in mean can explain a significant enhancement at the high end of the distribution; if a group is 10% smarter on average, it can have several times more members at the highest end in a per capita sense. It will also still hav

The authors piece together evidence from their wide-ranging, largely self-taught fields of expertise to flesh out their thesis that cultural and biological evolution go hand-in-hand. It seems probable that the publicity they got for their article two years ago on Ashkenazi Jewish intelligence convinced them that the time was right for a book. The Jewish piece, relatively little changed, appears as their final chapter. The findings are new and the book feels a little raw. The authors know that many of their findings are subject to restatement on the basis of further research. One has the feeling that their objective is not to have the final word, but to reframe the argument. Intelligence researchers and others have long contended that there are statistically significant, measurable differences among populations. The essence of the counterargument has been "No, that can't be. There has not been enough time." Cochran and Harpending cite a vast body of evidence to the effect that yes, evolution can create vast differences among populations in the timeframe under discussion. They cite the great variety to be observed among dogs and other animals, and cultivated crops, just within the last century or two. The authors claim that the thesis that there have been no significant evolutionary changes in Homo sapiens over the past 50,000 years is about as likely as dumping a bag full of silver dollars on the floor and observing that they all land on edge. Simply impossible. They are bold to suggest that interbreeding with Neanderthals may have sparked what they call the "great leap forward" and others refer to as the "Neolithic Revolution." They argue two ways. First, they establish the proximity of Neanderthals and modern humans for about 10,000 years during this timeframe, roughly 40,000 years ago. They point to evidence, admittedly rather meager, that there was cultural exchange between the hominids, and on the basis of what we know about ourselves, if they were that close, they almost inevitably interbred. They then argue by analogy with several better studied examples of introgression - the recombination of breeding groups that had become isolated - to argue that while modern humans coming out of Africa may have been overall superior competitors, it is quite likely that they could have benefited by borrowing a few well adapted genes from the Neanderthals. Whether or not the Neanderthal thesis turns out to be valid, the presentation in itself is very informative. Harpending and Cochran frequently cite Jared Diamond. Surprisingly, some very prominent people one expects would be sympathetic to their findings are absent from their bibliography, among them Steven Pinker, Luigi Cavalli Sforza, Spencer Wells, Nicholas Wade, and even Philippe Rushton, whom they thank in their forward. They appear more driven to put forward provocative new ideas, and less affected by the fear of being shown to be partially an error. The authors are extremely aware that t

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 w

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.

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.