Cochran G. and Harpending, H., The 10,000 Year Explosion: How Civilization Accelerated Human Evolution, Perseus Books, NY, 2009.
In an earlier cb review of a book on the role of culture and education on American intelligence (Nisbett’s Intelligence and How to Get It:, I mentioned a hypothesis by physicist and iconoclast scholar Gregory Cochran suggesting a genetic basis for Ashkenazi intelligence scores (slightly less than one standard deviation above the American population’s average). Nisbett noted that this slight difference in average IQ translated into massive differences in the distribution of individuals at the very highest IQ levels (140+).
Cochran, and anthropologist Henry Harpending, have now written a fuller discussion of their Ashkenazi hypothesis within the context of a much wider contrarian, and occasionally irreverent, book on the new discoveries in human genetics affecting our understanding of the evolution of modern humans. The authors explicitly reject the convential wisdom that human evolution largely stalled with the emergence of Homo sapiens sapiens as the sole hominid species on the planet.
With new techniques for examining the human genome, it’s possible to give approximate dates on the major recent changes to human physiology triggered by migrations into new environments or the adoption of new economic lifestyles (such as pastoralism or agriculture). Key physiological adaptations such as lactose tolerance, resistance to diabetes or obesity, Vitamin D absorption through skin, malarial protections (subject to recessive genetic disease such as sickle-cell anemia), high-altitude occupation, and the aforementioned Ashkenazis’ IQ, now have associated dates and timetables … and new research promises to nail down the timing and nature of similar genetic changes amongst the world’s populations. The impact of such genetic changes, and associated vulnerabilities, on the human occupation of Europe, North America, and Africa/Asia for the last 50,000 years are the focus of this book.
In contrast to most authors in the biological and social sciences, Cochran and Harpending believe that significant and influential human evolution has occurred in the recent past and that the pace of such evolution continues and even accelerates as selective pressures on modern populations intensify. The larger population pools in turn make it more likely that valuable mutations can spread widely and relatively quickly … often in ways that are completely independent of the X and Y sex chromosomes first used to map human genetic history. For example, Cochran and Harpending suggest that there may well have been an exchange of advantageous genetic mutations (through “introgression”) from Neanderthals to Cro-Magnon/H. sapiens sapiens without any associated impact on the paternal or maternal lines of genetic material associated with our species.
By looking back into post-Neanderthal human prehistory with new genetic data, scholars can track the movement of humans out of Africa and into Asia, Europe, Australia, and the Americas. They can also begin to hypothesize about the role that genetic change played in the relative reproductive success of Upper Paleolithic hunters, the first agricultural communities in Eurasia, and the Indo-Europeans who left their cultural and linguistic imprint on roughly 3 billion of the people in the world today.
Table of Contents
1. Overview, Conventional Wisdom 
2. The Neanderthal Within 
3. Agriculture, The Big Change 
4. Consequences of Agriculture 
5. Gene Flow 
6. Expansions 
7. Medieval Evolution: How the Ashkenazi Jews Got Their Smarts 
The 10,000 Year Explosion is a fast-paced book which covers a lot of terrain, often at the leading edge of genetic research. It’s written in straightforward language for the general reader but a familiarity with the basics of human genetics, disease, and prehistory would be helpful. As such, the specifics of any given argument made by the authors is liable to change relatively quickly as scholars engage the arguments and new data is discovered.
The overall argument proposed by the authors, that the pace of human evolution is actually picking up, is a very useful perspective for assessing such new information as it appears. The suite of ailments and genetic predispositions that face an industrialized and tightly-linked world is radically different that the hunter-gatherer environment of 10,000 years ago. Who lives, who dies, who successfully reproduces, and at what rate. That’s demography and genetics in constant interplay. As the authors describe, we aren’t exactly alike under the skin. One small fascinating case in point is the two physiologically distinct ways in which Tibetan and Andean peoples adapted physically to high-altitude living. The invisible history of these adaptations, at the physiological and genetic levels, is only now being understood.
Individual mutations have had a massive impact on the history of the planet (cf. the disease vulnerabilities of Native Americans, absent in Africa and Asia, or the significant economic advantage of lactose tolerance amongst pastoralists). The mix of genetic vulnerabilities or slight reproductive advantages that particular peoples maintain after decades, hundreds, or thousands of years of exposure to agriculture are also as unique as a fingerprint. Why, indeed, would the pace of that change be slowing if humans continue to move into new urban environments with brand-new combinations of environmental and genetic pressures?
With the acceleration of digital computation, storage, and transmission speeds, we can count on new surprises coming out of genomic research. As entire genomes (rather than just small chunks of human DNA) are compared (between individuals and between populations), “genetic archaeology” will enter a new phase of describing/dating population movement and subsequent admixture in far greater detail. This is bound to rewrite large chunks of history before the modern era, and dramatically change our understanding of prehistory, if only to highlight circumstances where favourable adaptations spread throughout world populations and led to some marginally greater rate of survival for particular peoples. Rather than a story of population replacement, often genetic prehistory was the story of genes or adaptations independently expanding through extant populations.
And rather than a conclusive statement about their hypothesis, the authors provide a solid opening salvo in an argument about the nature of humanity, past and present. Our society currently has a schizophrenic attitude to genetic variability in modern populations. On the one hand, an obsession with genetic testing for medical purposes but simultaneously a desire to deny the historical circumstances that led to such variation in the first place. In the next decade or two, as genotyping becomes more closely associated with both disease diagnosis and therapeutic prescription, the hidden history of humans in the last 10,000 years will get more air time.
Cochran and Harpending ensure that it will be difficult to put this genetic genie back in the bottle. Strongly recommended as a birthday or holiday gift for biology students (high school and above) and for those that follow theoretical arguments in medicine and biology. If you liked Jared Diamond’s Guns, Germs, and Steel you’ll also enjoy the briefer The 10,000 Year Explosion. The book is also recommended as a library check-out for anyone with an interest in human evolution, Neanderthal-CroMagnon interaction, the history of American and African colonization, the effects of agriculture on human prehistory, and the causes for the dramatic Indo-European expansion from the steppes.
Controversial, a bit flippant at times, but an enjoyable read, the 10,000 Year Explosion signals a new and exciting phase in science and history.