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

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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.

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 have some members who are dumb as rocks, just fewer in a per capita sense. Which is why individual performance can't be assessed based on group statistics.) Their argument is that Ashkenazi Jews were effectively an isolated breeding population for many generations, while at the same time pressed into occupations (related to money lending) that favored strong math skills. Thus the population was, inadvertently, "breed" for intelligence, even at the cost of a few members suffering debilitating genetic diseases. (Evolution is about population adaption, not perfection.) There are certainly many who reject this theory, but their attempts at refutation need to be based more on evidence of flaws in the theory and less on distaste for the theory than has so far been the case.

The book is not without flaws. While the authors' enthusiasm is generally a good thing, there are times when their metaphors and jokes are a bit over the top. This is both jarring and offers unnecessary opportunities for opponents to criticize the book. A harsh editor could have helped with this matter.

Over all, however, it is refreshing to read a book that takes evolution seriously, and follows the possibilities wherever they lead. This book is thought provoking and well worth reading.

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 they are baiting the bears of political correctness. Their thesis directly challenges the dogma of the American Anthropological Association, which stands behind its resolution that "WHEREAS all human beings are members of one species, Homo sapiens, and WHEREAS, differentiating species into biologically defined "races" has proven meaningless and unscientific as a way of explaining variation (whether in intelligence or other traits), THEREFORE, the American Anthropological Association urges the academy, our political leaders and our communities to affirm, without distraction by mistaken claims of racially determined intelligence, the common stake in assuring equal opportunity, in respecting diversity and in securing a harmonious quality of life for all people.

Keeping their exposure to a minimum, the authors make few observations on the broader implications of their findings. They make the commonsense observation that peoples who have dealt in farming and commerce for many millennia probably evolved skills that give them a competitive advantage. They dryly note that the Amerindians' lack of such historical experience perhaps "... underlies a current wave of discontent with liberal economic policies in South America." There is certainly more to be said, and one suspects the authors would readily tell it in a cocktail party conversation, but it would defeat their purpose to invite imbroglios such as greeted "The Bell Curve." Their objective is to get research pointed in more fruitful directions. As a former member of the American Educational Research Association, I say "Amen." We have spent far too much time, money, and psychic energy time trying to solve insoluble problems because we refuse to examine untenable hypotheses.

The most part prominent scientist to debunk the notions that human populations differ significantly in any fundamental way, and by the way, that IQ testing is meaningless, was the late Stephen Jay Gould. Cochran and Harpending take Gould all on directly on several occasions.

Take this book for what it is, an exposition of exciting new findings and an invitation to apply what we are learning in the field of genetics to bodies of knowledge within other disciplines, among them anthropology, paleontology, psychology, and history. I am sure that their hope is that in the end these studies will be able to enlighten public policy.

This book makes the astounding claim that our evolution has sped up 100 times faster in the past 10,000 years than the previous six million years. Even people 4,000 years ago were genetically and culturally different from us.

How do we know this? One way is from looking at both human and chimpanzee DNA. We know we split off from chimps about 6 million years ago, so we can compare the genetic differences and thus the long-term rate of genetic change. The rate of change the past few thousand years is 100 times greater than the long-term rate over the past few million years. If we'd always evolved at such a fast rate, the difference between chimp and human DNA would be much greater than it is.

If evolution this fast seems impossible, then consider how different dogs are from wolves. It took less than 15,000 years to go from wolf to a Chihuahua. There's no other mammal on earth with more varied forms and sizes than dogs. Dogs also vary widely in behavior. For example, some can learn much quicker than others. Border collies just need 5 repetitions of a new command to learn it and follow the command correctly 95% of the time, but a basset hound will need 80 to 100 repetitions and only obey correctly 25% of the time.

And it isn't just a dogs appearance, dogs are much better at understanding our commands and gestures than wolves are.

Russian scientist Dmitri Belyaev created a domestic fox in just 40 years by selecting the most tame foxes in each generation.

As far as humans go, it's pretty obvious evolution has taken place the past 50,000 years - just look at all the varieties of skin, eye, and hair color. Such skin-deep appearances were all we could see until recently, but with genetic testing we can see more than superficial differences - we also vary in bones, liver and brain function, disease resistance, etc from each other quite a bit. All of us can speak and have evolved better hearing as well to understand complex language and perhaps to better eavesdrop.

For a long time scientists have been baffled about why humans made a very sudden shift about 50,000 years ago - suddenly advanced, complex art, culture, tools, and weapons came on the scene. For several decades now scientists have been trying to understand what happened.

This is different from the overall "prime mover" - of why we are the way we are. Recent evidence supports the thermal hypothesis, other proposals include Man the Hunter, tool making, speech, social intelligence, taming fire, a constantly changing climate, etc and most likely of all, a synergy of these and many factors not listed as Peter Corning explains so well in "Nature's Magic".

Once our amazing culture evolved, we were no longer bound by natural selection - we didn't need to evolve fur when we moved into colder climates, because we could make warm clothes, and we didn't need to evolve strong muscles to hunt large animals - we could build better weapons.

And once we had better weapons, such as the long distance spear throwing atlatl, humans didn't have to be muscular heavy hulks risking their lives every time they hunted. We became smaller, needed less food, and perhaps that's why we out-competed Neanderthals.

But how could we have evolved so rapidly 50,000 years ago? Here's the bombshell theory - we interbred with Neanderthals!

This book came out before the recent discovery we have one to four percent Neanderthal DNA. But none of the articles about this discussed the implications - that this is why we underwent such an explosive cultural change roughly 50,000 years ago and became fully modern humans.

The authors explain that a common misconception is that people think that Neanderthals were closer to apes than people, but that is not at all true. They also had large brains, speech, and cooperated highly with each other when they hunted together.

We had too small a population to have enough mutations to evolve quickly, the only way it makes sense for this sudden change to have happened is for us to have acquired useful genes from Neanderthals. All it would have take is for a few dozen half human - half-Neanderthal babies over thousands of years for us to gain their best genetic strengths.

What would be interesting to know is whether it was mainly male humans and female Neanderthals or the reverse. Such analyses were done on the ancestry of Mexicans, and their maternal ancestry is mainly Amerindian, but their paternal ancestry is Spanish.

Ultimately, the most important result of our recent evolution was our ability to innovate. Every new innovation led to new selective pressures, which caused us to evolve in new ways. The most important innovation, and the one that caused the most evolution the past 10,000 years, was the invention of agriculture.

Once we had agriculture, the human population grew enormously, which meant a much larger pool of potentially beneficial mutations happening - 100 times more than in the Pleistocene.

Agriculture also created diets early farmers weren't adapted to. They ate way more carbohydrates and less protein, didn't get all the vitamins they needed, and lived much shorter and unhealthier lives.

But mutations arose that changed that. Here's just one example (that you may know): About 8,000 years ago the ability to drink milk as an adult arose in Europe, and now about 95% of people in Denmark and Sweden have no problems with digesting dairy products, and 80% of the rest of Europeans, on average. A different mutation that did the same thing arose in East Africa, and now 90% of the Tutsi are lactose tolerant. Densely populated areas evolved disease resistance, the ability to drink alcohol, and many other non-skin-deep abilities that we can now "see" with genetic studies.

At times in the Old World, when war wasn't the main source of deaths, famine and malnutrition limited populations that reached carrying capacity. The poorest were so short on food that they didn't reproduce themselves, while the elite had more than the two children required to replace themselves and had twice the number of surviving offspring as the poor. The least successful rich children became the new farmers, with the result that after a thousand years or so, everyone was descended from the wealthy classes.

Once the ruling elites existed, they didn't have a hard time controlling farmers, who couldn't leave their land in protest, or they'd die, which stuck them with paying whatever taxes, being conscripted into wars and in general endure whatever the elites dished out.

The authors suggest that in the end, people were ultimately domesticated by elite rulers, who weeded out aggressive fighting peasants, just as farmers weed out their most aggressive animals. The elites selected for a population that submitted to authority. Attention deficit disorder doesn't exist in China - the elites completely bred that behavior out of the population. I found the whole idea fascinating and scary, the full discussion is on pages 110-113. Maybe that explains why Americans have allowed the greatest disparity in wealth between rich and poor in our nation's history to exist, haven't marched with torches and pitchforks on Wall Street, and so on.

A chapter of the book is devoted to why Ashkenazi Jews are so much brighter than other populations. Although they comprise less than one in 600 people, they've won one in four of all Nobel science and too many other achievements to list here. Basically the hypothesis is that because they were forced to hold difficult white collar jobs for centuries in finance and related areas, and couldn't marry outside their group, evolution selected for intelligence. Unfortunately, this selection comes with genetic disorders of Tay Sachs and other diseases.

Well of course the problem with book reviews is that they're too short and have no peer-reviewed scientific references, unlike the book, nor can the logic and details be explained, so if you think any or all of the above is crazy, read the book. And if you're at all interested in the mystery of how we evolved, this fills in a few of the puzzle pieces that I haven't seen explained elsewhere

Another book I think everyone should read because it both expands our understanding and peaks our curiosity about human genetics. The premise of "The 10,000 Year Explosion" is the rate of human evolution is accelerating. With modern techniques for dissecting the human genome science is now able to better approximate the dates of the major changes in human evolution. While factors such as migration, mutation, etc were discussed (as in other books) the authors believe that the significant changes in evolution have occurred much more recently than previously believed.

Unlike more technical books on this subject, "The 10,000 Year Explosion" is compact and easy to read (and understand) despite the span of time it covers. What I liked best is that this book made me think about what I was taught in school and made me want to read more on the subject. Any book that makes me want to read more is a book worth reading. Highly, highly recommended.

This is a fun book written by authors with a lively intelligence. Their main thesis is obvious and controversial at the same time: the human race has evolved significantly over the last 10,000 years. They cite both the introduction of agriculture, and the accompanying explosion in population which increases the number of random mutations. Their other important thesis is that the leap forward in human cognitive abilities which others have remarked on, and which took place sometime during the last 100,000 years ago (date is highly controversial), was due to acquisition of some beneficial Neanderthal alleles. While not mentioned, 60% of the Neanderthal genome has been sequenced [...], but it will be a long time before the Neanderthal hypothesis can be confirmed, since we do not even have definitive knowledge as to which genes are most important in distinguishing our cognitive capabilities from chimpanzees, and we haven't sequenced genomes from our distant ancestors.

The discussion of possible Jewish intellectual superiority was particularly good. A small increase in average IQ, e.g. 10 points, can result in a lot more individuals in what were the tails of the distribution. As with many other evolutionary changes discussed, it is simply a matter of selecting for favorable alleles rather than a new mutation; in the Jewish case, circumstances were such that selection only worked on Ashkenazi Jews, not all Jews, and just during the last several centuries. The best example of selection making dramatic changes was the breeding of tame foxes.

The reader should be aware that what the authors portray as facts about human history are often just theories with counter-arguments. I include: that war was the primary check on hunter-gatherer population size; that the first immigrants to North America were responsible for the extermination of the large mammals; that syphilis originated in North America. (For a discussion of pre-European America, Charles C Mann's book is terrific). Also, the authors don't take a lot of time in elaborating on the biology underpinning their efforts, so some general readers may have to take some things on faith.

This book is very interesting and presented a fascinating theory. I enjoyed the no-holds barred look at the truth, regardless of whether the findings will be popular and politically correct. Such should be the essence of science. Most of the time I found myself nodding in agreement but as much as I would like this hypothesis to be true, I couldn't help but feeling as if the author's evidence was at times on shaky ground. Granted, most of the work is well supported and readily apparent. It just felt like some parts were insufficiently argued. This is often because the area hasn't been studied thoroughly enough or it is difficult, nigh impossible to find results. But overall a very interesting read that presents a compelling case for their hypothesis. For years, the recent evolution of humanity has been off limits as if everybody knew there was nothing to study, but yet nobody had studied it. The authors present a compelling case for why this should deserve scrutiny.

This book was fun to read just because much of the speculation in it is so ridiculous. And it is rife with speculation. Bushmen have a hard time adapting to life as shepherds - it must be genetic. Odd, I have the same problem learning Mandarin: Is that genetic too? Tay-Sachs and Gaucher's exist at such high frequencies amongst Jews and everyone knows Jews are smart; heterozygous Jews must be smarter than the rest of us. Oddly, Tay-Sachs heterozygosity hasn't had the same impact on French-Canadians and Cajun populations, which also have high frequencies of the disease alleles, or among the Irish who have very high levels of phenotypic heterzygousity (half the normal enzymatic activity as typical homozygotes). Gaucher's heterozygousity is likely to be advantageous in environments that have frequent outbreaks of influenza and TB (if you're familiar with Pubmed, do some searches to find out how Gaucher's affects the immune system). Just a few years ago the author's of the book were hailing the discovery of a new allele for the microcephalin gene that emerged around 40,000 yrs ago. Since microcephalin is known to have an impact on brain size the emergence of this allele must be one of the reasons Europeans are so smart. Unfortunately, it's now been clearly demonstrated that the allele has no impact on IQ. It's also strange that the authors never mention the Flynn effect (raw IQ scores among populations tend to increase with each passing generation; the Flynn effect has been correlated with urbanization and family literacy). The book is worth reading if you're reasonably well-informed and don't just accept the authors' take on something when they express an opinion. Finally, I've been a biologist for 20 years (with a reasonably extensive background in microbiology, developmental biology and evolutionary biology) and I can't recall a single colleague every suggesting that human evolution came to a grinding halt thousands of years ago. Suggesting such a thing would be silly.