The 10,000 Year Explosion, is a revolutionary new look at modern human evolution with several important implications for the future.
The traditional view among both natural and social scientists is that human evolution stopped before the advent of civilization and that all human progress in the millennia that followed was a result of cultural rather than physical evolution. The belief is that complex brains enable humans to create and harness the power of new technology, making biological evolution unnecessary. In order to fly, modern humans do not have to mutate and sprout wings, they can instead invent the airplane. Darwinian natural selection now is applied to ideas, technologies, and economic systems rather than to the human genome.
Cochran and Harpending take a very different view. Rather than make continued evolution unnecessary, civilization and its new innovations actually accelerated human evolution by increasing the rate of reproduction and creating new criteria for reproductive fitness and advantage. As the authors describe their approach,
"Conventional social sciences, such as history and anthropology, chiefly concern themselves with brain software, by which we mean cultural developments such as mores, mythology, or social structure. Genetic history addresses changes in the underlying hardware, changes in the body and brain, which also matter. If they didn't, dogs really could play poker."
Those early humans who were better adapted to a settled, agrarian lifestyle had more children survive than average and thus left a larger genetic "footprint" on the human race over the course of several generations. Over time, genes favored in a given cultural and economic environment spread to an ever-larger percentage of the population. One such example is lactose tolerance. Early humans were lactose intolerant. Those lucky enough to have developed the mutation that allowed them to drink animal milk well into adulthood were able to enjoy a higher-calorie diet at a lower cost (it's far cheaper per calorie to milk cows than to slaughter them for meat). The benefits of this are obvious. Healthier, stronger, and more energetic adults will be more economically productive and will have an advantage in military struggles as well. As a result, the lactose tolerant had a significantly higher fertility rate than the intolerant, and today lactose tolerance is the norm.
Other, more regional mutations are also obvious today. Sub-Saharan Africans developed a mutation that gave them strong genetic resistance to malaria. It's not hard to see how this mutation could spread quickly across a continent; resistance to such a deadly disease would obviously enable the first Africans who developed it to enjoy a much higher fertility rate and also a military advantage over their disease-weakened rivals. (Sickle-cell anemia, which is common among African Americans, is an unfortunate genetic side effect of the malaria-protection gene.) This beneficial mutation also kept Sub-Saharan Africans safe from outside invaders for centuries, until the British began mixing their gin with tonic water flavored with quinine--thus acquiring "medically" what native Africans were lucky to be born with.
Europeans, like Africans, also developed mutations that gave them resistance to certain diseases, such as smallpox. This, as Jared Diamond outlines in his excellent study
Guns, Germs, and Steel
, is what enabled a small band of Spanish conquistadors to conquer entire empires in the Americas. As a result, the Spanish and Portuguese were able to leave a cultural as well as genetic imprint that is far more significant than in other areas of European colonization.
Speeding Up Natural Selection
For those familiar with animal husbandry, none of this would be surprising. Horse and dog breeds have been created by nothing more than human tinkering. Selective pairing over the centuries (or in some cases, only decades) has given us breeds as diverse as Chihuahuas and Great Danes, to use the authors' examples.
Likewise, the Peruvian Paso Horse has been bred over the past 400 years for its distinctive high-step gait, considered by many to be the smoothest in the world. The Peruvian is one of the few horse breeds that walks with an even "1-2-3-4" hoof beat rather than the "2-2" trot common in most other breeds. This behavior is not learned; the horses are born with it. (I only know this because my wife is from a family of Peruvian horse breeders.)
This brings up interesting points for human behavior, although we wouldn't consider gait one of them. No one would say with a straight face that John Wayne's cowboy strut was a genetic phenomenon caused by selective breeding. (Although George W. Bush did defend his own distinct gait in his 2004 speech at the Republican convention by saying, "In Texas, we call that walking.") But could other human behaviors be introduced through breeding?
Cochran and Harpending suggest that Ashkenazi (Northern European) Jews were, quite literally, born to be bankers. Their existence in northern Europe for 1,200 years as an unassimilated subpopulation make them an interesting case study. Today, Ashkenazi Jews are measurably more intelligent on average that the overall human population, on the basis of IQ tests, Nobel prizes won, and representation in academia and among the upper echelons of the business and even entertainment worlds. As a tiny minority, their achievement is almost unbelievable.
It was not always that way, however. According to the authors, the Jews were considered to be of average intelligence in the classical and early medieval world; nothing more, nothing less. As a culture they certainly had nothing to match the body of scientific and philosophical work of their Greek contemporaries. So what changed?
The socioeconomic conditions in Northern Europe created unique selective pressures that had never before been reproduced in history and likely never will be again. The Ashkenazi Jews, due to their own religious prohibition against intermarriage and due to European bigotry against them, remained a relatively small, isolated community--and thus provided a perfect "laboratory" for natural selection.
The Ashkenazim were attracted to the profitable professions of trade and banking because, as a religious minority, they were exempt from the Catholic prohibitions on the charging of interest. Many times, they were excluded from landowning or from other trades as well, making finance one of the few career options available. What followed, in the view of Cochran and Harpending, was an acceleration of the natural selection process. Jews who had a natural talent for finance--including a high degree of literacy and mathematical and abstract thinking skills--were far more likely to have economic success. With economic success came better marriage prospects. (Even today, successful bankers are considered highly eligible bachelors.) Furthermore, with economic success came better nutrition and a higher percentage of surviving children. As a result, over the course of several generations, an increasing percentage of the Ashkenazim began to exhibit the traits that made for successful financiers. The less adept Ashkenazim had lower prospects for marriage and children--and thus gradually were weeded out of the gene pool.
So, due to a truly unique set of selective pressures, the Jews of Europe evolved into a measurably more intelligent subset of population over the course of 40 generations (roughly 1,000 years).
It's Good to Be King
We've written in the past about Gregory Clark's groundbreaking work
A Farewell to Alms
. Clark proposed an unorthodox theory for why the Industrial Revolution happened in Britain and not elsewhere. Clark argues that the prevailing theories--that the UK industrialized first due to its relative political stability and traditions of liberty and property rights--do not hold water. He instead makes the case that the change was cultural, based on breeding. The upper and middle classes in medieval England had more surviving children than the national average. At the same time, primogeniture laws required that only the eldest son inherit the family estates. This left quite a few "second sons" to make their own fortune. The end result was what Clark called "downward mobility," i.e., upper and middle class Englishman were forced down the economic ladder. There is, after all, only so much room at the top. This situation caused "bourgeoisie" values, such as hard work, delayed gratification, and an appreciation for learning, to trickle down the economic rungs of society, which provided a fertile ground for the Industrial Revolution to take root.
Clark's theory is based on culture, not genetics. However, a genetic argument certainly can be made, and Cochran and Harpending do exactly that. Throughout much of human history, elites did reproduce themselves at much higher rates.
For example, Alexander the Great did more than just spread Greek culture; he also spread Greek genes. Today, distinctly Greek chromosomes can be found as far east as Afghanistan.
Implications for the Future
Today, in the post-WWII era of urban mass affluence, reproductive realities are far different. In all developed countries, birthrates have fallen to between 1 and 3 children per woman, and it is often the most educated and most successful economically who have the fewest children. A large family is now an economic burden, and having several children limits the time and monetary resources that can be dedicated to each child. Attempting to send six children to elite prep schools en route to Harvard would bankrupt all but the richest among us. Americans and Europeans have recreated a de facto system of primogeniture, except that rather than exclude younger children from their would-be inheritance the younger children are simply never born to begin with.
Those who do have large families tend to do so for religious reasons. Many evangelical Christians and Catholics take the Bible's command to "be fruitful and multiply" seriously, as do Mormons, Orthodox Jews, and devout Muslims.
This brings up several questions for the future. What will the world look like in a few generations? Demographer Philip Longman (whose work we highly recommend) wrote an insightful article in 2006 titled "The Return of Patriarchy." Longman, tracking birth trends, sees a cultural shift underway. Social conservatives tend to have more children than social liberals, and children more often than not tend to adopt the political and social views of their parents. All else equal, this points to a less libertine future, perhaps within our lifetime. This is not necessarily bad, of course. Societal views change over time. As we wrote in the April newsletter, summarizing the views of Thomas Sowell, social views on gender roles were actually more conservative in the 1950s than they were in the early 1900s. Views change and life goes on.
Of course, we see that this trend could be problematic in certain parts of the world, such as the Middle East. Barring significant immigration of socially liberal Jews from abroad, Israel will quickly become a more conservative country as more orthodox sects of Judaism have much higher birthrates than do secular Israelis. In a small country like Israel, the entire character of the state could change, for better or for worse.
Likewise, the elites of many Muslim states tend to be secular, but the majorities of their populations are not. As birthrates among the secular elite have fallen to Western levels and decreased levels of infant mortality have enabled more children of the poor to survive to adulthood, the balance of power inevitably will shift. A case in point is Turkey. The Turkish state founded by Mustafa Kemal Ataturk after WWI was militantly secular. Ataturk himself made a strong effort to "de-Islamify" the country as a way of pulling it into the Western sphere. Ataturk went so far as to officially drop Arabic script from written Turkish, moving the language to a Latin-based alphabet instead. (To appreciate how truly radical this was, imagine today being told by the U.S. government that henceforth, English will be written in Japanese characters or in the Greek alphabet. Wouldn't that be fun?)
It's hard to imagine a time when a guy won't be able to enjoy a drink overlooking the Bosphorus in Istanbul, but that day might come. Turkey is becoming more Islamic--not because of a shift in values among Turks but because devout families simply have more children.
Again, this is not to say that any of these trends are "bad" (unless you're a bar owner in Turkey). Unlike the biological changes described by Cochran and Harpending, these changes are cultural and thus more capable of quicker adaptation. Devout Turks may suddenly decide that big-city living is more to their liking. At any rate, these shifts in attitudes are what they are: another chapter in human history.
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