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The 10,000 Year Explosion Summary Chapter 1 Overview We intend to make the case hat human evolution has accelerated in the past 10,000 years rather than slowing or stopping, and is happening now 100 times faster than the long-term average over the 6 million years of existence. The argument that behavioral modernity frees us from natural selection is contingent on the assumption that our environment is static. Only in a static environment can we claim that we have already evolved to our biology optimum and that no new mutation could give us new comparative advantages. The assumption, however, is utterly wrong: the invention of spear thrower weapons gives advantages to lightly built people over heavily built ones; teeth shrink with new methods of food preparation; the development of language selects for changes in hearing. The environment has changed dramatically with our behavioral modernity. One might also argue that 10,000 years are too short for real changes to take place. This is also not true, as changes could happen extremely rapidly. For example, dogs are domesticated from wolves around 15,000 year ago, and Dmitri Belyaev domesticates fox in only forty years in controlled environment. Another argument, that complex adaptation is evolutionarily impossible because of its innate complexity, underestimates the change of simple adaptations. Dogs can exhibit significant changes from wolves by simply keeping juvenile behaviors to adulthood. We expect human evolutionary changes, though shallow, could still remain very significant. Our differences on the skin turn out lasting all the way to the bone. Some may argue that differences between humans are small and not significant compared to genetic variations within population groups. The “small” part turns out true, as cross-group differences only account for 30% of all genetic variations. But this distribution tells us nothing about how these genetic variations impact performances. Changes in genes could be completely neutral (causing no change of performance), or extremely important (such as defense to malaria). The assumption underlying the argument that average impact of genetic variant is the same for the two categories of variants is simply incorrect. In fact, given the short time since human expansion out of Africa, observable differences between populations in different regions can only happen if these differences give the groups strong selective advantages. Alleles such as skin color, eye color, lactose tolerance and dry earwax are linked to gene variants that have recently increased in frequency and had major fitness effects. The case of accelerated evolution is also proved by the hundreds of cases of long haplotypes found in recent studies. Haplotype is a pattern of genetic variation. If a haplotype gives people a strong enough selection advantage, the mutated haplotype could become rapidly common before recombination reshuffles its original haplotype. The process is rapid enough the people bearing that mutation also carry the original local haplotype that surrounded the mutation when it first came into existence. The existence of hundreds of long haplotypes, as well as the fact that we see far more alleles with moderate frequencies (showing they are in the process of spreading), shows that many significant mutations have occurred in recent time. Chapter 2 The Neanderthal within After human expanded out of Africa, our ancestors replaced the Neanderthals in Europe. The replacement could be due to many reasons: disease or parasite we carried, our language capability, or our more advanced weapons. Since the replacement is quite slow and most likely undramatic, it is quite possible that the actual advance was a mix of all the factors. But the more important thing here is that the product of the modern humans who displaced Neanderthals 30,000 to 40,000 years ago is significantly different (in the genetic aspect) from the humans at the last phase of the Old Stone Age. The most noticeable part is our increased ability to create and invent. Modern humans who replaced Neanderthals showed tremendous changes in tools, weaponry and art from their ancestors. Our argument is that the change is due to introgression. That is, we pick up genes and alleles from Neanderthals. Here is how mechanism of evolution works for alleles of Neanderthals to spread: suppose a new allele gives its carrier a 10 percent fitness advantage, the carrier would produce an average of 2.2 offspring instead of 2, the latter being her peer’s number. Although there would be a 23.75% chance that the allele disappears in the first generation, there is a 20% (10% x 2, same is true for other rates) chance of it becoming universal eventually. But if many alleles of this kind appear at the same time, the chance of eventual universality would be drastically higher. What we have picked up from Neanderthals? It could be their adaptation abiligty to European environment, or their alternative behavioral strategies, both of which integrated to our genes through introgression. Our exchange of genes with Neanderthals greatly increased our ability to innovate, which speeds up the cultural change by tens of times. Chapter 3 Agriculture: The Big Change The advent of agriculture accelerates the evolution and brings tremendous changes to our lifestyles and our genes. Firstly, agriculture increases the size of human population by nearly a hundredfold from 10,000BC to AD1. Since all mutations occur by change, a larger size means favorable mutations also occur more often. And since the spread of mutation is exponential, it does not take that much longer for the new mutation to spread (twice as long to cover 100million over 10,000). Agriculture also changes life in many aspects: (1) It vastly increased food production, of larger amount but worse quality. This led to bone abnormality of early agriculturalists due to lack of vitamins. (2) It did not increase the average standard of living, as population quickly catches up with increased productivity. In fact, A Farewell to Alms argues that it reduces the living standard drastically. (3) Higher population density and contact with domesticated animals greatly increased the prevalence of infectious disease. (4) The sedentary lifestyle and storable grain products allows humans to accumulate wealth and allows for generation of nonproductive elites The point is that over 400 generations of agricultural lifestyle, humans responded to the changes by adapting their own genes. They evolved better resistance to infectious disease, mechanisms to generate vitamins and better digesting abilities for carbohydrates including a insulin regulation mechanism. Populations who have never adopted agriculture exhibit none of those changes: American Indians are far more susceptible to infectious diseases, and Navajo people are far more likely to get diabetes when leading an unhealthy lifestyle (meaning they are not used high-carbo diets). Chapter 4 Consequences of Agriculture First, human developed better defense of diseases, sometimes at expensive costs of genetic diseases. Second, human skeleton has become more lightly built over the past 10,000 years. Some skeletal changes are much more recent. People who did in the Black Death around 650 years ago had a different shape of skull from the ones who died 450 years ago. Third, there are changes to our nerve system. For example, several of the new alleles have effects on serotonin, a neurotransmitter involved in the regulation of mood and emotion. Changes in dystrophin may have sacrificed muscle strength for higher intelligence. Fourth, as famine and malnutrition replace war to become the main limiting factors of population, the wealthy class’s continuingly high fertility rate means that after generations everyone in the society is from the wealthy class. Since wealth was not acquired the same way everywhere, the selection favors different traits in different societies. Elites in agricultural societies could enjoy amazing reproductive advantages. Today 16 million me in central Asia are his direct male descendants. Fifth, farming made people more submissive to authority. Your ancestors were the ones who decided it was better to live on their knees than to die on their feet. This is particularly true in strong, long-lived states. The 7R allele of the DRD4 gene, associated with ADHD, is almost totally absent in East Asia. It is possible that the individuals bearing these alleles were eliminated in China’s long history of strong dynasties. Sixth, agriculture selects for bourgeois values, such as the ability to defer gratification for long periods of time. Foragers, by comparison, were bad at self-denial: efforts to teach Bushman to become herders frequently fail when they eat all their grains. Seventh, agriculture leads to the birth of property. Farmers hence have to be selfish, while foragers share resources and remain egalitarian. Eighth, farming decreases laziness. Farmers could build long-lasting improvements like irrigation to boost productivity, while there is no way for foragers to accumulate wealth when all foods are perishable. For foragers, being lazy makes biological sense as it consumes less energy. Ninth, agriculture selects for traits that enable people to engage successfully in trade, as people need to sell their wheat. Groups that became agriculturalists, such as Amerindians and South Americans, were slow to master new social and technical developments. But it is not just the types of traits that matter. Different distribution of same traits could present very different social patterns (just imagine a dove majority and a hawk majority society). Even modest difference in mean traits (such as puzzle-solving ability) could have very significant effects on the frequency with which members of a group exceeds a high threshold. This could be a much higher chance of producing Issac Newton and Charles Darwin for some groups. Yet the author believes that there was no direct selection for creativity itself, and creative individuals may be by-products of other traits, such as low time preference or ability to make metal tools. Economists have shown that the age the transition to agriculture has a strong influence on economic development even in recent decades, suggesting that this is probably not due to mere cultural factors. If this is true, conventional methods for modernization for late agriculturalist societies may turn out problematic. Chapter 5 Gene Flow In sedentary agricultural societies mutations could spread very slowly if done through marrying people nearby. In 400 generations a gene with a 5 percent advantage could only spread 600 miles. Hence the speed of spreading is determined more by rare, long distance marriages. Oceans and the Himalaya are barriers that make it almost impossible for gene flow to happen. Ways of gene flow: (1) Trade (2) Colonization (3) Military movement (4) Imperial politics, such as forced relocation of people Chapter 6 Expansions Expansions could be driven by factors other than cultural or technical advantages. The driving forces could be genetic. Cultural and technical advantages can be easily copied, but biological advantages are enduring and hard to copy. (a) The European expansion into the Americas was driven by biological differences. The long agricultural history and contact with domesticated animals gave Europeans stronger defense against infectious diseases, defenses that non-herding Amerindians have little (they killed all suitable candidate animals upon arrival, before they attempted domestication). In fact, when you are not surrounded by diseases, stronger immune system works against you, inducing higher risk of autoimmune disorders. The epidemic played a crucial role in European colonization as those early attempts at conquest were only marginal. (b) Europeans’ failed attempt to colonize Africa is also due to biological factors. Powerful tropical diseases, combined with the local biological defenses (evolved at vast cost), kept Europeans at bay. (c) The spread Indo-Europeans- the largest expansion ever, since they took over half of total population – was likely driven by a single mutation, their lactose tolerance. The Proto-Indo-Europeans were likely a pastoral group that spread their genes through a series of expansions, some of which might even be gradual and peaceful. The expansion happens because dairying, enabled by lactose tolerance gene, is much more efficient than raising cattle for slaughter: It produces about five times as many calories per acre. The higher carrying capacity enables tribes to have more population, and hence more army and military power. Pastoral group’s mobility is also a military advantage. Chapter 7 Medieval Evolution: How the Ashkenazi Jews Got Their Smarts Ashkenazi Jews are around 11 million in population, with largest concentration in the United States and Israel. They have the highest IQ of any ethnic group known: 112-115 compared to the European norm of 100. IQ is the best available (and only- compared to EQ, AQ etc.) predictor for academic subjects and many jobs. Though not a sufficient indicator, it does have some predictive power. The author claims that Ashkenazi Jews have a genetic advantage in intelligence that arose from natural selection for success in white-collar occupations during their sojourn in northern Europe. It selects for alleles that boost IQ in carriers while causing harm to the homozygotes. This evolution is very recent, from roughly 800 to 1650 or 1700. A modest difference of 12 points in IQ score does not mean a typical Ashkenazi Jew is especially intelligent, but it is enough to greatly increase the fraction of individuals of high intelligence, since the intelligence distribution follows the bell curve (see figure). If two groups’ average IQ are 100 vs. 110, the percentage of people with IQ exceeding 140 is 4/1000 vs. 23/1000. The most visible result of this is the overrepresentation of Nobel prize winners of Ashkenazi Jewish origin.
Moreover, IQ is highly heritable, as an individual’s IQ is partially determined by genetic factors. IQ in adulthood is as heritable as height, and the way child is raised seems to have no effect on adult IQ. So how does this happen? Because of persecution and limitation of job options, most of Ashkenazi Jews became moneylenders by 1100. Occupations like trade and finance have high IQ demands, and the successful ones became rich. At that time, a rich family was able to afford better nutrition, medical care, better sanitary conditions and larger rooms, and therefore had much more children. Poorer families had much less children. Over generations all families became descendants of wealthy, high IQ individuals.
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