Eurasian history for millennia. The threat receded as agricultural peoples built strong states, intensified again in the Middle Ages as states weakened and steppe techniques improved (reaching an apogee with Genghis Khan), and ended only with the invention of gunpowder.
Our picture of the Indo-European expansion begins with a very rapid spread across the steppe as soon as the increased frequency of the lactase-persistence mutation became common enough to allow the switch to a dairying economy. This rapid spread would have resulted in a population that spoke similar dialects over a wide region all the way from the Ukraine to the Urals—similar because there hadn't been time for linguistic divergence. The wave of advance continued on into Europe, where dairying was ecologically competitive with early agriculture and produced a far more aggressive culture. Most likely, Indo-European culture also became more warlike as their mobility, superior numbers, and better nutrition allowed them to win battles more often than other peoples. Their victories, in turn, may have led to further advantages in military efficiency: Success feeds success.
Judging from their relatively low contribution to the European gene pool, Indo-Europeans appear to have practiced elite dominance, conquering rather than exterminating and replacing the previous inhabitants. A relatively small elite population can often impose its language on the rest of the population. In addition, the Indo-Europeans would have added the lactose- tolerance allele to the local mix. Although it appears to have been rare or nonexistent in Europe before the Indo-European invasions, it became common in those areas where a dairying economy was favored, particularly in northern Europe.20 Indo-
European languages and culture spread past those regions in which dairying was favored—for example, into southern Europe and Iran—but strong states probably limited their expansion into the Middle East.
As much as anything, those peripheral expansions were probably driven by what might be called historical momentum: Peoples with a long record of success in war and raiding kept expanding even in areas where they had no special ecological advantages. Something similar happened when the Indo-Aryans moved into India: Internal weaknesses, possibly even collapse, of the Indus civilization may have allowed that expansion to occur. Today the LCT 13910-T lactase variant has reached almost 100 percent frequency in some parts of northern Europe; it is common in northern India and can even be found at low levels among some pastoral peoples of sub-Saharan Africa, such as the Fulani and Hausa.
Moreover, there is reason to think that this historical phenomenon has happened at least three times. Cattle herders of East Africa in the region of the Upper Nile and further south are lactase-tolerant milk drinkers due to a younger mutation of their own.21 They, too, have expanded: They have become warlike, and there are fascinating parallels between their religions and social structure and those of the ancestral Indo-Europeans.22 Another separate pair of mutations causing lactose tolerance happened in the Arabian peninsula, driven in this case by the domestication of camels. This may have been an important cause of the explosive growth of Islam and the Arab conquests of the seventh century AD and later.23
If this picture is correct, the occurrence of a single mutation in a particular group of pastoralists some 8,000 years agoeventually determined the spoken language of half of mankind. It may not be possible to reconcile this with Tolstoy's ideas of the unimportance of the individual in history. Of course, champions of individual importance have typically emphasized ideas, intelligence, and character—not digestion.
7
MEDIEVAL EVOLUTION: HOW THE ASHKENAZI JEWS GOT THEIR SMARTS
The Ashkenazi Jews—the Jews of Europe—began as a distinct community about 1,200 years ago along the Rhine. The word "Ashkenaz" was the Hebrew name for Germany, so the Ashke- nazim are literally "German Jews," although they later came to inhabit other areas, particularly Poland.
Today the Ashkenazi Jews, some 11 million strong, live throughout the world, with the largest concentrations in Israel and the United States. There are many other Jewish communities— such as the Sephardic Jews who once lived in Spain, the Mizrahi Jews of the Middle East and North Africa, and the Bene Israel of India—but the vast majority of the world's Jews are Ashkenazi.
They have had a surprisingly large influence on the world over the past couple of centuries, and they have played an out- sized role in science, literature, and entertainment. Might they be smarter than other groups of people?
Apparently so. Ashkenazi Jews have the highest IQof any ethnic group known. They average around 112-115, well above the European norm of 100. This fact has social significance, because IQ(as measured by IQtests and their equivalents, like the Graduate Record Exam [GRE] or the Scholastic Aptitude Test [SAT]) is the best available predictor of success in academic subjects and many jobs.1 Jews are just as successful in such jobs as their tested IQwould predict, and they are hugely overrepre- sented in those jobs and accomplishments with the highest cognitive demands.
We're not the first to notice this. Popular opinion has held that European Jews are smart for a long time. At the turn of the century in London, for example, Jews took a disproportionate share of prizes and awards in the school system.2 This was not the case in classical times: Surviving writings from the ancient Greeks and Romans offer no hint that the Jews were considered unusually smart.
So why are the Ashkenazim especially intelligent?
To solve this puzzle, it may be useful to look at what we know about the DNA of the Ashkenazi Jews, because it turns out that they have another interesting characteristic. Namely, they have an unusual set of serious genetic diseases, such as Tay-Sachs disease, Gaucher's disease, familial dysautonomia, and two different forms of hereditary breast cancer (BRCA1 and BRCA2), and these diseases are up to 100 times more common in Ashkenazi Jews than in other European populations. For a
long time, those disorders have posed another puzzle—why are they so common in this particular group?
We believe that these two puzzles have a single explanation. We propose that the 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. Strong selection for intelligence also produced some unpleasant side effects, in the form of alleles that boost IQ in carriers while causing harm to homozygotes.
This kind of explanation is controversial, of course. It is true that many dismiss the idea that intelligence is measurable, is influenced by genes, or can vary from group to group. These criticisms and dismissals, interestingly, hardly ever come from scientists working in the area of cognitive testing and its outcomes: There is little or no controversy within the field. IQ tests work—they predict academic achievement and other life outcomes, and IQ scores are highly heritable. If genes influence intelligence, then, over time, a situation in which intelligence boosts fertility must result in higher intelligence. That simple logic is the very essence of the theory of evolution by natural selection: Genes that cause increased reproduction gradually become more and more common in a population.
ASHKENAZI INTELLECTUAL PROMINENCE
Jewish intellectual prominence is striking. As we have said, Ashkenazi Jews are vastly overrepresented in science. Their numbers among prominent scientists are roughly ten times greater than you'd expect from their share of the population in the United States and Europe. Over the past two generations
they have won more than a quarter of all Nobel science prizes, although they make up less than one-six-hundredth of the world's population. Although they represent less than 3 percent of the U.S. population, they won 27 percent of the U.S. Nobel Prizes in science during that period3 and 25 percent of the A. M. Turing Awards (given annually by the Association for Computing Machinery).4 Ashkenazi Jews account for half of twentieth-century world chess champions. American Jews are also overrepresented in other areas, such as business (where they account for about a fifth of CEOs5) and academia (where they make up about 22 percent of Ivy League students6). Although thes
e statistics show intelligence in a broad range of disciplines, we emphasize measures of scientific and mathematical achievement in our present argument because we believe they are more objective measures than the others. Everyone agrees about what constitutes important discoveries in science and mathematics, whereas there are no comparable objective criteria to evaluate accomplishments in art and literature. Was Freudian theory, for example, a landmark achievement in psychology or the equivalent of the pet rock, a silly passing fad? We don't know (although we do have a strong suspicion), and we have no objective way of finding the answer.
The statistics about Ashkenazi accomplishment may seem pretty dry, but they're referring to people like Albert Einstein, who developed the special theory of relativity. This theory unified mechanics and electromagnetism and led to atomic energy. We're talking about John von Neumann, who was one of the developers of game theory and who played an important part in the Manhattan Project and in the development of the hydrogen bomb; and about Richard Feynman, Julian Schwinger, and
Murray Gell-Mann, who developed many of the most important ideas in particle physics.
The trend continues today, with scientists of Ashkenazi descent such as Ed Witten and Grigori Perelman. Witten, a professor of physics at the Institute for Advanced Study, has done important work in string theory and on emerging connections between mathematical physics and low-dimensional topology. He was the first physicist to win the Fields Medal (in 1990), the highest international award in mathematics, and won the Crafoord Prize, an international science award, in 2008. In 2002, Perelman, a Russian-Jewish mathematician, proved the Poincare conjecture, the most famous unsolved problem in topology. For this work, he was offered—but refused—the Fields Medal (his refusal had to do with attempts by others to claim credit for his solution and his disappointment with the ethical standards of professional mathematics).
None of this means that typical Ashkenazi Jews are especially intelligent. Their average IQis around 112, about three- quarters of a standard deviation above the European mean. However, a modest difference like this has a very strong impact on the number of individuals out at the far edge of the distribution because of the shape of the bell curve. It's enough to greatly increase the fraction of individuals with high intelligence.
This pattern among the Ashkenazim is far more interesting than most other kinds of human diversity. If a particular ethnic group had incredibly large ears, for example, we'd be amazed, but it wouldn't have much impact on our lives. Ideas originated by Ashkenazi Jews, such as special relativity and game theory, however, affect our lives every day, whether we know it or not. Their intelligence has influenced the world in important ways,driving many of the most significant developments, advances, and creative works of our time.
Ashkenazi intellectual prominence is also very recent, in evolutionary terms. This high level of intellectual achievement among the Ashkenazi Jews is less than two centuries old.
ASHKENAZI HISTORY UP TO 1800
Two bell curves with different means
The ancient Jewish population suffered remarkable vicissitudes— the Babylonian exile, the Hellenistic conquest and Hasmonean state, and the revolts against the Roman Empire, for example— but most of that history is irrelevant to our thesis, except to the extent that it helped create necessary cultural preconditions. That history is irrelevant because the Jews, in those days, were much like other people. Most Jews then were farmers, just likemost other people in settled populations, and they must have experienced evolutionary pressures similar to those experienced by other agricultural peoples. They were not intellectually prominent at that time.
They made no contributions to the mathematics and proto- science of the classical era. A fair amount of classical commentary on the Jews has been preserved, and there is no sign that anyone then had the impression that Jews were unusually intelligent. By "no sign," we mean that there is apparently no single statement to that effect anywhere in preserved classical literature.7 This is in strong contrast with the classical Greeks, whom everyone thought unusually clever.
The key cultural precondition among the Jews—key, that is, to later events among the Ashkenazim—was a pattern of social organization that required literacy, that strongly discouraged intermarriage, and that could propagate itself over long periods of time with little change. That pattern (Rabbinical Judaism) had not always existed but gradually emerged in the centuries after Titus's destruction of the Temple in the first revolt against the Roman Empire in AD 70. This happened first in Israel, then later in the Jewish community of Mesopotamia. It coincided with the development of the Talmud, a collection of writings about Jewish law, customs, and history. The Torah and the Talmud are the central documents of rabbinical Judaism.
Literacy, which does not itself require high intelligence, was probably important to the Jews in their shift from a nation to an urban occupational caste during and following the Diaspora, acting as an entree to many urban professions in which they at first had no special biological advantages.8 The prohibition against intermarriage mattered, because local selective pressurescannot change a population that freely mixes with neighbors. Intermarriage quickly dilutes the effect of beneficial alleles within a population, since the introduction of alleles from outside easily swamps the effects of selection within the group. Rabbinical Judaism's long-term stability was also key, since natural selection takes many generations to effect large changes.
In fact, pre-Diaspora Jewish genetics seems not to have been remarkable in any way. We make use of genetic markers indicating the amount of Middle Eastern ancestry among the Ashke- nazim, but that is only important to our thesis insofar as it helps us estimate the extent of gene flow between the Ashkenazim and neighboring populations. In much the same way, the details of the Ashkenazi settlement of and migrations in Europe interest us because of their potential for creating genetic bottlenecks.
After the Bar-Kochba revolt of AD 135, most Jews lived outside of Israel. They were concentrated in the Parthian (later Sassanid) Empire and in the eastern half of the Roman Empire. There was a substantial population of Roman Jews, and there were other western settlements, such as Cologne, though these are poorly documented. The Jewish Diaspora in classical times was largely urban, but those Jews were on average poor; they were artisans and laborers rather than moneylenders or man- agers.9 There is a temptation to project recent cultural patterns, such as Jewish concentration in finance or Talmudic scholarship, back into the past, well before those patterns came into existence—but this is a mistake. After the Muslim conquests, the majority of Jews lived under Islamic rule.
The Ashkenazim, the Jews living north of the Alps and the Pyrenees, appear in the historical record in the eighth and ninth centuries. Their origins are somewhat unclear. There are threedifferent threads of history that may have led to the foundation of the Ashkenazi Jews in the centuries preceding, but the relative strengths of the theories are uncertain.
The first possibility is that the Ashkenazim—or some fraction of them—had already lived in France and the Rhineland for a long time, perhaps going back to Roman times. We know that there were Jews in Cologne around AD 300, and that there were Jews living in France under the Merovingian monarchs in the fifth and sixth centuries.10 However, in 629 King Dagobert of the Franks ordered the Jews of his lands to convert, leave, or face execution. This conversion edict may have pushed them out of most of France. Certainly we hear little about French Jews for the next 150 years or so. The size and even the existence of this population is uncertain.
The second thread involves Jewish merchants originating from the lands of Islam as distant as Palestine and Iraq. The Carolingian kings encouraged and protected these merchants, who brought luxury items such as silks and spices from the East, according to Agobard of Lyons.11 A few such traders served as interpreters on diplomatic missions; one brought Charlemagne an elephant from Haroun al-Rashid.
The third thread, generally thought to be the best supported, is that most of
the founding Ashkenazi population migrated from southern Europe, especially Italy. There are accounts of particular Jews—both individuals and families— moving from Italy to this area in the early Middle Ages. One was the Kalonymus family, which is said to have migrated from Lucca in Italy to Mainz in 917.12
When they first appear in the historical record, the Ashke- nazim are long-distance merchants who trade with the Muslimworld. This is the beginning of a unique occupational pattern; there were no other European groups—or other Jewish groups, for that matter—who were noted for this. The majority ofJews had already given up agriculture, but the Jews of Islam, although urban, mostly worked in various crafts.13 The Ashkenazim apparently seldom had such jobs. This pattern is detailed by one historian as follows: "Two entirely different patterns in the practice of crafts and their place in Jewish life and society are discernible throughout the Middle Ages. One characterizes the communities in countries around the Mediterranean, including in the south those in the continents of Asia and Africa, and in the north extending more or less to an imaginary demarcation line from the Pyrenees to the northern end of the Balkans. The other, in the Christian countries of Europe, was more or less north of the Pyrenees-Balkans line."14 Furthermore, "North of the Pyrenees and in the Balkans crafts played a very small role as a Jewish occupation, from the inception ofJewish settlement there."
The Ashkenazi population, established in northern France by the early 900s, prospered and expanded. They settled in the Rhineland and then, after the Norman Conquest, in England. At first they were international merchants who acted as intermediaries with the Muslim world. As Muslims and Christians, especially Italians, increasingly found it possible to do business directly, Ashkenazi merchants moved more and more into local trade. When persecution became a serious problem and the security required for long-distance travel no longer existed, the Ashkenazim increasingly specialized in one occupation, finance, left open to them because of the Christian prohibition of usury. The majority of the Ashkenazim seem to have beenmoneylenders by 1100, and this pattern continued for several centuries.15 Such occupations (trade and finance) had high IQ demands, and we know of no other population that had such a large fraction of cognitively demanding jobs for an extended period.
The 10,000 Year Explosion Page 17