An Unnatural History of Jewish Population Genetics

Howard Metzenberg

June 7, 2005

This article is a review of “The Natural History of Ashkenazi Intelligence”, by Gregory Cochran, Jason Hardy, and Henry Harpending. The original article (PDF) can be found at the authors’ own website at the following URL:

Cochran, Hardy, and Harpending have presented a new paper, recently accepted for publication in the Journal of Biosocial Sciences, which argues that high Ashkenazi intelligence is the result of recent natural selection that occurred between 800 CE and 1700 CE, and is associated with a characteristic cluster of genetic disorders. The authors propose that these genetic disorders, which are autosomal and recessive, promote high intelligence when a single allele is present. Thus, their high frequency in an Ashkenazi population that concentrated in intellectual occupations during the Middle Ages is the result of natural selection, and reflects a dynamic equilibrium similar to the presence of sickle cell anemia in populations from malarial regions.

In this commentary, I will show that other factors, more cultural than biological, are probably responsible for the high measured IQs of European Jews. Although the Cochran-Harpending paper presents a hypothesis that is coherent, it reflects a Merchant of Venice view of Jewish history, in which the bulk of Jews were involved in usury and financial occupations. The actual occupations of Jews, especially before 1700, are poorly documented.

My commentary focuses not on the scientific plausibility of their argument, but on the concordance of their theory with the historical record. I will make the following points:

  1. Jews are a self-selected minority group, and their high intelligence is the result of self selection, not natural selection.
  2. Jewish intellectual achievement was already well established by 800 CE. Above average Jewish intelligence can be traced to the origins of rabbinical Judaism itself around the time of the destruction of the Temple in Jerusalem.
  3. Self-selection and group selection for religious scholarship created a distinct Jewish population with a higher than average IQ.
  4. Above average intelligence is characteristic not only of Ashkenazi Jews, but also of large portions of the Sephardic and Mizrahi (oriental) Jewish populations. Furthermore, the Jews living in urban centers of North Africa and the Middle East were concentrated in intellectual occupations just as the European Jews were.

Most Jewish history before the 19th century is intellectual history and focuses on the development and interplay of ideas. Jewish scholarship is concerned primarily with Jewish law, not with the population dynamics or economic survival of Jews as a people. My interpretation of the transition between ancient and rabbinical Judaism is based on my study of other fields of history, and is not a mainstream view of Jewish history. In particular, my characterization of Jews as a “self-selected minority group” might be controversial to many Jews, although I don’t think it will be hurtful to anyone.

Jews are a self-selected minority group, and their high intelligence is the result of self selection, not natural selection.

The authors view the Jewish population as a relatively closed population in which high intelligence evolved endogenously through natural selection. But the actual mechanism that created a genetically distinct population with high intelligence was cultural, not biological. Jews have had many opportunities throughout history to not be Jewish.

It is often remarked that the Jewish people are a nation or tribe as well as a religion. The modern Jewish population is actually a heavily self-selected group, the result of several defining population events. The first of these occurred in the later years of the Roman Empire, when the bulk of the Jewish population in the Roman Empire was probably converted to Christianity. Those who remained Jewish were principally the Pharisees, a movement of activists and scholars. Thus, the development of a distinct Jewish population with a higher average IQ dates not to the Middle Ages, but to the Talmudic period many centuries earlier.

In the ancient world of Greece and Rome, Judaism was a proselytizing religion and took in many converts. It has been estimated that in the 1st and 2nd centuries, about 10% of the population of the Roman Empire was Jewish, and as many as 25% in the Greek speaking cities of the Eastern Mediterranean. It was for this largely Greek speaking population that the Septuagint (a Greek translation of Hebrew scriptures) was produced. And it was amongst this Greek speaking Jewish population that Paul of Tarsus traveled, proselytizing Christianity.

Cochran, Hardy, and Harpending remark that no commentary survives that would suggest that ancient Jewish populations were set off from other peoples by ability or intelligence. Of course, no such documentation exists for any other group, for there were no social scientists and modern concepts of intelligence did not exist in ancient times.

Even so, it is likely that Jews already had a distinctive occupational structure in the Roman Empire. Historical sources suggest that male literacy was already universal among Jews in Roman times, although it is hard to say what level of literacy was attained. Diaspora communities had been established for more than 500 years, and the dispersion of the Jewish people around the Roman and Parthian (Persian) empires, as well as universal literacy among them, facilitated long distance trade.

The peak of Jewish population as a share of world population probably dates to the Roman era. So what happened to all those Jews?

Partly, the answer is that the population of Europe and the Mediterranean region declined precipitously at the end of the Roman era. The Romans had presided over an era of prosperity, in which Western Europe became progressively Romanized, speaking a common language, with a network of roads and other infrastructure to promote economic growth and trade. With the decline of the Roman Empire, which actually began long before the sacking of Rome in 410 CE, populations collapsed throughout Western Europe. Invasions of so-called “barbarians” were a symptom as much as a cause of this decline. In the Greek-speaking east, the decline was postponed for a century or more, but was ultimately almost as severe. In the reign of the Emperor Justinian during the 6th Century, the entire empire was decimated by plague.

Thus, the collapse of Roman authority was an economic catastrophe for the ancient world. In many regions, literacy came to an end and the written record of civilization vanishes for hundreds of years. Jewish populations, like urban populations in general, declined to a tiny remnant. How many of the Jews died in plagues or famines, and how many converted to Christianity and later Islam, is undocumented. Those that remained, a self-conscious and self-selected minority, created a unique intellectual culture, and it is that culture that survives today as modern Judaism.

Jewish intellectual achievement was already well established by 800 CE. Above average Jewish intelligence can be traced to the origins of rabbinical Judaism itself around the time of the destruction of the Temple in Jerusalem.

High measured Jewish intelligence results not from the unusual occupational structure of Ashkenazi Jews in the Middle Ages, but from the origins of rabbinical Judaism hundreds of years earlier. At the beginning of the Christian Era, Judaism was deeply divided and in ferment between several competing religious factions, notably the Pharisees and the Sadducees. Both movements were elites. Although the Pharisees are best known outside of Judaism from Jesus’ rebuke in the Gospel of Matthew, there are other historical sources, from Josephus’ History of the Jews to the Mishna, a compilation of Jewish law that was initiated by the Pharisees after the fall of Jerusalem.

Since they are history’s losers, we know about the Sadducees mostly from the negative viewpoint of the Pharisees, who survived the destruction of the Temple and went on to compile their oral tradition as the Talmud. The Sadducees had been the local ruling elite in Jerusalem and other urban centers prior to the destruction of the Temple. They favored the power and privileges of Judaism’s aristocracy and hereditary priesthood, and they accommodated rather than resisted the pressures of Hellenization (assimilation into the dominant Greek and Roman culture).

By contrast, the Pharisees were a democratizing movement that sought to redefine Jewish observance, promoting talent over birthright, and extending the rituals and laws of purity from the priesthood of the Temple to the general population. The consummate Pharisee was Hillel, a kind of “hero-scholar” who traveled to Palestine from Babylon and lived a simple and humble life in order to dedicate himself to the study of Torah. It was the Pharisees that maintained the study of ancient text in Hebrew, no longer the vernacular of the Jewish people, and promoted the ideal of scholarship.

Thus, the Jewish population that survived the destruction of the Second Temple in 70 CE, the plunder of Mesopotamia under Trajan, and the suppression of the Bar Kochba revolts (132–135 CE) was a self- selected remnant population of intellectuals. Of the religious movements that existed in the time of Jesus, it is the Pharisees that formed the basis of modern rabbinical Judaism.

Followers of the Sadducees, and [also] the great mass of people that were not such partisan believers, probably assimilated in large numbers into Christian and Greek cultures and disappeared from Jewish history. But the Pharisees, conscious of themselves as scholars in exile, redoubled their efforts, compiling the works that form the basis of modern Jewish law. The Pharisees certainly had intellectual and verbal skills far beyond the level of the general population, and they are the progenitors in disproportionate numbers of modern Jewish populations.

Self-selection and group selection for religious scholarship created a distinct Jewish population with a higher than average IQ.

Judaism’s survival after the fall of Jerusalem reflects the intellectual achievement of the surviving Pharisees, whom I will henceforth refer to as “rabbis” with a lowercase r. In an intellectual effort that lasted hundreds of years, they compiled Jewish oral tradition into a series of tractates or volumes of encyclopedic scope, known collectively as the Talmud. It is through this written record that we know so much about ancient Judaism, at least about the Judaism of the Second Temple period.

Compilation of the Talmud began shortly after the fall of the Temple, with the founding of an academy at Yavneh in what is today modern Israel and the compilation of the Mishna or [and later the] Palestinian Talmud. After the Bar Kochba rebellion (132-135 CE), such intellectual activity became [increasingly] impossible within the Roman Empire, and [many of] the remaining rabbis and their intellectual descendants relocated in the Parthian (Persian) empire, near modern Baghdad. Compilation of Talmudic learning and later commentary continues after conditions began to deteriorate in the Middle East, moving first to Spain and later to Northern and Eastern Europe in the Middle Ages.

In the Judaism of the Second Temple period, Jews had supported a professional class of priests who by tradition are descendants of Aaron, the brother of Moses. Modern Judaism retains a few ceremonial roles for the descendants of priests, known as kohanim, but it is unlikely that membership in the Jewish priesthood was a “sexually selected marker” after the fall of Jerusalem. To paraphrase the authors, rich families preferred to marry their daughters to men who excelled as scholars and intellectuals.

Cochran, Hardy, and Harpending find it implausible that Jewish scholarship as an occupational choice has contributed to high Jewish IQs. The authors seem to have concluded that this is implausible by taking the modern concentration of professional rabbis and Jewish scholars and projecting it backwards in time. They write: “Another theory suggests that there was selective breeding for Talmudic scholarship. This seems unlikely to have been an important selective factor, since there weren’t very many professional rabbis, certainly less than one percent of the population. A selective force that only affects a tiny fraction of the population can never be strong enough to cause important evolutionary change in tens of generations.”

Because they didn’t understand the structure of Medieval Jewish societies, which were in place until the 18th or 19th century throughout much of Europe and the Middle East, the authors dismiss the effect of Jewish scholarship on Jewish intellectual achievement. Until the Enlightenment and the grant of citizenship which followed the French Revolution, Jews lived in separate, self-governing communities and paid taxes to the ruling Christian aristocracy as a community rather than as individuals.

Cochran, Hardy, and Harpending assert, with absolutely no evidence, that less than one percent of the Jewish population was part of a professional class of rabbis and scholars. They seem to be imagining that Jewish rabbis have always functioned like Christian ministers, as professionals leading congregations, although the modern Jewish congregation was a product of the 19th and 20th centuries, and a reaction to the organization of Protestant Christianity.

Although no occupational or census information exists, religious scholarship was a vast enterprise within the Jewish community. The best evidence for this is that such a large body of scholarship survives, even from a period when there was no printing or reproduction technology.

This scholarship, and the class of scholars who produced it, preserved not only the written record itself, but also the two ancient languages in which most of it was written: Hebrew and Aramaic. Although real fluency and literacy in these languages was probably limited in Medieval Europe, ordinary Jews were required to learn them, not only for ritual in the synagogue, but also for ceremonies in the home.

Rabbinical scholarship did not just determine what direction to face while praying, or in what order to light the Chanukah candles. If a neighbor’s donkey damaged your shop, Jewish law determined his obligations to pay you damages. And if a tradesman died owing money, rabbinical law determined the obligations of his widow.

Jewish scholarship involved far more than the one percent of adult males suggested by Cochran, Hardy, and Harpending. Indeed, every male in a traditional Jewish community is considered to have an obligation to study and learn Jewish law. Jewish scholarship was concerned not just with abstract, spiritual, and ceremonial manners, but also with civil law, administration, government, commerce, tax collection, social welfare, and the regulation of everyday life, including marriage and child rearing.

The rabbis whose discussions are preserved in the Babylonian Talmud, known as the Amoraim, were not professional rabbis. The academies of Pumedita and Sura where the Talmud was compiled, located near Babylon in modern Iraq, met during the off-season, and closed during the growing season so that their attendees could tend their crops.

Scholars and commentators of subsequent generations were also not professional rabbis. The two greatest scholars of the Middle Ages were Rashi and Maimonides. Rashi, whose 11th century commentary is traditionally printed near the spine on every page of Talmud, tended a vineyard in France. Maimonides, who might be considered the consummate Sephardic Jewish scholar, was a physician.

Of course, Jewish scholarship and literacy contributed to Jewish survival during the Middle Ages. Hebrew script came to be used not only for sacred writing, but for everyday spoken language as well, including the Yiddish spoken by Ashkenazi Jews and the Judeo-Spanish or Ladino spoken by Sephardic Jews. This ability to write and record information facilitated the development of international trading and financial networks through which Jews supported themselves as they moved into Europe. At a time when most Europeans were peasant farmers and literacy was confined primarily to religious orders, the Jewish community was an alternate source of commercial talent, capable of conducting long-distance financial transactions.

In both Medieval Europe and in the Caliphates and Sultanates of the Middle East, small numbers of Jewish intellectuals were hired as “court Jews”, offering their skills in finance, administration, and government as retainers for the Christian and Islamic royal elites. The success of this small and visible minority brought protection and prestige to the larger Jewish community, and reflects the survival of scholarship within that community.

Perhaps the ultimate testimony to the importance of religious scholarship among Jews is that Hebrew, an ancient language used only for religious purposes for nearly 2500 years, has been reborn as a modern language.

Above average intelligence is characteristic not only of Ashkenazi Jews, but also of large portions of the Sephardic and Mizrahi (oriental) Jewish populations. Furthermore, the Jews living in urban centers of North Africa and the Middle East were concentrated in intellectual occupations just as the European Jews were.

Cochran, Hardy, and Harpending cite several comparative studies of intelligence, achievement, and educational attainment by Ashkenazi versus Sephardic and Mizrahi Jews. Of course, these studies and the conclusions they reach are very controversial in Israel. This final point is central to their thesis, and my critique of it, because the authors claim that only Ashkenazi Jews have a higher mean IQ, and that only Ashkenazi Jews had the unique occupational structure which lead to natural selection for high IQ.

Because I wanted to respond very quickly to their paper, I am going to partially duck this issue. I have not personally read the studies these authors cite, though I do intend to when I can find them. (I’m confident that my many high IQ Sephardi and Mizraḥi friends will move quickly to support me here!)

All of these sources were published before the Internet was available, and they are not available to me as abstracts. I do not have a university library at my disposal. I am admitting my prejudice here, but I believe even without having read these papers (the most recent of which was published in 1990) that further analysis will show that they are based on old data and old measurement concepts that are invalid, or that they simply don’t measure and support what Cochran, Hardy, and Harpending claim they measure.

The truth is that any evaluation of these papers today is at best an intellectual exercise, because the communities that they purport to measure no longer exist, and may never really have existed. The ethnic fabric of modern Israel is a complex tapestry of overlapping groups, some difficult to define. There would be no way to repeat the studies today with modern testing procedures because the groups themselves have started to assimilate into one another.

Two years ago, I was the guest of an Iraqi Jewish family at a Passover Seder in Israel. “Look at my beautiful family,” said the grandfather, pointing to his daughters and his grandchildren. “This one has married a Jew from Poland, that one a Jew from India, that one a Jew from Libya. I have the whole Diaspora in my family!”

Was it really an Iraqi Seder? His wife was born in Morocco, so the cuisine was actually Moroccan. But the Moroccan Jewish community itself is a mixture of Sephardim from Spain and the original Magrebi Jews who lived there before the Spanish Inquisition. In some parts of Morocco the two groups assimilated into each other, and in others they did not. It would never have occurred to me at the time to ask her which Moroccan community she came from.

Israel is the only place where Sephardic, Mizrahi, and Ashkenazi Jews have lived side-by-side. When the state of Israel was formed, about 900,000 Jews of Arab and North African countries were forced to flee. Most of them settled in Israel, but a disproportionate number from the professional elites chose the United States, Canada, Australia, the United Kingdom, or France, especially those who were fluent in English or French. Thus, the refugee population that came to Israel after 1948 was also self selected, with a bias towards those with the fewest skills.

In the 1950s and 60s, Ashkenazi Jews were the mainstream culture of Israel, part of a Hebrew-speaking community that had been established since the 1920s or earlier. At that time, Mizrahi Jews were still newcomers, not fluent in the language, living in great poverty in tents or temporary housing. Israel was a poor country, where eggs, cheese, and milk were rationed. Its not surprising that non-Ashkenazi Jews scored poorly on the IQ tests of the time. Disadvantaged groups have always fared poorly on IQ tests. Since the 1960s, Israeli society has attained a standard of living comparable to European countries, and the gaps between Ashkenazi, Sephardi, and Mizrahi Jews have narrowed.

Israeli data is based on national origin, not on a true ethnographic definition of peoples as being Sephardi, Ashkenazi, and so forth. The Mizrahi Jewish population is actually the most complex, for there were many small communities in the Middle East, North Africa, and Central Asia that survived intact to modern times, perhaps as genetic isolates.

It may be that these groups, which probably have remained in isolation since Roman times, did not experience the self-selection effects that characterized the birth of rabbinical Judaism.

One of the reasons that the authors could find no evidence of a population bottleneck in the Ashkenazi Jewish population is that the Ashkenazi population has never been as distinct or isolated as they imagine. The original Ashkenazi population probably descends from Italian Jews who migrated north in the early Middle Ages. Genetic testing of Y-Chromosome phenotypes supports the theory that Ashkenzi Jewish males are closely related to the remnant community of Romaniote Jews, who by tradition are the descendants of Judeans brought to Italy and Greece as captives after the many religious wars and rebellions in the Middle East. Throughout the Middle Ages, Jews of Europe were engaged in trade with the Middle East, and it was through those trade routes that Jewish scholarship from the Middle East entered Europe. Later on, there was considerable gene flow from Sephardic populations escaping the Inquisition into the Ashkenazi community, and this is reflected in language and surnames.

In fact, a considerable portion of the Jews that migrated to Israel from western European countries such as England, France, and Holland were of Sephardic origin. As evidence of high Ashkenazi intelligence, Cochran, Hardy, and Harpending cite IQ data from London schools in the early 20th century. But the wealthiest and most established Jews in London at that time were descendants of Sephardim who came to England in the 18th century, not of more recent Ashkenazi immigrants.

My point is really that there is no way to measure Ashkenazi versus Sephardic and Mizrahi intelligence today, and there probably never was. The original Sephardic and Mizrahi communities were dissolved before IQ tests could be administered, and there is no way to reassemble their inhabitants. Sephardic communities such as Sarajevo and Thessalonica were destroyed in the Holocaust, while Mizrahi and Sephardic communities in North Africa and the Middle East were forced to flee en masse after the founding of Israel in 1948.

One source of confusion in any discussion of the relative intellectual performance of different Jewish groups, is that the label “Sephardic” is sometimes attached to all non-Ashkenazi Jews, although some are more accurately labeled Mizrahi, and others such as the Ethiopians, are none of the above. There is actually a religious reason for this, because there are slight differences in religious practice between the two groups. For a religious Jew living in Israel (where most Jews are relatively secular), it is a matter of which rabbinical court has jurisdiction. An Ashkenazi Jew would go to an Ashkenazi religious court to settle a divorce matter, while a non-Ashkenazi Jew would go to a Sephardic court.

The best evidence is that Jews of the urban Sephardic and Mizrahi communities in countries such as Egypt, Iraq, and Iran were concentrated in intellectual occupations just as the European Jews were. If those countries had gone through an intellectual transformation like the Enlightenment in Europe, then their native Jewish populations would have flourished just as European Jews did before the Holocaust.

There is a considerable literature in Spanish, written in the late 19th and early 20th centuries, about the Sephardic communities of the Balkans and the Ottoman Empire. After the repeal of the Inquisition, philosemitic Spaniards rediscovered these communities in the late 1800s, and some advocated repatriating them and restoring their Spanish citizenship. They generally noted the high level of professional and occupational achievement of Sephardic Jews in their host societies. Unfortunately, the Sephardic communities of Greece and the Balkans were destroyed in the 1940s, before modern psychometric measurement techniques could be tried.

The Jews of Babylon and Persia, descendants of the rabbis who compiled the Talmud, were active throughout the Middle East as traders, often trading with India and China, where they established small communities that survived to modern times. Before the founding of Israel, when the Iraqi Jewish community was dissolved and 130,000 Jews were forced to flee, Jews formed much of the urban middle class in Baghdad and other Iraqi cities.

Cochran, Hardy, and Harpending suggest that the Jews in Islamic countries were involved more in “dirty” occupations. In fact, they have chosen their evidence about Jewish occupations in these countries very selectively, while exaggerating the involvement of European Jews in finance and money lending. They might be surprised that the Jews of Europe also had to be their own butchers and bakers, because of Jewish dietary laws. And there may have been an even greater need for Jews to serve as money lenders in early Islamic societies, because Islamic law prohibits charging interest.


Although I disagree with the authors’ hypothesis that [Ashkenazi] Jewish intellectual achievement is the result of natural selection in a people that were restricted to a limited range of occupations, I welcome their paper. Even though their hypothesis is wrong, it is at least testable! It can be accepted or rejected on its own merits.

While I take for granted that there are innate differences between communities and ethnic groups, and that these may reflect biological as well as cultural differences, I personally fall more on the “nurture” side of the “nature versus nurture” debate when it comes to IQ and intelligence. Because the authors relied too heavily on biological explanations and mechanisms, they ignored cultural ones, and they failed to grasp that Jewish populations are actually open and partially self-selected. I have not even touched on any of the cultural or environmental reasons why Jews are high achievers.

I have characterized the Cochran-Harpending theory as being based on a Merchant of Venice view of Jewish history. If anyone reads this paper, that is surely the sound-bite they will take away, but I don’t mean this perjoratively. I don’t want anyone who comments on my paper to say that I accused these authors of using stereotypes or caricatures of Jews.

This is my first entry in the “Blogosphere”. I am not writing this commentary to extract a pound of flesh from the authors. Although I don’t agree with them, I do applaud them for tackling a difficult subject that crosses many fields, and for daring to talk of issues that mainstream academia has ignored because of “political correctness”.

This paper is in the public domain. It can be reproduced anywhere without cost or special permission. I encourage people to copy it rather than linking to it here, if that suits them. Please cite me as a courtesy, and spell my name correctly.

Howard Metzenberg; metzenberg[nospam]

Skrivarstuå – editor: Olve Utne
Updated 10 December 2006 - 10 Kislév 5766