A Troublesome Inheritance: Genes, Race and Human History (22 page)

The Utah researchers make a plausible enough general case that the selective pressure from a cognitively demanding occupational niche would have selected for higher intelligence among Ashkenazim. They then go on to identify what they believe are the causative genes. Their proposals, if confirmed, would give specific plausibility to the general argument but, if false, would not bring it down.

The genetic argument concerns the mutations that cause Mendelian diseases. Mendelian, or simple, diseases are those that result from a mutation that disables a single gene, as opposed to complex diseases like cancer or diabetes, which are the product of several causative variant genes.

Every population has its own pattern of Mendelian diseases. Among Jews, some Mendelian mutations, like familial
Mediterranean fever, are very ancient, being shared with other Middle Eastern populations like Turks and Druze, while others are found among only Ashkenazim or Sephardim and so must have occurred after the two populations separated.

The Utah team’s analysis focuses on a group of four Mendelian diseases that occur in Ashkenazim and affect an obscure biochemical function, the storage of fats known as sphingolipids. The four diseases are known as Tay-Sachs, Gaucher’s, Niemann-Pick and mucolipidosis type IV.

Inheriting a single copy of any of these variant genes does no great harm: the good copy inherited from the other parent compensates for the defective allele. But inheriting a double dose of the variant alleles can cause serious impairment in the case of Gaucher’s and is lethal in the case of the other three diseases.

The variant genes that cause the four diseases are found in relatively high proportions in the Ashkenazi population. When a version of gene is more common than expected, geneticists usually assume one of two causes. One is natural selection and the other is the influence known as a founder effect.

Why should natural selection favor a variant gene associated with a lethal disease? This can happen when the variant, though lethal in a double dose, confers some advantage when inherited from only one parent. A well-known example is that of sickle-cell anemia. A person with one copy of the variant gene is protected from malaria, but those who inherit two copies suffer from a serious blood disease. The allele will be favored by natural selection because the many single-allele carriers, who are protected from malaria, far outnumber the carriers of two alleles, who die or suffer impairment.

The other reason why a variant gene can be more common than expected is that it happened to occur at high frequency in a small population that later expanded. Any rare mutation carried by one of
the population’s founders will be inherited by his or her descendants and attain a higher frequency in that population than in most others, a situation known as a founder effect.

The geneticist Neil Risch has concluded that the Ashkenazi Jewish mutations are founder effects that arose around 1,000 years ago. Since the mutations all arose at the same time, they must have the same cause, and that must be a founder effect, Risch argues, because such a variety of mutations is unlikely to offer any specific advantage that natural selection might favor.
¹¹

But this argument is neatly turned around by the Utah team. They agree that the Ashkenazi mutations arose within the past 1,000 years but argue that the mutations were indeed all favored by natural selection at the same time because they all promote intelligence.

If the founder effect argument is rejected, a plausible reason for the commonness of Ashkenazi Mendelian mutations would be that they protect against some serious disease. But no such protective effect has yet been detected. In any case, Ashkenazi Jews and the European populations they lived among suffered from the same diseases, yet there is no similar pattern of mutations in Europeans.

The only significant difference in the Ashkenazi way of life was that they worked in cognitively demanding occupations, the Utah team argues, so this must be the selective pressure that drove the Ashkenazi Mendelian mutations to such relatively high levels.

Another reason for assuming natural selection is at work, rather than a founder effect, is that some of the Ashkenazi mutations occur in clusters. This is highly unusual because mutations strike at random throughout the genome so should not be concentrated in genes that all have the same function. One set of Ashkenazi mutations occurs in the cluster of genes that controls the sphingolipid storage pathway mentioned above. For four mutations to be found in a specific pathway is a strong indication of natural selection. The Utah team points
to experimental evidence, though there is not very much of it, suggesting that disruption of sphingolipid storage induces neurons to make more connections than usual.

A second cluster of four mutations is found in a DNA repair pathway. Two of the mutations occur in the BRCA1 and BRCA2 genes and are associated with breast and ovarian cancer. The other two mutations cause the diseases Fanconi’s anemia type C and Bloom syndrome. It is hard to see how disruptions of DNA repair systems could be beneficial in any context, especially in the case of the two BRCA mutations, which carry risk even when an individual has a single copy of the mutated gene. The Utah team notes that BRCA1 can limit cell proliferation in neuronal stem cells in the embryo and adult, so that impairing the gene could allow extra brain cells to be generated. They suggest there may be similar advantages, yet to be discovered, in the other DNA repair mutations.

Though the exact role of the Mendelian mutations in promoting intelligence has yet to be clarified, they are strikingly common among Ashkenazim. Some 15% of Ashkenazi Jews carry one of the sphingolipid or DNA repair mutations, and 60% carry either these or one of the other Mendelian disease mutations special to Ashkenazim. As already noted, the mutations are harmless when inherited from just one parent. The Utah team’s explanation seems the best so far for this strange pattern of mutations, and in particular for those that exist in clusters. Moreover, it is a great virtue in a scientific hypothesis to be easily testable, as the Utah team’s theory is. The theory implies that people carrying one of the Ashkenazic mutations will be found to have higher IQ scores, on average, than people who do not. Anyone with access to a population of Ashkenazim could test the prediction that high IQ is associated with the Ashkenazic mutations. Strange to say, no one has yet done so or, if they have, they have not published their findings.

Without being able to test a living population, the Utah team
obtained indirect evidence that Gaucher’s disease raises IQ. They found that of 255 working age patients at a Gaucher’s clinic in Israel, one third were in fields like science, accountancy or medicine, which require high IQs, a far greater proportion than in the population as a whole.

A possible weakness of the Utah team’s proposal is the assertion that enhanced cognitive capacity is confined to the Ashkenazic branch of the Jewish population. Sephardim have given the world Spinoza, Disraeli, Ricardo and many other distinguished individuals. It is hard to find specific measurements of Sephardic IQ, and the Utah team offer none in their article. Measurements of IQ in Israel report that Ashkenazi IQ is higher than that of non-Ashkenazim, but the latter group includes Oriental Jews as well as Sephardim. The Utah team focuses on Ashkenazi Jews because the Mendelian mutations found in Ashkenazim seem to have originated around 1000
AD
, after Ashkenazim and Sephardim became separate populations. But even if the Utah team’s thesis has merit, there is no reason why Jews should not have enjoyed special cognitive capacities from much earlier in their history; if so, these traits could later have been enhanced among Ashkenazim in the manner the Utah team describes.

A new perspective on Jewish history has recently been developed by two economic historians, Maristella Botticini and Zvi Eckstein. Botticini specializes in medieval contracts and marriage markets and teaches at Bocconi University in Milan. Eckstein is a distinguished economist who has served as deputy governor of the Bank of Israel. Their interest in Jewish history is focused on population numbers and occupation. They allude hardly at all to intelligence or genetics,
yet their economic history makes abundantly clear how selection pressures could have acted on the Jewish population so as to enhance cognitive capacity.

The widely held conventional explanation for Jewish occupational history is that Jews were forbidden by their Christian host nations to own land and drifted into moneylending because it was the only profession open to them. Because of frequent expulsions and persecutions, according to this view, Jewish communities were dispersed in towns all over Europe and the Mediterranean world.

Botticini and Eckstein reject this explanation, arguing with a wealth of historical detail that Jews were not forced into moneylending but rather chose it because it was so profitable, and that they generally dispersed not because of persecution but because there were jobs for only so many moneylenders in each town.

But how did Jews come to choose this unusual occupation? Botticini and Eckstein develop a simple but forceful explanation that goes back to the beginnings of rabbinical Judaism in the 1st century
AD
.

Before the rabbinical era, Israelite religion was focused on the temple in Jerusalem and on copious animal sacrifices. Its leaders promoted three major insurrections against Roman rule, the first of which culminated in the destruction of the Jerusalem temple in 70
AD
. The loss of the temple strengthened the position of the Pharisees, one of several sects, and led them to develop a quite different version of Judaism in which the temple and animal sacrifice were replaced as central components of the religion by study of the Torah.

The rabbinical form of Judaism that emerged from this movement emphasized literacy and the skills to read and interpret the Torah. Even before the destruction of the temple, the Pharisee high priest Joshua ben Gamla issued a requirement in 63 or 65
AD
that every Jewish father should send his sons to school at age six or seven. The goal of the Pharisees was universal male literacy so that everyone could understand and obey Jewish laws. Between 200 and 600
AD
,
this goal was largely attained, as Judaism became transformed into a religion based on study of the Torah (the first five books of the Bible) and the Talmud (a compendium of rabbinic commentaries).

This remarkable educational reform was not accomplished without difficulty. Most Jews at the time earned their living by farming, as did everyone else. It was expensive for farmers to educate their sons and the education had no practical value. Many seem to have been unwilling to do so because the Talmud is full of imprecations against the
ammei ha-aretz,
which in Talmudic usage means boorish country folk who refuse to educate their children. Fathers are advised on no account to let their daughters marry the untutored sons of the
ammei ha-aretz.

The scorned country folk could escape this hectoring without totally abandoning Judaism. They could switch to a form of Judaism Lite developed by a diaspora Jew, one that did not require literacy or study of the Torah and was growing in popularity throughout this period. The diaspora Jew was Paul of Tarsus, and Christianity, the religion he developed, seamlessly wraps Judaism around the mystery cult creed of an agricultural vegetation god who dies in the fall and is resurrected in the spring.
¹²

As evidence that many Jews did indeed convert to Christianity, Botticini and Eckstein cite estimates showing that the Jewish population declined dramatically from around 5.5 million in 65
AD
to a mere 1.2 million in 650
AD
. There is little else to account for such a dramatic decline other than a high rate of conversion away from Judaism.

Botticini and Eckstein make no mention of the genetic forces that would have been brought into play by such a conversion. But if Jews who lacked the ability or commitment to become literate were shed from the community generation after generation, the propensity for literacy of those remaining would steadily rise. The rabbinical requirement for universal male literacy may thus have been the first
step toward a genetic enhancement of Jewish cognitive capacity. A second step was to come later, when the literacy was put to great practical effect.

By 650
AD
, Jews had almost entirely disappeared from regions where Christianity was strong, including Syria, Lebanon, Egypt and even Israel itself. The center of the Jewish world shifted to Iraq and Persia. There was also a shift in Jewish occupations. Jews abandoned farming and moved to towns, where they entered trade and commercial activities or became shopkeepers and artisans.

After the establishment of the Abbasid caliphate in 750
AD
, Jews migrated to the newly prospering towns and cities. By 900
AD
, almost all Jews were engaged in urban occupations, dealing with crafts, trade, moneylending and medicine. Why did Jews choose professions in these particular fields? Common belief is they were forbidden to own land and denied entry to certain crafts. Botticini and Eckstein say there is little or no evidence for such prohibitions. Jews concentrated in professions like trade and moneylending, they argue, for a simple reason. In a world where most people were illiterate, the literacy of almost all Jews gave them a decided advantage in any occupation that required reading contracts or keeping accounts.

Jews enjoyed another practical benefit conferred by their religion. Jewish communities were subject to law, as laid out in the Talmud, and rabbinic courts oversaw contract enforcement and disputes. Because of the presence of Jewish communities in many cities of Europe and the Near East, Jews had access to a natural trading network of their coreligionists. Both the network and the dispute resolution mechanism were unusual and gave Jews a special advantage in long-distance commerce.

As trade and urbanization started to flourish in the Muslim world under the Abbasids, the “higher literacy of the Jewish people,” Botticini and Eckstein write, “gave the Jews a comparative advantage over non-Jews in crafts, trade, commerce and money-lending.”
¹³

The sack of Baghdad by the Mongols in 1258 destroyed the political and cultural center of the Abbasid empire, and large regions of Iraq and Persia became depopulated. The population center of the Jewish community now shifted to Europe, where Jews increasingly specialized in moneylending.

This occupational pattern had a profound demographic consequence. Because moneylending was so profitable, despite its high risks, Jews could afford to support large families and, like other wealthy people, could ensure that more of their children survived to adulthood. After the devastation of the Jewish communities in Iraq and Persia and the expulsion of European Jews from England, France and many regions of Germany, their total population fell to fewer than 1 million in 1500
AD
. But propelled by their new wealth, the Jewish population started to increase rapidly and by 1939 had reached 16.5 million globally.

From an evolutionary perspective, the population increase was the result of a successful adaptation. Because of the requirement for literacy, Jews found themselves better able than non-Jews to cope with the new cognitive demands of urban commerce. “Jews had the behavioral traits conducive to success in a capitalist society,” writes the historian Jerry Z. Muller. “They entered commercializing societies with a stock of know-how from their families and communities about how markets work, about calculating profit and loss, about assessing and taking risks. Most important, though hardest to specify, Jews demonstrated a propensity for discovering new wants and to bringing underused resources to market.”
¹⁴

Like Chinese immigrant communities, Jews have brought enormous benefits to the economies in which they worked. Unfortunately their success, like that of the immigrant Chinese, has in many cases elicited not gratitude but envy, followed by discrimination or murderous reprisals, a response that reflects more strongly on the greed than the intelligence of their host populations.

From a glance at an Eskimo’s physique, it is easy to recognize an evolutionary process at work that has molded the human form for better survival in an arctic environment. Populations that live at high altitudes, like Tibetans, represent another adaptation to extreme environments; in this case, the changes in blood cell regulation are less visible but have been identified genetically. The adaptation of Jews to capitalism is another such evolutionary process, though harder to recognize because the niche to which Jews are adapted is one that has required a behavioral change, not a physical one.

Because of this adaptation, the Jewish population includes proportionately more individuals of higher cognitive capacity than do most others. It thus punches above its weight in endeavors requiring high intelligence. Traits like intelligence are distributed in the shape of a bell, with large numbers of people having the average value and progressively fewer as one moves toward either the higher or lower extreme. It takes only a slight upward shift in the average value to yield significantly more at the upper extreme. Average northern European IQ is 100, by definition, and 4 people per 1,000 in such a population would be expected to have IQs above 140 points. But among Ashkenazim, if the average IQ is taken as 110, then 23 Ashkenazim per 1,000 should exceed 140, the Utah team calculates, a proportion almost six times greater than that in northern Europe. This helps explain why the Jewish population, despite its small size, has produced so many Nobel Prize winners and others of intellectual distinction.