The same process was going on in other European nations, but to varying extents. I commented on this point in the following letter to Commentary (which was never published):

In "Jewish Genius" [April] Charles Murray states that selection for intelligence has historically been stronger in some occupations than in others, being notably stronger in sales, finance, and trade than in farming. Insofar as he is right, the reason lies not in the occupation itself but in its relations of production.

In the Middle Ages and earlier, farmers had little scope for economic achievement—and just as little for the intelligence that contributes to achievement. Most farmers were peasants who produced enough for themselves, plus a surplus for the landowner. A peasant could produce a larger surplus, but what then? Sell it on the local market? The possibilities there were slim because most people grew their own food. Sell it on several markets both near and far? That would mean dealing with a lot of surly highwaymen. And what would stop the landowner from seizing the entire surplus? After all, it was his land and his peasant.

The situation changes with farmers who own their land and sell their produce over a wide geographical area. Consider the "Yankee" farmers who spread westward out of New England in the 18th and 19th centuries. They contributed very disproportionately to American inventiveness, literature, education, and philanthropy. Although they lived primarily from farming, they did not at all have the characteristics we associate with the word "peasant."

Conversely, trade and finance have not always been synonymous with high achievement. In the Middle Ages, the slow growth economy allowed little room for expanding a business within one's immediate locality, and expansion further afield was hindered by brigandage and bad roads. Furthermore, the static economic environment created few novel situations that required true intelligence. How strong is selection for intelligence among people who deal with the same clients, perform the same transactions, and charge the same prices year in and year out?

This point has a bearing on the reported IQ differences between Ashkenazi and Sephardi Jews. Charles Murray, like others, believes that the Ashkenazim were more strongly selected for intelligence because they were more concentrated than the Sephardim in sales, finance, and trade, especially during the Middle Ages. Now, we have no good data on the occupations of medieval Ashkenazim and Sephardim. But the earliest censuses (18th century for Polish Jews and 19th century for Algerian Jews) show little difference, with the bulk of both groups working in crafts.

There was, however, one major demographic difference. While the Sephardim grew slowly in numbers up to the 20th century, the Ashkenazim increased from about 500,000 in 1650 to 10 million in 1900. The same period saw strong population growth among Europeans in general. This boom used to be attributed to falling death rates alone, but demographers now recognize that rising birth rates were also responsible, in some countries more so. In England, the rise in fertility contributed two and a half times as much to the increase in growth rates as did the fall in mortality, largely through a decline in the age of first marriage.

This trend toward early marriage coincided with growing use of roads, canals and, later, railways to distribute goods over a much larger geographical area. The baby boom was particularly concentrated among semi-rural artisans who produced on contract for urban merchants and who could ably exploit these larger, more elastic markets. "They were not specialized craftsmen in life-trades with skills developed through long years of apprenticeship; they were semi-skilled family labour teams which set up in a line of business very quickly, adapting to shifts in market demand" (Seccombe 1992. A Millennium of Family Change. p. 182). Their workforce was their household. In more successful households, the workers would marry earlier and have as many children as possible. In less successful ones, they would postpone marriage, or never marry.

In Western Europe, these cottage industries were concentrated in areas like Ulster, Lancashire, Yorkshire, Brittany, Flanders, Alsace, Westphalia, Saxony, the Zurich uplands, the Piedmont, and Lombardy. In Eastern Europe, they were concentrated among Ashkenazi Jews. Selection for intelligence among the Ashkenazim may thus have been part of a larger European-wide selection for intelligence among cottage industry workers. These entrepreneurial artisans had optimal conditions for selection: 1) a tight linkage between success on an intelligence-demanding task and economic achievement; 2) considerable scope for economic achievement; 3) a tight linkage between economic achievement and reproductive success; and 4) considerable scope for reproductive success. Such artisans were a minority in Western Europe. Among the Ashkenazim, they appear to have been the majority.

In the late 19th century, cottage industries gave way to factories and the tight linkage between economic achievement and reproductive success came undone. Entrepreneurs could now expand production by hiring more workers. Henry Ford, for instance, produced millions of his famous Model T but had only one child.

In conclusion, Charles Murray errs in thinking that selection for intelligence is driven by the type of occupation. The relations of production seem to be more important, in particular whether the worker owns the means of production, whether there is scope for economic achievement, and whether increases in production are driven by increases in family size.