CAN SOCIAL PRESSURE TO BE SMART HAVE ALTERED GENES?

Date: Saturday, June 11, 2005

When my husband and I were in graduate school in mathematics, at Northwestern University in the early 1960s, his dissertation adviser had a theory about why Jews were so prominent in mathematics departments.

Ashkenazi Jews, that is the population among the Jewish diaspora that settled in Europe roughly north of the Alps, were subject to discrimination and worse for two millennia, Izzie Weinzweig proposed. The brightest boys, the ones who excelled at sudying Talmud, became rabbis, and for the daughters of the richest merchants the rabbi was the best catch, so their children had the best chance of surviving poverty and persecution.

Hey, I was a Presbyterian at the time, but it sounded plausible to me.

I've encountered versions of this theory since, but Gregory Cochran has brought it up to date with an explanation that marries anthropology with biology: Natural selection made the Ashkenazim smart.

Those who lived, that is. Unfortunately, it also ensured they carried a very high load of potentially lethal genetic mutations, of which Tay-Sachs is the best known.

Cochran's an interesting, and frequently controversial, person. He's a freelance physicist in Albuquerque -- it did not occur to me, when I talked with him Monday, to inquire how a freelance physicist earns a living, given that physicists normally work with large and very expensive gadgets -- but he fizzes with ideas on everything under the sun. In this case, he's teamed up with two anthropologists from the University of Utah in Salt Lake City, Jason Hardy and Henry Harpending.

A draft of their paper, which is scheduled to appear in the Journal of Biosocial Science, is available at

http://harpend.dsl.xmission.com/Documents/ AshkenaziIQ.jbiosocsci.pdf on the Web.

The clues Cochran and his co-authors have put together:

* There was almost no intermarriage between the Ashkenazim and their gentile neighbors.

* For a long period -- the paper suggests roughly 800 A.D. to 1600 A.D. -- the Ashkenazim were restricted to occupations that the broader society despised, banking and finance to put it nicely, otherwise known as moneylending and tax collection.

* These occupations, even today, put a premium on high intelligence and disproportionately reward it.

* Families that were more successful financially were also more successful at raising their children to adulthood.

* And finally, there are several disease clusters, "groups of biochemically related mutations that could not plausibly have reached their present high frequencies by chance, that are not common in adjacent populations, and that have physiological effects that could increase intelligence."

Four of these diseases affect sphingolipid storage (you can look it up), and three of them are lethal in children who get copies of the mutated gene from both parents. The authors believe carriers, those who get just one copy, are likely on average to be smarter than non-carriers. Another group of genetic alterations has to do with DNA repair, which makes people more likely to get cancer.

This is a brutal bargain, but it was made, altogether unknowingly, in a brutal time. When two Tay-Sachs carriers married and had children, a quarter of them would die of the disease, but half of all children died anyway; their remaining children had a better chance of surviving to adulthood. Mothers with a mutation that makes them smarter but also leads to breast cancer would die of it, but probably not before their children were born, so natural selection wouldn't care.

Many of you will recognize that the same dynamic has operated in areas where malaria is endemic; mutations that protect carriers against malaria cause a variety of anemias, especially sickle-cell anemia, in people who have two copies of the mutated gene.

You might wonder whether eight centuries is long enough to accomplish changes like this. On IQ tests, the Ashkenazim are nearly one standard deviation above the European norm, and the pattern of scores -- high on verbal factors and the part of mathematics that doesn't depend on spatial visualization -- is unlike that of any other group.

But it's 40 generations or more; that's plenty of time. Also, Cochran said, there's no evidence in antiquity that anybody thought Jews were particularly smart. It was the kind of thing people noticed and commented on -- the Ionian Greeks were widely thought to be clever. And whatever influenced the Ashkenazim apparently did not have similar effects on other Jewish populations, a fact of some social significance in Israel today.

You shouldn't think of people getting married with the intention of having smart kids; that would be more like Lamarck than Darwin. Rather, imagine you could go back in time and administer culture-fair IQ tests to a suitably chosen sample of the population every generation or so. What you'd see is that bell curve for the Ashkenazim would shift slowly upward, a point or two every century, while the distribution for their neighbors didn't change.

Cochran is well aware that this is all very politically incorrect, not that he cares, but he also knows that his hypothesis is empirically testable; just establish whether there is a statistically significant IQ difference between carriers of these diseases and non-carriers.

He and his co-authors predict it will be about five points. Does anyone want to know whether he's right?