June 21, 2005

Cochran, Hardy, Harpending, and me

I haven't posted anything to my blog in over a week, being very busy lately, and with the Shavu`ot holiday taking up a couple of days in the middle. There is also another reason: this paper (pdf), which was reported on by the New York Times, and The Economist, to name a few, and picked up on across the blogosphere. Gene Expression, which has been talking about this subject for a while, has a series of posts up on the subject:

Overclocking
Natural history of Ashkenazi I.Q.
The Urban Sink
Bad science?
The history of the Jews...a very special people...sort of
Medieval Jewish achievement
Metzenberg on Jews

Briefly, for those who have not yet heard about it, the paper (Natural History of Ashkenazi Intelligence, by Gregory Cochran, Jason Hardy, and Henry Harpending) claims that the average IQ of Ashkenazis is around 115, about one standard deviation above the general average of 100, and that this is the result of natural selection acting on an Ashkanazi population which for centuries specialized in intellectually demanding tasks like commerce and banking. 

One of the consequences of this selection pressure, they claim, is the spread among the Ashkenazi population of genetic diseases which have the a effect of raising intelligence. They hypothesize that common Ashkenazi genetic diseases such as Tay-Sachs and Dysautonomia are among them.

As one of the specimens under the microscope, I have been following the Ashkenazi selection debate with keenly-felt trepidation and intense curiosity. Curiosity, because, well, they're talking about me. Trepidation, because it puts the Jews under a dangerous spotlight - those who claim that such fears are out of date need only look at the generation that experienced the Holocaust: they thought the same thing - and the rising anti-Semitism among the Left and around the world.

Which doesn't mean that I think it should be suppressed. While a case can be made that this piece of knowledge or that does more harm than good in the world (nuclear bombs, for example) the only way to suppress knowledge is totalitarianism, and that bears a far higher price. You can't get away from the problem: Quis custodiet ipsos custodes, who will decide which knowledge is permissible and which not? The only way forward is to seek the truth, and deal with it. The proper response to truth is more truth. Just don't forget your morals along the way, or the possibility that you might be wrong.

Overall, I find the paper's thesis extremely plausible (I feel no need to actually make a judgment: its conclusions are testable, though the precise historical mechanism isn't - we will soon find out). Natural selection is everywhere, you can't get away from it. Every population is selected for its habitat, including our own at this time. In that vein, I would like to add some observations. First of all, intellectually demanding occupations were not the only characteristic of the Ashkenazi environment. For example: Ashkenazis have been living in an urban environment for over 1000 years, I would expect some adaptations to reflect that. Another thing: Judaism. For example, Judaism prohibits sex during menstruation (but for a minimum of 5 days), plus 7 days thereafter, so women with short cycles or long periods can have trouble conceiving. Do Jewish woman have more regular cycles as a result?

And what about the other way around? The paper implicitly denys or minimizes the role of Judaism in Ashkenazi intellectual success. The tradition of sending sons to school at age 3, Talmudic study, and the intellectual character of Judaism in general, would be a correlated side-effect rather than causal factor, according to this story. But perhaps it has a different role, perhaps Judaism is an evolved response to the Jewish habitat? Hygiene, for example: Jews are required to wash their hands after urinating or defecating, and before eating. 

But that is of little relevance in this day and age. More relevant: it is striking to me how much the historical habitat of the Jews resembles today's habitat for everyone. IQ is correlated with economic success in today's world like never before. Agriculture occupys a tiny fraction of the population. The vast majority are urban. And fertility today is below replacement rate in every modern society - as has been historically true for urban populations in general. Moreover, the tendency of high-IQ individuals having low fertility seems to an ancient pattern. How many children did Aristote or Plato have? The founding fathers of the US? The professors of Oxford and Cambridge? The Jewish population, urban, intellectual, fit this pattern: it was in decline for many centuries (10% of the Roman Empire was once Jewish, that would correspond to hundreds of millions today). Perhaps after centuries in their challenging habitat, Jewish culture evolved mechanisms for its survival? Observant Jews, with a birthrate of 4.5 children per woman, are likely the US's most fertile native-born urban population. In contrast, non-observant Jews are one of the least fertile sectors of the US population (way below replacement rate).

What can these mechanisms be? Well, for one thing, as I indicated above, Judaism strongly encourages sex on the 14th day of a woman's cycle (the first day that it is permitted, usually the night of the 13th day by non-Jewish reckoning, since the day begins at sundown) - just when she is most likely to be ovulating, and in general the religion encourages sex between husband and wife. But more important than that, I think, Judaism has strong cultural institutions for maintaining society against the background of urban life. 

(I have frequently talked about this subject in the past, for example hereherehere.)

Posted by David Boxenhorn at June 21, 2005 10:57 AM
Comments & Trackbacks

Almost all incidents of Tay Sachs occur among non-Jews these days, since people believe it to be an all-ashkenazic disease, so Jews take precautions while non-jews don't. The truth of the matter is that it isn't, it is just more common for ashkenazim to be carriers (1/50 as opposed to 1/300, or something like that.

The reasons you named for why askenazy Jews have a higher average IQ than most others is just one theory. I personally think it is just one of those things we can't explain. I also don't think that this discussion should have to harm Jews. People just need to get over this obsession with "measuring intelligence". IQ tests are only reliable to an extent (and not a great one), and only in certain societies. I know many Jews who are very or even exceptionally intelligent, but I've certainly known some incredibly stupid jews. The most intelligent person I've ever known, my father, was not Jewish.
I think it's a pity that people are so fixated on numbers.

Posted by: Maria at June 22, 2005 08:06 PM Permalink

I certainly don't think that genius = high IQ! Note, I was careful to say IQ and not intelligence. IQ is nothing more than the score you get on an IQ test. It measures what it measures. However, whatever that is is one factor in success in many areas.

Posted by: David Boxenhorn at June 22, 2005 10:26 PM Permalink

The post is fascinating.But I disagree with the evolutionary hipothesis. The commonly accepted intuition is that evolutions is very slow, and one thousand years is a compratively short period. Survivance patterns and genetical mix make the reproductive process very random, and to separate "noise" from signal you really need lots of iterations.

Posted by: Kantor at June 22, 2005 10:28 PM Permalink

Kantor: Read the paper, they specifically deal with your objection.

Posted by: David Boxenhorn at June 22, 2005 10:34 PM Permalink

"Almost all incidents of Tay Sachs occur among non-Jews these days, since people believe it to be an all-ashkenazic disease, so Jews take precautions while non-jews don't. The truth of the matter is that it isn't, it is just more common for ashkenazim to be carriers (1/50 as opposed to 1/300, or something like that."

duh...There's a huge difference between being a carrier and actually having it. Did you even read the study? What Cochran et al are sepculating is that certain genes for these diseases increase intelligence as heterozygous alleles. Sheesh.

"IQ tests are only reliable to an extent (and not a great one), and only in certain societies. I know many Jews who are very or even exceptionally intelligent, but I've certainly known some incredibly stupid jews."

Aren't you contradicting yourself? First you imply that IQ tests are subjective, then you talk about dumb and intelligent Jews you've met. Sorry, but an IQ score holds more weight than your personal opinion.

Seriously, just read the freaking paper or quit yapping.

Posted by: A Reminder at June 23, 2005 10:45 AM Permalink

"A reminder":
No I didn't read the study. I have, on the other hand, studied genetics, so you don't need to lecture me.

"Aren't you contradicting yourself?"

No I wasn't. You just didn't understand what I was saying.

"Sorry, but an IQ score holds more weight than your personal opinion."

I don't quite understand why you think I'd care about your opinion.

Posted by: Maria at June 26, 2005 04:05 AM Permalink

(((David)))
This is so very good. Even Henry and Greg should remember that the mechanisms of inheritance are infintely subtle and infinitely complex. The crude tools of statistics that we employ are woefully inadequate to section and assign individual causality to parameters.
Judaism is an error correcting code that has evolved to be extremely robust and flexible, even in the modern world.
I am waiting anxiously for your IQ post. ;)

Posted by: jinnderella at June 27, 2005 02:16 PM Permalink

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