Friday, June 03, 2005

Ashkenazi Jews, genetic diseases, and intelligence

As this article appearing in today's NY Times itself mentions, the theory isn't very PC.

I see some possible flaws in the reasoning--at least as it's described in the article. Of course I'm no scientist (obligatory disclaimer), but I do have a bit more than the general reader's knowledge of evolution. Judge for yourself, though, and read the article.

Once again, because of the Times's requirement for registration, I will reproduce more of the original article than is my usual practice:

A team of scientists at the University of Utah has proposed that the unusual pattern of genetic diseases seen among Jews of central or northern European origin, or Ashkenazim, is the result of natural selection for enhanced intellectual ability. The selective force was the restriction of Ashkenazim in medieval Europe to occupations that required more than usual mental agility, the researchers say...

He and two colleagues at the University of Utah, Gregory Cochran and Jason Hardy, see the pattern of genetic disease among the Ashkenazi Jewish population as reminiscent of blood disorders like sickle cell anemia that occur in populations exposed to malaria, a disease that is only 5,000 years old.

In both cases, the Utah researchers argue, evolution has had to counter a sudden threat by favoring any mutation that protected against it, whatever the side effects. Ashkenazic diseases like Tay-Sachs, they say, are a side effect of genes that promote intelligence.

The explanation that the Ashkenazic disease genes must have some hidden value has long been accepted by other researchers, but no one could find a convincing infectious disease or other threat to which the Ashkenazic genetic ailments might confer protection.

A second suggestion, wrote Dr. Jared Diamond of the University of California, Los Angeles, in a 1994 article, "is selection in Jews for the intelligence putatively required to survive recurrent persecution, and also to make a living by commerce, because Jews were barred from the agricultural jobs available to the non-Jewish population."

The article then goes on to discuss whether the authors are correct in their interpretation of the existence of the genetic diseases and the possible link to intelligence, or whether the existence of the diseases have no connection to intelligence, but can be explained by something called "founder effect," which involves the amplification of random mutations in small populations. I took an entire course in population genetics in college, and so I remember a few basics, but the finer points have long departed my brain. So I have no idea which camp is correct. But the part that interested me most was this:

In describing what they see as the result of the Ashkenazic mutations, the researchers cite the fact that Ashkenazi Jews make up 3 percent of the American population but won 27 percent of its Nobel prizes, and account for more than half of world chess champions. They say that the reason for this unusual record may be that differences in Ashkenazic and northern European I.Q. are not large at the average, where most people fall, but become more noticeable at the extremes; for people with an I.Q. over 140, the proportion is 4 per 1,000 among northern Europeans but 23 per 1,000 with Ashkenazim.

The Utah researchers describe their proposal as a hypothesis. Unlike many speculations, it makes a testable prediction: that people who carry one of the sphingolipid or other Ashkenazic disease mutations should do better than average on I.Q. tests.

Whoa, that's some statistic! What the researchers are saying about the distribution of intelligence in the Ashkenazi Jewish population is very interesting, and it happens to somewhat parallel the argument Larry Summers was making (remember that?) about men vs. women in science--that is, that the major and important difference occurred not near the middle of the scale, but at the far extreme, the "genius" level many standard deviations away from the mean.

But to me, this fact makes the Utah scientists' arguments somewhat puzzling. Why would a selection process (if such a process actually did occur) for smarts that would confer an advantage in business and money-lending and surviving persection end up increasing the numbers of extreme intellectual outliers in a population, rather than just the average IQ of that population? Perhaps there's an explanation in there somewhere, but I don't see it. One would expect an increase in general intelligence, but not necessarily a greater increase in phenomenal intelligence; an increase in the ability to do arithmetic, perhaps, but not entry in such disproportionate numbers into the stratospheric regions of abstract math. I always thought arithmetic and higher math were not all that closely linked. And what about the ability to play chess? Chess is a game of strategy, to be sure, but it's a game of a special kind of strategy--spatial strategy (again, linked to higher math)--and it's hard to see how that ability would have been selected for by the processes these scientists describe, an aptitude for business, or the need to escape the Cossacks or whoever might be the persecutors du jour.

Fascinating, though. I'll be interested to learn whether people who carry these mutations in their benign single-cell form actually are especially smart. Somehow, I doubt it--but I expect we'll see when the results of the proposed research come out.


At 4:12 PM, June 03, 2005, Blogger Dr. Sanity said...

Extremely interesting article. If their hypothesis is true, then it opens up a Pandora's box for the PC crowd. That intelligence could be selected for in certain populations (and not in others)makes sense. Other traits--such as height, or strength for example--may also be characteristics that are subjected to evolutionary pressures. I think we will just have to celebrate our diversity!

At 5:33 PM, June 03, 2005, Blogger Bookworm said...

I'd love to think I'm genetically smarter, but I suspect that there is primarily a cultural component. For almost a century in America, Jewish families have placed exceptional emphasis on academic achievement. This means that the really smart kids present in any population will have a better chance to cultivate their gifts.

As the current generation of Jews becomes more and more interested in feeling good than in thinking well, I suspect the numbers will change. And in 20 years, the same research group will come out with some article linking the striking intellectual achievements of Asian-Americans to a propensity to eat with chopsticks or a craving for dim sum.

At 7:52 PM, June 03, 2005, Blogger WichitaBoy said...

I have long suspected that there is a Jewish paranoia gene. Although not universal, I've noticed over and over a higher than expected propensity toward excessive fear in the face of adversity among some Jewish friends. This takes various forms, such as Woody Allen's screen hypochondria, to take one example everybody knows. If there is such a factor, it is easy to see how it could have arisen through selective culling of the population during the pogroms.

On the other hand, I've been told by a chess master acquaintance, though I haven't personally verified it, that there are studies which indicate that high skill at chess is strongly correlated with paranoia.

The observation about Jewish chess masters would be partially explained if both of these suppositions are true. There is an obvious caveat one must consider before further speculations in this direction, namely, almost all serious chess activity in the United States occurs in NYC, which also happens to be the home of the largest concentration of Jews. This could indicate a cultural, rather than genetic, causation when it comes to chess. A careful study would attempt to remove this possibility for bias. I would like to see a more extensive study which considers Jewish and chess populations in other countries.

You are correct in asserting that this argument, by considering the shape of the statistical distribution, rather than simply the location of the mean, is similar to Larry Summers's speculations (I don't believe he was proferring a hypothesis). But the arguments are not actually the same: Summers rightly pointed out that dispersion of intelligence is larger within the male population, i.e., the standard deviation is significantly greater. This happens because the number of men exceeds the number of women in both statistical tails. I don't believe that is quite the argument that is being made here with respect to the Jewish population. In fact the argument here seems to be implicitly asserting that the mean of the Jewish population is higher than that of the general population. If this is so, and if the Jewish population historically largely avoided intermarriage with non-Jews, then genetic pressures could explain larger numbers of Jews in the higher-end tail of the distribution. Essentially, the Jewish population is likely to be a tighter bell curve moved slightly to the right. It wouldn't take too much rightward movement of the mean to cause significant dominance in the tail.

At 9:01 PM, June 03, 2005, Blogger Goesh said...

The specificity of natural evolution is well known and long documented. Researchers have now just genetically tagged a disease uniquely common to male sand dwellers. This disease, Femalius Irrationitis, mimics the etilogy and pathology of brain fungus, yet is totally distinct. The symptoms of Femalius Irrationitis have been long held to be the purview of psychiatrists and psychologists, who traditionally have labeled their observations simply as psychotic manifestations. Research at the cellular/molecular level now clearly gives this condition its own distinct, genetic etilogy.
The most recent outbreak of Femalius Irrationitis occured in Saudi Arabia last week when a one Mohammed al-Zulfa, some type elected official, suggested that some Saudi women be allowed to drive. Strange and bizarre utterances began to immediately manifest among the male population in response to this stimuli. Some males called for al-Zulfa to be stripped of his citizenship. Prayers were sent up to allah requesting his blood be frozen and accusations were made that al-Zufra is driven by carnal instincts. Anticipation and prediction of total social and moral collapse is another symptom presently occuring amongst the male population. "Driving by women leads to evil" wrote a one Munir al-Shahrani to a local newspaper. Others have strongly asserted that women will unduly expose their eyes while driving and will interact with strange men, such as traffic police and mechanics. Many believe that women at the wheel will create situations for sinful temptations. The last outbreak of Femalius Irrationitis with specific vehicular symptoms occured in 1990, when US troops were in Saudi and 50 American women violated the ban on female driving . All were jailed for one day and their passports were confiscated.

Western Theologians and other academics argue that all of the above can simply be attributed to islam, but the scientific data on Femalius Irrationitis is going to be released next month in several journals, and will quickly and forever put the former assertions to rest. Your post on the Ashkenazi Jews is timely indeed, Neo.

At 10:04 PM, June 03, 2005, Anonymous Promethea said...

How do the geneticists explain the high level of achievement among Iraqi and Iranian Jews? They aren't Ashkenazi, and are not especially susceptible to Tay-Sachs disease.

Regarding Jewish achievement in America--I would be very surprised to find that Jews can keep their edge over Korean, Chinese and Indian (South Asian) students. Jews all over the world have always had higher literacy rates than the surrounding populations, including Muslim Iraqis and Iranians, but now they're facing major competition from the East and South Asians.

One advantage that Jews may still have--they seem to be especially adept at independent thinking. (I say this even though most Jews I know are LLL-to-the max.) The explanation I've always heard is that they traditionally engaged in "pilpul," talmudic argument similar to the kinds of arguments lawyers engage in.

As to whether Jews can shine in the face of East and South Asian competition--Time will tell.

At 11:27 PM, June 03, 2005, Anonymous Anonymous said...

See also the discussion and links here: GNXP

You can also download a pdf of the entire paper.

At 12:32 AM, June 04, 2005, Blogger jj mollo said...

Look at the distribution shift this way.

Assume that you have two similar samples from identical normal distributions. Now if you were to order the data in both and place the list of data points side by side, like the sides of a ladder, where rung holes represent the data at appropriate heights, you would expect the rungs to line up rather nicely in the middle, becoming rarer and more irregular at the top and bottom, but still pretty well matched. Now before you put in any rungs, slide one side up a fixed distance. You can see that there may still be lots of matching rung holes near the center, but many unmatchable holes at one side of the top and the other side of the bottom.

At 12:53 AM, June 04, 2005, Blogger jj mollo said...

Here is the elephant in the room.

At 1:59 AM, June 04, 2005, Blogger Bookworm said...

Just FYI, I was so intrigued by the ideas expressed in your post, I've linked to it over on my blog.

At 10:44 AM, June 04, 2005, Anonymous Joseph said...

Well, I'm Jewish and a descendant of Northern European Jews in both sides, but I do believe that it is at least as much cultural as genetic. I have often wondered how much the two over generations might some how intertwine in human development, or in other words culture and family traditions through time may affect genetics.

During the Roman Empire the Britons were definitely dim-witted savages to the Romans, yet who would assume the British as below average and dim-witted today? What I find further interesting is the origin of this report... Utah? I know that there is only one group of people in our nation that out perform Jews in most measurable categories, and that group is the Mormons, and the fact is they are more a religion and culture then race. They live the longest, are less affected by desease, produce more millionaires, college graduates, high school graduates and have more people listed in the Who's Who as well as members of Mensa (also other categories) per capita then any other group including Jews, so how does this not imply culture has a huge impact? The inventor of the television was a Mormon and I could go on, so while as a Jew it would be wonderful to think that I have some inherent quality that gives me some leg up on other people, but I can tell you the drive to succeed and to leave ones mark is very cultural, areas of interest are often passed on (being a doctor etc.), but how this impacts genetic development through generations for me is a question worthy of much ponder.

I know that this doesn't explain much, in fact probably just begs more to question, yet to me the point is it is like trying to separate spiritual aspects of living from the temporal or physical aspects, we must keep evaluating and learning, but at some point I believe we must realize that the two are somehow inter-connected. In a certain sense not believing we can effect our posterity in all possible areas in positive means is at some level to be without hope, but again this implies effecting such things through decisions. Is this not implying that spiritual aspects of living can affect the temporal? This of course implies the reverse is possible, but indeed does not the rise and fall of civilizations prove as much?

When the first settlers arrived in the America's they in many cases came upon people that where in a state of obvious decline, but European culture also had declined and they through exploration and the Renaissance were building back. Yet this decline was very culture based, of course disease played a part, but how disease, behavior effect genetic composition of society is something to ponder, but at some level I believe civilization and culture must effect genetics. Within civilizations, cultures, and groups, habits must further effect measurable differences in the population, how else to explain the Mormons?

Of course I offer nothing scientific just deductive reasoning, but of course this is because I don't come from the stereotypical positon of the scientific Jew, rather that of the the money grubbing type. :-)

At 10:52 AM, June 04, 2005, Blogger Gerard said...

Increased number of outliers may have to do with increased number of sports thrown off by mutation.

At 11:32 AM, June 04, 2005, Anonymous neo-neocon said...

I agree that one cannot possibly discount the effects of cultural and familial environment. However, knowing what I do about my own higher math abilities (not so hot), I tend to think there's a strong genetic component to that sort of thing--although, of course, an encouraging environment ordinarily must be present for it to reach its full fruition. Most math geniuses seem to be "different" in that way from the start--their brains seem sort of hard-wired for it, and they are also "different" from people who are merely very good at math (at least, that's my observation, in my very unscientific and only anecdotal study of the phenomenon).

As far as outliers go (Gerard's theory), and the distribution shift (so well-explained by jjmollo that I think even I understand it)--well, I see a problem with each, and it's the same problem. I can see how it would definitely explain a slight difference between populations--that is, if there were slightly more Jews represented among Nobel prize winners and among chess players. But the numbers of outliers seems way too high (especially given the tiny Jewish population) for me to feel that they can be explained by either theory. Especially the chess champions--half of the world chess champions?

WichitaBoy's comments about chess champions and paranoia is fascinating. I know very little about chess champions, but if Bobby Fischer is at all typical (and it's hard to think he's typical of anything--he seems, quite fortunately, to be sui generis), then paranoia and chess do seem linked (see this for more on the subject).

At 6:34 PM, June 04, 2005, Blogger Brian H said...

Actually the outliers explanation by curve shift is quite strong; bumping a small proportion of the next lower "category" into the most extreme one has a disproportionate ratio impact, so to speak, since the fall-off in absolute numbers is so great between categories.

Remember that there are 2 major factors shaping evolution: survival/fecundity through reproductive years, and sexual selection. If higher IQ meant more likelihood of living to bring surviving children to adulthood, that would select for it. And if culture shaped female and/or male choices to favour the brightest mates, that would have an even quicker and more potent effect.

And, as many have commented, the "bottleneck" effect of a population pinch can amplify the potential degree and speed of such changes; in effect, all surviving members of a small group have much increased chances of being a "founder".

The Ashkenazi sub-group distinction may just be an artifact of the study's focus. Anti-Semitism was widespread enough in the last 2000 years to put similar pressures on virtually all sub-groups.

There is also the over-arching issue of cultural norms; if high intelligence and associated roles in the community are given high status, it will make marriage into those groups or professions a goal of other best-and-brightest. To the extent that this remains a meritocratic self-selection process for many generations, instead of a caste/clan/aristocratic locked-in one, the "breeding" effect could be very powerful.

Intelligence is in principle no harder to select for than anything else. Consider the border collie, e.g. !

At 5:53 PM, June 05, 2005, Blogger Alex said...

brian h is absolutely right that a small shift in means will have increasingly large effects the farther out that we look on the tail. However, this is only true if we assume normal distributions. And while many natural phenomena are well-approximated by normal distributions, the quality of the approximation usually worsens the farther we go from the center. In other words, normal distributions are great approximations of natural phenomena close to the mean, but can be really bad approximations in the tail.

Most real-world phenomena do not stretch into infinity, as normal distributions do, but instead have bounds. If we suppose there is some sort of hypothetical limit to intelligence (not a crazy assumption, I think) then we could easily see the advantage growing or shrinking in the tail, depending on how close we are to the limit.

I'm not exactly arguing against the idea that a shift in means explains the large difference in the tail. I just wanted to point out that it relies on a fairly strong assumption about the distribution of intelligence.


Post a Comment

<< Home

Powered by Blogger