As we all know, the Jewish population has had a turbulent and nomadic history. The Romans destroyed the Temple in 70 A.D. causing yet another exodus of the Jews this time into smaller groups rather than just one large group. One of these groups, the Ashkenazi, settled in central Europe only to be persecuted yet again by Christians roughly one thousand years latter. Since the Christians were not the dominant population, the Jews were restricted to occupations that did not appeal to the host Christian’s population, specifically, banking and trading. According to this segregation, coupled with strict social boundaries upheld by the Ashkenazi by intermarriage, is said to have caused the mutation of certain neurological genes leading to a variety of neurological diseases, and also in some instances, higher intelligence within the Ashkenazi population (Wade, 251-255).
The reason why neurological diseases became so prevalent within the Ashkenazi community was through the Founder effect. According to Montgomery Slatkin, A founder effect can result either from a true founder event (i.e., the establishment of a new population from individuals derived from a much larger population) or from an extreme reduction in population size (i.e., a bottleneck in size (2004). So when the Romans forced the Jews out of Israel, a rare mutated gene was included in the population that relocated. Because the mutated gene was so rare, the mutated gene should have been eradicated by genetic drift. However, the Jewish custom was to procreate within their population. This caused the rare gene to become more familiar. Unfortunately, this gene also is the reason for a higher percentage of neurological diseases.
The genetic mutation, the same one that gave rise to neurological diseases, was also to have caused a strange side effect: higher intelligence. Because the diseases had a direct physical effect on neurons, it was also possible that extra cognitive skills were acquired to adapt to the diseases (Wade, 255). The Jews having jobs that required more cognitive exercise throughout the Middle Ages also augmented this.
Slatkin, M. American Journal of Human Genetics; Aug2004, Vol. 75 Issue 2, p282-293, 12p
Wade, N. (2006) Before The Dawn: Recovering The Lost History of Our Ancestors. New York: The Penguin Press.
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In the essay above, it described how genetic mutations that arise in a particular individual when combine with the founder effect can cause a small isolated population to become dominantly affected with that disease. In one of my class, Biology 117, I was taught with similar ideas and terminology. The course central theme is human genetics. This class is related to the essay by the fact that marriage within family, among relatives, or people within the community can strengthen the characteristic of a mutation and cause it to become more prominent. The course explains that when a person who is homozygous dominant (a person with both alleles for the disease) with the disease marries a person who is recessive (a person without any allele of the disease) will produce children who will all possess the heterozygous allele (people with one dominant gene and one recessive gene for the disease). When the situation above occurred, over time, the mutation will increase and becomes dominant in the population.
ReplyDeleteAn example of the situation above is best explain if you visualize a normal phenotypic male who has family with the disease call Down syndrome. This male might be a potential carrier of the disease. If this male decides to have sexual relationship with one of his normal phenotypic cousin and have children, there will be a high possibility that one of their children will have Down syndrome. (The situation described in the above example is only one of the possibilities that I studied, there are other explanations which will take too much time to explain in detail) Marriages within family members are tabooed in modern society in order to decrease the likelihood of a disease to spread prominently within a community like the Jewish community described in the above essay.
Obviously the higher rates of disease in certain populations due to endogamy are indisputable. But I am little skeptical about the endogamy leading to higher rates of intelligence within the Ashkenazi Jews. I know several scholars on the SJSU campus, and elsewhere, would disagree with this theory. Rather, they would claim that it is cultural values instilled in Jewish youth which has led to higher rates of intelligence within the population. Many Jews, especially in antiquity, are polyglots (multi-lingual). And there is a lot varying research correlating multilingualism to intelligence. I've also heard a scholar argue that the study the Talmud (rabbinic law) from such an early age has led to higher rates of intelligence.
ReplyDeleteThere is also a lot of data out there stating that though some aspects of intelligence is hereditary, much of intelligence development is due to socio-economic status.
I feel like I am on the same page with thuggee on this. I agree that endogamy can lead to higher rates of disease, but I also don't fully agree that it can be a cause for higher intelligence. It seems like it would be extremely difficult to determine the root of intelligence within the Ashkenazi Jewish population. Although it is a debatable topic, it is an interesting one, and I enjoyed reading your thoughts on it.
ReplyDeleteGood Blog very well thought out. I also agree with thuggee in the sense that much of intelligence is developed through socio-economic status. Another portion of the reading on the Ashkenazi jews alludes to the idea that it was not the founder effect that caused the mutations but instead natural selection. Cochran and Harpening found no evidence for any of the reductions in population size required to cause Risch;s founder effect. In addition there was no clear historical evidence that the Ashkenazi jewish population ever dwindled to the low numbers necessary to produce the founders effect again according to Cochran and Harpening. Also I am curious as to the other two jewish groups both Sephardic and Oriental have they not also encountered the founders effect? It would seem logical due to the fact that they are both smaller in number when compared to the Ashkenazi.
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