13 December 2007

Dor Yesharim - Upright Generations

Every once in a while, I stumble on a book that is so fascinating that I mentally schedule myself to re-read at a later date. It's rare that I actually do follow up and re-read it, but this recent book I read was so interesting that it's unlikely I won't get to it again at a future date..

'Before the Dawn' by Nicholas Wade is a fascinating journey through Human Evolution from our supposed split from the Ape line when we departed ways from our cousins around 5 million years ago. I say supposed for two reasons. Primarily because I don't want to turn away the believers before the important end of this post. Additionally, despite the hard evidence, I still find it mind-boggling that we evolved from lower species. Yet the case for Human Evolution is so powerful that it cannot be dismissed with a wave of the hand.

By all accounts this book is speculative. It goes beyond the Facts of Evolution and discusses detective work such as determining when Man started wearing clothing by studying the genetics of the Body louse. The book discusses difference and similarities between us and our cousins - Chimps and Bonobos. It discusses earlier hominids, the Neanderthals and Homo-Erectus and offers speculations that Modern man and Neanderthals came into contact. One of the most interesting sections of the book, is how it traces migration of our ancestral population from Africa and describes the migration across the globe. The migration across the globe and human evolution are intertwined with earth's climate (ice ages) and it is fascinating how the pieces fit together like a jigsaw puzzle.

A lot of the book is dedicated to the linguistic aspects of human evolution, a topic that did not interest me much.

Wade discusses controversial aspects of evolution such as Human culture, race, skin color, intelligence, current human evolution and where the Human race might be heading. Yes, Evolution has not stopped. An example of human evolution is the ability for some adults to digest lactose which is directly tied to the domestication of milk producing animals.

Another interesting topic concerns the Y Chromosome and the fact that unlike other Chromosomes, the Y chromosome gets passed down from father to son unchanged. Unchanged that is, barring slight mutations that occur at a known rate. The fact that the Y chromosome is for the most part unchanged, yet does undergo some change at rates that are understood, allows for some interesting detective work in tracing geneaology and in establishing paternity along the male line. For example, recent DNA analysis has seemed to close the book on the issue of Thomas Jefferson siring the children of his slave, Sally Hemings.

This brings us to issue of Kohanim & Leviim. Today's Kohanim claim they are directly descended without interuption on the male line to a single individual going all the way back to Moshe's time; Specifically to Moshe's brother Aharon who was the first Cohen. Well genetic testing seems to bear out the antiquity of the Cohen line. The Cohen Gene seems to date to around 1,000 BC . Not quite what some might hope for, but still pretty impressive! Furthermore, a large percentage of Cohanim, both Ashkenazi and Sephardi are of the same Haplotype. A large percentage but not all. Again, not quite what some might hope for.

This correlation is true for Leviim as well, but with a few major differences. Firstly the number of related Leviim is much less than that of Kohanim. More importantly, the Levite line only goes back to around 2000 years ago and there is no commonality between Sephardic and Ashkenazi Levites.

Another topic discussed is that Ashkenazic Jewry, but not Sephardic Jewry, has a higher than average IQ; about 115 if I recall correctly. The author states that Jewish lore attributes this to the following logic. The smart talmudic scholar was always highly prized and was supported in relative leisure and comfort and thus had larger family sizes and was more successful in passing down his intelligence. I never heard of this but it sounds interesting. More on Jewish smarts later.

Another tidbit is that geneticists believe that the Bene Israel of India were started by Jewish traders who married local Indian women. The maternal line (mtDna) shows a local origin.

This brings us to Jewish Disease. (I must apologize in advance if I don't have all the technicalities and it's not as precise as it could be, but I don't have this information at hand). As an introduction, consider this. If natural selection is so efficient, why are there "Bad Genes" out there? Other than mutations that can occur at random, why has not natural selection gotten rid of carriers of disease such as Sickle Cell Anemia? (Which by the way is another example of recent human evolution.) The answer is that when not directly causing disease, the inferior allele of a Gene which causes such illness must confer some special advantage to it's bearer. I believe this is known as balanced polymorphism.

In other words, if you get one copy of the troublesome gene you have some unspecified advantage over individuals without the "bad" gene. If you are unfortunate to get two copies, one from each parent, then you get some devastating diseases such as Tay Sachs or Sickle cell anemia. It has been determined that the advantage conferred by the "bad" allele for Sickle Cell Anemia is protection against Malaria. This explains why Africans are at risk for SCA , and is explained by the relative recent deforestation of areas which caused an increase in carriers of the malarial parasite.

Likewise, Ashkenazic Jewry, but not Sephardi Jewry, is highly susceptible to some genetic diseases in which the disease only manifests itself if an individual inherits the defective gene from both parents. So the question arises, what genetic advantage was conferred by passing down these alleles that cause diseases such as Gaucher, Tay-Sachs, etc?

(Note, there are different genetic diseases in the Sephardic community that are not the subject of this topic)

A theory has recently been proposed by Greogory Cochran that posits that the defects in these genes, known as sphingolipid mutations, are correlated with higher intelligence. The theory holds that in the Middle Ages jews were driven and forced into the occupations that required higher intelligence. This resulted in natural selection favoring these genes for enhanced intelligence but pre-disposed the Jews to genetic disease when an unfortunate individual inherited two of these genes.

This explains why higher than average intelligence and these Genetic disease are to be found in the Ashkenazi communities but not in the Sephardim.

Additionally, in the words of Future Pundit "The hypothesis could be tested fairly rapidly. Recruit some thousands of Ashkenazi Jews to take IQ tests and to have a few dozen genes tested for assorted genetic variations. Compare the IQ test results to the genetic tests and see if all the known genetic variations in sphingolipid storage metabolism, DNA repair, and several other categories account for a large proportion of Ashkenazi Jewish genetic variations."

Kudos to the Chariedi community that arranges for genetic testing at shidduch age through Dor Yesharim. The purpose of this program is to prevent two carriers from dating seriously and thus marrying. It does this by not divulging carrier status to an individual. Individuals are only informed of their carrier status if they attempt to pair up with another carrier. Hopefully, this is checked early enough in the dating process before emotional attachements are formed.

Anyhow, I address this to all my single friends out there. I know that you skeptics are especially bright and have high IQ's. Similiarly, all of you sitting in the Bais Medrash are probably very bright too. According to Cochran's theory you might be a carrier. So please, take advantage of Genetic testing as appropriate.

So, you might ask, what about my IQ? Well, I happen to know that I have a very high IQ. When I was young my mother told me she's so proud of me because I scored in the high 80's on my IQ test.

That must count for something, no?

P.S. And you thought I meant Dor Yesharim (Upright Generations) as an allusion to evolution from Ape to human. I wonder what gave you that idea.


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