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Ashkenazi Jews & Intelligence

Ashkenazi Jews & Intelligence. Freud, Einstein, Mahler. Kristy Brady 8 February 2006. Outline. Heterozygote advantage Example: sickle-cell anemia & malaria A brief history of Ashkenazi Jews Observations on Ashkenazi Jew intelligence & disease Hypothesis correlating intelligence & disease

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Ashkenazi Jews & Intelligence

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  1. Ashkenazi Jews & Intelligence Freud, Einstein, Mahler Kristy Brady8 February 2006

  2. Outline • Heterozygote advantage • Example: sickle-cell anemia & malaria • A brief history of Ashkenazi Jews • Observations on Ashkenazi Jew intelligence & disease • Hypothesis correlating intelligence & disease • Proposed evolutionary mechanisms • Alternative hypotheses

  3. Heterozygote Advantage (aka: overdominance) • A case in which heterozygotes have a higher fitness than homozygotes at a given locus. Maintains genetic polymorphism in a population. • e.g., sickle-cell allele & malaria tolerance • e.g., cystic fibrosis allele & TB resistance

  4. Distribution of sickle-cell anemia & malaria Green: regions with malaria Red stripes: regions with high frequency of sickle-cell trait

  5. malaria sickle-cell Heterozygote Advantage Genotypes (S = wild-type allele, s = sickle-cell allele) SS: no sickle-cell trait, not malaria tolerant Ss: no sickle-cell disease, malaria tolerant ss: sickle-cell disease

  6. Ashkenazi Jews: Observations • Have the highest average IQ test scores of any ethnic group (for which there are data). • During the 20th century, comprised ~3% of the U.S. population, but won 27% of Nobel prizes awarded to U.S. scientists. • Represent over half of the world chess champions. • High incidence of sphingolipid storage diseases: Tay-Sachs, Gaucher, Niemann-Pick. • High incidence of certain cancers (DNA repair cluster mutations).

  7. Ashkenazi Jews: A brief history • 3 Jewish groups: Ashkenazi (blue), Middle Eastern (green), Sephardic (red) • Ashkenazi Jews (from Hebrew word for German) moved north of Alps in 1st millennium A.D. Settled in Rhineland during 800s. • In 12th & 13th centuries, expelled from Western Europe. Moved to Poland & Lithuania where Ashkenazi center remained for 5 centuries.

  8. Ashkenazi Jews: A brief history • In 19th & 20th centuries, large migration to W. Europe, Americas, Australia, & South Africa

  9. Sphingolipid Storage Diseases – neurological disorders Sphingolipids: A member of a class of lipids derived from the aliphatic amino alcohol sphingosine. They play an important role in signal transmission and cell-cell recognition. • Gaucher: accumulation of sphingolipid that promotes growth & branching of axons. • Niemann-Pick & Tay-Sachs: accumulation of sphingolipids that promote growth of dendrites.

  10. Hypothesis • Heterozygote advantage (e.g., Gaucher allele, recessive) • GG: wild-type • Gg: no disease, moderate increased linkage between brain cells yields increased intelligence • gg: Gaucher disease, increased linkage between brain cells yields increased intelligence (as measured by IQ tests) • Similar scenarios for heterozygotes with Niemann-Pick or Tay-Sachs alleles.

  11. Evolutionary mechanisms • Selective pressures • money-related occupations (e.g., banking, tax farming); today IQ and success are positively correlated in these professions • Assortative mating/no gene flow • Ashkenazim tend to marry among themselves

  12. Evolutionary mechanisms • Fitness • in Europe, prior to the 18th century, affluent families tended to have more children surviving to adulthood than poorer families • Effective population size • ~40% of Ashkenazi Jews are descended from 4 women living sometime in the last 2,000 yrs (Am. J. Hum. Gen. 2006, 78:487-97)

  13. Evolutionary mechanisms • Heritability of IQ • in youth “in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse.” (Psych. Sci. 2003, 14:623-8) • in youth “past experiences…influence today’s IQ only because of their effect on past IQ and the effect of past IQ on today’s environment” (Psych. Rev. 2001, 108:346-69) • adult IQ largely affected by adult environment (Psych. Rev. 2001, 108:346-69)

  14. Alternatives to selection? • Genetic drift • evidence of genetic bottleneck • Diet • quantity of omega-3 fatty acids consumed by a pregnant mother greatly influences a child’s verbal IQ & social skills • Culture • education highly valued

  15. Potential Experiments • IQ tests controlled for genotypes • Environmental effect studies • dietary controls

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