Ashkenazi Jews & Intelligence

Freud, Einstein, Mahler

Kristy Brady8 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• Proposed evolutionary mechanisms• Alternative hypotheses

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

Distribution of sickle-cell anemia & malaria

Green: regions with malaria

Red stripes: regions with high frequency of sickle-cell trait

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

Heterozygote Advantage

sickle-cell malaria

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).

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.

Ashkenazi Jews: A brief history

• In 19th & 20th centuries, large migration to W. Europe, Americas, Australia, & South Africa

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.

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.

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

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)

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)

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

Potential Experiments

• IQ tests controlled for genotypes

• Environmental effect studies

– dietary controls