HERITABILITY OF INTELLIGENCE: (WK34):

CONTROVERSIAL HISTORY:

  • Galton (1883) introduced an area of intelligence besides individual differences

  • eugenics = the study of how the ‘stock’ of a society can be improved

    • traits such as health, energy, ability

    • ‘positive’ eugenics = encouraging the higher class to marry and reproduce responsibly

    • ‘negative’ eugenics = encouraging the undesirable sections of society not to reproduce

  • example: the Kallilak family

HEREDITARIANISM AND IQ:

  • Gould (1981, 1995) describes the contribution of hereditarian theories of intelligence

    • low IQ associated with criminality

    • conflated idea of innateness with fixedness

    • prejudice and discriminatory according to class/race/social group

    • influenced social policies

  • example: case of Buck vs. Bell (1927)

    • 17 yr old Carrie Buck picked as first person to be sterilised in Virginia

    • resident in asylum, had a baby despite being unmarried → her family was said to be part of the ‘ignorant and worthless class of anti-social whites of the South’

    • the judge then agreed that Carrie should be sterilised because… ‘it is better for all the world … degenerate offspring of crime … society can prevent those who manifest as unfit from continuing their crime’

THE RISE AND FALL (AND RISE) OF EUGENICS:

  • 1907 Eugenics society founded n the UK

  • 1917 restricted immigrants

  • 1910s-1970s over 60,000 people sterilised enforcibly

  • 1912, 1921, 1932 held International Eugenics conferences

  • 1930s association of eugenics with Nazism

  • 1939 the ‘euthanasia program’

  • 1933, 1945 genocide of 6 million due to Nazis

WHAT IS HERITABILITY?

  • heritability = the proportion of population variance in a trait that can be attributed to genetic factors

  • basics:

    • we all have 46 chromosomes in 23 pairs

    • 22 pairs are XX, the last is either XX or XY

    • 20,000-25,000 total genes, with each one having different possible variants (alleles)

CONCORDANCE RATES:

  • how similar on average the scores are for a kind of relationship

    • can vary from 0-100%

    • can only be calculated for groups

  • twin studies

    • mz = .86

    • dz = .55

    • we typically use twins because of their genetic similarity, meaning any differences would be environmental

  • adoption studies also provide the same explanation, not entirely genetic influence

HERITABILITY OF IQ:

  • many researchers have gotten numbers like: 40-80%, 30-75%, 50-80%

  • this suggests that iq definitely has a heritable component

  • a group difference can be entirely environmental even if a trait has high heritability

  • limits:

    • assumes all family members share the same environment

    • no allowance for situations like adoption