IQ and intelligence

History of IQ tests

• Early IQ tests were developed by Alfred Binet (1904–1911) to identify children who needed educational support.

• Binet explicitly warned that:

  • Intelligence is not inborn.

  • Tests do not measure intelligence.

  • Tests should not be used to rank people.

• IQ was later reinterpreted by others (e.g., Goddard) as evidence of inherited ability, contradicting Binet’s intent.

What do IQ tests measure

• Measure performance on specific cognitive tasks:

  • Vocabulary.

  • Pattern recognition.

  • Analogies.

  • Logical reasoning.

• Strongly influenced by:

  • Education.

  • Culture.

  • Language.

  • Test familiarity.

• In lecture: IQ tests do not directly measure “intelligence,” but test-taking performance in a given context.

Intelligence

• No single agreed-upon definition.

• Often framed as:

  • Ability to solve problems.

  • Learn from experience.

  • Adapt to new situations.

• Lecture emphasized that intelligence is multidimensional, not reducible to one number (IQ or “g”).

Positive eugenics

• Encouraging reproduction among those deemed “fit” or superior.

• Associated with Francis Galton.

• Examples:

  • “Fitter family” contests.

  • Incentivizing reproduction among wealthy, educated, or “high-IQ” individuals.

• Framed as socially progressive at the time, but rooted in false assumptions about heredity.

Negative eugenics

• Preventing reproduction among those labeled “unfit”.

• Included:

  • Forced sterilization

  • Institutionalization

  • Immigration restriction

• Justified using IQ scores as evidence of genetic inferiority.

• Central to US and Canadian eugenics programs.

Eugenics in Canada

• Alberta (1928–1972) and BC (1933–1973) sterilization laws.

  • Alberta Eugenics Board: the Sexual Sterilization Act of 1928.

  • 4725 cases approved for sterilization, 2832 carried out.

  • Leilani Muir of Calgary.

• Targeted Indigenous peoples, poor women, immigrants, and unwed mothers.

• Forced sterilization of Indigenous women continued into the 2000s.

Eugenics in the USA

• By 1941, 33 states had sterilization laws.

• 100,000 people sterilized without consent (disproportionately black, indigenous, and latina).

• Upheld by Buck v. Bell (1927) (“Three generations of imbeciles are enough).

  • Carrie and Doris Buck were considered textbook examples (had kids outside of marriage so they are feebleminded and promiscuous).

Conclusions from the Bell Curve

Murray and Herrnstein.

• Intelligence exists and is measurable via IQ.

• IQ is the strongest predictor of life outcomes.

• IQ is highly heritable (~70%).

• IQ is largely fixed and immutable.

• Social inequality reflects differences in cognitive ability.

• Public policy should reduce social programs rather than attempt intervention.

Critical evaluation of the Bell Curve

• Relies on flawed assumptions:

  • Race treated as a biological category.

  • Intelligence reduced to a single number (“g”).

  • High heritability misinterpreted as immutability.

• Ignores:

  • Gene–environment interaction.

  • Structural inequality.

  • Within-group variation (greater than between-group variation).

• If any one premise fails, the argument collapses.

Heritability of different measures of cognitive ability

• IQ heritability varies by:

  • Age (increases with age).

  • Environment.

  • Measure used (verbal, spatial, memory, etc.).

• High heritability does not imply:

  • Genetic determinism.

  • Immutability.

• Heritability explains variation, not cause

Pros of Twin Studies

• Allow estimation of genetic vs environmental contributions.

• Compare monozygotic (MZ) and dizygotic (DZ) twins.

• Useful when experiments are unethical or impossible.

• Foundational for heritability estimates in humans.

Cons of Twin Studies

• Assume equal environments for MZ and DZ twins (often false).

• Cannot identify specific genes.

• Do not capture gene–environment interaction well.

• Easily misinterpreted as proof of genetic determinism.

GWAS and Educational Attainment

• Genome-wide association studies identify many SNPs linked to years of education.

• Each SNP has a very small effect.

• Results are:

  • Population-specific.

  • Heavily confounded by social structure.

• GWAS shows correlation, not causation and does not justify policy conclusions