IQ differences of identical twins reared apart are influenced by education
New research on identical twins raised apart suggests that differences in schooling and environment can shift IQ scores by roughly one standard deviation (about 15 points), challenging simple claims that intelligence is mostly genetic. Commenters debate what IQ actually measures, how reliable and trainable the tests are, and how factors like motivation, culture, nutrition, and educational stratification shape outcomes. The thread also touches on broader issues such as the misuse of IQ in scientific racism, the limits of heritability estimates, and the policy implications for education systems.
Size and meaning of IQ differences
- Multiple comments note 15 IQ points ≈ one standard deviation, roughly “average” vs “top ~16%,” and considered a meaningful but not extreme gap.
- Others question whether it’s valid to treat IQ as a linear interval scale at all; they argue it’s essentially a ranking constructed to be normally distributed, so “5 IQ points difference” may not have a clear real-world magnitude.
- Several people stress that any one person’s IQ is not a fixed single number; scores vary with fatigue, stress, practice, and test-taking skill.
What IQ is actually measuring
- One view: modern IQ tests are designed primarily to detect cognitive deficits and guide interventions, and are misused as a general “intelligence ranking.”
- Another view: IQ is a useful composite marker correlated with reasoning, knowledge, working memory, processing speed, and spatial ability, and tracks a general factor (g).
- Critics emphasize multidimensional intelligence (social, creative, spatial, etc.) and say a single scalar inevitably hides important variation.
- There’s debate over bias: some argue tests favor upper-middle-class culture and particular learning styles; others say modern tests try explicitly to avoid that.
- Motivation and rewards can significantly shift scores, raising the possibility that tests partly measure persistence/effort rather than pure ability.
Education, culture, and environment
- Several comments focus on how education, test practice, and exposure to “test culture” improve standardized-test performance, including IQ.
- Twin and heritability points are reframed: heritability is a correlation inside a particular environment; if nutrition, schooling, and health vary, environment can dominate.
- The Flynn effect and international IQ shifts are cited (within the thread) as evidence that environmental changes can move population scores substantially.
- Epigenetics is discussed as complicating simple nature/nurture splits, but heritable epigenetics in humans is described as still uncertain.
Critiques of the twin-study analysis
- The “very dissimilar education” category reportedly includes only 10 twin pairs; commenters see this as a very weak basis for strong claims.
- Some question the scoring scheme for “educational differences” (years of schooling capped, location weighted heavily), suspecting it’s capturing non-educational factors.
- Awkward or broken prose in the paper and questions about the authors’ research background cause some to doubt the overall rigor.
Broader implications and ideology
- Several posts argue that environmental leverage (education quality, tutoring, societal changes) can swamp genetic differences in IQ for most people.
- Others highlight how IQ heritability has been weaponized in “scientific racism,” often by downplaying environmental factors.
- There’s disagreement over policy relevance: some see this kind of result as support for investing heavily in education; others think debates about “innate IQ” are overemphasized relative to obvious educational and social reforms.