IQ differences of identical twins reared apart are influenced by education

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.