Amplification Explains Rising Cognitive Heritability

A meta-analysis of longitudinal twin and adoption studies finds that new genetic influences on cognition appear mainly in early childhood but quickly wane, while preexisting genetic influences are amplified over time — and this amplification after about age 8 drives the observed increase in heritability. The result comes from pooled models of 11,500 reared‑together twin and sibling pairs measured between 6 months and 18 years. — If genetic effects are amplified rather than continuously novel across development, policy and intervention debates should focus on how environments interact with early genetic differences and when interventions might be most or least effective.