Amplification explains rising IQ heritability

Longitudinal twin and adoption data show that new genetic influences on cognition appear in very early childhood but quickly fade, while the amplification (growth in effect size) of early genetic differences after about age eight accounts for the bulk of the increase in heritability across development. In plain terms, the same genetic differences become more consequential over time rather than many new genes continually emerging as drivers. — If rising heritability is driven by amplification, policy and interventions should focus on how environments interact with early dispositions (and when) rather than assuming entirely new genetic causes emerge through adolescence.