"Intelligence is genetic and stable across life, but it is not fixed. Twin studies reveal strong heritability, showing correlations of .70-.80 in IQ for twins raised apart. That means the environment still counts, as much as 25-30% of variation in intelligence is non-genetic. Genes set the stage, but we direct the play, biology provides the scaffolding but we build the structures."
"Although individual scores tend to stay relatively stable across one's life, we also know IQ is by no means completely fixed. For example, studies like Deary et al.'s (2000) show how correlations between childhood and later-life scores are often in the 0.60-0.70 range, leaving much space for development over age. And yet, the same studies show how the impact of genes on intelligence is an inescapable fact."
Intelligence shows strong genetic influence alongside measurable stability across the lifespan, while remaining partly malleable. Twin studies report correlations of .70–.80 in IQ for twins raised apart, indicating high heritability yet leaving roughly 25–30% of variation to non-genetic factors. Longitudinal research finds correlations between childhood and later-life scores commonly around 0.60–0.70, signaling continuity and scope for development. Genes provide biological scaffolding and set potential limits, while environments, experiences, and individual choices shape realized cognitive outcomes. Analogies with height illustrate how DNA sets potentials while variable environments determine realized outcomes.
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