The heritability of intelligence in Japan

Abstract
Japanese data for 543 monozygotic (MZ) twins and 134 dizygotic (DZ) twins tested for intelligence at the age of 12 give correlation coefficients of. 782 and .491, respectively, indicating a heritability of .582. Heavier twins at birth have significantly higher IQs at the age of 12, suggesting that prenatal nutrition exerts a significant effect on intelligence.