“There is, then, a critical difference between the way we estimate the ‘heritability’ of a trait and the way we usually interpret such estimates. Since there is no practical method for separating the physical and social effects of genes, heritability estimates include both. This means that heritability estimates set a lower bound on the explanatory power of the environment, not an upper bound. If genetic variation explains 60 percent of the variation in IQ scores, environmental variation must explain the remaining 40 percent, but it may explain as much as 100 percent. If, for example, genes affected IQ scores solely by affecting children’s appearance or behavior, and their appearance or behavior then affected the way they were treated at home or at school, everything genes explained would also be explicable by environmental factors.”

Christopher Jencks, Genes and Crime (1987)