‘Heritability’ is a measure of the relative importance of genes in determining variation in qualitative traits among individuals. However, the calculated heritability value is unique to the population in which it was measured and to the environment of that population. The specificity of heritability means that we should be very cautious when using heritability to measure the general importance of genes to the development of a trait. A famous misapplication of heritability comes from the book The Bell Curve, by Charles Herrnstein and Richard Murray, published in 1994. In this book, the authors report that IQ scores differ among subpopulations in the United States. Among white Americans, IQ averages are around 100 while among African-American populations, IQ averages are nearly 15 points lower. Using a conservative estimate of the heritability of intelligence, they argued that the IQ differences between whites and blacks are primarily due to a genetic difference in intelligence between these groups. However, on closer look, we can see that Herrnstein and Murray’s conclusion is flawed. These differences could be entirely due to environment. Given the history and current social and economic status of African-Americans in the United States, it is certainly possible that their environment is less enriched than the average environment experienced by a white individual.