The definition, measurement and heritability of intelligence are highly contentious subjects, involving both scientific and political issues. From a scientific point of view, it might seem logical to investigate such a key human attribute as intelligence from as many angles as possible, and to apply the tools of genetics that have become central to biology. However, because intelligence testing can be subject to cultural bias, it has occasionally been used to "track" students into different educational opportunities, and has even been applied to discredited eugenics schemes.

Intelligence testing began in the nineteenth century, as psychologists began the systematic study of differences in human behavior and performance. In France, Alfred Binet began studying "subnormal" children in Paris schools, and in 1905, together with physician Theodore Simon, developed what was considered to be a diagnostic test for intelligence in...