Molecular genetic research on IQ: can it be done? Should it be done?

An obvious requirement before embarking on molecular genetic investigation of a trait is prior evidence from ‘classic’ genetic studies that there is indeed a genetic component. Many behavioural traits are familial and these range from comparatively uncommon single gene disorders such as Huntington's disease which has a typical mendelian dominant pattern of transmission, to much commoner characteristics such as career choice or religious denomination which, it might be assumed, are heavily influenced by cultural factors. In between, there is a wide range of attributes including personality type, cognitive ability and liability to common disorders such as depression, that show a tendency to run in families, and which could conceivably be explained by shared genes, shared environment or a combination of the two.