Nonshared environment: Real but random

In the excitement about genomics, it is easy to lose sight of one of the most important findings from behavioural genetics: At least half of the variance of psychopathology is caused by environmental effects that are not shared by children growing up in the same family, which includes error of measurement. However, a 30-year search for the systematic causes of nonshared environment in a line-up of the usual suspects, especially parenting, has not identified the culprits.