The Precariat

Abstract

When genetic similarity is controlled, siblings often appear no more alike than individuals selected atrandom from the population. Since R. Plomin and D. Daniels' seminal 1987 review, it has become widelyaccepted that the source of this dissimilarity is a variance component called nonshared environment. Theauthors review the conceptual foundations of nonshared environment, with emphasis on distinctionsbetween components of environmental variance and causal properties of environmental events andbetween the effective and objective aspects of the environment. A statistical model of shared andnonshared environmental variables is developed. A quantitative review shows that measured nonsharedenvironmental variables do not account for a substantial portion of the nonshared variability posited bybiometric studies of behavior. Other explanations of the preponderance of nonshared environmentalvariability are suggested.