Three Laws of Behavior Genetics and What They Mean

TLDR

Behavior genetics shows that genetic variance contributes to behavioral outcomes, yet family variation is limited, leading critics to overstate heritability and partisans to dismiss environmental influence, while the inherently nonlinear, interactive nature of development and the use of twin studies as a shortcut do not prove genes are more fundamental than environments. Twin studies serve as a methodological shortcut but do not demonstrate that genes are more fundamental than environments. Both the critics’ and partisans’ views are incorrect; genotype is a more systematic source of variability than environment, though this is due to methodological rather than substantive reasons.

Abstract

Behavior genetics has demonstrated that genetic variance is an important component of variation for all behavioral outcomes, but variation among families is not. These results have led some critics of behavior genetics to conclude that heritability is so ubiquitous as to have few consequences for scientific understanding of development, while some behavior genetic partisans have concluded that family environment is not an important cause of developmental outcomes. Both views are incorrect. Genotype is in fact a more systematic source of variability than environment, but for reasons that are methodological rather than substantive. Development is fundamentally nonlinear, interactive, and difficult to control experimentally. Twin studies offer a useful methodological shortcut, but do not show that genes are more fundamental than environments.