Abstract
Genetic and environmental influences on behaviour and development can be examined by studying more than one individual within a family, using quantitative genetic theory and behavioural genetic (BG) methodology. Specific environmental and genetic influences can be measured and effect sizes estimated, and many assumptions of the methodology can be explicitly tested. BG designs can identify specific aspects of the environment that have the greatest influence on behavioural variation, and they can pinpoint critical periods in which environmental influences are most malleable, both of which are useful when designing interventions. Traits that are shown to be the most heritable through traditional family resemblance methods can now be explored further and actual genes may be identified, using new molecular methods. By identifying specific genetic and environmental influences on behaviour, and modelling the structure of these influences over time, we can rapidly advance our understanding of human development.
