Three Promising Directions in the Study of Intelligence With Genetic Methods

A genome-wide association study (GWAS) tests whether each of several million sites in the human genome is correlated with a trait of interest. For a number of reasons, including replication of GWAS results within families, we can be confident that significant correlations reflect in part the causal effects of DNA-level variation on the studied trait. This level of causal inference, much stronger than in most observational studies, enables some far-reaching conclusions about the antecedents and structure of human intelligence. We discuss some of these conclusions regarding whether brain size affects intelligence and the long-debated issue of how different intelligence tests are related to each other.