Figure 1. All the ‘-omic’ pathways between the genome and behavior are important for understanding individual differences.

However, DNA sequence variation in the genome is ultimately responsible for hereditary influences on behavior. Correlations between DNA sequence variation and behavior are causal, as indicated by the single-headed arrow from the genome to behavior. Although behavior is often referred to as the observable ‘phenome’, all levels between the genome and behavior can be considered as phenotypes, which we show as connected by double-headed arrows signifying possible two-way directions of effect. The genetic and environmental origins of individual differences in these phenotypes need to be assessed rather than assumed.