A third and final example concerns the interface between nature and nurture (Rutter, 2006). Every quantitative genetic study is as much a study of the environment as it is a study of genetics, whereas molecular genetic research is intrinsically limited to genetics. Quantitative genetic research provides the best available evidence for the importance of the environment because heritabilities for common disorders are never 100 percent and are usually 50 percent or less. It is at least as important to identify the environmental causes of psychopathology as it is genetic causes. A major clue from quantitative genetic research is that the salient environmental influences are non-shared, that is not shared by children growing up in the same family; identifying these non-shared environmental influences in genetically sensitive designs remains for future research (Plomin, Asbury, & Dunn, 2001; Turkheimer & Waldron, 2000). Another surprising finding from quantitative genetics is that many environmental measures widely used in the behavioural sciences show genetic influence (Jaffee & Price, 2007; Kendler & Baker, 2007). This finding suggests that people create their own experiences in part for genetic
