ABSTRACT
Twin and adoption studies show that the development of many psychological characteristics, such as temperament and intelligence, is in part influenced by genetic factors (Deary, 2000; Matthews, Deary & Whiteman, 2003; McGuffin et al., 2002). The size of this influence is of the order of 30-60% of overall variation within a population for most such characteristics. The mechanism of influence is usually polygenetic. With the possible exceptions of conditions such as autism, Down syndrome and bipolar affective disorder, genetic factors determine the development of specific psychological problems through their influence on broader psychological characteristics such as temperament. Current evidence does not support the view that childhood psychological problems are unalterably genetically determined.
