A second aspect of scientific advancement is the integration of lower order phenomena into higher order, integrative theories. In many areas of science, the pursuit of integrative theories is a central task of scientists. The pursuit of a unified field theory in physics (Georgi & Glashow, 1972); the development of theories to integrate biological evolutionary processes at the multiple levels of gene, organism, and species (Keller, 1999); and, closer to home, the development of comprehensive theories of human personality (Costa & McCrae, 1994; Digman, 1990) are among the many examples of this process. Integrative theory is fundamentally important: It organizes diverse phenomena into meaningful wholes; it provides insight into etiology and, in clinical science, intervention; and it generates hypotheses that lead to the identification of previously unrecognized processes.
