Freud's metapsychological assumption, which split the mind from the brain, is increasingly recognized as limiting the growth of psychoanalysis and its integration with other fields, including psychiatry. The dual-aspect monist position, sometimes used to rationalize the mind/body split, is seen to contain a mereological (category) error, which can be avoided by the introduction of the paradigm of psychodynamic science, and by the use of a nondualistic, symbiotic mind/brain formulation, well justified by the study of cultural and organic evolution. Therapeutic action may now be seen as a special case of development that occurs within the interactional context of cultural evolution, personal history, and the genome. Human evolution is increasingly dominated by culture operating on the mind/brain through downward causation. This concept refers to the influence of higher organizational entities (e.g., mind) upon lower ones (e.g., brain). Although little recognized, downward causation is tacitly assumed in psychotherapeutic interventions, and is illustrated in recent fMRI studies. The clinical integration of the downward causation concept links therapeutic action to the power of cultural evolution, and facilitates reunion with traditional science.