This effort can be divided arbitrarily into three components consisting of a theory, the data supporting it, and practical clinical applications. The theory, in a somewhat simplified version, is that separation, real or imagined, represents an extraordinarily severe trauma to an infant. This trauma, if severe enough, alters the child's biological and psychological development and predisposes that child to a risk of flashbacks to the earlier developmental period of the initial trauma. Posttraumatic stress disorder is offered as a model for the mechanisms involved in all serious mental disorders. The flashback is particularly damaging when these initial traumatic events occur early in development because it involves a reversal to the infantile brain development available at that time. With persistence of the presence of the infantile brain mechanisms there is a disuse atrophy of the adult brain areas. The flashback is produced by a second severe trauma, which is both intense and similar to the initial trauma and produces a physiological and psychological return to the period of the initial trauma. Schizophrenia, according to this theory, involves an initial trauma before the age of 24 months. In an effort to support this theory, the authors look at the birth of a sibling as a trauma that can be placed precisely in time and that can be experienced by the older infant as extremely noxious.