Characteristics of mania describe individuals who are human counterparts of "alpha" members of nonhuman species. Depressive characteristics described low rank or "omega" persons. These similarities provided initial support for a model of manic-depressive disorder that hypothesizes these bipolar states to be (1) basically identical to an organismic state also experienced by persons at the corresponding extremes of social rank, (2) triggered unusually easily and maintained unusually rigorously in spite of social reality (in contrast to those for whom the organismic state and social reality are congruent), and (3) genetically transmitted via mechanisms that enhance this ease of onset and rigidity of maintenance (v mechanisms presumed to be state specific). This theoretic model defines some illness components as variations of normal states, others as pathologic, and still others as reactive. This conception may guide investigative work with experimental animals.