Evolutionary aspects of bipolar affective illness

Bipolar affective illness (bipolar disorder - BD), also known as manic-depressive illness, is characterized by periodic opposite states of mood, activity, and motivation (mania and depression) sometimes of extreme intensity. The development and maintenance of such states in evolution can betoken a possibility of their adaptive character, enabling adaptation to an unfavorable external situation (depression) and a mobilization to using resources when available (mania). In the article, the main focus is put on the evolutionary aspect of "bipolarity" and manic/hypomanic states. Molecular-genetic studies show that in evolution, the genes connected with a predisposition to BD have been conserved. In the paper, the evolutionary adaptive concepts connected with the functioning of Homo sapiens during the middle and late Pleistocene periods were discussed as well as the "mismatch" theories associated with not befitting brain functioning to contemporary conditions. The benefits of mania and hypomania, also in the context of their link to depression were delineated, indicating their relationship to the increase in reproductive success. They result from such features of mania/hypomania as increased exploratory, psychomotor and sexual activity, and prompt risk-taking. The reproductive success can be connected with hyperthymic and cyclothymic temperaments, most frequently occurring in subjects with BD. The hyperthymic temperament often leads to increased social status and a tendency to leadership, and the cyclothymic temperament can increase creativity. Examples of the relationship between manic/hypomanic states and the phenomenon of emigration as well as the advancement of American society are provided.