Introduction: The objective of this paper is to verify if traits and symptoms defined as pathological and maladjusted in certain contexts may produce adaptive effects in other contexts, especially if they occur in sub-threshold forms.
Methods: A historical examination of how the symptoms of depression have changed in front of great social changes and an analysis of Sardinian migrants' thymic profiles toward several metropolises.
Results and conclusions: Mood disorders have been increasing since the "English malady" in the 17th century, and we suppose that some forms of mood disorders might have an adaptive advantage. Otherwise, the increase of such an epidemic would have been self-limited. From a sociobiological point of view, it is highly probable that the environment of a rapidly evolving society can select people who are explorers and able to support accelerated biorhythms and that the condition of social change stimulates psychological and psychopathologic changes. It is also possible that hyperthymic persons modulate and create the new environment. If this model can explain the epidemic of mood disorders, its verification should guide future research.
Keywords: Adaptation sociale; Behavior; Bipolar disorder; Comportement; Depression; Dépression; Evolution; Hypomania; Hypomanie; Social adaptation; Trouble bipolaire; Évolution.
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