Abstract
INTRODUCTION: The objective of this paper is to see if behaviours defined as pathological and maladjusted in certain contexts may produce adaptive effects in other contexts, especially if they occur in attenuated form. Interactions between environment and behaviour are studied from an evolutionary standpoint in an attempt to understand how new attitudes emerge in an evolving context. METHODOLOGY: Narrative review. Following an historical examination of how the description of depression in Western society has changed, we examine a series of studies performed in areas where great changes have taken place as well as research on emigration from Sardinia in the 1960s and 70s and immigration to Sardinia in the 1990s. RESULTS AND CONCLUSIONS: If we postulate that mood disorders are on the increase and that the epidemic began in the 17th century with the "English malady", we must suppose that at least the "light" forms have an adaptive advantage, otherwise the expansion of the disorder would have been self-limiting. "Compulsive hyper-responsabilization", as well as explorative behaviours, may represent a base for adaptation in certain conditions of social change. The social emphasis in individualism and responsibility may have changed not only the frequency, but also the phenomenology of mood disorders particularly the increases in bipolar disorders. From the sociobiological standpoint the conditions that may favour "subthreshold" bipolar or depressive features are to be considered in relation to the contextual role of gender and the different risks of the two disorders in males and females.