[Evolutionary aspects of affective disorders, critical review and proposal of a new model]

Evolutionary psychopathology incorporates psychiatry into biology via theory of evolution, generating new etiological hypothesis for mental disorders. For evolutionary psychopathology emotions are a response system or a genetically programmed, specialized state of functioning, formed by natural selection, that allows us to adapt to the environment, increasing the ability to cope with threats and opportunities. Emotions exert their function by coordinated physiological, psychological and behavioral changes. Many functions have been suggested for low mood or depression, including communicating a need for help, signaling yielding in a hierarchy conflict, fostering disengagement for commitments to unreachable goals, regulating patterns of investment, parallelism with despair phase of separation from mother situation in monkeys, hibernation, etc. Despite other evolutionary models, our model not only tries to explain depression but mania, hypomania and other affective disorders as well. For us, most affective disorders are pathological states (and not adaptive ones), due to dysfunction of an innate precipitating mechanism (IPM). IPM function is to regulate energy and activity levels according to intensity and duration of light (namely IPM-A). This IPM-A is responsible for vegetative, endocrine and behavioral responses that are present in humans and more ancient phylogenetic animals. More recently in the phylogeny, other mechanisms (IPM-AA) have coupled to this IPM-A. In the human being, the precipitating factors of IPM-AA are predominately social. IPM-AA add new responses (such as mood) to the older responses of IPM-A.