Mood may be considered the module of the human mind, which has evolved to tune the activity ofthe organism to the specific environmental conditions in a better way. In some cases depression may be adaptive, for example in aborting the activity associated with too many obstacles. At the same time hypomania may be related to the capability of mobilising the organism to gain many resources in a short period of time. Severe mood disorders may be related to the genetic variants, eg. of the serotonin transporter or brain-derived neurotrophic factor, which in several situations may give some evolutionary advantage. Affective temperaments, observed in the relatives of patients with affective disorders may be associated with some benefits in the social life. The relationship between early adversities and adult depression may be related to the phenomenon of the stress axis programming, which has deep evolutionary roots. Some infectious factors may cause behaviours similar to the affective symptoms, which may increase their reproductive success. The evolutionary perspective, which is complementary to the current etiopathogenic theories may help in understanding, why genes and traits which