An Evolutionary Psychoneuroimmunological Approach to Major Depressive Disorder

Abstract

Abstract Major depressive disorder (MDD) is not a unitary disorder. From an evolutionary perspective, it should be divided into different subtypes based on triggering factors. Some of the symptoms of depression are adaptations to solve adaptive problems that trigger mood swings, while some others are maladaptive. MDD has become more common in societies that have adopted modern “Western” lifestyles. The evolutionary mismatch hypothesis suggests that this is because the human mind and body are not adapted to live under the characteristics of modern “Western” lifestyles. The evolutionary psychoneuroimmunological approach suggests that modern lifestyles increase the prevalence of systemic low-grade inflammation and chronic stress, which underlies neuroinflammation. Neuroinflammation triggers sickness behavior symptoms, many of which are the same as those observed in MDD, likely changing the previously adaptive mood into a maladaptive state of MDD.