 The fitness benefits of forming cooperative bonds with others have long been recognised—during the Pleistocene period, for instance, social ties were vital for food foraging and finding protection from predators.As such, depression is seen to represent an adaptive, risk-averse response to the threat of exclusion from social relationships that would have had a critical impact on the survival and reproductive success of our ancestors.Multiple lines of evidence on the mechanisms and phenomenology of depression suggest that mild to moderate (or "normative") depressed states preserve an individual's inclusion in key social contexts via three intersecting features