 The social navigation or niche change hypothesis proposes that depression is a social navigation adaptation of last resort, designed especially to help individuals overcome costly, complex contractual constraints on their social niche.The hypothesis combines the analytical rumination and bargaining hypotheses and suggests that depression, operationally defined as a combination of prolonged anhedonia and psychomotor retardation or agitation, provides a focused sober perspective on socially imposed constraints hindering a person's pursuit of major fitness enhancing projects.Simultaneously, publicly displayed symptoms, which reduce the depressive's ability to conduct basic life activities, serve as a social signal of need; the signal's costliness for the depressive certifies its honesty.