To the Editor.—
Gardner, in his article "Mechanisms in Manic-Depressive Disorder: An Evolutionary Model," in the Archives,1 delineates how an evolutionary model could contribute to an understanding of psychiatric disorder. Our purpose in writing is to emphasize the broad scope and value of this approach. Our own studies of depression from the functional, evolutionary point of view have increasingly drawn us to models that depict depression as intimately concerned with social competition,2,3 and it is into this social competition category of model that the social hierarchy model proposed by Gardner falls. The evolution of the depressive response depends on the fact that competitive behavior has been ritualized, and the function of depression is to provide the social incapacity that would otherwise be provided by physical incapacity or death. This incapacity or yielding behavior extends in time the result of competition so that adjustment may be made to a