Depression: immunological resignation of the will to live?

Evolution is assumed to promote the survival of the fittest by the greater success of the reproductive potential of those with the characteristics most suited to their environment. Little thought is given to how those least adapted fail to survive to reproduce. If the species, rather than the individual, has a drive to adaptation and survival, there should be a specific mechanism for those least adapted to withdraw from life. The immunological changes accompanying depression may facilitate heart disease, infection, parasitic infestation or other ill health, so that depression is a mechanism for those least resilient, or faced with most adversity, to succumb to illness. If depression is a state facilitating withdrawal from competition for reproductive success, major depressive illness may be the inappropriate and spontaneous occurrence of a mental state which has advantages for the species in allowing those 'least fit' to fail to survive. This hypothesis gives an empirically testable challenge to the view that the species has no evolutionary drive to survival and increased adaptedness to the environment, as well as explaining the more and more frequent occurrence of a specific mental state and its associated changes in the immune system.