Anxiety and depression may have an evolutionary role as negative reinforcers, encouraging socialisation.

Anxiety and depression are both very common mental states and both are quite unpleasant. Their high prevalence and preservation make it likely they have considerable evolutionary significance and in some way improve the chances of an individual's survival. The following article proposes that much of the anxiety and depression we experience is primarily acting as a negative reinforcer, encouraging socialisation. These feelings are experienced most intensely when we are isolated and have evolved to discourage this highly maladaptive behaviour, there being major advantages for being with other people. Particular problems are considered, including aspects of autism and alcohol and tranquilliser abuse. How the presence of other people may alter the expression of anxiety and depression is considered, in addition to implications for psychiatry.