A new comprehensive evolutionary model of depression and anxiety.

Difference amplification was the process whereby the difference in fitness between two competing individuals in early man was magnified by the results of the competition. It arises from adaptive and maladaptive cycles (characterized by depression and anxiety) that are initiated by winning and losing agonistic encounters. Those who were most successful were likely to find mates that were also successful and vice versa. This would have contributed to well-endowed progeny and accelerated phylogenetic evolution. The adaptive and maladaptive cycles of the difference amplification model are also a feature of the social rank and attachment models. Ineffective operation of social rank and attachment systems is associated with anxiety and depression. This paper introduces the notion that the efficient operation of these two systems in hierarchical encounters accelerates the phylogenetic adaptation of the individual's genetic line. This suggests an adaptive function of attachment and social rank mechanisms that has not been previously described. Social rank, attachment and difference amplification should be viewed as different aspects of a comprehensive evolutionary model of depression and anxiety. This new model has psychotherapeutic implications.