FAMILY STIGMA, SEXUAL SELECTION AND THE EVOLUTIONARY ORIGINS OF SEVERE DEPRESSION’S PHYSIOLOGICAL CONSEQUENCES.

It is now known that in addition to their psychological and behavioural symptoms, chronic depressive illnesses have damaging effects on both the immune and cardiovascular systems. Given that similar patterns are found in other species, there is a need to determine how such seemingly disadvantageous mechanisms could have persisted over evolutionary timescales. This paper offers an answer by applying inclusive fitness theory to the process of mate selection. To mate selectors, the value of direct observation is limited by the phenotype/genotype disparity. Although it does not seem to have been previously suggested, there is evidence that natural selection has partially circumvented this limitation by favouring the use of the stockbreeding technique of obtaining additional genetic information from a candidate’s close kin. One implication of this is that individuals much less well fitted than their kin can have a negative impact upon the reproductive success of their abler relatives. Indeed, the point could be reached at which the aggregate reputational damage they inadvertently cause imposes reproductive penalties across their kin group substantially in excess of their own likely reproductive contribution. Under such circumstances, as a form of damage control, inclusive fitness considerations would favour the emergence of autonomic mechanisms serving rapidly to eliminate the less well fitted individual. Severe depression, given how life-threatening its symptoms would have been in any imaginable Era of Evolutionary Adaption, could have evolved to bring this about. In this paper, literature relating to: mate choice among peacocks, an island population affected by a debilitating genetic disease, the stigmatisation of families of psychiatric patients, the determinants of self-esteem, and the psychological factors underpinning human health and happiness has been reviewed against four hypotheses derived what the author terms "stigma theory". Although much remains to be done, the initial findings are strongly supportive. Stigma theory’s relevance to non-reciprocal altruism to unrelated others, social conformity and the current epidemic of depressive illness are discussed.