I am glad to have an opportunity to reply to a few of the many letters received about my article.
Dr Longley is confident that depression is an adaptation because such a prevalent and costly genetic predisposition is difficult to explain in terms of mutation selection balance. While this principle makes sense in general, geneticists have so much trouble defining exactly when it applies1 that I do not believe it offers strong support for the adaptive significance of depression. Wilson notes that evolutionary epidemiology can help us find new subcategories for depression.2 I agree with this, and I look forward, in particular, to further studies investigating the personalities and reproductive success of individuals whose relatives have manic-depressive illness. While questions about genetic variation are of great interest, my article was restricted to the question as to why all humans seem to share a capacity for low mood (and perhaps depression). On another occasion, I will write about the very separate question as to why natural selection has not eliminated variation in susceptibility to depression. In general, I am impressed that most anxiety and depressive disorders occur in the 15% of people who are "sensitive." I suspect that these people experience benefits as well as costs. If the benefits turn out to be related to their increased concern about the feelings of other people, this will be very important as we decide how to use our impending genetic knowledge.
Nesse RM. Ethical Dilemmas in Prescribing Antidepressants—Reply. Arch Gen Psychiatry. 2001;58(11):1085-1086. doi: