Speaking on BBC Breakfast, Mr Campbell said it was the best thing that happened to him as “he sorted himself out after it” but that “it is a horrible, intense experience”.
I don’t want to overstate Campbell’s point – in the interview he’s obviously anxious that we don’t draw such a simplistic conclusion – but this argument does, of course, echo the position taken by evolutionary psychologists, who claim that, if depression is in part genetic, then such a seemingly costly and dangerous set of behaviours must, at some point, be of some adaptive value. i.e. they must be of some benefit to the individual or their offspring.
More on evolutionary theories of depression here.