Illness is the dark side of our transactions with nature. It’s a reminder of the routineness of death, of the disposability of individuals, of the fact that living systems can be ruthless and unpredictable in their constant manoevring. But, at first sight, depression doesn’t fit into even this austere picture. There’s no random physical ‘accident’ behind it and nothing which benefits, no opportunist virus or evolutionary climber. It seems to have no connection with the biological business of living at all. And what it did to me was unearthly, in that it negated, cut dead, all the things in which I most believed: the importance of sensual engagement with the world, the link between feeling and intelligence, the inseparability of nature and culture. And it began to grow at the most unexpected time, when by all conventional psychological theories, I should have been awash with the sense of well-being that comes from high status and achievement.
— Richard Mabey, Nature Cure