About twenty years ago there was a documentary made about the work of Dian Fossey who followed a tribe of chimps for several years. It gets cited in various guises around the interweb by people interested in the role of mental illness in society. The gist is that in all chimp troops, there always exists a small number that are anxious/depressed and that tend to retreat to the outskirts of the troop, often socially disengaged. Fossey decided to remove these agitated chimps to see what would happen. Six months later the entire community was dead. It was suggested that the anxious chimps were pivotal for survival. Outsiders, they were the ones who were sleeping in the trees on the edge, on the border, on the boundary of the community. Hyper-sensitive and vigilant, the smallest noise freaked them out and disturbed them so they were awake much of the night anyway. We label such symptoms anxiety, but back when we were in trees, they were the early warning system for the troop. They were the first to scream, 'Look out! Look out!'