One of the most puzzling things about veterans who experience PTSD is that the majority never even saw combat-and yet they feel deeply alienated and out of place back home. The reason may lie in our natural inclination, as a species, to live in groups of thirty to fifty people who are entirely reliant on one another for safety, comfort and a sense of meaning: in short, the life of a soldier. It is one of the ironies of the modern age that as affluence rises in a society, so do rates of suicide, depression and of course PTSD. In a wealthy society people don't need to cooperate with one another, so they often lead much lonelier lives that lead to psychological distress. There is a way for modern society to reverse this trend, however, and studying how veterans react to coming home may provide a clue to how to do it. But it won't be easy.