“People have always dressed for an audience. Anthropologists simply forget that they are sometimes part of the audience.”… The helicopter arrived just before sunset. It was an old utility aircraft, its metal skin patched in several places and its cabin vibrating with the uneven rhythm of an aging turbine. It settled onto a gravel bar beside a tributary of the Amazon, throwing leaves, dust, and river sand into the faces of everyone waiting there. Dr. Lukas Meier, a Swiss anthropologist, stepped out first. Behind him came Camille De Smet, a Belgian official working for a United Nations field program on indigenous rights and community governance. They had spent eight days in the region studying something they had described in their research proposal as “informal systems of punishment and social control in non-state societies.” Their central question was simple: What makes people obey rules when there is no police force, courthouse, or...