Environmentalism in the United States historically has been divided into its utilitarian and preservationist impulses, represented by Gifford Pinchot and John Muir, respectively. Pinchot advocated conservation of natural resources to be used for human purposes; Muir advocated protection from humans, for nature’s own sake. In the first half of the twentieth century, natural resource economics was firmly on Pinchot's side of that schism. That position began to change as the postwar environmental movement gained momentum. In particular, John Krutilla, an economist at Resources for the Future, pushed economics to the point where it could embrace Muir’s vision as well as Pinchot’s. Krutilla argued that if humans preferred a preserved state to a developed one, then such preferences were every bit as "economic"—either way, opportunity costs exist and economic choices must be made.