The rift between Gifford Pinchot and John Muir, between the conservationist and preservationist movements, left an unsatisfactory state of affairs for economists working on early environmental policy questions. Moreover, midway through the 20th Century, economics was still defined as the study of material welfare. An interdiciplinary social scientist like Aldo Leopold concluded that economics thus could have little to say about the value of preserved landscapes or species. Yet economics was relevant for preservation because incentives mattered. He advocated a new interdiciplinary ecological economics to overcome these problems. Meanwhile, economists in government were beginning to confront environmental questions, such as the value of outdoor recreation, in their benefit-cost analyses of dams and other water projects. They too concluded such questions were outside their field and could not be addressed. Thus, at mid-century, the future existence of a field called environmental economics was very much in doubt.