The economic position is increasingly recognised by ecologists who, among other things, attempt to apply it as an argument for halting ongoing loss of biological diversity. Implicitly, conservation can be promoted by demonstrating that “saving” species and ecosystems promises higher monetary value than their conversion into other assets (Costanza et al. 1997). Thus, for example, Ehrlich and Wilson (1991) argue that we should care about biodiversity because "... humanity has already obtained enormous direct economic benefits from biodiversity in the form of foods, medicines and industrial products, and has the potential for gaining many more.” In addition, there is the “ ... array of essential services provided by natural ecosystems, of which diverse species are the working parts” (p.760). Ehrlich and Wilson also mention that preserving biodiversity is a moral responsibility, an important issue to which we return later in this chapter.