Green theory is a development within literary and cultural studies which is informed by the insights of ecology (a branch of science which deals with the relation between organisms and their environments). The root of the term lies in two ancient Greek words: oikos (household) and logos (word); ecology is the study of the earth as our home. As a science, it began in the mid-nineteenth century; but its impact on critical theory as an academic discipline was not felt until the later twentieth century, when the relationship between human beings and their total environment had become manifestly unstable, and the damage being done to nature had become an unavoidable challenge.