What makes us human? Where is the limit between human and animal? Is the human species the contingent result of blind evolutionary processes? These pressing questions haunt literature in the wake of Darwin's shocking claim that humans and apes are descended from a common ancestor. Anxiety concerning the status of humankind is a central theme in Victorian and modernist fiction, ranging from 'ape narratives' (e.g. the Tarzan series) to fantastic encounters with missing links, primeval men and 'races of the future'. All are pervaded by the spectres of degeneration and dehumanisation as well as by apocalyptic visions of the end of humankind. The exploration of these existential anxieties and their various literary expressions stands at the centre of this study which offers detailed and original analyses of a broad range of literary texts, covering the period between the publication of the Origin of Species and the beginning of the Second World War.