Because the discipline of anthropology encompases both the social and physical sciences, and because the practice of archaelogy, a subdiscipline of anthropology, involves the physical excavation and identification of species and races long extinct, it provides the facts upon which mankind can develop knowledge of his origins. By understanding through scientific means the origins of species (with apologies to Darwin) and the causes of their destruction, we can better understand the nature of man as he exists today.
Through the discipline of anthropology, races and civilizations of humans, to say nothing of numerous species of animals, have been studied so that the causes of their disappearance from the Earth can be understood and that knowledge applied to contemporary societal problems that may threaten our own extinction. As much as any discipline, anthropology provides knowledge that is existential -- it helps us to understand who we are and where we came from. The study of linguistics and sociocultural anthropology help us to understand different cultures around the world, some of which we may come into contact with under extraordinary circumstances. How well we understand those cultures can spell the difference between success and failure in negotiating foreign terrain.
Physical anthropology, the study of human biology through the excavation of human remains, has been essential to the development of knowledge of the evolution of the human species. By studying earlier iterations of contemporary humans, we can better understand how people adapted to their environments -- or failed to -- and how they interacted across linguistic or cultural barriers.
In short, anthropoligical concepts tell us more about our own existence than any other field of study.