Though we cannot perfect the endeavour we should strive for it: the will-to-live constantly renews itself, for it is both an evolutionary necessity and a spiritual phenomenon. Life and love are rooted in this same principle, in a personal spiritual relationship to the universe. Ethics themselves proceed from the need to respect the wish of other beings to exist as one does towards oneself. Even so, Schweitzer found many instances in world religions and philosophies in which the principle was denied, not least in the European Middle Ages, and in the Indian Brahminic philosophy.