In the same way, Marx's conception of "human nature" (Gattungswesen) is problematic, since he opposed himself to the traditional conception of an eternal human nature which remained the same in all places and times. Later, Friedrich Engels wrote the Dialectics of Nature (1883), in opposition to German Naturphilosophie. Marx and Engels' thought was then codified into "dialectical materialism", which is what is usually referred to when speaking of a "Marxist philosophy of nature".