However, prior to the publication of Darwin’s Origin of Species in 1859 Marx and Engels still lacked a biological grounding for their theory of dialectical materialism. Writing in the Grundrisse in 1858 or shortly before, Marx alluded to the need for a coherent conceptualization of humanity’s relationship with the earth: “It is not the unity of living and active humanity with the natural, inorganic conditions of their metabolic exchange with nature, and hence their appropriation of nature, which requires explanation or is the result of a historic process, but rather the separation between these inorganic conditions of human existence and this active existence, a separation which is completely posited only in the relation of wage labour and capital.”[3]