Labour, first of all, a process between man and nature, a process by which man, through his own actions, mediates, regulates and controls the metabolism between himself and nature. He confronts the materials of nature as a force of nature. He sets in motion the natural forces which belong to his own body, his arms, legs, head and hands, in order to appropriate the materials of nature in a form adapted to his own needs. Through this movement he acts upon external nature and changes it, and in this way the simultaneously changes his own nature () is the universal condition for the metabolic interaction between man and nature, the everlasting nature-imposed condition of human existence.

Karl Marx, Capital, I




The universality of man manifests itself in practice in that universality which makes the whole of nature as his inorganic body, as a direct means of life and the matter, the object and the tool of his activity. Nature is mans inorganic body, that is to say, nature in so far as it is not the human body. Man lives from nature, i.e. nature is his body, and he must maintain  a continuing dialogue with it if he is not to die. To say that mans physical and mental life is linked to nature simply means that nature is linked to itself, for ma n is a part of nature,

Karl Marx, Economic and Philosophical Manuscripts of 1844




The view of nature which has grown up under the regime of private property and money is an actual contempt for and practical degradation of nature,

Karl Marx, On the Jewish Question