Both social authors and natural scientists proposed theories on urban sustainability.
Natural scientists, such as Jacob Moleschott (1852) and Justus von Liebig (1855), among others also pointed out this relationship:
The main concept behind these antecedents is that of metabolic notion: the city and the environment exchange energy and substances.
The city is conceived as an organism, which receives from the environment and gives away to the environment. This exchange is vital:
Karl Marx incorporated this idea in Capital by Karl Marx (1981  p. 949):
Marx also described the consequences of the metabolic division in Capital (1981  p. 949).