Lei de von Liebig
"[W]e
need to step outside the usual economic or political frames of thought,
go back two-thirds of a century before the 1929 crash, and reexamine
for its profound human relevance a principle of agricultural chemistry
formulated in 1863 by a German scientist, Justus von Liebig. That
principle set forth with great clarity the concept of the “limiting
factor” [...] Carrying capacity is limited not just by food supply, but
potentially by any substance or circumstance that is indispensable but
inadequate. The fundamental principle is this: whatever necessity is
least abundantly available (relative to per capita requirements) sets an
environment’s carrying capacity.
While
there is no way to repeal this principle, which is known as “the law of
the minimum,” or Liebig's law, there is a way to make its application
less restrictive. People living in an environment where carrying
capacity is limited by a shortage of one essential resource can develop
exchange relationships with residents of another area that happens to be
blessed with a surplus of that resource but happens to lack some other
resource that is plentiful where the first one was scarce.
Trade
does not repeal Liebig’s law. Only by knowing Liebig’s law, however,
can we see clearly what trade does do, in ecological terms. Trade
enlarges the scope of application of the law of the minimum. The
composite carrying capacity of two or more areas with different resource
configurations can be greater than the sum of their separate carrying
capacities. ...] A good many of the events of human history need to be
seen as efforts to implement the principle of scope enlargement." Overshoot, William R. Catton
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