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