We often hear the phrase “the natural rate of interest…” The origin is, if i lend you thirty cows for a year you should pay me back the thirty plus the “natural rate of increase, ” the calves. This happened very early Mesopotamia. Our current economics is a modest modification of deeply organic ancient systems. Everything important in economics happened before Adam Smith.

The word for interst in Greece was the world used also for calf, a new head of cattle, (capital)

Wonderful description of the pre-greek middle east in
Money Changes Everything: How Finance Made Civilization Possible Hardcover – April 12, 2016
by William N. Goetzmann (Author)

Much found in his Financing Civilization
Source: http://viking.som.yale.edu/will/finciv/chapter1.htm