Although this example may at first seem only hypothetical, in fact it help to explain a major change in the U.S. economy over the past century. Two hundred year ago, most American live on farms. Knowledge about farm methods was sufficiently primitive that most of us had to be farmers to produce enough food.Yet, over time, advances in farm technology increased the amount of food that each farmer could produce. This increase in food supply, together with inelastic food demand, caused farm revenues to fall, which in turn encouraged people to leave farming.