Hubbert laid this out in the Technocracy Study Course: Should the fruit flies continue to multiply at their initial compound interest rate, it can be shown by computation that in a relatively few weeks the number would be considerably greater than the capacity of the bottle. This being so, it is a very simple matter to see why there is a definite limit to the number of fruit flies that can live in the bottle. Once the number is reached, the death rate is equal to the birth rate, and population growth ceases. Very little thought and examination of the facts should suffice to convince one that in the case of the production of coal, pig iron, or automobiles, circumstances are not essentially different.