Population as a GDP proxy in Adam Smith

How do we measure economic growth? In the 18th century, well before the birth of Gross Domestic Product commonly used today, looking at the sign of the balance of trade was a way to take the pulse of a nation’s economy. Adam Smith rejects this measure and instead suggests that we should look at population growth. Nations that are able to produce enough to support the life of a growing population have growing economies; nations with constant population have stagnant economies, and nations that face a declining population have a contracting economy. Thus, population for Adam Smith is a proxy for our Gross Domestic Product, indicating the changes in production in a country over time