Well then it is a chicken or egg questions. What came first? When we were hunter and gathered we could not afford a large pop because food source was uncertain. With agriculture there was more efficiency. It took less effort/calories to products x calories of food. So we could support a large population Note that population growth is negative or slow in industrialized countries while pop growth is high in non-industrialized countries. Note that output of industrialized countries often goes to other industrialized countries because they are the once with the $$$. Look at the poor farmers in india and vietnam - many are still living in pre industrial existence with use of draught animals for agriculture.