I think that you fail to understand the reasons behind the wealth increase. Wealth increase does not usually happen by itself. It happens mostly because people

I think that you fail to understand the reasons behind the wealth increase. Wealth increase does not usually happen by itself. It happens mostly because people do something differently. This change is very often gradual inside the society. Correlation between wealth increase and fertility rate in a single country is a very good indicator of this. The main question posed in my original post is actually different.