How has the population of underdeveloped countries changed since 1950?

The population has rised exponentially

The correct answer to this open question is the following.

The population of underdeveloped countries has dramatically changed since 1950. It has increased rapidly, and in some cases has doubled or tripled, according to some underdeveloping countries.

Each underdeveloping country has is special cases. But generally speaking, these countries had decreased the mortality rate since the 1950s, which has allowed them to reduce diseases and increases the years lived by their citizens. Another key issue is the lack of a well-planned natality program that controls families having children. There are cases such as México, Argentina or Brazil that have dramatically increased their population since the 1950s.