It is the year 2200 and the world has 250 million people. What has happened? Was there a total nuclear war and followed by a famine? Was there a terrible super-pandemic? How can the world have fallen from over 8.1 billion people in 2023 to 250 million. How can there be only 3% of the world population? Perhaps, artificial super intelligence was created and it nearly wiped out humanity.

This is what happens if all countries have a total fertility rate of 1.0 or less. This is the situation in South Korea and Taiwan. Falling below replacement levels of 2.1 means that the average women no longer has an average of 1 daughter. If fertility rates go to 1.0 or less that means the total of all women have half of a daughter. This means the next generation (30 years later) has half as many fertile women. In 60 years there are 25% as many fertile women and in 90 years there are 12.5% as many fertile women.

Almost 80% of the population of the world is below replacement. This includes India and Bangladesh, which are very poor countries. Japan fell below replacement in 1976 and in 2008 its population began shrinking. This was in spite of having among the longest life expectancy in the world at over 80 years. Continued population growth is from the momentum of previous higher birth rates increasing the pool of women who have chosen not to fully replace themselves