→What do TFR values look like?
Historical TFR data extends back to 1800, but for the initial period, such data was not collected every year but rather based on occasional [[census]] estimates. In 1800, the mean TFR (unweighted) of all countries was about 6.1, and the standard deviation was about 0.8, with very few countries having values significantly higher than 7. The United States had among the higher TFRs of the world, at slightly over 7, reflecting the very low population density relative to the size of the land. There is good reason to believe that TFR values had remained in this range for large parts of human history, because a fertility rate higher than 6 would be biologically relatively difficulty, and also because the other related indicators had not changed much in human history until 1800.
Proper data collection around the world began in 1950, with the United Nations playing an important coordinating role. In 1950, the unweighted mean of the TFR values of all countries recorded was about 5.4. It stayed steady at that level until about 1965, at which point it started seeing a steady decline with the decline initially being 0.1/year (for the first decade), then slowing down to 0.08/year (for the next decade), then slowing down to about 0.05/year. In the entire period from 1950 to 2012, the standard deviation remained study at about 1.5, suggesting that "all fertilities were coming down together."