I don't know of Wolfram's statistics include population
   estimates of non-counted (no Census) populations or not, so it
   _might_ be misleading. The pink area stops at 1750AD. But
   considering that governments have been counting heads for as
   long as we've had cities, it's at least accurate for as long as
   we've had cities and populations willing to be counted. 1750 AD
   shows the beginning of a big "jump". It also coincides with
   explorations of otherwise "uncharted" lands and people's; the
   exploits of travelers and[1]pop-of-world their head-counting of
   "natives" likely added to the number.
   So, it's more a chart of "civilizations who counted people"
   rather than absolutely fact. Nevertheless, interesting. It helps
   explain why a few people in ancient times had such HUGE IMPACTS
   on the millenia that followed: There were fewer people.

References

   Visible links
   1. http://icopiedyou.com/wp-content/uploads/2015/09/pop-of-world.jpg