The beginning of the common era generated a total population of 250 million people, which has multiplied throughout the years.  Eurasia was home to many of these people a long with Africa, but there were many differences between the two.  Africa was bisected near the equator and due to the warm weather it caused poorer fertile soil and less productive agriculture unlike in Eurasia.
Mesoamerica and the Andes were also a set of civilizations during the common era and they housed the vast majority of the American population.  In Mesoamerica people shared an agricultural technology to raising crops, practiced religion, and human sacrifices. Human sacrifices sounds outrages because if that were done today someone would be facing life in prison. It's interesting to learn about the different eras and the beliefs these civilizations had because with time the world has definitely changed.