Answer: The per capita income level of the world grew very slowly prior to the increase of GDP after the 1800's.
Explanation:
As the world population expanded the per capital income level grew as well. The per capital income level is the average income level that is earned for a person in a given area. To find this, take the total area (city, country, state) and divide it by the population in that area to solve for the PCI (per capita income).