People with our present brain capacity lived primarily as hunter-gatherers for at least 60 thousand years before changing to agrarian societies about 12 thousand years ago. The world’ human population began increasing about 4 thousand years ago and increased again since 1950. Human societies began shifting to a “technological/industrial phase” about 400 years ago and recently to the Anthropocene, when people started affecting the Earth strongly. As countries develop, people migrate to cities, concentrate agriculture, and develop complex societies with new occupations and few people engaged in resource production. The result has been crowded cities, lower fertility rates, stable or increased forest area, and less fuelwood use. Populations continued to have more young people in poorly developed countries and stable to decreasing numbers in developed countries. The world population will continue to grow because the world fertility rate is still above replacement and because the older age class will “fill out” over time. World population is expected to reach over nine billion by 2050. The world population is probably so high that uncontrollable diseases or famines could occur.