As of Oct. 31, 2011, there were 7 billion people on Earth, according to the United Nations. This latest milestone was part of the rapid rise in Earth's population over the course of the 20th century — there were just 2.6 billion people in 1950 and 5 billion people in 1987. The population explosion has its roots in the decrease in mortality (because of a better understanding of disease and new treatments) that began in the 19th century and continued through the 20th, moving from the developed world into the developing world, to some extent. In June 2013, the United Nations released a new report on estimates of population rise through the 21st century. It found through a new statistical analysis that the world's population could hit 11 billion by 2100, faster than it had previously predicted, in part because birthrates in Africa were not declining as quickly as predicted. The rapid rise in the human population presents a set of challenges in terms of straining Earth's resources, from putting pressure on other species, to providing enough water, food and basic sanitation to all populations.