The United Nations projected that the population would reach eight billion people Tuesday because of a combination of higher fertility rates in some countries and longer lifespans in others.

The UN found that countries with relatively high fertility rates tended to be those with some of the lowest reported incomes per capita. Globally, life expectancy has increased since 1990 by almost nine years, with female and male life expectancies standing at 73.8 and 68.4, respectively, according to a UN report. 

When will the population reach nine billion? The report said it will take longer to go from eight to nine billion than it did to go from seven to eight billion.

It took the global population 12 years to reach eight billion, but they project it will take about 15 years to reach nine billion. More than half of that growth is expected to come from eight low-income countries. 

This story originally appeared in WORLD. © 2022, reprinted with permission. All rights reserved.