Seun Dupe sits with her newborn twins in a maternity hospital in Lagos, Nigeria. Nigeria is Africa's most populous country with more than 160 million people. UNICEF estimates that number will swell to nearly 1 billion by 2100.
The crowded scene on "Black Friday" at Macy's in Manhattan. The U.S. population is projected to hit 400 million in 2051, Census says, up from 321 million in 2015.
Stan Honda /AFP/Getty Images
Indian schoolchildren write English alphabets on slates at a primary school outside Hyderabad in June. India is on track to overtake China as the most populous nation in just 16 years.
Noah Seelam/AFP/Getty Images