This fall, the world's population reached seven billion. A sobering thought. How did we get to this point? Producer Adam Cole and photographer Maggie Starbard of National Public Radio have put the world's accelerating population growth in perspective in a two-and-a-half minute video, above.

In those two and a half minutes, 638 babies will be born worldwide, according to statistics from the United States Census Bureau, and 265 people will die. That's a net gain of 373 people, just while you watch the film. The biggest growth, according to NPR, is happening in sub-Saharan Africa, where access to family planning is low and infant mortality rates are high.

It may seem counter-intuitive that population growth rates are high where infant survival rates are low, but as Swedish global health expert Hans Rosling put it during a recent TED talk, "Only by child survival can we control population growth." Because population growth and infant mortality rates are both correlated to poverty rates, he argues, eliminating poverty is the key to achieving a sustainable world population. You can learn more in our November 1 feature, "Hans Rosling Uses IKEA Props to Explain World of 7 Billion People."