CHICAGO, IL - OCTOBER 31: Commuters fill the sidewalk as they make their way toward the train station on October 31, 2011 in Chicago, Illinois. The United Nations Population Fund estimates that today... more 
CHICAGO, IL - OCTOBER 31: Commuters fill the sidewalk as they make their way toward the train station on October 31, 2011 in Chicago, Illinois. The United Nations Population Fund estimates that today the world's population reached seven billion people. The U.N. also estimates the world's population will reach eight billion by 2025 and 10 billion by 2083. (Photo by Scott Olson/Getty Images) less 
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Getty Images | Photo By Scott Olson / Getty Images
Mon, Oct 31, 2011 8:04 PM EDT