On or around Oct. 31, 2011, the world's 7 billionth person will be born, the United Nation estimates.
Even more staggering is that of the 7 billion people on Earth, about 1.4 billion of them will be old enough to have observed the arrivals of the 6 billionth, 5 billionth, 4 billionth and 3 billionth people in the world. About 42.5 million people could have blown the party horn for the birth of the 2 billionth baby.
Yes, population has risen very quickly over the last century. Demographers do expect a decline in the population growth rate, but absolute numbers will continue to rise, likely hitting 9 billion by 2050. Meanwhile, we look back at history's past population milestones, asking: "How has the world changed?"