Five Radical Changes in 21st Century

In terms of evolution, the species Homo sapiens is extremely successful. The populations of other species that are positioned similar to us on the food chain tend to max out at about 20 million. We, by contrast, took just 120,000 years to achieve our first billion members, and then needed only another 206 years to add 6 billion more. According to the United Nations Population Division, our population will hit 7 billion on Oct. 31, and though fertility rates have begun to decline across much of the globe, we're still projected to reach 9 billion by mid-century and level off at around 10 billion by 2100.