A couple of hundred years ago, the human population simmered around the 1 billion people mark (that's as many people who watched the 2014 World Cup championship). It took 123 years to double that number and 33 more to triple it. Since then the population has been on a voracious sprint. We totaled 7 billion in 2012, are predicted to soar to 9 billion by 2050, and we could reach 17 billion by the end of the century. The upshot? Cultures, resources and nature are colliding like never before with magnificent, inspiring, heartbreaking and frightening results. How will we choose to grow? That's the question.