When he went on the popular television show Larry King Live, Professor Stephen Hawking of Cambridge University was asked what worries him the most. Hawking, often referred to as the most intelligent man alive, replied that his biggest worry was population growth, saying that "if it continues at the current rate, we will be standing shoulder to shoulder in 2600. Something has to happen, and I don't want it to be a disaster" ("World").
Hawking has sound reason to worry about the growing population of Earth's human inhabitants. Our numbers are increasing at rates unprecedented in history, adding our last billion people in a mere twelve years ("World"). None can say for sure what impact we will have on the planet that we call home, but one thing is for certain, the Earth has only so many resources, which we surely cannot survive without, and we are consuming them at an alarming and unsustainable rate. We will run out of resources, it's simply a question of when.
One of the most important resources, one which does not usually spring to mind when natural resources are thought of, is space. The Earth is only so big, with only so much space for us to live, grow our food on, raise our animals on, and to move around over. The planet is a giant island, and no island is infinite. Some argue that space is of no concern - we are moving into urban areas in increasing numbers, areas where large amounts of people can be fit into very tall buildings that take up a minimal amount of square feet. They say that if we cannot fit everyone on ground level, we will simply move ever-upward.
While it is true that we have the capability to fit many people into small spaces, urbanization has very definite setbacks. A high concentration of people makes for a high concentration of pollution and disease that is impossible to escape from unless one were to leave such an environment. As one site put it, "All of the population of the world can fit into the state of Texas.