“It’s a small world” may be a cliché, but people don’t fully believe it. For many people, then, the most surprising thing about a journalist preparing to walk around the world as part of a National Geographic project (described in the BBC News Magazine story “Paul Salopek: Going for a seven-year walk”) is that such a thing is possible. The story of humans taking 75,000 years to occupy the world is so often repeated that it is hard to interrupt this narrative to explain that the actual duration of such a walk could be less than a lifetime, conceivably as short as two years. As a marathon runner, I like to compare the distance around the world to the distance of a marathon. A walk around the world might be 100 million steps. That’s 1,000 times the distance of a marathon, but consider that good runners (and even runners like me) complete a marathon in a single morning. My hope is that this planned journey, a walk to South America from Africa over the next seven years, helps more people understand how small the world really is.