Why do we travel? Some 60,000 years ago we humans began to journey out of the ecological niche we shared with our primate cousins in Africa to explore the unknown. Our curiosity led us from the savanna to coasts, deserts, forests, valleys, mountains, and ice caps. Evolution made us ever more curious, and so we traveled to learn more. On a to-do list written by Leonardo da Vinci around 1490, most of the tasks he wanted to accomplish involved visiting various masters in their fields. Travel allows us to, a Montaigne put it, “rub and polish our brains” against people from different regions and cultures.