Starry Messenger: Cosmic Perspectives on Civilization

by Neil deGrasse Tyson

Africa is indeed the “cradle of mankind.” A few hundred thousand years ago, early humans wandered north and then west and east, populating Europe, Asia, and ultimately the Americas. Our peripatetic ancestors carried the base African genome all around the world. Those journeys took less time than you might think. Let’s do the math. If you walked 25,000 miles (Earth’s circumference) at 2 miles per hour—a leisurely pace—and you did it for eight hours per day, you would circumnavigate the globe in 4.3 years. Of course there’s no actual path or road that goes around Earth, and there’s desert and bodies of water and mountains and other stuff in the way. Nonetheless, before agriculture, generations upon generations of Africans, one after another, had plenty of time to reach every contiguous nook of Earth’s surface—driven by the search for food or by a sense of wonder about what lay beyond their horizons.