Human society began some 3 million years ago with the first evolutionary ancestors that walked upright and gradually developed rudimentary tools made of bone, wood, and stone. Over time, these crude groups evolved into tribes that roamed the planet, developing ever more complex tools and social norms, thus giving way to Mesolithic (middle stone age) and Neolithic (new stone age) periods. Starting with the Neolithic period, humans developed agriculture and became sedentary. The finding of copper, tin, and iron in subsequent centuries completes the Prehistory timeline, which ends with the Greek Classical period, between 900-800 B.C