A German entomologist looking for butterflies in Olduvai Gorge in 1911 found fossil bones of a prehistoric horse. Louis Leakey became convinced that Olduvai held more than horses’ bones. He and his wife, Mary, started digging in 1931 and found stone tools, many more bones and finally a skull which showed that this dusty 31-mile-long (50-km) gorge has been continuously occupied by humans for almost two million years. Perhaps longer, since Mary Leakey found footprints, identical to modern-day humans’, in a 3.5-million-year-old site at Laetoli, not faraway. Other discoveries have followed—remains of the famous “Lucy” and more than 150 animal species among which these hominids lived: prototype elephants, hippos, rhinos, antelopes, lions, baboons, warthogs. Some, like black-backed jackals, appear unchanged over the millennia. Research continues. Olduvai, 120 miles (200 km) northwest of Arusha and not far from Lake Manyara, has a museum and guides. Along the route are giraffes and others, some almost certainly descendants of that early now-fossilized wildlife.