In 1974, a team of scientists were searching the dusty ground in a part of Ethiopia called the Afar region. One of them spotted a small piece of arm bone. Slowly, carefully, they uncovered more pieces - 47 bones in total. It was one of the most complete skeletons of an early human ancestor ever found anywhere in the world.
The scientists nicknamed her Lucy, because they were listening to a Beatles song called 'Lucy in the Sky with Diamonds' the night they celebrated. Her proper scientific name is Australopithecus afarensis - 'the southern ape from Afar'.
Lucy was small - only about 1.1 metres tall, the size of a 5-year-old today. But she walked upright on two legs, just like we do. That was a huge discovery, because it showed that our ancestors started walking upright millions of years before they started having bigger brains.
Lucy now lives carefully kept in the National Museum of Ethiopia in the capital, Addis Ababa. Visitors come from all over the world to see her. She is one of the most famous fossils ever found, and Ethiopians often call their country 'the cradle of humanity' because of her.