Fifty years on, how Lucy, the mother of humanity, changed our understanding of evolution

Lucy, the 3.2m-year-old skeleton of an Australopithecus afarensis female, on display at the National Museum of Ethiopia, Addis Ababa. Photograph: Edwin Remsberg/Alamy

On 24 November 1974, the US anthropologist Donald Johanson was scrabbling through a ravine at Hadar in the Afar region of Ethiopia with his research student, Tom Gray. The pair were looking for fossilised animal bones in the surrounding silt and ash when Johanson spotted a tiny fragment of arm bone – and realised it belonged to a human-like creature.

“We looked up the slope,” Johanson later recalled. “There, incredibly, lay a multitude of bone fragments – a nearly complete lower jaw, a thighbone, ribs, vertebrae, and more! Tom and I yelled, hugged each other, and danced, mad as any Englishman in the midday sun!”