About 3.2 million years ago, a small female lived in what is now the Afar region of Ethiopia. When her bones were found in 1974, she became the most famous fossil of an early human relative: Lucy. Her species, Australopithecus afarensis, lived in East Africa for about 900 000 years. Its brain was only about a fifth larger than a chimpanzee’s, but it walked upright on two legs.
Lucy
Lucy was found on 24 November 1974 at Hadar by the palaeoanthropologist Johanson and the graduate student Gray. She was an adult, about 105 cm tall and weighing about 28 kg. Four years later Johanson, White and Coppens named her species. Its males appear to have been much larger, averaging about 151 cm and 42 kg against about 105 cm and 29 kg for females, though the size of that gap is debated.
In 2023 a researcher at the University of Cambridge used scans of Lucy’s bones to rebuild 36 muscles in each of her legs in three dimensions. Muscle made up about 74 per cent of the mass of her thigh, compared with about 50 per cent in people today, and her knees could straighten as fully as ours: she could stand as upright as we can.
Walking and climbing
Lucy’s species walked upright as a matter of course, but it had not given up the trees. Its arms were long and strong and its fingers curved, which would have helped with climbing. On the ground it was no sprinter. A 2024 study simulated how fast Lucy could run and found a top speed of about 5 m per second, well below a modern human sprinter, at a much higher energy cost.
Its brain was small, usually under 500 cm³, and organised more like a chimpanzee’s than ours. But a 2020 study of fossil braincases found that the brain grew slowly over a long childhood, as human brains do.
Footprints in the ash
The most vivid evidence of their walking is at Laetoli in Tanzania. About 3.66 million years ago, early humans walked across a layer of fresh, damp volcanic ash, and their prints hardened and were buried. At Site G, three individuals left a trail about 24 m long, discovered in 1976 and excavated by Leakey’s team by 1978. More prints of two individuals were found nearby in 2015, including one who may have stood about 165 cm tall.
A third set of five prints, at Site A, has a strange cross-stepping pattern. A 2021 study argued that it was made by a different kind of human relative living alongside Lucy’s species, though not everyone agrees.
Our ancestor?
Lucy’s species has long been considered a likely ancestor of later humans, including our own genus, Homo. That picture is being questioned. In 2025 a team led by Haile-Selassie described new jaws and teeth from Ethiopia confirming a second species, Australopithecus deyiremeda, that lived alongside Lucy’s between 3.5 and 3.3 million years ago, ate leaves, fruit and nuts and climbed more. They suggested that an older species, Australopithecus anamensis, may be the common root of the later branches instead.
No stone tools have been firmly linked to Lucy’s species. Cut marks on animal bones about 3.4 million years old from Dikika in Ethiopia have been read as butchery, but that interpretation is disputed. The species disappears from the fossil record about 2.95 million years ago, perhaps evolving into later forms rather than simply dying out.
