Australopithecus afarensis walked upright like a human, but its body proportions were like those of a chimpanzee. Like chimps, afarensis had a small brain, long, dangly arms, short legs and a cone-shaped torso with a large belly.

Around 3.2 million years ago, this bipedal ape roamed a mixed habitat of savannah and woodland beside lakes and floodplains. It foraged for fruit, seeds and nuts and may even have eaten some meat.

Australopithecus afarensis probably climbed into trees to avoid sabre-toothed cats like Dinofelis and to sleep in safety at night.

This hominid seems to have lived in social groups of between 20 and 30. These groups were probably like those of chimpanzees, with dominance hierarchies in which each individual knows their place. Male afarensis probably cooperated to drive away predators. Once mature, females may have joined other troops of afarensis.

Chimp cousins

Chimpanzees are our closest relatives. Genetic studies show humans and chimpanzees shared a common ancestor that lived in the African rainforest 7-8 million years ago. The descendants of this common ancestor split into two lineages: one that led to chimps and another that led to us.

Chimpanzees are our closest relatives It is thought that the human lineage developed routine bipedalism as a strategy for living on the ground when climate change decimated the forest, leaving wide belts of open terrain with no trees.

Discovery of Lucy

On 24 November 1974 in the Afar region of Ethiopia, anthropologists Donald. Johanson and Tom Gray made one of the most famous fossil discoveries ever.

While out fossil hunting in sandy ravines near the River Awash, they discovered a 40% complete skeleton dating to 3.2 million years ago. They named the find 'Lucy'. Lucy's species, Australopithecus afarensis, have small canine teeth compared with apes. This suggests males may have been cooperating.

Examinations of Lucy's knee joint and pelvis demonstrate that she walked upright. And footprints left in volcanic tuff at Laetoli in Tanzania by afarensis suggest it walked with a human-like stride.