A study of the limb bones of the Little Foot skeleton, around 3.67 million years old and found in the Sterkfontein Caves in South Africa, suggests there was a major shift in how human ancestors moved between about 3 million and 1.8 million years ago. The work was published in Science Advances.
According to the researchers, Australopithecus combined regular tree-climbing with walking on two legs. Its arm bones were strong relative to its thigh bones, in a pattern closer to African apes, although Little Foot’s lower-limb proportions already resembled those of modern humans.
By about 1.8 million years ago, fossils of early Homo, including those from Dmanisi in Georgia, showed limb strength patterns much closer to today’s, which the authors interpret as a stronger commitment to life on the ground. The scientists propose this shift as a ‘threshold’ between Australopithecus and Homo, but acknowledge they do not yet know what caused it.
The transition coincided with a period of increasing brain size in the human lineage, although lead researcher Kristian Carlson stresses that the team is not saying one change caused the other.
