A fossil discovered in Ethiopia suggests that humans’ prehistoric relatives may have lived in the trees for a million years longer than was previously thought. The find may be our first glimpse of a separate, extinct, branch of the human family, collectively called hominins. It also hints that there may have been several evolutionary paths leading to feet adapted for walking upright.

The fossil, a partial foot, was found in 3.4-million-year-old rocks at Woranso-Mille in the Afar region of Ethiopia. Bones of the hominin Australopithecus afarensis — the species to which the famous ‘Lucy’ skeleton belongs — have also been found in this location and from the same period. But unlike Au. afarensis, the latest find has an opposable big toe — rather like a thumb on the foot — that would have allowed the species to grasp branches while climbing. Modern apes have similar toes, but the youngest hominin previously known to have them is Ardipithecus ramidus, which lived about 4.4 million years ago.