MADRID, SPAIN—Scientists have discovered a 1.84-million-year-old fossilized hand bone in Tanzania’s Olduvai Gorge that they believe is the oldest to resemble that of a modern human. The bone is most likely part of the little finger of the left hand of an adult belonging to an unknown species similar to Homo erectus. It measures around 1.4 inches long, comparable to the size of the same bone in the hands of modern humans, which suggests its owner would have been larger than known human relatives living at the same time—probably around five feet nine inches tall. The bone is straight, which suggests that, like modern humans, its owner was adapted to use tools and live on land rather than to climb trees. "A modernlike hand in the past would tell us when humans became fully terrestrial and when and how efficiently our ancestors used tools," Manuel Domínguez-Rodrigo, a paleoanthropologist at Complutense University of Madrid, told Live Science. To read about the earliest known stone tools, go to “The First Toolkit.”