Denise Su/The Conversation In 1974, on a survey in Hadar in the remote badlands of Ethiopia, U.S. paleoanthropologist Donald Johanson and graduate student Tom Gray found a piece of an elbow joint jutting from the dirt in a gully. It proved to be the first of 47 bones of a single individual – an early human ancestor whom Johanson nicknamed “Lucy.” Her discovery would overturn what scientists thought they knew about the evolution of our own lineage. Lucy was a member of the species Australopithecus afarensis, an extinct hominin – a group that includes humans and our fossil relatives. Australopithecus afarensis lived from 3.8 million years ago to 2.9 million years ago, in the region that is now Ethiopia, Kenya and Tanzania. Dated to 3.2 million years ago, Lucy was the oldest and most complete human ancestor ever found at the time of her discovery. Two features set humans apart from all other primates: big brains and standing and walking on two legs instead of four. Prior to Lucy’s discovery, scientists thought that our large brains must have evolved first, because all known human fossils at the time already had large brains. But Lucy stood on two feet and had a small brain, not much larger than that of a chimpanzee. Read moreSection: NewsEvolution & Human OriginsRead Later