This past fall marked the 50th anniversary of the discovery of Lucy, one of the first hominin fossils to become a household name. At the time, she was by far the most complete early hominin known, with a skeleton around 40% complete. Her bone structures suggested that early hominems were walking around on 2 feet nearly 3.2 million years ago—much early than previously believed.

In this interview with Donald Johansen–the palentologist who discovered Lucy’s remains in Ethiopia in 1974–he discusses the shapes that indicate she was not an ape; what we know as the human family tree; the biggest unanswered questions about human origins…and whether the study of early hominems can give clues to the future of our own species.