The genus Australopithecus includes seven species—a whole family of early hominins, the group that includes humans and their ancestors. But one species of Australopithecus gets the most attention: A. afarensis, which lived approximately 3.9 to 3.0 million years ago. It is represented by the largest number of fossil specimens—hundreds of fragments from most parts of the skeleton, and several partially complete individuals, including the famous Lucy. Many scientists believe that it is on the direct path to modern humans, although some experts argue instead for A. africanus, from southern Africa. Scientists know for certain that A. afarensis was bipedal. One of the most important finds supporting this conclusion are the 3.6-million-year-old footprints found at Laetoli, which have been attributed to A. afarensis. The shift to bipedalism is thought to have driven many of the anatomical and behavioral changes that occurred in hominins, ultimately resulting in people like us.
─Alice J. Dunn