Bones from the skeleton of 'Lucy', a young female Australopithecus afarensis hominid. The bones are around 3.3 million years old, and are generally thought to represent the earliest known ancestor of humans. The skeleton was found in the Afar region of Ethiopia in 1974. A. afarensis lived between 3.9 and 2.9 million years ago. It is thought to have been bipedal, evidence coming from the structure of the pelvis and legs, and from a set of fossilized footprints found in Laetoli, Tanzania, that date from around 3.5 mya. A. afarensis was a gracile australopithecine, differentiated from the robust types (such as A. boisei) by its slighter build.