In this video segment adapted from NOVA, see how paleoanthropologists—including Don Johanson, with his famous discovery of the Australopithecus afarensis "Lucy"—have used the fossil record to identify a large number of fairly similar bipedal species that encompass ancestors of humans and related species. These species, which walked upright like humans, but resembled apes in small brain size and in facial structure, flourished as a group for millions of years. Scientists still debate which of these species was our direct ancestor. The video features a comparison of Lucy's fossilized pelvis bone with that of an ape, and shows how strikingly similar Lucy's is to a human one.