Researchers have unveiled the oldest known skeleton of a putative human ancestor–and it is full of surprises. Although the creature, named Ardipithecus ramidus, had a brain and body the size of a chimpanzee, it did not knuckle-walk or swing through the trees like an ape. Instead, “Ardi” walked upright, with a big, stiff foot and short, wide pelvis, researchers report in Science. “We thought Lucy was the find of the century,” says paleoanthropologist Andrew Hill of Yale University, referring to the famous 3.2-million-year-old skeleton that revolutionized thinking about human origins. “But in retrospect, it was not.”
Researchers have long argued about whether our early ancestors passed through a great-ape stage in which they looked like protochimpanzees, with short backs; arms adapted for swinging through the trees; and a pelvis and limbs adapted for knuckle-walking (Science, 21 November 1969, p. 953). This “troglodytian,” or chimpanzee, model for early human behavior (named for the common chimpanzee, Pan troglodytes) suggests that our ancestors lost many of the key adaptations still found in chimpanzees, bonobos, and gorillas, such as daggerlike canines and knuckle-walking, which those apes were thought to have inherited from a common ancestor.