Tel Aviv University anthropologists say they have disproven the theory that "Lucy" - the world-famous 3.2-million-year-old Australopithecus afarensis skeleton found in Ethiopia 33 years ago - is the last ancestor common to humans and another branch of the great apes family known as the "Robust hominids."

The jaw bone of Lucy and the jaw bone of Australopithecus afarensis.
Photo: Courtesy

The specific structure found in Lucy also appears in a species called Australopithecus robustus. Prof. Yoel Rak and colleagues at the Sackler School of Medicine's department of anatomy and anthropology wrote, "The presence of the morphology in both the latter and Australopithecus afarensis and its absence in modern humans cast doubt on the role of [Lucy] as a common ancestor."

The robust hominids were discovered in southern Africa 69 years ago and are believed to have lived between 2 million and 1.2 million years ago. Their jaws and jaw muscles were adapted to the dry environment in which they lived.

Rak and colleagues studied 146 mature primate bone specimens, including those from modern humans, gorillas, chimpanzees and orangutans and found that the "ramus element" of the mandible connecting the lower jaw to the skull is like that of the robust forms, therefore eliminating the possibility that Lucy and her kind are Man's direct ancestors. They should therefore, the Israeli researchers said, "be placed as the beginning of the branch that evolved in parallel to ours."

Their research has just been published in the on-line edition of PNAS, the Proceedings of the [US] National Academy of Sciences.

Lucy, which means "you are wonderful" in Amharic, was discovered (40 percent of its skeleton) by the International Afar Research Expedition in Ethiopia's Awash Valley. Fitting the bones together, they said it was an upright walking hominid (Homo sapiens, which comprises modern Man and extinct manlike species). They later found its jaws and additional bones.

Further analysis led the Afar researchers to believe it was of a female, and the skeleton listed as AL 288-1 was nicknamed Lucy because the Beatles' song "Lucy in the Sky With Diamonds" was often played at the camp.

The specimen was only 1.1 meters tall, estimated to weigh 29 kilograms and look somewhat like a common chimpanzee. Although it had a small brain, the pelvis and leg bones were almost identical in function with those of modern humans, proving that these hominids had walked erect.

Although fossils closer to chimpanzees have been found since then, Lucy - which is housed in the national museum in Addis Ababa - is prized by anthropologists who study Man's origin.

Rak and his colleagues also wrote that the structure of Lucy's mandibular ramus closely matches that of gorillas, which was "unexpected" because chimpanzees are the closest living relatives of humans, and not gorillas.