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July 12, 2001

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New Ethiopian Fossils May Represent Oldest Human Ancestor Yet

By Kate Wong

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Researchers working in Ethiopia have unearthed the remains of a creature thought to occupy a spot on the family tree quite close the evolutionary branching point between humans and chimpanzees. According to a report published today in the journal Nature, these remains belong to a new subspecies of the hominid genus Ardipithecus, previously known fossils of which date to 4.4 million years ago. The new fossils, however, come from sediments dated to between 5.2 and 5.8 million years ago, and thus may represent the earliest known human ancestor.

Yohannes Haile-Selassie, a doctoral candidate at the University of California at Berkeley, discovered the fossils in Ethiopia's Middle Awash study area, a locale famous for yielding other key fossils, such as the 4.4 million-year-old Ardipithecus ramidus and the 2.5 million-year-old Australopithecus garhi. Subsequent analyses of the fragmentary remains¿which include a jawbone with teeth; hand, foot and arm bones; and a piece of collar bone¿revealed a bipedal creature with teeth similar to those of later hominids. These teeth and certain skeletal features are more primitive than those belonging to Ardipithecus ramidus, however, thus leading Haile-Selassie to designate the fossils as a new subspecies, Ardipithecus ramidus kadabba.

A.r.kadabba is not without competition for the distinction of being the earliest human ancestor. Earlier this year a French team unveiled the 6 million-year-old remains of Orrorin tugenensis, a new species that the discoverers regard as hominid. (These researchers consider Ardipithecus a chimpanzee ancestor.) For his part, Haile-Selassie asserts that more information is required to resolve Orrorin's place in the family tree. And with excavations resuming in the Middle Awash this fall, more clues to our elusive evolutionary past may yet come from Ardipithecus.

Kate Wong is an award-winning science writer and was formerly senior editor for features at Scientific American, where she focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for nearly 30 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home to the shores of Kenya’s Lake Turkana in search of the oldest stone tools in the world, as well as to Madagascar on an expedition to unearth ancient mammals and dinosaurs, the icy waters of Antarctica, where humpback whales feast on krill, and a “Big Day” race around the state of Connecticut to find as many bird species as possible in 24 hours. Wong is co-author, with Donald Johanson, of Lucy’s Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow her on Bluesky @katewong.bsky.social

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