NGS grantee Yohannes Haile-Selassie, shown here at his dig in Ethiopia at Woranso-Mille, was the discoverer of the most complete specimen of Ardipithecus ramidus at nearby Aramis in 1994. He also discovered Ar. ramidus's 5.5 to 5.8 million-year-old ancestor, Ar. kadabba. Photo © Liz Russell, courtesy of Yohannes Haile-Selassie.

Today the world will witness the long-awaited roll out of Ardipithecus ramidus. And what a roll out! This new member of the hominin lineage has features that are quite unexpected because they are unlike what we see in living great apes, which share common ancestry with humans. A whole issue of Science is devoted to this creature and the work of a dedicated group of scientists who spent many years in the desolate Middle Awash project area of the Afar depression in Ethiopia.

I've had the pleasure of meeting many of the Middle Awash team members over the years. Among them are many Ethiopians who started their careers in the Middle Awash more than 15 years ago as bright, dedicated students. Now they are PhDs who are spread throughout the world at prestigious institutions making significant contributions to science, not the least of which are the many papers being announced today concerning the anatomy and environment of Ardipithecus ramidus.

Buried in these scientific papers is a significant mention that may pass right by many readers. In the paper entiltled "Ardipithecus ramidus and the Paleobiology of Early Hominids," the authors mention how in the early 1990s, after much looking, they were only finding scrappy bits of early human fossils at Aramis. They go on to say, however, that "... on 5 November 1994, Y.H. S. collected two hominid metacarpal fragments (ARA-VP-6/5001a and b) from the surface of an exposed silty clay..." Those hand bones were the first bits found of what would become the substance of much of today's press announcement—the most complete skeleton of an adult early hominin since the discovery of Lucy, the australopith, in 1974. Who is its discoverer, Y.H.S.? It was none other than Yohannes Haile-Selassie, one of the Ethiopian students I mentioned.

This image compares the canines of a chimpanzee (left) to those of Ardipithecus kadabba (right). In many apes, as with Ar. kadabba, the rubbing of the upper canines against teeth in the lower jaw keeps them sharp. Tim White/UC Berkeley, courtesy Science Magazine.

While today's news celebrates Ardipithecus ramidus, the significance of Ardipithecus kadabba should not be underestimated. First of all, the great age of Ar. kadabba pushes it back into a time zone between 7 and 5 million years ago when two other very early hominins, Sahelanthropus tchadensis and Orrorin tugenensis, also lived in Africa. Second, Ar. kadabba is definitely more primitive than Ar. ramidus. Of particular interest is that it still had what is called the canine-premolar honing complex, an arrangement of the teeth that sharpens the canines during chewing. Ar. kadabba's honing complex was significantly diminished from what living great apes have to keep their large, dagger-like canines in working order, but it was there. By the time of Ar. ramidus, the honing complex and the need to keep upper canines sharp seems to have disappeared. The large upper canines of males continued to reduce in size in our lineage, apparently as male agression (which is what big canines are good for) became less important to reproduction and survival.

Haile-Selassie, who is now the curator and head of physical anthropology at the Cleveland Museum of Natural History, commented in 2004 that Ar. kadabba may represent "the first species on the human branch of the family tree just after the evolutionary split between lines leading to modern chimpanzees and humans." This, and other comments from researchers involved in today's revelations about Ar. ramidus, suggests that all known early hominins, including Sahelanthropus and Orrorin, may be the same thing, Ardipithecus kadabba. More fossils will help clarify the picture.

Meanwhile, the National Geographic Society has been funding Dr. Haile-Selassie since 2005 at a new research site called Woranso-Mille in the Afar depression of Ethiopia. There his team found 4 million-year-old hominins that may help clarify a transition that occurred after Ardipithecus, the transition from Australopithecus anamensis to Lucy's species, Au. afarensis. With his impressive track record for significant discoveries and research publications, there is one thing we can be sure of—we have not heard the last from Dr. Yohannes Haile-Selassie.

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