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.

The big news in the journal Science tomorrow is the discovery of the oldest human skeleton—a small-brained, 110-pound female of the species Ardipithecus ramidus, nicknamed “Ardi.” She lived in what is now Ethiopia 4.4 million years ago, which makes her over a million years older than the famous “Lucy” fossil, found in the same region thirty-five years ago.

Buried among the slew of papers about the new find is one about the creature’s sex life. It makes fascinating reading, especially if you like learning why human females don’t know when they are ovulating, and men lack the clacker-sized testicles and bristly penises sported by chimpanzees.

One of the defining attributes of Lucy and all other hominids—members of our evolutionary lineage, including ourselves—is that they walk upright on two legs. While Ardi also walked on two legs on the ground, the species also clambered about on four legs in the trees. Ardi thus offers a fascinating glimpse of an ape caught in the act of becoming human.

The problem is it is doing it in the wrong place at the wrong time—at least according to conventional wisdom, which says our kind first stood up on two legs when they moved out of the forest and onto open savanna grasslands. At the time Ardi lived, her environment was a woodland, much cooler and wetter than the desert there today.

So why did her species become bipedal while it was still living partly in the trees, especially since walking on two legs is a much less efficient way of getting about?