New Details on our Oldest Ancestors

Ardipithecus kadabbaPaleoanthropologist Yohannes Haile-Selassie, co-editor of Ardipithecus kadabba and member of the team that discovered the hominid “Ardi”, is the leader of a team that has just announced another major discovery in human evolution.

Working in Ethiopia’s Afar region, Haile-Selassie’s team uncovered the 3.6 million-year-old partial skeleton of a male Australopithecus afarensis—the same species as the famous “Lucy”, but 400,000 years older and almost 2 feet taller. The skeleton, named “Kadanuumuu”, reveals surprising details about this human ancestor and sheds new light on human origins.

Until now, Lucy was the only partial Australopithecus afarensis skeleton known to science. Her short legs and small size led researchers to conclude that her species did not walk upright, but Kadanuumuu reveals otherwise. His bones suggest he walked upright much like we do, said the team.

The findings indicate that upright walking emerged much earlier in human evolution than was previously thought, said Haile-Selassie: “As a result of this discovery, we can now confidently say that ‘Lucy’ and her relatives were as proficient as ourselves walking on two legs. Human-like bipedality has deeper roots.”

Kadanuumuu’s shoulder bone was also remarkably similar to a human shoulder, showing that this feature has hardly changed in 3.6 million years or more, and suggesting, as Ardi’s skeleton did, that our earliest ancestors did not look like chimpanzees.

New Chapters in the Story of Life

The Komodo dragon is a carnivore, while its newly discovered cousin eats fruit. Photo by Kevin Flay

Nature is full of surprises. Last week, researchers working in the Philippines confirmed that a giant tree-dwelling monitor lizard is a newly discovered species, Varanus bitatawa—a cousin of the Komodo dragon. Quietly going about its business in the treetops, it has until now evaded the gaze of science.

If you’ve been reading Life or watching the show on the Discovery Channel, you know that the Komodo dragon is a meat-eater, feeding on carrion and subduing living prey with venomous bites. But the elusive 6.5-foot Varanus bitatawa, which lives in the isolated forests of the Sierra Madre mountain range, eats mostly fruit. In an interview with the Associated Press, Eric Pianka, co-author of Lizards: Windows to the Evolution of Diversity, called the lizard “a spectacular discovery”.

Meanwhile, scientists working in South Africa announced that a new hominid species, Australopithecus sediba, had been unearthed in a cave along with the bones of sabertoothed cats, mongooses, hyenas, and other animals. In Science Magazine, the authors reported that Au. sediba walked the earth almost 2 million years ago, and shares certain characteristics with the genus Homo. While scientists debate whether Au. sediba is a human ancestor or a separate branch that died out, its discovery adds a new piece to the puzzle of human evolution, as the discovery of Ardipithecus ramidus (“Ardi”) did last year.

The bones of Ardi, a female who lived 4.4 million years ago, were discovered in Ethiopia’s Middle Awash region by a 47-member team that included UC Press authors Giday WoldeGabriel and Yohannes Haile-Selassie, co-editors of Ardipithecus kadabba, Berhane Asfaw, co-editor of Homo Erectus, and Tim White, editor of the UC Press Middle Awash series. Her skeleton is the most complete fossil evidence of a hominid earlier than the Australopithecus “Lucy”, and helps fill in a gaping hole in human lineage.

Scientists have long thought of human evolution as a chain, and sought a “missing link” between apes and humans. But Ardi’s discovery changes the story, indicating that humans and apes may have evolved on entirely separate trajectories, from a shared ancestor that was neither human nor ape. The Middle Awash team published its findings in the October 2 issue of Science Magazine. In the video below, also from Science Magazine, Yohannes Haile-Selassie, Giday WoldeGabriel, Tim White, and Owen Lovejoy discuss Ardi and her implications for paleoanthropology.

The Middle Awash region of Ethiopia, and the South African site where Au. sediba was found, will likely yield more secrets to hominid evolution, and the newly classified monitor lizard may be only the first of many unique species to emerge from the Sierra Madre forests. One living, one long extinct, these species are two of the latest chapters in the ever-unfolding story of life on earth.