This month, the scientific world was rocked by the news that researchers working in Ethiopia have found one of the 'missing links' in the chain of human evolution. The 4.2-million-year-old fossil helps explain how human ancestors made the giant leap from one species to another. That's because this newest fossil was found in the same region where other human-like species spanning nearly six million years have been discovered. ideastream's Karen Schaefer spoke with Dr. Yohannes Haile-Selassie, curator of physical anthropology at the Cleveland Museum of Natural History and one of the co-authors of the recent report on the find in the journal Nature.
Listen to the Extended Version.
Dr. Yohannes Haile-Selassie isn't the only Ohio scientist who's been involved in this latest discovery about human evolution. But he may be one of the best-known outside of purely scientific circles. Haile-Selassie is curator of physical anthropology at the Cleveland Museum of Natural History. He's also an active fossil-hunter who made his first discoveries of human ancestors in Africa while he was still a graduate student. Since 1989, he's been returning every year to his native Ethiopia to the Awash River in East Africa's great Rift Valley, sometimes called the 'cradle of mankind' and home to most of the world's greatest discoveries of early human fossils.
Yohannes Haile-Selassie: The Rift Valley is very attractive because almost all the water that comes down from the highlands goes to the lowlands. And water by itself attracts life. That's where vegetation grows, where trees grow and animals have to drink water to survive, so they all congregate in these water systems and they live there and they die there.
Haile-Selassie says the fossil record shows animals have been living and dying in the Awash region for six million years. Among those animals are hominids whose only living examples are human beings. But Haile-Selassie says it hasn't always been easy to tell which fossils belong to our direct ancestors and which ones were distant cousins that became extinct, a kind of evolutionary dead-end.
Yohannes Haile-Selassie: We had so many missing evidence from different time periods and whenever we go back and find new fossils we are filling up this lacking fossil evidence.
Last December an international team of scientists discovered new fossils they believe fill a critical gap in the evolutionary record. The new specimens - about 4.2-million years old - are from the same group of hominids that includes the famous Lucy skeleton, but are much older and more primitive. Haile-Selassie says there is now good evidence to show that Lucy and her relatives were the direct descendants of these older hominids. And he says the new fossils strengthen the argument that that group evolved directly from an even older group of ape-like creatures, small of brain and large of tooth, but who nonetheless - like us - walked upright.
Yohannes Haile-Selassie: When we look at the entire time span... we're looking at at least 4.8 million years of history before even the emergence of our genus homo.
The genus homo, which includes our modern human species, homo sapiens, emerged about a million years ago. Along with other fossils previously discovered in the Awash region, researchers say they now have a nearly uninterrupted picture of human evolution over the past six million years. But Haile-Selassie says there are still gaps to be filled, among them finding a common ancestor for the species that led to both modern humans and our closest cousins - chimpanzees.
Yohannes Haile-Selassie: Whenever we find fossils and answer a question, there will always be another new question arising from... the question that we answered. And that's what keeps us interested in going back to the middle of nowhere and finding more fossils.
Yohannes Haile-Selassie will be going back to the middle Awash region of Ethiopia this summer. He hopes to find more fossils that will further clarify our understanding of how humans evolved. Karen Schaefer, 90.3.