News

New Information On Our Bipedal Ancestors

Aired July 20, 2001

Last week in the journal Nature, paleontologists working in Ethiopia announced the discovery of some new human fossils that push back the date for the origin of our species to nearly six million years ago. The finds also show that walking upright - a trait researchers have long used to distinguish humans from other primates - is as old as humankind itself. 90.3 WCPN®'s Karen Schaefer reports.

Karen Schaefer–In 1997, a young Ethiopian graduate student at the University of California Berkley found a piece of a jawbone in the Afar region of Ethiopia. That's the same area where twenty years before a young member of another research team - Donald Johanson - found the nearly complete skeleton that later became known as Lucy. At 3.2 million years, Lucy was the oldest hominid - or human ancestor - yet found. Since then other hominid fossil remains have been dated to about 4-million years. But this latest discovery - including a diagnostic toe bone - shows that upright-walking human ancestors date back far longer. This week's cover story in Time Magazine details the finds, dated at between 5.2 and 5.8 million years. In the article, Dr. Owen Lovejoy, a paleontologist at Kent State University and one of the world's foremost experts on bipedalism - or upright walking - confirms the findings. Lovejoy - who co-authored the original report on Lucy - says the new fossils show that hominids were walking upright in Africa nearly six million years ago.

Owen Lovejoy–This is one of the most significant finds in the past three or four decades. We have material that probably takes us back to the point in time where - well, we're going to get to a point very soon now, with this kind of time depth, where when you find something you will never know whether you're looking at the ancestor of a hominid or the ancestor of a human.

KS–These latest fossils are not the first discoveries of a new hominid species now called ardepithecus ramidus kadabba, a name derived from the local Afar language. But both Lovejoy and the fossils' discoverer, Johannes Haile-Sellasie, believe that the new ardepithecus finds take our understanding of human evolution much closer to the time when human and ape species diverged. And that's not all.

OL–When we look at the environmental conditions of these animals, the things we call ardepithecus, we've found that it's essentially forest or forest edge. So we have very early hominids and we have a toe bone from one of these things that is pretty distinctive in telling us that it's habitually upright. We don't know to what degree it was adapted to walking upright, but we know that it habitually did so.

KS–For decades, researchers have tried to define what makes us distinctly human. An opposable thumb, a large brain and the development of speech have all been characterized as important steps on our evolutionary path. But in the fossil record, it's clear that walking upright preceded all these other adaptations. Most theories have assumed that a changing climate dried up the forests where primates evolved and brought human ancestors down from the trees and onto the savannahs. But these ardepithecus hominids - walking upright - lived in a forest, not an open grassland. Lovejoy believes that fact overturns existing theories on why we evolved the bipedal adaptation.

OL–If we look at ourselves as the product of biological evolution - which we are - we've evolved a brain size that three times the size of that of a chimpanzee, we've evolved articulate speech. All of these things are produced by biological selection. No, we didn't become bipedal to pick fruit off trees or to see over tall grass. We became bipedal as part of a very complex evolutionary, ecological adaptation.

KS–Lovejoy believes the essence of what makes us human may have been defined at the very moment when apes and humans started on their separate evolutionary paths.

OL–Bipedality now, we know from Johannes' find, goes all the way back to the beginning. This toe, associated with a canine tooth that's clearly of a hominid, tells us interestingly enough, that the two things that appeared to define early hominids in the specimens that have come from around 4 million now go all the way back to the origin of the separation of hominids from pongids.

KS–But the story won't end there. While the scientific community debates the meaning of these latest finds, another discovery announced earlier this year by a team of French paleontologists working in Kenya may push human origins back even further. Lovejoy believes that the 6-million-year-old remains of a similar - but so far, apparently different - hominid species, may eventually be grouped with ardepithecus. And that would bring our understanding of human evolution to almost the beginnings of humankind. In Kent, Karen Schaefer, 90.3 WCPN® News.