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Out of Africa: Human Fossil Discoveries

June 13, 2003 at 12:00 AM EDT


RAY SUAREZ: A rare find of fossils in Africa may be the key to finding the origins of modern man. Archaeologists found three human skulls in 1997 in the Ethiopian village of Herto, about 150 miles northeast of Addis Ababa. It took six years of excavating, cleaning and testing before scientists dated the skulls of two adults and a child at about 160,000 years old. The child’s skull alone was pieced together from more than 200 scattered fragments of the cranium. Researchers have long sought to better understand a time gap between 100,000 and 300,000 years ago of the evolution toward modern humans began. By examining the structure of the skulls, researchers determined these African ancestors were the bridge between pre-humans and modern Homosapians. The new findings, they say, add strong evidence to the theory that modern humans first evolved from Africa and migrated across the world.

We get more findings now. It comes from the leader of the team that discovered the skulls, Tim White. He’s a paleoanthropologist at the University of California in Berkeley.

Professor White, help us understand what this fills in about the picture of how we got to be who we are.

PROFESSOR TIM WHITE: Well, Ray, this is a problem that people have been working on for more than a century and a half. Where did anatomically modern people come from? There have been finds in Europe stretching back into the past, but they involve an ancestor called Neanderthal, an ancestor only of Neanderthal. These are creatures that these new finds in Ethiopia show to be a side branch. In Ethiopia, in eastern Ethiopia, in the low lands, we have evidence now that anatomically modern people just like ourselves were living there 160,000 years ago.

RAY SUAREZ: How is the dating done that leaves you so confident of that 160,000 year date?

PROFESSOR TIM WHITE: Well, what we do in this desert region is we reap the harvest of geology. There are three major rift valleys that come together out there in eastern Ethiopia and this sets up a tectonic setting so you have lakes and rivers stretching back into the past along the shores of which we have a lot of remains of animals, stone tools left by humans, and sometimes human ancestors themselves. They’re surrounded in this environment by these tectonic forces and they’re associated with volcanism, large volcanoes that blanketed the landscape with volcanic ash. By using these volcanic ash horizons, we can sandwich the fossils in time. We can date ones above and ones below. And this cranium from Herto, Ethiopia, was dated by the volcanic ash above it which is 154,000 years.

RAY SUAREZ: And when we look at that skull and what you’ve been able to reassemble of it, what makes it distinctly different from things that we know are older and what makes it man-like — close to modern human?

PROFESSOR TIM WHITE: Well, when we look at the face of a modern human being, we’re struck by the fact that the face is quite small compared to earlier forms that we found in Africa. We find that the structure here of the cheekbone is very different, not only different from earlier ancestors in Africa but also different from these creatures known as Neanderthals. The new fossil from Ethiopia and this is just a replica here == this fossil shows a face that is very modern in its conformation and distinct from the fish face that we see in this Neanderthal fossil from Europe. And yet this modern anatomy predates the demise of the European Neanderthals by many, many millennium. And so that’s why we are saying it is very similar to this anatomically human cranium, although there are a few differences, it is already close enough to anatomically modern humans to place into our own species, Homosapians and thereby represent the earliest evidence of our species.

RAY SUAREZ: I know you paleoanthropologists deduce a lot from what you can find. In this skulls were found and some teeth. Can you figure out from that how tall, how big this person was, what they ate, the kind of place where they live?

PROFESSOR TIM WHITE: Those are great questions. You know, for the last 20 years, genetic data have been compiling that point the way to Africa as the source of all anatomically modern humans but these genes can only tell us about relationships. They can’t tell us what the people look like. For that we need anatomically evidence. And that’s why it is exciting to get a cranium like this so intact. And also in the same horizon, the same geological layer, we have artifactual remains, the tools made and use by these people to butcher mammals like hippopotamus. So we have the whole package here, the dating, the anatomy and some of the behaviors that open up this window on the past.

RAY SUAREZ: Was it a wet place, a swampy place, a forested place? Do we know much about Ethiopia 160,000 years ago?

PROFESSOR TIM WHITE: Well, we haven’t known anything about Africa at 160,000 years ago. Ethiopia now has provided this first window into this critically important part of the human evolutionary story. By getting in and getting this basic knowledge of what the world was like there at 160,000 years ago, we can finally make comparisons with what it was like in Europe. And in Europe, you have at 160,000, a thick blanket, a continental ice sheet. And on the southern end of the ice sheet, we have the Neanderthals, these uniquely structured hominids that now are shown to be not ancestral, rather the African populations of Homosapians ancestral to ourselves, replacing these European Neanderthals. The final ones went extinct at 130,000 years ago.

RAY SUAREZ: Professor, I’m sure you know there are people who say that Neanderthals are part of the human family and that this find doesn’t necessarily change what we know about the human family tree. What closes the sale for you?

PROFESSOR TIM WHITE: I think it’s the combination of overwhelming genetic data showing the very shallow roots of anatomically modern people. And we have not only that, now have a very good fossil record in Africa. Remember, you’re looking here at the face of a virtually anatomically modern human that’s 160,000 years old and very distinct from these specialized European forms that were replaced by people that look very much like your or I. So we have very strong fossil evidence now from Africa where previously we’ve only had that good European record.

RAY SUAREZ: Quickly, are you heading back to Ethiopia to look for more?

PROFESSOR TIM WHITE: Yes. The National Science Foundation supports this work. And it is a large international team involving 14 countries. We go out every autumn and in a collective effort, we are trying to push a little deeper into the past. We’d like to know exactly what the ancestor of this individual looked like and we’ll do that in deposits we’ve already identified at around a quarter of a million years ago.

RAY SUAREZ: Professor White, good luck to your next trip and thanks for being with us.