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‘Mind-boggling’ skull discovery offers researchers a view into the ancient past

October 18, 2013 at 12:00 AM EST
The discovery of a 1.8 million-year-old skull at Dmanisi in Georgia has revolutionized scientists' idea of human evolution. Paleoanthropologist Donald Johanson of the Institute of Human Origins at Arizona State University joins Jeffrey Brown to discuss what these ancient remains teach us about our ancestors and origins.
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JEFFREY BROWN: One of those scientists joins me now. Donald Johanson is professor of human evolution and social change and founding director of the Institute of Human Origins at Arizona State University. In 1974, during an anthropological dig in Ethiopia, he discovered the 3.2 million-year-old hominid skeleton popularly known as Lucy.

Well, welcome to you.

So, part of what makes this so exciting and unusual is just having a complete skull from that period, right?

DONALD JOHANSON, Arizona State University: Well, I think it’s absolutely mind-boggling.

 The preservation of this specimen from Georgia is extraordinary. It looks like something that you would find in a dissection room. It’s so complete. It’s got the lower jaw, the entire face, the complete brain case. It’s a view into the past into what our earliest ancestors in our own genus, Homo, looked like that none of us had anticipated.

JEFFREY BROWN: And then there’s the grouping of these remains at the site. Now, explain to us why this is important.

DONALD JOHANSON: Well, at the site of Dmanisi, which is just about 20 kilometers north of Armenia in Georgia, there is a single geological layer, almost a snapshot in geological time, of a collection of bones, including five skulls. The most recent one announced, of course, is skull five, but also limb bones of the arms and legs and associated animal bones.

And we know from the geological studies that this stratum samples a very, very thin period of time, maybe just over a few years. It was about 1.8 million years ago when probably saber-toothed cats killed and fed upon these early humans and dragged these skeletons into the cave, where they were preserved, they didn’t see light until 1.8 million years later.

JEFFREY BROWN: All right, so that grisly past gives us some interesting clues to what might have happened, though.

So, to try to explain this in layman terms why this all interesting for the history of evolution, the thinking has been that there were various species, right, that some died out, some kept going through to our own, but that this at least raises the possibility that they were all part of one species?

DONALD JOHANSON: Well, I think it’s a little bit premature to include all of the specimens of our human genus, Homo, that have been found in Africa, that have been found in Asia, and now in Dmanisi, together in a single species.

I think that the level of variation that we look at, the differences in the shape of the skull, and the face and the teeth and the jaws and so on, exceeds the definition of a single species. And, in Africa, it appears that we have several different species.

So, this is not unusual for the evolution of a mammalian groups. All mammals undergo a certain degree of diversification. Darwin knew that. When he drew a family tree, it had many branches on it. This is one of those branches, but I think what we see in the variation in the African fossils is the presence of several different species.

JEFFREY BROWN: What is that the researchers at Dmanisi, at this site, what they saying that they see that suggests something a little more linear to them?

DONALD JOHANSON: Well, they see a clear connection, as we all do, between the Dmanisi fossils themselves in the shape of the face and the teeth and the jaws with fossils in Africa that reach back over two million years.

So I think they see a lineage of Homo coming out of Africa. But I think there were other experiments in Africa that didn’t give rise to anything, that actually were extinct side branches. So what they see really is a direct connection between their fossils and a form or a species in Eastern Africa known as Homo ergaster, which means really the workman.

And that was a species that we know goes back over two million years and probably was the progenitor for that lineage to that led out of Africa and is being picked up now in places like Dmanisi.

JEFFREY BROWN: And is it — this Dmanisi site, is it strange that a discovery — this discovery was made in what’s now Georgia on the Eurasian continent, rather than in Africa? Does it — what does it tell us about early ancestors, and does it change anything in our thinking about origins in Africa? DONALD JOHANSON: Well, I think almost every time we hear about a new discovery of a human ancestor, it points to Africa.

But here is a totally unanticipated place, between the Caspian Sea and the Black Sea, where hardly anybody ever thought of looking, except these Georgian scientists who were working there, and came up — have come up with discoveries that really revolutionize our ideas of when and why our ancestors left Africa.

We used to think that we only got out of Africa maybe 500,000, maybe a million years ago. These are 1.8 million years old. We used to think that we didn’t get out of Africa until we had controlled fire, that we had sophisticated technology. There’s no evidence for fire at this site. They had very rudimentary, simple flake stone tools.

This was man the explorer. This was part of what it means to be human, I think, that we are inquisitive, searching animals, and we are interested in knowing what’s beyond the next mountain, what’s around the next sand dune or whatever. And this is the first exploration of our genus outside of Africa, and that’s pretty mind-blowing.

JEFFREY BROWN: And just briefly, just to — can you tell us what this creature, whatever it was, this skull, what would it have looked like and what would it have done?

DONALD JOHANSON: Well, I think that that’s part of the importance of having a series of five skulls.

We know, for example, that there was differences — it was a significant difference in size. Males were much larger, more heavily built with thick browridges across the tops of their orbits, very heavy muscle insertions, probably around five-and-a-half, maybe six feet in stature, females someone shorter, much more lightly built, creatures that still had relatively small brains, but much bigger than the ape man fossils that we study in Africa, we call this tongue twister Australopithecus.

But this was an advancement in evolutionary change. This was a time where we were undergoing a major transition from these more apelike creatures to more humanlike creatures. And the few features we see, like an increase in brain size, are very significant, because it means that these are creatures that were much more intelligent, that had a degree of inquisitiveness and ability that we have not anticipated.

JEFFREY BROWN: OK, a very exciting discovery, and much more work to come.

Donald Johanson at Arizona State University, thanks so much.

DONALD JOHANSON: Thank you.