December 10, 1998
PHIL PONCE: The bones are old, about 3 ½ million years old. They were discovered recently by a team of scientists in a cave near Johannesburg, South Africa. Here to tell us about it and what it means about evolution is Richard Potts, director of the Human Origins program at the Smithsonian Museum of Natural History.
PHIL PONCE: Welcome, Mr. Potts. First of all, tell us, what exactly did the scientists find?
|An early human predecessor.|
| RICHARD POTTS, Smithsonian Institution: Well, they found a complete
or nearly complete skeleton of an early form of human predecessor, possibly
a direct ancestor of human beings, dating back to about 3 ½ million years
PHIL PONCE: And we're looking at a picture here from - that came out in the newspaper today. What is it we're looking at right now?
RICHARD POTTS: What we see there is the skull. From the side you can see toward the bottom the teeth - the lower jaw and the teeth - and then you can follow up on the left-hand side toward the eye socket and then the brain case just behind it. And so there's not only a fairly complete or what looks to be a complete skull but also a complete rest of the skeleton, the rest of the body. And that's extremely rare in the study of human evolution. Usually, we put together our understanding about human evolution from a fragment of bone here, a fragment of fossil bone over there. And now we have a complete individual, which is a spectacular find at this time range.
PHIL PONCE: So what kind of information can you get from a complete skeleton like this that you weren't able to get from the fragments you were talking about?
RICHARD POTTS: Well, for the kind of ancestor - potential ancestor we're talking about we usually can measure the size of the brain, the inside of the brain case from some bits and pieces of the fossil skull. We can measure something about the size of the body from an arm bone of one individual and a leg bone of another. Well, what we'll be able to do is to put together a picture of a whole body and its brain size of this creature relative to its body size from one single individual.
PHIL PONCE: And, again, earlier scientists have inferred that information from fragments. Now they have the entire skeleton. So this is a pretty big deal?
RICHARD POTTS: Yes. Exactly. I mean, if you could imagine taking the arm bone from Kareem Abdul-Jabar and a leg bone of Danny DeVito, you might think that you'd get a fairly distorted picture of what our skeleton looked like. Well, the same is true as you go back into the past. And so to have a complete one individual is very spectacular.
PHIL PONCE: You have some models here that further illustrate what it was the scientists found. What do you have?
RICHARD POTTS: That's right. Well, what we have here is an exact replica of Australopithecus. Now Australopithecus is the group of early humans that we're talking about that range from about 5 million years ago up to about 2 million years ago, and it's - this is a replica of the skull that comes from the exact same site but is a bit younger in age. This is about 2 ½ million years ago.
PHIL PONCE: This is very similar to the picture that we just saw.
RICHARD POTTS: Exactly. But you can see it has a small brain case. What we have here is a modern human skull for comparison. And you can see that the face was large in this early Australopithecus. The face - our face is quite small, relative to the size of the brain.
PHIL PONCE: Describe what the specimen that was found today - what it would - what people think it might have looked like. What are they inferring about its appearance?
RICHARD POTTS: Well, so far we know about Australopithecus that it walked upright on two legs, but it's a really amazing combination of features that we see in its skeleton. We see very long arms and short legs, suggesting -
PHIL PONCE: I'm looking at a picture right now.
RICHARD POTTS: Suggesting that it could climb trees. It could not only walk on the ground but also climb trees. Well, again, this inference has been made from bits and pieces of fossil here and there, and so we'll be able to tell more about how this early predecessor of human beings moved around in that way.
PHIL PONCE: And why is it so important to know how this predecessor moved around?
RICHARD POTTS: Well, the earliest hallmark of our evolutionary history is walking upright on two legs. There's one camp of researchers who claim that these early Australopithecus species moved on two legs just like we did. There's another camp that said, no, their station in life was mainly in the trees. And we've had this very heated debate for about 20 years, and hopefully, with fossils such as this we'll be able to test those ideas a little bit more carefully. And I think that what's going on here is that we have really this amalgam of a very --of an ancestor who's not really like an ape and not really like a human - exactly what you'd expect for this time range in human evolutionary history.
PHIL PONCE: So you have this new evidence which will give - which will give more information about bones. How can you tell from bones that something was capable of walking upright?
RICHARD POTTS: Well, for example, this, in fact, shows a thigh bone, the right side of the body, the thigh bone. And you can see from the part that sticks into the hip bone and from its shaft, and we also have other fossils that show the knee joint, that this was a creature that was largely, had a hip bone like ourselves and, therefore, designed for and evolved for walking around on two legs.
PHIL PONCE: So the shape of a bone either suggest that a creature walks or that a creature climbs.
RICHARD POTTS: Yes. That's -
PHIL PONCE: Rely on one's arms.
RICHARD POTTS: Exactly. And what we have here is something that's in between. We have hip bones and a pelvis and a foot that looks something like ourselves but arms that were very powerful, capable of climbing trees very easily.
|The "missing link"?|
PHIL PONCE: Okay. The big question - one of the big questions - is this the "missing link?"
RICHARD POTTS: The idea of a missing link is a bit outmoded, outdated. The idea of a missing link developed from when we thought that our family tree was just a line through time. Well, we now know that our family tree was extremely diverse, diverse just like it is in most other organisms that we know about.
PHIL PONCE: We have a sketch of a family tree that you brought with us.
RICHARD POTTS: Right.
PHIL PONCE: At the bottom we have that Australopithecus that you were talking about.
RICHARD POTTS: Exactly. And the one from South Africa is the one on the right, Australopithecus africanus, and the new find may belong to that species. We have Homo sapiens at the top. What we have there is 5 million years -- from the bottom to the top -- of human evolutionary history as scientists would now draw it.
PHIL PONCE: Well, Richard Potts, thank you very much.
RICHARD POTTS: My pleasure. Thanks.