IRA FLATOW, host:
This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow. Later in the hour, we'll be talking with Lester Brown. But first, you've heard of Lucy. Now meet Ardi -Ardipithecus ramidus, or Ardi for short. Scientists revealed this week fossils of a skeleton that predates the well-known human ancestor Lucy by over a million years. The fossil has some features of modern humans, some features of modern apes, and some features that aren't present at all today.
Joining me now to talk about the find and how it fits into the overall picture of human evolution is Ian Tattersall. He's curator of anthropology at the American Museum of Natural History in New York, author of several books, including "The Fossil Trail: How We Know What We Think We Know About Human Evolution," published last year by Oxford University Press. Welcome back to SCIENCE FRIDAY.
Dr. IAN TATTERSALL (Anthropologist; Curator, American Museum of Natural History; Author): Thank you.
FLATOW: Tell us about this new find. What are the main features of the fossil that have made scientists so excited?
Dr. TATTERSALL: Well, everybody is indeed very excited about this. It's a discovery that's been rumored for many years, but we - this is the first time we have any substantive information about it. And it's quite different from any other early hominid that's ever been described.
FLATOW: In what ways?
Dr. TATTERSALL: Well, the earliest human skeleton or early hominid skeleton that we've had up to now has been the skeleton of Lucy, as you pointed out in your introduction. And Lucy is the 3.2-million-year-old member of a species called Australopithecus afarensis. And she is already a committed biped on the ground. That is to say her skeleton has evidence of an arboreal ancestry, and she certainly spent a lot of time in the trees. But definitely when she came to the ground, she walked upright.
This new skeleton, something like a million years older than Lucy or a bit more, doesn't have all those hallmarks of bipedalism that you might expect to find in an immediate ancestor of Lucy. In fact, some people are even suggesting there's not much evidence for bipedality at all, although the describers are suggesting this.
FLATOW: Is this the - you know, they're always looking for - I hate to say -the missing link. Scientists believe that humans did not descend from apes, but that apes and humans have a common ancestry. Could this be that fossil?
Dr. TATTERSALL: Well, the problem is that, of course, if it's a link, it's not missing. And if it's missing, it's not a link.
(Soundbite of laughter)
Dr. TATTERSALL: So that anything you actually know about actually forms part of a real chain. This was certainly not something that you would have looked for as the intermediary between Lucy and what we would have thought her immediate ancestor to look like.
FLATOW: Uh-huh. What's interesting from the accounts I've been reading about the fossil is an interesting aspect are the hands that this fossil had. They look more human than they thought they should, correct?
Dr. TATTERSALL: Well, the hands themselves look like those of a palmigrade quadruped in the trees, obviously with a grasping hand. Our hand is a grasping hand, clearly, and we share with this fossil a thumb that's adducted from the other digits. And so yes, indeed, we have that. But, of course, apes have that, too. Apes have a grasping hand with an adducted thumb. And so that is obviously a characteristic that goes back much further in time than the ape-human ancestor.
FLATOW: So where do they go from here? And why was it - let me first ask why it took 15 years. Why was this skeleton in the closet for 15 years, because it was discovered, what, in 1993, something like that?
Dr. TATTERSALL: Yeah. It was discovered back in the 1990s, but it was an incredible find in the first place, in a very difficult part of the world where it's difficult to operate. And the condition of the bones as they came out of the ground, as they came out of the rocks they were enclosed in, was extremely delicate.
They had to go through a very, very complex process in the field of hardening up the bones so they could take them out of the rock, so they didn't crumble as they were being removed. And then they had to be transported to a lab and then very painstakingly removed from the matrix in which they were. And then it turns out that the specimen itself had probably been trampled by a large animal before it was fossilized, and so it had to be reconstructed as it would have been before it had been distorted in this way. So it was a very long and drawn-out and complicated process.
FLATOW: And what size would it compare to Lucy?
Dr. TATTERSALL: Well, it would have been about, I think, the same size as Lucy. I think they have an estimate of about four feet high for the individual for whom the - from whom the skeleton came. And so that would actually have made her a bit taller than Lucy.
FLATOW: Mm-hmm. And so where do they go from here? Is this a site that you can now concentrate on and focus to find more of these skeletons?
Dr. TATTERSALL: Well, this particular find is part of one of the most extraordinary fossil-producing areas in the world that has produced fossils from virtually every major time period of human evolution.
This was an extraordinary, unexpected find. To think that you might duplicate this is maybe to expect a little bit too much, but they'll certainly be going back to look for more.
FLATOW: And where does that put us now, textbook-wise, about what we know about the human tree here and our descent?
Dr. TATTERSALL: Well, what it indicates to me, certainly, is that here we have another very early hominid - it doesn't look quite like anything else that we know about - in this period between about three million years ago and six million years ago, in which there really is not very much record of what was going on in human evolution.
But already, we find - you put this specimen together or this new taxon, Ardipithecus together with other forms known in this time period from Kenya and from Chad, over in central-western Africa, and you see there was an enormous variety of early hominids around at this time. And this makes the early years of hominid evolution much like the later areas of hominid evolution, which are much better documented, in which there's a huge diversity of hominids out there. And it's very unusual for us to be the only member of our family in the world.
FLATOW: You mean they were all living at the same time?
Dr. TATTERSALL: Yeah, they were all living at about the same time - in this early time period, anyway. I mean, it's very badly sampled, this time period. But what we have from the small sample in there indicates a great diversity. And that has been - is now becoming ever more evident that this is characteristic of our family the whole way through. We're not the offshoot of a single, gradually modifying lineage that was eventually perfected in ourselves, if you were.
FLATOW: So, in other words, no direct line someplace, lots of shoots that we came out of.
Dr. TATTERSALL: That's right. Obviously, we have a direct ancestry that connects us to the very bottom of the tree, but the tree itself is extremely bushy.
FLATOW: So where do we go from here? Where do anthropologists - what do they do now after 15 years and this great find?
Dr. TATTERSALL: Right. Well, anthropologists now are going to have to really rethink what their expectations of the very earliest hominids were like. Many people have thought that since our closest relative in nature today is reckoned to be the chimpanzee, largely because Darwin predicted that an African ape would have been our progenitor and because the molecular record shows pretty well that we're most genetically similar to a chimpanzee, the expectation therefore had been that you had, as you went back in time, the chimpanzee lineages and the human lineages would sort of converge on each other and that very early hominids would in some way resemble - in a limited way, at least -resemble chimpanzees.
FLATOW: And this fossil does away with that idea.
Dr. TATTERSALL: Absolutely. I think it absolutely knocks that one out of consideration.
FLATOW: So what would be, then, the best candidate?
Dr. TATTERSALL: Well, right now, with - the missing link, of course. You know, this is - we're back to something that we don't know of that doesn't currently exist, in not currently known.
FLATOW: Wow. So we're waiting to find that ancestor that's common to all of us.
Dr. TATTERSALL: We're still waiting to find that.
FLATOW: Dr. Tattersall, thank you for taking time to be with us.
Dr. TATTERSALL: My pleasure.
FLATOW: Ian Tattersall is curator of anthropology at the American Museum of Natural History in New York and author of "The Fossil Trail: How We Know What We Think We Know About Human Evolution." Transcript provided by NPR, Copyright NPR.