Fossil Finger Points To New Human Relatives

Genetic analysis of mitochondrial DNA taken from a single prehistoric finger bone found in a Siberian cave may signal a new branch of the human family tree, separate from Neanderthals and modern humans. Anthropologist Ian Tattersall discusses the significance of the find.

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In 2008, researchers excavating in a cave in Siberia found a tiny, human finger bone, and they probably think it's probably a child's pinkie, about 40,000 -40,000 years old.

And writing this week in the journal Nature, a team of researchers reports that it's analyzed the DNA found in the finger, and they analyzed the mitochondrial DNA, that's the kind that can trace maternal relationships through the years. And what they found, really, was a surprise. They found that the finger bone, the DNA in it, indicates that the ancestors of that hominid did not come out of African with Homo erectus, the predecessors of modern humans; and also, it didn't come from Neanderthals.

In fact, the DNA evidence suggests that this hominid may represent a whole separate branch of the human family tree. And joining me now to talk about it, help put this find in context, is Ian Tattersall. He is curator of anthropology at the American Museum of Natural History in New York, and author of several books, including "The Fossil Trail: How We Know What We Think We Know About Human Evolution." Welcome back to SCIENCE FRIDAY, Dr. Tattersall.

Dr. IAN TATTERSALL (Curator of Anthropology, American Museum of Natural History; Author, "The Fossil Trail: How We Know What We Think We Know About Human Evolution"): Thank you.

FLATOW: How significant is this finding? Give us a perspective on what it does.

Dr. TATTERSALL: Well, this really a wonderful find, although I think what I describe it as is more unexpected than as being really surprising.

FLATOW: Okay.

Dr. TATTERSALL: Unexpected because this - it comes from Siberia, southern Siberia, which is a part of the world that's very poorly known from the point of view of archeology and the search for early hominids - but not really surprising, because we already know that there were multiple lineages of hominids living in various parts of the old world during the ice ages, when this was found.

FLATOW: And so what does this do? Does it say that there might have been lots of different human-like species living at the same time in different parts of the world?

Dr. TATTERSALL: It does indeed. It reinforces the very strong signal we've been getting from the fossil record that the evolutionary history of humans has been sort of one of experimentation, of producing multiple species that succeeded or failed in the ecological arena, rather than a single, slow progression from primitiveness to perfection.

FLATOW: And so what we're saying here, if I hear you correctly, and what the article is saying is that whatever group this hominid of hominid that this finger belongs to seems to have migrated out of Africa at a different time than Homo erectus or Neanderthal.

Dr. TATTERSALL: Yeah, I think that is certainly the implication of the age that they've derived for the split-point between this hominid and the one that led to us.

FLATOW: And the fact that it was living in Siberia, does that mean it had to really put up with some terribly cold weather?

Dr. TATTERSALL: Well, it did. I mean, it was living not that long before the peak of the last ice age, and it would have been, you know, a fairly marginal environment for any hominids; although our own ancestors, by about 20,000 years ago, when the environment was coldest, had actually got all the way up to the Arctic Circle.

FLATOW: 1-800-989-8255 is our number. You can also send us a tweet @scifri, that's @-S-C-I-F-R-I. Is that really, is one bone enough to change our views and say there's possibly a new species, or do we have to wait for a few more bones to be discovered?

Dr. TATTERSALL: Well, I think the signal that they're getting from the genome, the mitochondrial genome of this individual, seems to be pretty clear. Whether it's a new species that we don't know about is another question because we only have genomes from Neanderthals and from ourselves, modern Homo sapiens.

We don't have them yet from any other hominid that we know, but we do know a lot of fossil hominids. So it's possible that this finger bone, which is not really by itself diagnostic to any particular species, might actually belong to a species or at least a group that we already know in the fossil record.

FLATOW: Oh, because we have no other DNA to compare it to?

Dr. TATTERSALL: That's exactly right, yes.

FLATOW: Is it possible to get more DNA from other species that we're looking to compare it to?

Dr. TATTERSALL: Well, we're certainly hoping that it is, and that as technology advances, it will be possible. Right now, we're only able to get DNA, and then only occasionally, from specimens that are up to about the age of this individual - that lived either at high latitudes, where it was cold, and preservation is best, or at high altitudes, where it's also cold.

So we're a bit limited, because the human story, obviously, originated in Africa, and their climates are much warmer.

FLATOW: But it is possible that we did have the same ancestry as this...?

Dr. TATTERSALL: Yes, indeed. We clearly have an ancestry in common with all other hominids at some point in time. And they're extrapolating, from the differences in the DNA, that in this case, the common ancestor probably lived about a million years ago.

FLATOW: And where then you partially answered that question, but I'm going to ask it anyhow. Where, then, would this fit in with some of our other recent discoveries, particularly such as Ardi, the big thing that happened recently?

Dr. TATTERSALL: Yeah, Ardipithecus, of course, is the subject of great debate, and whatever it is, it seems to be really sort of an outlier in human evolution. And of course, it's four million years old and represents a very early stage in the history of the human family.

This specimen, being only about 40,000 years old, plus or minus, represents a much more recent relative of ours, and it's very it's very tantalizing because it's distinct from Homo sapiens, and yet, clearly, it's not in the region today.

The same thing happened in Europe where the Neanderthals, Homo sapiens comes in right around that time, 40,000 years ago, and pretty soon, the Neanderthals are gone. And the same thing happening also in Eastern Asia with Homo erectus that had been there for a long, long time - last date is around 40,000 years ago -and after that, only Homo sapiens. So there's a sort of a pattern developing here.

FLATOW: Well, who's to say that there couldn't be another half-dozen out there?

Dr. TATTERSALL: Nobody. Nobody. I think, quite possibly, there were several other branches out there. And the fossil record that we have, whether we diagnose it through DNA or whether we can diagnose it through what the actual fossils look like, is always going to be incomplete.

FLATOW: And as you say, though, that the best-preserved DNA species would be ones that are in the high altitudes or in the colder climates.

Dr. TATTERSALL: That's right, that's right.

FLATOW: And that makes discovery a little more difficult, I would think.

Dr. TATTERSALL: Yes, it does. It does. We can always hope there's some undiscovered cave near the summit of Kilimanjaro.

(Soundbite of laughter)

Dr. TATTERSALL: But it's unlikely to happen.

FLATOW: And how was this cave discovered? Why was it discovered?

Dr. TATTERSALL: It's been known for some time, you know, apparently to archeologists, but it hasn't really been investigated very closely until recently.

You know, Siberia is a vast area, and it's very, very poorly populated. So whereas we know lots of sites from Europe that fielded Neanderthals and early modern humans and so on, because there's a lot of people around looking.

FLATOW: It reminds me, you know, of finding all these dinosaur bones in Mongolia, right? It's very sparsely populated - you can find these things.

Dr. TATTERSALL: Well, that's right, but you can find these dinosaur bones and so forth really on the basis of the geology - once the geology is mapped. A cave like the Denisova cave that we have here, is kind of unpredictable. Caves occur in a much less predictable way, especially outside a limestone area like this one.

FLATOW: And as far as this discovery is concerned, in order for you or other anthropologists to say this is a new species, what would it take?

Dr. TATTERSALL: Oh, well, I would really want to have, ideally, a, you know, a skeleton. A complete skeleton would be the obviously wonderful thing to have. How much genetic difference you need to diagnose a species is something that really hasn't been agreed upon, certainly in hominids, yet. And so I think the people who made this discovery are very wise to be a little bit circumspect about what they have.

FLATOW: I would imagine more people are looking in more caves in Siberia.

Dr. TATTERSALL: Oh, I can imagine so, and I hope so very much, because, you know, if there is one place like this, there will be others. And there's clearly a story here to be discovered.

FLATOW: And thank you for taking time to tell us about it, Dr. Tattersall.

Dr. TATTERSALL: Oh, it's my pleasure.

FLATOW: Ian Tattersall is a curator of anthropology at the famous American Museum of Natural History in New York and author of several books, including "The Fossil Trail: How We Know What We Know About Human Evolution."

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