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Hobbit's Big Feet Offer Clues To Its Origin

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Hobbit's Big Feet Offer Clues To Its Origin

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Hobbit's Big Feet Offer Clues To Its Origin

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You're listening to SCIENCE FRIDAY. I'm Ira Flatow. Now for the latest chapter in the continuing story of the mysterious hobbit bones of Indonesia.

Let me recap for you where we are now. Let's go back to the beginning. In 2003, an international team of scientists was digging on a remote island in Indonesia and unearthed something mysterious. It's a tiny, hominid skeleton that didn't look exactly like a human or our ancestors or anything else.

Scientists who discovered the fossils claim that they represented a whole new ancient species never seen before. Well, the critics said not so fast. They could be bones from diseased pygmies, and they're not really anything to get that excited about. They're really humans, but they're pygmies who would have a disease that makes their heads a little smaller.

But evidence that these fossils are, indeed, a new species in our genus has mounted over the last few years, and the latest research published this week in the journal Nature focuses on the so-called hobbit's feet. These feet happened to be remarkably large, and many paleontologists got a chance to see the bones - the feet bones, foot bones, up close and personal. Last week, they got to see them when they were shown to public for, really, for the first time.

Did that change anybody's mind? Well, here to talk about it are my guests: William Jungers, who's chairman of the Department of Anatomical Science at Stony Brook University Medical Center. He is the author of one of the papers this week, and he joins us by phone from Chicago. Welcome to SCIENCE FRIDAY.

Dr. WILLIAM JUNGERS (Chairman, Department of Anatomical Sciences, Stony Brook University Medical Center): Thank you for having me.

FLATOW: You're welcome. Daniel Lieberman is a biological anthropologist at Harvard. He is the author of another Nature article, commenting on the research, and he joins us by phone from his office there. Welcome to SCIENCE FRIDAY, Dr. Lieberman.

Dr. DANIEL E. LIEBERMAN (Department of Anthropology, Harvard University): I'm delighted to be here.

FLATOW: Bill, tell us about these foot bones. Why are they so important?

Dr. JUNGERS: I think the foot bones are a window into the past, even though they're only 17,000 years old. I think they give us a glimpse into what the primitive, ancestral morphology of the first foot of our own genus homo probably looked like.

So in that sense, they're unexpected and they're exciting, and they also reveal a foot that really isn't modern in aspect. It's a foot of a biped, a perfectly efficient biped in terms of walking, but it lacks some of the design features that we associate with our own foot, and actually some of those features have been spelled out very nicely by Dr. Lieberman.

FLATOW: Dr. Lieberman, tell us about the features.

Dr. LIEBERMAN: Well, it's - I have to say, it's a jaw-dropping foot. When I first saw the paper, I actually ended up writing wow in the margin of the PDF because I was astonished. So it's like a human foot in a bunch of ways. It's got very robust toe bones. They're called the metatarsals. They're the bones sort of in the middle of your foot before the individual toes start spreading out. And it's got sort of an ankle joint that would've been clearly very good at the kinds of movements that a human has, and it's got a little locking mechanism in the middle of the foot so when we pick our heel off the ground when we're walking, it keeps the middle of our foot rigid.

So all that looks like what you expect to find in a biped. But what I was so astonished by was this one bone in particular that, for me, sold it, and it's called the navicular, and it's a little bone on the top of the inside of your arch. It's like the keystone of the arch of your foot. And in humans, it's a tiny little bone, and it never touches the ground unless you're flat-footed.

But in this critter, you know, just looking at the photo, you could see it has this great, big, huge tuberosity, this big, large process, essentially, on the navicular, which you find in chimpanzees. And that's indicative of that - that this bone was actually in contact with the ground. And that means that it didn't have the kind of arch that you and I had. So…

Dr. JUNGERS: That's the flat-footed part, yeah.

Dr. LIEBERMAN: Yeah, so it still could've walked, but it probably wouldn't have been so good at running. And it's got - so it's like our feet in some ways, but it's unlike our feet in other ways. And as Bill Jungers mentioned, it's like a window into the past because we don't have any really good feet from early on.

So this is actually our best view of what an early hominid foot looks like, before they became completely modern.

FLATOW: So was this the clincher for you about this being a new species?

Dr. LIEBERMAN: I wouldn't say it was the clincher, but it was one of a whole series of pieces of evidence that I was waiting for and looking for to make -to seal the deal for me.

So this is one of them. The wrist, which was published last year in other paper, and another paper that really kind of for me was very influential - two other papers - was the one on scaling and hippos, which is also in this issue in Nature, and also a very nice paper by Baab and McNulty, which is in a new version of - new edition of Journal of Human Evolution, which is a very careful scaling analysis, and asked the question if you took a homo erectus skull - or a homo habilis skull - and you scaled it down, you correct it for - you know, if you made it smaller, but you observed all the relationships between size and shape, what would be the shape of that skull?

And they find that this floresiensis skull falls right it should be. It looks like a very dwarfed, a very small, homo erectus or homo habilis. And you add all those bits of evidence together, then you have to start paying serious attention to the hypothesis that this is a real species and not a dwarf.

FLATOW: And I can't let your comment about the hippo paper being - the hippopotamus paper being related to this. Tell us how that was one of the pieces of the puzzle.

Dr. LIEBERMAN: Well, I think the most serious critique of the material has been that generally, when you make a species smaller, the brain doesn't get that much smaller. So if you compare a human being, such as most of the listeners to your program, with say a pygmy - somebody who's a bit smaller in body size -the body size can get considerably reduced, but brain size doesn't really change very much at all.

The slope of that line is very flat. So generally, when species get shrunk down in size, their brains don't get much smaller, and so a colleague in Chicago had argued that if you obey the scaling relationships that we typically know of in the world, you would have to make homo erectus, I think, six kilos in mass, in body mass, in order to get the brain size of floresiensis, which is of course impossible.

So that was a, you know, a serious critique. But one of the things that this hippo paper shows, and also some of the other papers that are in the - that Jungers and others have also published, is that A, the body size in this creature was already pretty small in the first place. So correct me, Bill, but I think that body mass of this skeleton is about 30 kilos.

Dr. JUNGERS: Very close to that, yeah, with a little range around it, but that's very close, yes.

Dr. LIEBERMAN: And then the other thing is that they were able to show that when hippos undergo island dwarfing in Madagascar, it can actually push the brain sizes way down below the - to slopes that are much, much deeper than we are told could be the case. And that's because brains are really costly.

You know, when you're sitting, listening to me, your brain is using about 20 to 30 percent of the calories of your body, which is a huge amount of energy. And if you're - imagine you're trapped on a small, little island, and there's not much to eat and you want to save energy, well, one of the ways that animals save energy is they reduce their body size. But another way to save energy is to reduce their brain size, and they can reduce their brain size far more than those scaling relationships predicted.

So that means that you really can dwarf down the brain of a creature and get something of the sort that you get in floresiensis. It obeys rules of biology that we see in other creatures.

FLATOW: Bill, I…

Dr. JUNGERS: Can I just add a note, a footnote, to that? I think one of the most exciting things about the hippo paper is that it reinforces a study that had been completed earlier on a dwarf bovid from Majorca and other parts of the Mediterranean that show that it looks like brain-size selection - that is, evolution can act on brain size independently of body size, and that's what allows us to hypothesize that, you know, this brain could be reduced beyond what one would expect based on small body size alone.

That's an exciting development, sort of that confirms some things that we didn't - it was a rule - in other words, this island-dwarfing rule has been broken, apparently repeatedly. And so floresiensis doesn't stick out that much, the way it did originally.

FLATOW: So what's your guess on where it originated from?

Dr. JUNGERS: I think there are really two sort of competing hypotheses on the table, and I think I know where Dan stands on this. I think that we already know that there is an early hominid in Southeast Asia, including Indonesia, as early as one-and-a-half million years ago.

That's called homo erectus, and homo erectus actually has a fairly modern body plan. So the hypothesis, one, is that this is a dwarf descendent of homo erectus that got under flurries and was isolated and underwent body-size reduction and disproportionate brain-size reduction.

The problem I have with that hypothesis, really, is that it requires a large suite of evolutionally reversals in other parts of the skeleton that don't make a heck of a lot of mechanical sense to me. You sort of give up things that homo erectus evolved in terms of long hind limbs and modern feet.

So is it possible? Yes. I just think it's not very probable. The alternative hypothesis that I tend to favor is - has people scratching their heads in terms of the biogeographical implications - I have suggested that perhaps Homo floresiensis is distended not from Homo erectus, but from an early hominin that's already quite small-bodied and has a relatively small brain in a more primitive overall skeletal anatomy.

And that's something like Homo habilis, known from Africa, well before two million years. You know, I think that neither one of those arguments, you know, sort of discounts the other completely. Some combination is possible. But I think those are the two arguments that are now in play.

FLATOW: Dan, do you agree?

Prof. LIEBERMAN: Well, I would add a third hypothesis, which is that Homo erectus is very variable and changed over its time period. Maybe we should split it into two species. But that - the very earliest Homo erectus fossils that we find are actually much more primitive in some respects than the later ones we find.

And so, for example, there are some fossils from a site in Georgia in the Caucasus that - called Dmanisi, and there are some skulls and skeletons, actually, that are between about 1.7 and 1.8 million years old. And unfortunately we don't have any feet or wrists from those things, but they do look primitive in a number of ways. The shoulder, for example. Actually, Bill has published some really neat data showing that the shoulder in that creature is kind of primitive. And primitive in a way that you sort of see in floresiensis.

And there's some early African Homo erectus specimens which might be pretty primitive. So, the third hypothesis would be that, so in addition to Homo erectus being the ancestor and Homo habilis being the ancestor, it could be that early Homo erectus is the ancestor. It got - and then it got somehow onto this island. I mean…

FLATOW: Yeah. Well, that was the question I was going to ask next. How did it somehow get there?

Prof. LIEBERMAN: That's a great question.

(Soundbite of laughter)

Prof. LIEBERMAN: It would've had to have swum or - considerably - or had a raft or something like that. Because we actually know that there's actually archeological data from that island, dated to about 800,000 years ago. So, somebody had gotten onto that island at least 800,000 years ago, presumably the ancestors of…

FLATOW: And they would know how to build a boat or a raft?

Prof. JUNGERS: Well, that was one of the news headlines when these were first reported in 1998, was that Homo erectus was a seafarer. That's pretty unlikely. But you do have to cross open water at least twice no matter which hominin got there, which - whatever hominin is the ancestor of Homo floresiensis had to cross relatively deep water.

The island of Flores has never been connected to the west or to the north, even at the lowest sea levels when glaciers tied up all the water. So it's a - that results in a very strong filter and that's why there's such a limited fauna on the island.

You have to realize that hominin named Homo floresiensis shared the island with pygmy Proboscideans called stegadon, the giant stork-like birds, big rats and oversized giant komodo dragons. And that's the bulk of the fauna. So, you're east of a line called Wallace's Line. It's a very profound biogeographical filter. So we're not sure how they got there, but something made it there, and not many things made it.

FLATOW: Wow. Well, let me just - I have to just jump in for a second and give a station break.

This is SCIENCE FRIDAY from NPR News.

I'm Ira Flatow talking with William Jungers and Daniel Lieberman. I think they're getting a new movie starring Jeff Goldblum together here.

(Soundbite of laughter)

FLATOW: For the other island where these creatures were living. Go ahead. I didn't mean to interrupt you. You had another take on it, Daniel?

Prof. LIEBERMAN: Well, no, it's just a - it's a facetious hypothesis. But, you know, stegadon obviously swum - these elephants that got to the island.


Prof. LIEBERMAN: So, you know, if Homo floresiensis or its ancestors, the Homo erectus or Homo habilis or whatever, didn't get on a raft or a tree that somehow, you know, there had to have been a male and a female, of course, maybe they got on the back of an elephant and…

(Soundbite of laughter)

Prof. JUNGERS: Yeah. My colleague, Mike Morwood, the archeologist in charge of this expedition, has looked at the currents. And he believes that there's an island to the north of Flores called Sulawesi. And there are actually some fairly early archeological sites there. We don't have any bones to go with them yet.

And he argues that the Last Glacial Maximum when Sulawesi was, in fact, closer to Flores than it is now - if the prevailing currents, which go from Sulawesi to Flores still persisted, that some kind of, you know, island hopping might have taken place. And then there's always the, you know, the tsunami lottery that drives something, you know, offshore as far out as Flores. But, again, we really are at a loss to come up with a concrete answer to that.

FLATOW: Yeah. Well, you know, when Carl Sagan was asked about little green men from outer space, he said extraordinary circumstances require extraordinary evidence. You know…

(Soundbite of laughter)

Prof. JUNGERS: Well, something got there. We know their tools were made almost 900,000 years ago by something, and that's probably the ancestor of the hobbits. You know, and Dan's points are well taken. We don't yet know for sure which hominin that was likely to be. But just to make a sort of a footnote to his comment, even the Homo erectus from Dmanisi already shows long hind limbs and features that we associate with endurance running, I believe. And those would have to be sacrificed as part of this evolutionary dwarfism, if that were the proper explanation. That's a hard sell for me.

FLATOW: Yeah, do you think you've won over many critics with this last show of the foot bones?

Prof. JUNGERS: You know, it's - I hope so. I mean there's been a very positive response. I've gotten a lot of email and telephone calls. But I have to think that there's been a lot of evidence that's already been published, but unfortunately, this is just another independent line of evidence that I think cumulatively has taken and pulled a lot of people off the fence. And I'm glad to hear that Dan is one of them, because I think that there is still a very vocal minority of people who are trying to discount this as a pathological human. But I think the evidence is overwhelmingly against that notion.

FLATOW: Dan, you're in that camp now?

Prof. LIEBERMAN: Yeah, I mean, I'm convinced. But, you know, the job of scientists is to be skeptical. I mean, that's what we're paid to do. We're not, you now, whenever - we train our graduate students when they open a paper, particularly if it's in science or nature, to read it with a critical eye and try to think of what's wrong of it. That's how science works at its best actually.

And, you know, it's still - it does still strain credulity to think about this, you know, little tiny creature with a brain size of 417 cubic centimeters, the size of a chimp on an island 17,000 years ago, connected 1.8 million years ago to some creatures in Africa. So…

FLATOW: All right. We're going to leave it at that.

Prof. LIEBERMAN: You know, it's enough to be skeptical, but on the other hand, there's a lot of data now which shows that, in terms of the shape of its head, the shape of its wrists, the shape of its feet, it does look like a small little early Homo. And so…

FLATOW: That's - we're going to have to leave it there with William Jungers and Daniel Lieberman. Stay with us. We'll come back after this short break.

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

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