It's been twenty months now since scientists reported discovering fossils on the Indonesian island of Flores belonging to a three-foot-tall hominid with a brain the size of a chimp that lived recently as 12,000 years ago. Homo floresiensis, as this hominid was dubbed, has inspired two clashing interpretations. Its discoverers declared it a separate species descended from another branch of hominids. In others words, the most recent common ancestor we share with Homo floresiensis lived two or even three million years ago. Skeptics argued that the fossils belonged to human pygmies. The one fossil of a Homo floresiensis brain-case belonged to a female with a rare genetic defect. In brief: healthy hominid versus deformed human.
Now comes a third theory. In brief: healthy human.
Before I get to this third theory, let me explain why others have argued in favor of the other two. (For longer treatments of both theories, see my archive of Hobbit posts.)
The discoverers of Homo floresiensis, a k a the Hobbit, argued that it was a separate species on the basis of a number of traits they claimed set it apart from humans. It had no chin, for example, but it had a very wide pelvis, thick limb bones that were also twisted in some cases, and, of course, that tiny brain. A scan of its brain-case also reveals a distinctive organ which the scientists argue does not resemble any well-studied human with the birth defect that creates small brains (known as microcephaly). The record of fossils also points to a long evolution on Flores, rather than the recent arrival of humans. Humans are generally believed to have arrived in East Asia about 50,000 years ago. But the oldest Homo floresiensis fossil, a fragment of an arm bone, is almost 100,000 years old. Stone tools found with the Hobbit fossils also resemble tools found elsewhere on Flores dating back 840,000 years ago.
Skeptics (who have now published three papers and have more in the works) have argued that the people of Flores were human pygmies, and that the small brain case belongs to an individual with a condition known as microcephaly, in which a mutation causes the brain to fail to develop completely. They've also cast doubt on the possibility that a separate small-brained hominid species could have evolved on the island. When mammals evolve to smaller sizes, their brains don't get quite so small, relatively speaking. Compared to other mammals, Homo floresiensis is far too tall at three feet for its brain. And finally, they've argued that a small-brained hominid couldn't have made the stone tools found with the fossils.
Now comes a different take, in a dense review published online today in the Journal of Evolutionary Biology. Gary Richards of the University of California at Berkeley argues that scientists who have tried to make sense of Homo floresiensis have not grappled yet with the full potential of the human genome to produce different sorts of bodies. They've been focused too much on this or that individual, when they should be considering the range of variations. Richards takes his own best shot, and comes away with the conclusion that the Hobbit is most likely a population of small-brained pygmy humans.
The evidence for the Hobbit being a separate species, Richards argues, loses its punch if you dig deep into the scientific literature on human variation. It was certainly short, but not more than ten or twenty centimeters shorter than the smallest human pygmies known today. Richards considers it eminently reasonable that the same genetic changes that have produced populations of human pygmies--which interfere with the action of growth hormones--could have had a somewhat stronger effect on the Hobbit. The discoverers of Homo floresiensis have put great weight on the twist in the humerus (the upper arm bone), but Richards points out that while it may not be universal in Homo sapiens, it does turn up in some populations of...yes, pygmies. Becoming a pygmy involves more than just becoming short, Richards argues. A person's development is influenced in many ways, perhaps partly because height-related genes also affect other aspects of the body, and perhaps because the human body responds to a short stature by developing differently. The wide pelvis and missing chin are also not that unusual compared to the pelvis and chin of living human pygmies. In fact, pygmies were for a long time thought to retain many "primitive" traits in their anatomy, when in fact those traits had evolved very quickly as they had evolved from taller ancestors. Richards argues that much of the alleged primitiveness in Homo floresiensis could have come about in much the same way.
When Homo floresiensis was originally described, some scientists argued that it couldn't have been a human pygmy because human pygmies only stop growing at puberty. Homo floresiensis would have had a very different skeleton if it had grown normally for all that time. But Richards argues that this is something of an urban legend. Early research did suggest that pygmies stopped growing at puberty, but it's now clear that they are significantly shorter from birth. Richards concludes that changes to human growth patterns similar to those in pygmies could have produced Homo floresiensis.
Then there is the matter of the brain. More than anything, Richards is critical of the way scientists have looked for one microcephalic brain to compare to Homo floresiensis. He points out that there are many genes that influence the size and structure of the brain, and there are thus many kinds of birth defects. It might seem as if microcephaly would leave a person essentially brain dead, but that's not the case. In some cases, it causes only mild retardation, leaving people able learn basic skills and with good motor control. Microcephaly is rare in the United States and Europe, with estimates ranging from 1 in 30,000 to 1 in 250,000 birth. But in communities with a lot of inbreeding, the rate can be far higher--45% in one Canadian community.
From this review, Richards offers up this scenario: tall, large-brained humans come to Flores. They settle there and become isolated from other people. As on many islands, they acquire mutations that make them very short. These mutations also lead to other changes in their skeletons. Other mutations also crop up in the people of Flores, including at least one that alters their brains. Because the population is small and inbred, these mutations become common. Not all of the Floresians may have been quite so small-brained, but a significant fraction of them were. The effect of these mutations on the mental abilities of Floresians wasn't catastrophic. They were still able to make stone tools and find food and survive. In fact, having a small brain may have actually been an advantage in some ways. Our brains demand 20% of the calories in our food. A smaller brain would demand less food--a potential boon on an island with limited resources.
"I argue that these remains do not represent diseased, pathological, or aberrant individuals," Richards concludes. Just a remarkable population of humans.
I have heard this argument before. When I interviewed Tim White, also of Berkeley, for a 2005 Discover story, he floated the idea of Hobbits as healthy humans. (I ended up leaving it out.) Richards is the first scientist I know of who has presented this work in a journal. I'm curious to hear what the other scientists in the debate think about this third way. (I've sent out requests for responses and will post them as they come in.)
To my mind there are a couple important issues that--while not scenario-killers--must be addressed one way or another. One is the age of Homo floresiensis fossils. The oldest fossils are nearly 100,000 years old. If they were actually Homo sapiens, it would be quite a big deal for them to be on a remote Indonesian island by then. Consider the evidence of the spread of Homo sapiens offered last week in a review published in the Proceedings of the National Academy of Sciences by Paul Mellars of Cambridge. He argues that our species evolved in Africa about 200,000 years ago. They expanded briefly into the Middle East 110,000 years ago but seem to have retreated back to Africa 90,000 years ago. It's not until 50,000 years ago that scientists find strong evidence of modern humans outside of Africa.
Instead of claiming that humans got to Asia over 100,000 years ago, Richards questions the oldest Homo floresiensis fossils. They consist of part of a lower arm bone (the radius) and some teeth. Richards claims that these bones are not distinctive enough to be definitely considered Homo floresiensis, leaving a population of humans that lived between 18,000 and 12,000 years ago. He argues that humans could have arrived 50,000 years ago and then evolved into the Hobbit form by the time the fossils were laid down. This might be true, but it leaves open just who left that arm bone and those teeth almost 100,000 years ago? Not to mention those 840,000 year old tools.
The other question that comes to my mind is why other humans who have settled on islands haven't gone all hobbity too. The people of the Andaman Islands, for example, have markers in their DNA suggesting they arrived on the islands a long time ago--perhaps during the initial spread of humans out of Africa. Some became pygmies, but their brains did not shrink to a third the size of their ancestors.
Still, I am curious to see the reaction this paper gets from other scientists studying Homo floresiensis. If Richards is right, you have to wonder just how malleable our species is. If we can become Hobbits, what else lies in our future?
Update:, 6/25/06 10:30 pm: Peter Brown, from the discovery team, disputes Richards thusly--
An interesting paper but not supported by the skeletal data from Flores. There are a number of early Holocene skeletons, with good archaeological contexts, from various caves on the island. None of these have the skeletal and dental features found in H. floresiensis. They have all been described in a thesis out of Leiden University, and a variety of other places. There were also a number of mesolithic human skeletons recovered from Liang Bua cave two decades ago (now in Tekeu Jacob's laboratory and some in Jakarta) which are also just modern human skeletons. They don't support the claims made by Teuku Jacob (which is one reason they have never been presented to the public), or the claims in the latest paper either. In other words the skeletal evidence does not, and never has, supported the claims for microcephaly. There are no syndromes which reproduce the combination of traits in H. floresiensis. If there was skeletal evidence would have been displayed by the sceptics long ago. The author of the latest paper has not seen any of the primary evidence, most importantly the skeletal evidence from Flores which he argues supports his story. The articles he quotes (eg, Jacob) do not provide the evidence either.
Update, 6/22/06 8:20 am: John Hawks offers his take: deformed human
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It seems that Richards' theory should be the null hypothesis--don't inovke other hominid species as a source for the hobbits. But your article provides evidence weighing against Richards' hypothesis. The one truth about evolution is that it produces bushy phylogenies. So there is no reason to dismiss a separate hominid speices existing with sapiens. Also, it is more parsimonious in terms of the stone tools, otherwise tools types dating back 850,000 years would ahve to have been made by different species, spawning a functionalist-ecological argument that the tool type is ideal for the environment, no matter the tool maker.
It's interesting to see that modern pygmies have sone similar traits to the Flores fossils, indicating that perturbation of the same growth pathways may be involved in dwarfing in each case. However, surely evo-devo would suggest this is a likely scenario whether it applies to humans or other hominids? There may simply be only so many ways you can get from a tall hominid to a viable short hominid.
Another intriguing question: How fertile/healthy are children from partnerships between pygmies and "normal" size people? At what point is it right to stop talking about remarkable sub-populations and start thinking of it as incipient speciation? If an archeologist of the future came across fossils of a pygmy and a "normal" person, would they classify them as the same species or as different subspecies? How right or wrong would they be to do so?
carl, you say: Some became pygmies, but their brains did not shrink to a third the size of their ancestors.
may be it didn't happen just because... it didn't happen... chance mutation...
Wasn't there another discovery around the same time? Of what appeared to be a specimen of Homo erectus in the Republic of Georgia? A specimen that had australopithicine traits that later H. erectus specimens lacked. A specimen that was reported to be 4 feet tall. How big was it's brain?
Has anybody considered the possibility that the hobbit was descended from a population of Homo erectus georgiensis? A short, small brained population at that?
And what about features similar to features found in H. erectus and australopithicines, but not found in modern humans?
Alan--Some people have floated the idea that floresiensis is descended from the small Georgia hominids. But I haven't seen a detailed argument published in favor of it. The fossils are very far apart, obviously, both in time and space.
You write: tall, large-brained humans come to Flores. They settle there and become isolated from other people. As on many islands, they acquire mutations that make them very short. These mutations also lead to other changes in their skeletons. Other mutations also crop up in the people of Flores, including at least one that alters their brains. Because the population is small and inbred, these mutations become common.
This sounds much like the standard process of speciation that occurs on islands. Taking the premise of this passage as correct, that the hobbits' ancestors were homo sapiens, at what point do we say that this population still consisted of homo sapiens, and when do we say that it had evolved to a new species? Since it is no longer extant, can't check for fertile hybrids.
Carl,
I'm thinking a point by point comparison of the two skulls might give some interesting results. Along with a point by point comparison of the two skulls plus skulls from H. sapiens, H. erectus, and A. afarensis.
Of course, finding more Georgia Man remains in the area between Georgia and Flores Island would make a big difference. As would more Flores Man skulls.
Still, as much as I bemoan scientific conservatism, it is better to make sure instead of going off on unsupported supposition. (So why do I do it? Because giving small kids ideas is fun. :) )
Just remembered something...
Technically speaking, Homo erectus, H. habilis, Rhodesian Man, Heidelberg Man, and even the Neanderthal were human. In that their species belonged in the genus, Homo.
Which means that at one time there might have been as many as 5 species of human living on this planet at one time. Those being:
H. sapiens
H. neanderthaliensis
H. heidelbergiensis
H. erectus
H. floresiensis
None of this article holds any water because:
Neanderthal man was fully human but deformed with rickets.
All evidence of Peking man mysteriously disappeared.
All Australopithecines were just apes.
Oiltdown Man was a hoax.
Nebraska Man was an example of an extinct pig making a monkey of an evolutionist.
And now "Flores man," which is really just another deformed human.
There is no evidence for evolution.
Carl Zimmer,
Alan Templeton's "Haplotype Trees and Modern Human Origins" that you did a nice piece on earlier this year presented genetic evidence pointing to humans leaving Africa about 130,000 years ago. That leaves 30,000 years to arrive in Flores, which seems time enough to me.
Peter Malin's short article that you linked above doesn't reference Templeton's paper and treats S. Oppenheimer's "Out of Eden" by simply saying there are opposing views... He seems to have failed to understand that the sea stand was about 90 m lower then, so most evidence of humans from that time is now under water. Anthropology and archeology are known to be hypothesis rich and data poor fields of research, but I thought Malin's paper quaint in the light of the evidence that Oppenheimer brought forth in his book, evidence which in some cases I have checked the literature he cited. Briefly, I think Malin is wrong in his dating given what Templeton and Oppenheimer have shown.
Now whether your hobbitses are H. sapiens or not might also depend on the definition of 'species'. The difference between 'could have' interbred and 'did' interbreed might be quite important that long ago, when there were so few individuals of genus Homo. In this, and other examples, I've stopped worrying about the species designation for individuals of genus Homo. They were all humans, just rather different. I don't know whether or not they 'could have' interbred, but separated by space and social custom, they did not. So your hobbitses were humans. Isn't that really quite enough?
They were still able to make stone tools and find food and survive. In fact, having a small brain may have actually been an advantage in some ways. Our brains demand 20% of the calories in our food. A smaller brain would demand less food--a potential boon on an island with limited resources.
This seems like an argument against the idea they were human. Our brains impose huge caloric costs/demands, along with the child birth fiasco. If our brains don't need to be this big, and it's that easy, it seems natural selection would've taken that path. Also, we see nothing else like this in human evolution even though we've spanned every world ecological niche. In my opinion, it seems the modern panoply of human diversity should put some meaningful constraints on ideas of humans this different. Carl nailed it with the Andaman Island example; there is no evidence for this extreme evolutionary pressure, and importantly, humans have examples to test the theory.
Another intriguing question: How fertile/healthy are children from partnerships between pygmies and "normal" size people? At what point is it right to stop talking about remarkable sub-populations and start thinking of it as incipient speciation?
The Lese neighbors of Efe pygmies are intermediate in stature from gene flow - there is nothing extraordinary about such admixture.
The Lese neighbors of Efe pygmies are intermediate in stature from gene flow - there is nothing extraordinary about such admixture.
Sure, but that's not quite what I asked. I was asking if there were any known examples of pygmies and normal-stature people having children, and what the fertility of those children was like. The fact that gene flow happens doesn't answer that (except inasmuch as we can deduce it doesn't result in total infertility). To answer my question, I guess we'd have to look at things like sperm count in the Lese/Efe admixtures, and also whether (for example) it takes longer for a Lese man and woman to have a child than a Lese man and an Efe woman.
It seems to me that there's a non-zero prezygotic barrier to interbreeding (in the main, pygmies and normal-stature people just don't find each other that attractive) - would be interesting to know if there are any postzygotic difficulties as well.
Could H. floresiensis be an example of the Founder's effect, where the first to land on the island (at least in the later group) were already genetically distinct upon arrival? Perhaps rather than compete with the larger majority, a minor few naturally short humans sought their own life, on an island, as far away as they could get.
Nonsense. The anatomical variations of the are not consistent with rickets. Plus, we're not talking about 1 skeleton here. There are hundreds of Neandertal specimens/individuals found.
So? One set of fossils gone missing during a war? Plus, this has nothing to do with all the other H. erectus specimens.
All humans are types of apes too. But Australopithecines were not "just apes" as you imply, but were rather a genus of intermediates creatures (appropriate in both their anatomy & their temporal/geographic location within the fossil record) between modern humans and the more "ape" like ancestors.
So? Piltdown was a single hoax played on the scientific community (not BY the scientific community as you imply) which was subsequently discovered and rejected by the scientific community and which plays no part at all on the modern theory.
Hardly. It was a short term speculation that got additional non-scientific speculation in the popular press. Again, this example has zero influence on the modern theory.
If you read the article, you'd see that there's still a lot of debate/research about this new find.
Baseless claim. So far you have only quoted irrelevant, individual fallicies and ignored the mountains of evidence, including the hundreds of homonid specimens (never mind all the other fossil species, genetic evidence, etc.)
This controversy is only too fitting. You see, in Tolkien's mythology, there are explicit accounts of the creation of men, elves and dwarfes (not much evolution going on, it's a "young Middle Earth"). Yet there is no single clue about the origin of hobbits. It has been, of course, a topic of speculation among the fans for decades, without (alas!) any remaining skull to guide them. Until now, I mean! :-)
I think the "healthy human" hypothesis should be explored further. As pointed out in the Loom before, there is an oral tradition in Flores (Rampasasa) that there was a race (for lack of a better term) of short, long-armed, hairy people that used stone tools and that had not mastered the technology of fire.
Moreover, there is a village that claims to be descended from the offspring of the union of "normal" humans and the small hairy people, only six generations ago.
Although Time Asia is less than a peer-reviewed scientific journal, I've wondered about the following article, and how cultural anthropology might contribute to the homo floresiensis controversy:
http://www.time.com/time/asia/magazine/article/0,13673,501050606-106696…
"We didn't have knives but used rocks," he explains. "We didn't even know how to make fire." Jurubu, a soft-spoken man with close-cropped gray hair, high cheekbones and deeply inset eyes, looks to the 30 or so villagers sitting in a circle around him for confirmation. They nod and grunt assent, and he proceeds to talk about the time their shy ancestors hid themselves from the outside world in Liang Bua, a high-ceilinged cavern scooped out of a limestone hill about a kilometer away. Again a chorus of agreement. ... it's hard not to notice the large number of very short people, particularly among the older folk, some of whom are the same height as a typical 10-year-old. Some six generations of intermarriage with outsiders, says Rampasasa's headman Alfredus Ontas, have left few truly tiny individuals. But to prove their antecedents, he and other locals eagerly display photos of recently deceased relatives whom they say were of purer "short people" stock. "The brothers in this photograph were only 110 cm," Ontas says proudly...Another elder is introduced, who, as well as measuring only 135 cm tall, has a pelt of hair covering his arms and legs. "It was because we were so hairy that our ancestors hid in Liang Bua," says Jurubu. "They were embarrassed."
... Viktor Jurubu is recounting the story of how Paju, a famous warrior, ran into one of the "normal" people in the woods one day while out hunting. "This beautiful lady lit a fire and cooked the wild boar Paju had killed," Jurubu says. "She wanted to marry him and knew she could tempt him with the taste of cooked meat. He did like the taste, so he agreed to marry her and come out of Liang Bua with the rest of the tribe, founding a new village."
And the bones in the cave? "Of course, they were our ancestors," says Jurubu, with a touch of rheumy indignation. "They must have retreated into the cave after a hunt and got caught there when the river rose. Who else could it be?"
The latest word:
"We explore the affinities of LB1 using cranial and postcranial metric and nonmetric analyses. LB1 is compared to early Homo, two microcephalic humans, a �pygmoid� excavated from another cave on Flores, H. sapiens (including African pygmies and Andaman Islanders), Australopithecus, and Paranthropus. Based on these comparisons, we conclude that it is unlikely that LB1 is a microcephalic human, and it cannot be attributed to any known species. Its attribution to a new species, Homo floresiensis, is supported."
New to paleo-archaeological debates, I see how the field is unnecessarily diminished by the historical division between "out of Africa" and "regionalist" camps, in the Homo floresiensis discussion for example.
Human mitochondrial DNA (mtDNA)/Y-chromosome phylogeography shows very strongly that homo sapiens came "out of Africa". But such explanation is generally too totalistic. Both sides tend to illogically totalise, fail to mention or see that, while homo sapiens and the hominid genus almost certainly came "out of Africa", Homo Erectus probably came out of Asia (Kohn 2006). Some homo erectus ancestors and other hominids may also have come "out of Asia".
Kohn writes: "homo erectus materialised almost simultaneously in Africa, east Asia and a point in between . . . and that the dates do not rule out the possibility that homo erectus evolved in Asia."
This difference between homo erectus, homo sapiens centres of endemism is not only true, it is also very telling, has implications. As I explain in (paper 5 page 6 of) my ebook at www.nodrift.com/vol_5/5.1.pdf :
"SEXUAL SELECTION THUS MOST IMPORTANT FOR HOMO SAPIENS
. . . evolutionary considerations AND homo sapiens evolving in AA Africa, coming "Out of [AA] Africa", not "Out of [IR] Asia", page 5, imply a corollary:
Conventions are very much a product of sexual selection. Sexual selection has thus evidently been more important than natural selection in evolution of homo sapiens, in contrast to evolution of homo erectus, where natural selection may have been more important than sexual selection."
REFERENCE: KOHN M. 2006. New Scientist. 2558, 1 July 2006, p35, p39.