Riddle of the Human Hobbits : An Equinox Special
Dr Martin Brookes
April 2005
Measuring little more than a metre in height, and with a brain the size of a grapefruit, Homo floresiensis may seem out of place on the human family tree. But according to the Indonesian and Australian scientists who discovered her fossilised skeleton on the island of Flores in Indonesia, Homo floresiensis, or 'Flo' for short, bears a strong resemblance to our closest evolutionary relative, albeit in miniature. Her relatively small teeth, prominent brow ridge, and low, broad brain case, all point towards a close affinity with that upright ancestor of ours, Homo erectus.
The Homo erectus link
In many ways, Homo erectus was the first rock star of the fossil world, leaving behind such celebrated remains as Java Man in Indonesia and Peking Man in China. But it was in Africa, almost two million years ago, where it all began. While other hominids were busy pursuing evolutionary dead ends, Homo erectus was discovering the joys of standing up straight. Here was the prototype human being.
Of course, the heavy brow, sloping forehead and invisible chin would stand out a mile in a modern identity parade, but in other respects, Homo erectus was remarkably similar to us. They stood erect, about 1.79 metres tall; they were agile and strong; and they certainly liked to travel. Fossils of Homo erectus have turned up throughout the Old World, which comprises Asia, Africa and Europe.
With a cranial capacity of about 1000 cubic centimetres, Homo erectus had a brain about three quarters the size of ours. But this was no numbskull. Here was a species that could make all kinds of innovative tools – vital objects, perhaps, in the transition from the hunted human to the human hunter. For Homo erectus was probably the first true hunter-gatherer; the first ancestor to make the shift from prey to predator.
Australopithecine angle
A link between Flo and Homo erectus is a plausible and compelling one, but it is by no means the only hypothesis in circulation. Finding consensus in the palaeo-anthropological community is more difficult than finding the missing link. With so many holes in the human story, opportunities for speculation are everywhere.
Her small stature and diminutive brain has led some researchers to suggest that Flo may be an offshoot of the australopithecines, a primitive group of hominids thought to be ancestral to Homo erectus. Certainly, in terms of size, there are australopithecine fossils that bear comparison to Flo. But there are serious problems with the australopithecine argument. Australopithecines have never been found outside Africa, and all fossil evidence suggests they died out about 1.5 million years ago. Flo, stuck on an Indonesian island, seems a little out of place, and, at 18,000 years old, a mere youngster by comparison. If Flo can count herself among their members, then a significant chapter of the human story will have to be rewritten.
The australopithecines first emerged about 4 million years ago. They seem to have been a diverse and successful group that roamed throughout Africa for about 2.5 million years. But the absence of australopithecine fossils beyond Africa suggests that they were probably not great colonisers.
The disappearance of australopithecines from the fossil record coincides with the gradual emergence of more modern human forms, characterised by larger body size, a more upright posture, striding limbs and an increase in brain capacity. Some have suggested that these evolutionary trends provided the necessary spur that set our ancestors on their migratory path throughout the Old World. It's a tempting tale scuppered somewhat by the recent discovery of a small and primitive 1.75 million-year-old hominid in Georgia, hundreds of miles north of Africa.
We're not alone
Whatever the truth about her identity, Flo has thrown a serious spanner in the works. It was widely assumed that when the Neanderthals went extinct, about 25,000 years ago, we were left as the planet's sole representatives of the Homo genus. Yet as Flo is estimated to have died only 18,000 years ago, her discovery not only challenges that claim, it distorts assumptions about the origins of our modern selves.
The conventional story goes something like this: modern humans first walked on Earth about 150,000 years ago. Our immediate ancestors were archaic forms of Homo sapiens, who were themselves descendants of Homo erectus. This much seems incontrovertible, for the time being at least. The disputes emerge in the details. How and where did this transition from the old to the new take place?
At one extreme, the 'Out of Africa', or replacement, hypothesis argues that modern humans evolved in Africa, from where they spread out to colonise and replace archaic populations across the globe. In this scenario, everyone alive today shares a relatively recent common ancestor of African origin. At the other extreme, the multiregional model argues that modern humans evolved separately, if simultaneously, in multiple locations throughout the Old World. If this version of events is true, it implies that the common ancestor of modern humans dates back 1.8 million years to Homo erectus in Africa.
Wherever the truth lies, the discoveries in Indonesia have taken both camps by surprise. In fact, Flo is just the latest in a string of remarkable finds. It was widely believed, for instance, that Homo erectus disappeared some 400,000 years ago. But recent excavations in Java have uncovered Homo erectus fossils dated at only 50,000 years old. Did these archaic populations come into contact with modern human populations then colonising Australasia, and how do they relate to the diminutive people of Flores?
Migration mystery
How did Flo get to Flores in the first place, and where did she come from? Based on geography alone, Homo erectus populations on nearby Java would seem like the most obvious source of original colonisers. But anatomically, Flo links up much more readily with diminutive hominid fossils found in Africa and Georgia. Could this mean that Flo came from an entirely separate migration of hominids? Nobody knows.
Whichever route her ancestors took, the last leg of their journey would have been treacherous. Flores has always been an island surrounded by deep water channels and dangerous currents. Swimming is out of the question. But the recent tsunami in Indonesia has highlighted one possibility. Were Flo's ancestors washed up on the beaches of Flores, clinging to driftwood?
Of course, a raft is an obvious mode of transport, but many palaeo-anthropologists doubt whether Homo erectus ever had the intelligence and cultural skills for complex tasks like raft-building. But that assumption has been called into question. Using CT scans, scientists have been able to construct a virtual model of Flo's brain. The results show that the brain case, though small, contained an amazingly complex organ. Advanced morphological features such as enlarged temporal and frontal lobes suggest that Flo was an individual with foresight, good memory and excellent problem-solving abilities. These observations also tally with circumstantial evidence found at the excavation site in Flores. Buried among the hominid fossils were sophisticated tools and the charred remains of animal bones. She may have been small, with a brain a third the size of our own, but Flo possibly had the intelligence to make fires, to fashion tools, and perhaps even to cook her own food.
Small but perfectly formed
Flo's discovery has turned up many unanswered questions, but the overwhelming enigma is her size. Doubts still linger in certain corners of the palaeo-anthropological community over whether Flo is truly representative of her kind, or merely a diseased individual with atypical characteristics. Flo's small head mimics a rare condition in modern humans known as microcephaly. But a recent and detailed examination of her skull suggests that the similarity is superficial. Further evidence against this idea comes from the discovery of at least five more diminutive individuals from the same spot where Flo was found. How likely is that they would all share the same rare pathology?
Animals that colonise islands often become giants or dwarves compared to their mainland relatives. The Galapagos has its tortoises, Mauritius had the Dodo, while the Seychelles has a frog no bigger than an ant. On Flores itself, there is that giant of the lizard world, the Komodo dragon, an extinct pygmy elephant, and an extinct species of giant rat. The forces underlying these evolutionary changes are still not properly understood, and the patterns often seem vague and unpredictable. But one general rule seems to be that large mammals get smaller, while anything smaller than a rabbit gets larger. Because islands have more limited resources, and contain fewer predators, a radical change in size may be the best way for a mammal to maximise its energy efficiency.
Whether this so-called 'island rule' can explain Flo's small stature is unclear. In mammals, selection for smaller bodies has only a marginal effect on brain size. But if Homo floresiensis descended from Javan populations of Homo erectus then Flo not only lost half her height, she also lost half her brain volume. Why would natural selection favour such a mammoth loss of grey matter? To answer that question we may have to wait for the next great fossil find.
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Find out more
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Websites
Bones of contention
www.guardian.co.uk/life/feature/story/0 ... 00,00.html
The discovery of a new species of human astounded the world, but is it what it seems? Read this fascinating article by John Vidal, who went to remotest Flores to find out.
Flores find
http://magma.nationalgeographic.com/ngm ... media.html
Scientists believe the small skeleton found inside a cave on the Indonesian island of Flores may represent a new human species, Homo floresiensis. Check out the video reconstructions of this tiny hominid.
Hobbit-like human ancestor found in Asia
http://news.nationalgeographic.com/news ... ensis.html
Article from National Geographic on the recent discovery of the Homo floresiensis skeletons. The article has accompanying photographs.
Little lady of Flores forces rethink of human evolution
www.nature.com/news/2004/041025/full/4311029a.html
Article published in Nature magazine about the discovery of Flo and its implications.
Prominent hominid fossils
www.talkorigins.org/faqs/homs/specimen.html
Offers a list of hominid fossils important for their scientific or historic interest. All are accompanied by photographs or drawings, plus information on where and when the discovery was made.
Q&A: Indonesian hominid find
http://news.bbc.co.uk/1/hi/sci/tech/3960001.stm
BBC online looks at some of the questions that the recent discovery of Flo raises.
Books
Adventures in the Bone Trade: The race to discover human ancestors in Ethiopia's Afar Depression by Jon E Kalb (Springer-Verlag, 2000)
Over the past 25 years, a stream of fossil and artefact discoveries in the Afar Depression of Ethiopia has produced the longest single record of human ancestors in the world. This book chronicles the exploration of this unique desert area, focusing on the 1970s when the valley was mapped and many fossils and archaeological sites were discovered.
www.amazon.co.uk/exec/obidos/ASIN/03879 ... ntmagaz-21
www.amazon.com/exec/obidos/ASIN/0387987 ... enantmc-20
The Human Story: Our evolution from prehistoric ancestors to today by Christopher Sloan (National Geographic Society, 2004)
Drawing on evidence from fossils and DNA testing, this authoritative overview of human evolution goes back 6 million years to a time when humans and chimpanzees had a common ancestor.
www.amazon.co.uk/exec/obidos/ASIN/07922 ... ntmagaz-21
www.amazon.com/exec/obidos/ASIN/0792263 ... enantmc-20
