SOME 13,000 years ago, on a tropical island at the heart of the Indonesian archipelago, an extraordinary group of dwarf-sized people lived alongside dwarf elephants and giant lizards. They belonged to a species whose existence has been revealed to the world for the first time this week. It is a species of human utterly new to science.
In two papers in Nature, a team of researchers from Australia and Indonesia detail the discovery of Homo floresiensis. So far the skull and some bones of one female, tentatively called LB1 or Ebu, and fragments from up to six other specimens of this extraordinary relative of ours, have been unearthed from the Liang Bua limestone caves 25 kilometres north of Ruteng on the western edge of the island of Flores in central Indonesia.
Their discovery is arguably the most remarkable find in palaeoanthropology for 50 years, and promises to transform the conventional picture of human evolution. Instead of following a simple evolutionary path culminating in modern Homo sapiens, the existence of H. floresiensis suggests that early humans may have evolved into many more varied forms than previously thought. And these novel types of human survived until very recently, out-surviving even our closest known relatives, the Neanderthals. The new specimens also show that humans with tiny brains could evolve without losing behavioural sophistication and intelligence.
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“It is literally jaw-dropping,” says Bernard Wood, an anthropologist at George Washington University in Washington DC. “It raises the whole issue of what it is to be human, or a member of the genus Homo,” adds Chris Stringer of the Natural History Museum in London. “It shows how little we know about human evolution.”
“It raises the whole issue of what it is to be human. It shows how little we know about human evolution”
H. floresiensis is thought to be descended from ancestors that became marooned on Flores some time during the past few hundred thousand years. The resulting island people evolved to grow no more than a metre tall with brains the size of a newborn modern human (see “Anatomy of Homo floresiensis”). Their small stature and brain size appear to be adaptations to isolated island conditions, where a low-calorie diet and the lack of large predators made small bodies advantageous.
The authenticity of the remains has been confirmed by three-dimensional X-ray images, which reveal the internal structure of the skull of LB1, something that would be almost impossible to fake. Accelerator mass spectrometry dating also suggests that LB1’s remains are 18,000 years old. However, 91av has learned that subsequent work has established that other H. floresiensis bone fragments found at the site could be as young as 13,000 years old. The oldest remains are 74,000 to 95,000 years old. That means H. floresiensis survived well beyond the last Neanderthals, which are thought to have disappeared from Europe and western Asia around 28,000 years ago. “The most remarkable thing is that there was a time not so long ago when two very different human species walked the planet,” says Peter Brown of the University of New England in New South Wales, Australia, who led the team that made the discovery.
Strangely, however, the remains from Liang Bua reveal both modern and ancient morphological traits. Femur and pelvis bones suggest that the species stood upright but walked in a manner resembling the earliest human ancestors that walked on two legs in Africa 4.5 million years ago. And H. floresiensis is the smallest species of Homo yet known, with the smallest brain relative to its body. Its cranium is even smaller than that of the earliest upright hominids, with a volume of just 380 cubic centimetres, a fraction of the brain volume of H. sapiens, which can reach 1650 cc.
In the overall shape of its skull and its teeth, the creature most closely resembles Homo erectus, which lived until 200,000 years ago and from which H. sapiens and Neanderthals are thought to descend. This means it is also likely to have directly descended from H. erectus.
Despite its small brain, evidence from Liang Bua suggests that H. floresiensis may have had relatively sophisticated patterns of behaviour. For example, a handful of stone tools from the same period were found in the caves. There is no evidence that they were inhabited by H. sapiens at the time, and Michael Morwood of the University of New England, who co-directed the archaeological excavation, says that H. floresiensis must have made the tools.
This would reveal remarkable intelligence, given the creature’s small cranium. “The internal structure of the brain – the neural pathways – must have been more human-like than ape-like to be able to make these types of tools,” Brown says.
The bones and teeth of several juvenile dwarf stegodons, an ancestor of the modern elephant, were also recovered from Liang Bua along with the remains of fish, and other mammals including bats, rodents. Some of these bones show signs of charring. This suggests H. floresiensis may have hunted such animals before roasting them on open fires.
The island on which these tiny humans lived lies just beyond the eastern tip of Java, between the islands of Sumbawa and Timor. It is divided by mountain chains and volcanoes and is inhabited by several ethnic groups, each with a unique language and traditions.
As there is no evidence the island was ever linked by land to other parts of south-east Asia, the ancestors of H. floresiensis might have used boats or rafts to reach it. But the fact that this population evidently became isolated suggests that they may have relied on hitherto unsuspected land links that later disappeared.
H. sapiens is thought to have colonised Flores between 55,000 and 35,000 years ago. So H. floresiensis may have coexisted with modern humans for tens of thousands of years. How the two populations interacted remains a mystery. H. sapiens might have outcompeted H. floresiensis for food and other resources, and this could have played a part in the demise of the smaller species. But it is just as likely that H. floresiensis was killed off by a volcanic eruption on the island that occurred around 12,000 years ago.
Ongoing excavation at Liang Bua could reveal much more about H. floresiensis. Further specimens might shed light on the species’ sexual dimorphism and the age at which individuals reached maturity, for example. Further examination of its hand bones could also reveal how dextrous it was.
But the discovery has already set the anthropological world in a spin. Morwood says even stranger prehistoric human forms may have inhabited the islands around Flores. “You are going to find many more weird Homo species running around south-east Asia. Most will be small and highly endemic. Some will be really weird,” he says. “The clear implication is that, given genetic isolation, genus Homo is much more morphologically flexible.”
“You are going to find many more weird Homo species running around the islands of south-east Asia”
Wood agrees. “It shows that the good Lord has a lot more tricks up his sleeve,” he says. “We haven’t seen the best of them yet.”
