Studies suggest Flores man was a distinct species.
From head to toe, the bones of a metre-tall species dating from somewhere between 17,000 and 95,000 years ago continue to reveal the potential complexities of human evolution.
Two articles published in Nature today focus on Homo floresiensis — one describes how its brain could have dwarfed to its unusually small size1, the other how its large feet, similar to those of chimps, would have allowed it to walk efficiently but probably not to run well on two legs2.
"It is a fascinating specimen — a combination of puzzling features never seen together before," says Jeremy DeSilva, a palaeoanthropologist at Worcester State College in Massachusetts, who wasn't involved in the research.
Discovered on the Indonesian island of Flores in 2003 and dubbed 'the Hobbit' after it was reported in 20043, the species triggered a worldwide debate about its origins.
In particular, a hard-core cadre of critics said that the skeleton was that of a human who was suffering from microcephaly — a disorder in which the head is much smaller than normal — limiting its brain to 417 cm3, a third the size of the average human brain. The team, hailing from Indonesia and Australia, that discovered the bones argued that the species' brain had probably shrunk owing to its isolation on an island with sparse resources, a phenomenon experienced by other insular animals.
Now Eleanor Weston and Adrian Lister of London's Natural History Museum have used brain-scaling data from extinct species of dwarf Madagascan hippopotamuses to show how the Hobbit's brain could easily have reached its proportions.
And William Jungers of Stony Brook University in New York and his colleagues report that analysis of the near-complete left foot and parts of the right foot indicate that the animal derives from a more primitive species than was previously believed.
Daniel Lieberman, a Harvard University biological anthropologist, called the results "considerable evidence" that H. floresiensis is a bona fide species4.
But Robert Martin — a biological anthropology curator at the Field Museum in Chicago, who maintains that the Hobbit's brain couldn't have shrunk from a human relative — remains unconvinced by the hippo article.
"I think that claim goes too far, based as it is on a single case relying on indirect evidence," he told Nature News.
DeSilva notes that whatever the view of palaeoanthropologists, the work by Jungers and his colleagues offers valuable glimpses of early bones seldom seen. The feet are important because they are crucial to understanding locomotion.
In the case of H. floresiensis, Jungers says, "it is a real mosaic of primitive and derived features".
The foot was long in relation to lower limb length, he says. The big toe was in line with the other toes, but it was short, whereas the other toes were long.
"No human on Earth has proportions like that," he says. Because of these characteristics, he adds, H. floresiensis would have been adept at walking but not a good runner.
He adds that the features suggest that H. floresiensis derived from either the earliest Homo erectus, which reached Southeast Asia by about 1.6 million years ago, or the more primitive Homo habilis, thought to have arrived about 1.8 million years ago.
To address the brain-size debate, mammal palaeontologists Weston and Lister examined about 50 skulls of two types of dwarf hippo, some of which lived as recently as about 1,200 years ago.
The authors scaled brain mass to body mass in these species. By applying a model of this scaling, they determined that H. floresiensis' brain could have shrunk to about the size known from the lone skull.
"Whatever the explanation for the tiny brain of H. floresiensis relative to its body size, the evidence presented here suggests that the phenomenon of insular dwarfism could have played a part in its evolution," they write.
Although Weston and Lister's study may not have convinced Martin, it was met with overwhelming enthusiasm by Jungers.
"The game is over," says Jungers. "The evidence is overwhelming."
The game is over. The evidence is overwhelming. William Jungers , Stony Brook University
But doubts still linger among those researchers who wonder how a species with such a little brain could make stone tools, hunt the island's pygmy elephants and dodge its giant lizards.
These palaeoanthropologists believe any Hobbit fossils discovered in the future will show that the species dwarfed rapidly from Homo sapiens — which first evolved more than 200,000 years ago in Africa — rather than an earlier ancestor.
In Indonesia, archaeologists Michael Morwood of the University of Wollongong in New South Wales, Australia, and Thomas Sutikna of National Research and Development Centre for Archaeology in Jakarta, members of the team that originally unearthed H. floresiensis, continue to excavate annually at the Liang Bua cave — which last summer yielded more H. floresiensis bones and teeth. Attempts will probably be made to identify DNA in this material; previous tests on teeth and bones have not yielded DNA.
An expanded excavation schedule also is planned if a pending grant is forthcoming, says Morwood.
Weston, E. M. & Lister, A. M. Nature 459, 85–88 (2009).
Jungers, W. L. et al. Nature 459, 81–84 (2009).
Brown, P. et al. Nature 431, 1055–1061 (2004).
Lieberman, D. E. Nature 459, 41–42 (2009).
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Dalton, R. 'Hobbit' was a dwarf with large feet. Nature (2009). https://doi.org/10.1038/news.2009.448