July 26, 2013 | 5
Morwood, who passed away on July 23 from cancer, made important contributions in research areas ranging from the rock art of Australia’s Kimberly region to the seafaring capabilities of Homo erectus. But he will be best remembered for a discovery he and his colleagues made on the Indonesian island of Flores: the remains of a miniature human species that shared the planet with our own ancestors not so long ago.
In 2001, Morwood, then at the University of New England in Armidale, Australia, and Raden Soejono of the Indonesian Center for Archaeology in Jakarta re-opened excavations at a large limestone cave in western Flores called Liang Bua. Morwood had previously discovered in central Flores crude stone artifacts from 840,000 years ago that presumably belonged to Homo erectus, and he was hoping to find traces of subsequent occupants of the island. In 2003, the Liang Bua team hit pay dirt. What they unearthed was stranger than anyone could have imagined: a skeleton of an adult female who stood barely a meter tall and had a brain the size of a chimp’s (among other primitive traits) yet lived just 17,000 years ago. Stone tools and burnt animal bones accompanied the enigmatic human remains.
The find jolted paleoanthropologists. H. sapiens was thought to be the sole human species on earth by 17,000 years ago, following the extinction of the Neandertals and other archaic cousins of ours millennia earlier. Even more astonishing, the only known members of the human family as small as the little Floresian were australopithecines—Lucy and her kind, who lived some three million years ago. That H. sapiens could have had a contemporary as primitive as H. floresiensis was unimaginable.
The team formally assigned this skeleton and some fragments representing other individuals to a new species, H. floresiensis. But they were nicknamed the hobbits, after J.R.R. Tolkien’s beloved characters.
The hobbits weren’t the only oddly sized denizens of Flores back then. Remains of enormous rats, dwarfed elephantlike creatures known as stegodonts, and giant lizards and storks turned up at Liang Bua, too. Morwood and his colleagues had uncovered a lost world like no other. And when the researchers published their initial description of the find, they emphasized the significance of that environment in molding H. floresiensis. The hobbit was probably a descendant of H. erectus that had gotten stranded on Flores and evolved its petite size as an adaptation to the limited food supply available there, they proposed. In that way, it appeared to follow the so-called island rule, which holds that animals larger than rabbits tend to shrink in island settings, whereas those smaller than rabbits become giants (possibly because larger bodies are more energetically efficient than small ones).
In suggesting that H. floresiensis followed the island rule, the researchers broke with conventional paleoanthropological wisdom, which holds that humans (particularly members of our genus, Homo) have adapted to many of the selective pressures that shape other species through culture—our ancestors dealt with the cold by fashioning clothes from animal hides and building fires, rather than evolving thick fur, for example.
Yet island dwarfing could not explain all of the hobbit’s other characteristics. For one thing, her brain (as judged from her braincase) seemed to be smaller than expected for her height. In addition, subsequent analyses revealed a number of other traits throughout the skeleton that appeared too primitive to have come from a H. erectus ancestor. And so over the next few years another hypothesis about the origin of H. floresiensis began to gain traction—one that was even more revolutionary than the first.
Perhaps H. floresiensis descended not from H. erectus but from an earlier, more primitive species, such as H. habilis, which in many ways more closely resembles australopithecines than members of our own genus. When I went to Indonesia in 2008 for a follow-up story on the discovery, this was the scenario Morwood was betting on. He shared his views as he showed me the fragile hobbit bones housed in Jakarta and the careful excavation he and Indonesian archaeologist Thomas Sutikna were conducting in Liang Bua. The ancestors of the hobbits were probably pre-erectus members of Homo who were already small when they arrived on Flores and then perhaps underwent some island dwarfing when they once they got there, he explained.
If so, scientists will have to rethink a watershed event in human evolution: the initial dispersal of human ancestors out of Africa. H. erectus, with its nearly modern proportions, was long thought to be the first human species to make it out of Africa, because the oldest human remains to have been found outside of Africa (1.78 million-year-old fossils from the Republic of Georgia) belong to that species. But if Morwood’s view is correct, the first member of the human family to blaze a trail out of the motherland began its journey hundreds of thousands of years earlier than that, and was an altogether different kind of pioneer than the one experts had in mind. And if that’s the case, then researchers have missed a two-million-year record of this wee wayfarer in the rocks between Africa and Southeast Asia.
That an entire chapter of the saga of human origins may be unaccounted for is not as implausible as it might sound: Asian hominins (anatomically modern humans and their ancestors) are poorly known, because rock exposures of the right age to contain such fossils are hard to come by. Yet the discovery of this bizarre cousin of ours on Flores underscores just how important it is to look for them. In recent years Morwood continued his search, looking for H. floresiensis and its ancestors at two sites on nearby Sulawesi.
It bears mentioning that some experts do not buy the argument that the Flores remains represent a previously unknown species. They suspect that the skeleton instead belongs to a H. sapiens individual who had a disease of some sort that produced the specimen’s unusual features. They have yet to come up with a diagnosis that can explain the hobbit’s unusual mix of traits to everyone’s satisfaction, however. The discovery of another small skull at the site would settle the matter in favor of the hobbit being a distinct species. Although excavators have recovered bones of some 14 hobbits from Liang Bua thus far, only one specimen—the largely complete skeleton found in 2003—preserves a skull.
Science needs shake-ups—findings that break all the rules, force researchers to reconsider what they thought they knew and remind us all that there is still so much to learn. Nine years after the Liang Bua team introduced the world to H. floresiensis, scholarly papers on it continue to fill the pages of scientific journals, presentations on it still attract standing room-only crowds at anthropology conferences, and the public remains enthralled with our hobbit cousin. No doubt Morwood’s discovery will continue to fire imaginations and inspire new inquiries for many more years to come.