The diminutive “hobbit” species, Homo floresiensis, was recently in the news because of a new analysis that suggested the species predated the arrival of modern humans to the region. But the discovery left a big unanswered question: how did the hobbit fit into the human family tree? A discovery of more fossils described in today’s issue of Nature helps piece together more about the species’ history, shedding light on its ancestry and suggesting that it was present in Indonesia as early as 700,000 years ago.

When first found, the tiny bones discovered on the Indonesian island of Flores were dated to around 20 kya (20 thousand years ago). That date was revised earlier this year, placing them between 100 kya and 60 kya. Since modern humans probably moved through the region around 50 kya—and since other species of humans have tended not to last long once our own species moves into the neighborhood—the older dates helped to resolve the mystery of how the hobbits had lived alongside us for so long. Basically, they hadn’t.

Still, this left a lot of other questions open. How long did hobbits live on the island? If hobbits and modern humans coexisted for even a short period of time, is it possible that they shared some of their genes with us like Neanderthals did? The latter question depends partly on their ancestry—if hobbits descended from Homo erectus, its evolutionary distance from humans would make interbreeding unlikely. The new finding suggests that's the case.

Ancient hobbits

These new fossils come from a different excavation site on Flores. While Liang Bua (the site of the original hobbit discovery) is a large cave, the Mata Menge site is out in the open. Excavation in the region has been ongoing since the 1950s, exposing rock layers in Mata Menge that date from 1.4 million years ago (Mya) to 500 kya.

These rocks are rich in fossils, with species like Komodo dragons, crocodiles, birds, pygmy elephants called Stegodons, and even giant rats all making appearances. However, accessing that rich fossil presence takes a lot of effort. Fossils in Mata Menge need to be extracted pronto, both because of the danger the tropical environment poses to the condition of the fossils and because they even run the risk of being trampled by livestock. A hoof through a hobbit skull is definitely something we'd like to avoid.

The dense vegetation makes them a lot harder to find, too. “The only way to find hominid fossils is to dig for them,” said Adam Brumm, an archaeologist conducting excavations in Indonesia.

There’s evidence of a human presence at the site in the form of stone tools that date back as far as 1 Mya. This coincides with Homo erectus, which was living in Java by 1 Mya. But hobbit remains at Mata Menge were elusive, even though everyone was looking for them after the first discovery at Liang Bua in 2004. “Finally, in October 2014, after years of systematic excavation... we discovered the first hominin fossil remains,” Brumm told a press conference.

What the researchers found was a very small collection: a piece of jaw and six teeth. The specimens came from at least three individuals and possibly more, said archaeologist Gerrit van den Bergh. Two of the teeth are so small that they must have come from children. The jaw fragment is also tiny—so tiny that it seemed likely to have also come from a child. But the jaw showed clearly that adult teeth had already erupted, said van den Bergh, meaning that it must have come from a very small adult.

In fact, these new remains are even smaller than the specimens of H. floresiensis found in Liang Bua. However, they share enough characteristics with one another that the researchers think it’s clearly an ancestor of the latter hobbit population. “Based on the material we have at hand, our working hypothesis is that this is a H. floresiensis-like hominin,” said Brumm.

The mandible also clearly shares features with Homo erectus, which helps to clarify the ancestry of the species. There have been two competing hypotheses about this, said van den Bergh. Either the hobbits descended from H. erectus, going through the well-attested process of island dwarfism to shrink dramatically, or they descended from a hominid species that was already on the small side, like Homo habilis or even an Australopithecus species.

The problem with the latter hypothesis is that there’s no evidence of these species having left Africa at all. The similarities between the Mata Menge remains and H. erectus features add extra weight to the H. erectus hypothesis, although there are still so few specimens available that the question isn't entirely resolved.

Dating for coherence

Several lines of evidence support a 700kya date for these remains. Abi Stone, a geochronologist at the University of Manchester who wasn’t involved in the hobbit research, told Ars that dating methods can be tricky things. The stars have to align, in a way: different methods can be applied to only certain materials and time periods, so you have to hope your material and time period line up.

Here, the researchers were fortunate to be able to work with a number of methods. Argon-argon dating was used to date the rock layers surrounding the specimens, turning up dates of around 1Mya and 800kya below the hobbit remains and 650kya in the layers above. That means a minimum age for the fossils of 650,000 years and a maximum age of around 800,000 years.

One of the teeth itself was also dated using uranium-series dating, which measures the amount of uranium that has decayed into thorium since the remains were buried. This is trickier; uranium-series dating rests on a lot of assumptions, which can leave the results with a very wide window according to Stone. A Stegodon tooth was also dated using uranium-series dating as well as electron spin resonance, which looks at trapped electrons. The range from these dates suggested that the youngest the bones could possibly be was between 360,000 and 690,000 years old. It’s a wide window of possibility, but the upper end of the range coincides neatly with the dates obtained from the surrounding rocks.

Some of the data needed for close scrutiny of the methods wasn’t reported in the paper, but on the whole “what they say makes a lot of sense,” says Stone. Having a range of methods being applied to the site is important, she explains; especially so when there’s some potential controversy.

Open questions

The discovery is exciting, but very far from conclusive, the authors warn. “We have only recovered a small number of isolated fossils from Mata Menge,” says van den Bergh. “More definitive conclusions about the identity of the Mata Menge hominins, and the origin and evolution of H. floresiensis, must await the discovery of additional fossil remains, especially more complete portions of the skull.”

One of the unresolved questions is the frankly alarming speed of shrinkage the remains seem to suggest. If the tools from 1 Mya were left by full-sized H. erectus, this implies only 300,000 years for the species to shrink down to hobbit size.

Island dwarfism is a well-known phenomenon, but we don’t have any primate examples of the process that could help to establish how fast it can occur. “Red deer from the island of Jersey had reduced to one-sixth of the body size in the ancestral population within about six millennia,” the authors write in the paper. Determining whether hominins could do the same may need to wait for more fossils.

Chris Stringer, a human evolution researcher at London’s Natural History Museum, agrees that the anatomy of the jaw suggests an “erectus-like ancestor." But he’s not so sure this means that H. erectus shrank dramatically over just 300,000 years.

“We don’t know how large the tool-makers at 1 million years actually were,” he told Ars. We also can’t be sure that there weren’t other hominins on Flores before 1 million years; that just happens to be the earliest evidence we have. It’s possible, he says, that the “dwarfing process could even have started on other islands before reaching Flores.”

Getting a clearer understanding of the story relies on finding more remains. Excavations are already underway, looking at earlier sites on Flores. “We want to know what the very, very first hominins to set foot on the island looked like,” said Brumm. “That requires finding the fossils that date to before 1 Mya to go with these unusual tools that we find at around that period of time.”

For van den Bergh, one of the most exciting conclusions to draw from this research is how little we still know about our closest relatives—and how much more there might still be to discover. “The fossil evidence from the continental area implies that the human body and brain size gradually increased during much of the Pleistocene, but the case on Flores tells us that the evolution of our genus is not necessarily unidirectional,” he said. “Human diversity could have been far greater than we have ever realised. So far, we have mainly looked on continents. On oceanic islands, things change, and there are many more oceanic islands than there are continents on our planet.”

Nature, 2016. DOI: 10.1038/nature17999 and 10.1038/nature17663 (About DOIs).