The New York Times, June 8, 2016
Scientists digging in the Liang Bua cave on the Indonesian island of Flores years ago found a tiny humanlike skull, then a pelvis, jaw and other bones, all between 60,000 and 100,000 years old.
The fossils, the scientists concluded, belonged to individuals who stood just three feet tall — an unknown species, related to modern humans, that they called Homo floresiensis or, more casually, the hobbits.
On Wednesday, researchers reported that they had discovered still older remains on the island, including teeth, a piece of a jaw and 149 stone tools dating back 700,000 years.
The finding suggests that the ancestors of the hobbits arrived on Flores about a million years ago, the scientists said, and evolved into their own distinct branch of the hominin tree.
But without other parts of a skeleton, such as the skull, hands or feet, they can’t be sure whether the newly discovered fossils also belong to Homo floresiensis or instead to some other ancient relative of humans (known generally as hominins).
“We have to be careful,” said Gert van den Bergh, a paleontologist at the University of Wollongong in Australia and a co-author of the new study. “Until we find those elements, we cannot really say much more about it.”
Dr. van den Bergh and his colleagues found the new fossils at Mata Menge, an archaeological site on Flores that had already yielded stone tools dating back 800,000 years — a clue that hominins of some sort had once lived there.
Starting in 2004, the researchers chiseled fossils out of the cementlike rock. For years, they found only animal fossils, including dwarf elephants.
In 2014, Dr. van den Bergh and his colleagues got their first stroke of good luck: six feet below the surface, they found a cracked molar. Very quickly they discovered six other teeth, as well as a piece of a jaw. The fossils come from three hominins.
The researchers were intrigued to find a wisdom tooth erupting from the jaw. “That means that it was an adult,” said Dr. van den Bergh.
Yet this adult must have been very small. The researchers estimate the jawbone was 23 percent smaller than the Homo floresiensis jaw found at Liang Bua.
“They were truly little people, smaller even than the Liang Bua hobbits,” said Richard Roberts of the University of Wollongong, who was part of the team that originally discovered Homo floresiensis but was not involved in the new study.
Critics have argued that the Liang Bua bones might have come from a member of our own species who suffered some kind of growth disorder, such as Down syndrome. Several experts agreed that the Mata Menge fossils put to rest any doubts that Homo floresiensis is its own distinct species.
In another study published on Wednesday in the journal PLOS One, Karen L. Baab, a paleoanthropologist at Midwestern University in Glendale, Ariz., and her colleagues compared skeletons of people with Down syndrome with the Liang Bua fossils.
The researchers concluded that any resemblance was superficial, and that the fossils belonged to a separate species. “There continues to be no very good evidence that this is a pathological modern human,” Dr. Baab said.
In their new study, Dr. van den Bergh and his colleagues propose that the hobbits evolved from a tall, relatively large-brained hominin called Homo erectus that lived in Indonesia at least 1.5 million years ago.
Dr. van den Bergh said it was unlikely that Homo erectus could have built boats that could have taken them to Flores. “Personally, I think it was some freak event like a tsunami,” he said.
By 700,000 years ago, the Mata Menge fossils suggest, the descendants of these castaways had shrunk to three feet in height. It’s possible that their brains shrank as well, as an adaptation to life on a small, harsh island.
Dr. Baab said the scenario was plausible, but not airtight. The hobbits have some anatomical similarities to Homo erectus in Indonesia, but they’re not just scaled-down versions.
For example, the fossils from the Liang Bua cave show that they had longer arms and shorter legs than Homo erectus. It’s possible that they evolved from a smaller, more primitive Asian population of Homo that scientists haven’t yet discovered.
A few critics of Homo floresiensis still aren’t convinced, saying the debate over whether this really was a species couldn’t be settled by the new finding.
“Isolated teeth and jaw fragments have nothing to contribute to that issue,” said Robert D. Martin, an emeritus curator at the Field Museum in Chicago, who has argued that the Liang Bua fossils belonged to a human with microcephaly.
Dr. van den Bergh is optimistic that he and his colleagues will find a skull and other bones at Mata Menge that may satisfy such critics. The layer of rock where they found the hominin teeth and jaw is chock-full of fossils from other species.
The geology of the rock indicates that the fossils come from a streambed that was suddenly buried in mudslides from a nearby volcanic eruption. The disaster seems to have claimed a number of victims at once — including, possibly, more hobbits.
“I’m sure we will find more stuff,” said Dr. van den Bergh.
Copyright 2016 The New York Times Company. Reprinted with permission.