Buried 6½ feet beneath volcanic rock on the Indonesian island of Flores, scientists have found the fossilized remains of a petite hominin that lived 700,000 years ago.
The discovery, described Wednesday in two papers in Nature, consists of just six tiny teeth and a fragment of a small lower jawbone. Still, the international research team says it is enough to suggest that the fossils belonged to a direct ancestor of the strange and diminutive human relative Homo floresiensis, also known as the “Hobbit.”
The new find could help scientists unravel the mysterious origins of this enigmatic human species that was isolated on a small island between Asia and Australia for at least 1 million years.
The world was first introduced to Homo floresiensis in 2004, when an international team of researchers announced the discovery of a never-before-seen hominin that had been found in the Liang Bua cave on Flores.
The fossil record suggests that these ancient human relatives lived between 100,000 and 50,000 years ago. Adults stood just 3½ feet tall – the height of an average 4-year old modern-day child. Their brains were roughly one-third the size of our own, or about the size of a chimpanzee’s brain.
Because of their miniature size, researchers nicknamed these unusual hominins the Hobbits.
Fossils from at least three hominin specimens unearthed in Indonesia. (Kinez Riza)
In the intervening years, two competing views of the Hobbits’ origins emerged. One hypothesis posits that Homo floresiensis descended from the large-bodied hominin Homo erectus that lived between 1.89 million and 143,000 years ago.
Scientists say it is possible that Homo erectus may have arrived on Flores from Java, perhaps after being washed out to sea by a tsunami. Over time, this species began to shrink on its new island home – a relatively common phenomenon known as island dwarfism.
“Lots of animals that end up on islands get smaller for a variety of reasons like limited food sources, or because there are no large predators to stay big for,” said Karen Baab, a paleoanthropologist at Midwestern University in Glendale, Ariz., who was not involved in the study. “We even see it in modern humans in certain environments that are home to pygmy populations.”
The other hypothesis states that Hobbits descended from smaller and more ancient hominins like Australopithecus africanusor Homo habilisthat were already diminutive at the time they reached the island.
Both theories have challenges. One might accept that Homo erectus grew smaller in stature by two-thirds over time. After all, a smaller body is easier to feed. But for some scientists, it is hard to believe that it made evolutionary sense for its brain to shrink by half. Losing brain power doesn’t seem like a likely evolutionary development.
On the other hand, if you buy that Homo floresiensis was descended from Australopithecus or Homo habilis, then you have to explain how either of these species made their way to Indonesia when their remains have never been found outside of Africa.
“There are issues with both scenarios in my opinion,” Baab said.
Other researchers are convinced that the Hobbit fossils belonged to anatomically modern humans who suffered from some type of disorder that was responsible for their extreme dwarfism. Both microcephaly and Down syndrome have been proposed.
Experts say the newly discovered fossils could clear up some of these controversies.
The seven specimens described in the paper were found in an ancient stream bed about 40 miles from Liang Bua at a site called Mata Menge.
Digging at Mata Menge is not easy. The fossils are embedded in solid rock, not sediments. To uncover them, researchers spent years chipping away at stone in unrelenting heat.
A total of 30,000 fossils were unearthed over the course of the excavations led by Gerrit van den Bergh of the University of Wollongong in New South Wales, Australia; Adam Brunn of Griffith University in Queensland, Australia; and Iwan Kurniawan of the Geological Museum in Bandung, Indonesia. They included the remains of stegodons – a small extinct elephant relative – Komodo dragons, giant rats and water birds.
The team also found many examples of simple stone tools similar to those discovered near Liang Bua, but the physical evidence of the hominins themselves proved elusive.
It wasn’t until 2014, 20 years after the work at Mata Menge began, that researchers recognized a molar belonging to a hominin in a layer of sandstone dated to 700,000 years ago.
A few days later the group unearthed a mandible fragment – the lower piece of a jawbone – in the same layer. A handful of other teeth followed.
The specimens were sent for analysis to Yousuke Kaifu, a biological anthropologist and ancient-hominin tooth specialist from the National Museum of Nature and Science in Tokyo.
Kaifu was shocked at the size of the fossils. The mandible was so tiny that at first he thought it must belong to a juvenile. However, after subjecting it to a high-resolution CT scan he discovered that a wisdom tooth had erupted from it, meaning it definitely belonged to an adult.
A close examination of the number and placement of cusps or bumps on the individual teeth revealed that they were very similar, although not identical, to teeth that had been discovered at Liang Bua. They were also, unexpectedly, up to 28% smaller than the teeth from Liang Bua.
“That was a surprise,” Van den Bergh said. “Mata Menge is more than half a million years older than Liang Bua. We thought we would find something bigger – something closer to the initial founder population.”
Kaifu also did a statistical analysis that showed that the Mata Menge teeth were more similar to Homo erectus teeth than to teeth from Australopithicus or Homo habilis.
“I then realized the significance of the new findings,” Kaifu said. “There were tiny Hobbit-like hominins as early as 700,000 years ago on Flores and the fossils are consistent with the hypothesis that Homo floresiensis originated from the early Asian Homo erectus.”
And so now, a more definitive story of the origin of the Hobbit can be told. The earliest known evidence of stone tools on Flores dates back to 1 million years ago, suggesting that hominins arrived on the island around that time. If these first colonizers were indeed Homo erectus, then it seems that they rapidly evolved a small stature within 300,000 years of their arrival – a shorter time span than was previously thought.
“It is certainly much faster than I would have envisaged but nothing surprises me about this island anymore,” said Kira Westaway, a geochronologist at Macquarie University in Sydney, Australia, who was not involved in the work.
While there is still much more to learn about the origins of Homo floresiensis, the authors say the study should at least dispel the idea that the more complete Hobbit skeleton from Liang Bua represents a diseased modern human.
Modern humans do not show up in the fossil record until 200,000 years ago – hundreds of thousands of years after the Mata Menge fossils were deposited.
“We can now say that Homo floresiensis does indeed represent a distinct branch of archaic hominins that appear to have lived in isolation on Flores for at least 1 million years,” Van den Bergh said.
He added that the origin story of the Hobbit suggests that human evolution is not always as straightforward as we might imagine.
Fossil evidence from the continents generally implies that the human body and brain size gradually increased over time, but that evolutionary pattern may not have been the best strategy for hominins that wound up on islands.
“The case on Flores tells us that the evolution of our genus is not necessarily uni-directional,” Van den Bergh said. “Human diversity could have been far greater than we ever realized.”