A new study describes 700,000-year-old teeth and arm bones from one of our most enigmatic relatives: a toddler-sized “hobbit” that lived on a tiny island between the Indian and Pacific oceans.
The study, published Tuesday in the journal Nature Communications, suggests that the species, Homo floresiensis, sometimes nicknamed hobbits, may have been even smaller than previously thought. But the findings continue to divide scientists over how such exceptional humans evolved.
The hobbits were first discovered 20 years ago inside Liang Bua Cave on the Indonesian island of Flores. Australian and Indonesian scientists discovered bones and teeth, along with stone tools that were probably used to butcher meat.
Based on those bones, the researchers calculated that Homo floresiensis was 106 centimeters tall, or about three and a half feet. More notable than its short stature was its tiny brain, one-third the size of a modern human’s. By analyzing the cave floor, the scientists determined that the Homo floresiensis bones were between 100,000 and 60,000 years old.
The sensational discovery left scientists scrambling to fit Homo floresiensis into the family tree of humans and their extinct relatives, a group known as hominins. The earliest known hominins were short, small-brained apes. But by two million years ago they had been replaced by taller, much larger-brained ones.
Some scientists hypothesized that the bones came from humans with growth disorders. But many researchers rejected that explanation, because the present-day anatomy of people with such growth disorders does not closely resemble that of the fossils.
The debate took a turn in 2016, when researchers reported a tantalizing batch of much older fossils from another area of Flores, called Mata Menge. The fossils, about 700,000 years old, consisted of six teeth and part of a jaw. The Mata Menge fossils were as small as those from Liang Bua, or even smaller.
And on Tuesday, Mata Menge’s team uncovered two more tiny teeth, as well as a piece of humerus, the upper arm bone.
“We couldn’t tell whether this belonged to a child or an adult,” said Yousuke Kaifu, a paleoanthropologist at the University of Tokyo. “That’s a key question.”
Dr. Kaifu and his colleagues compared the humerus with arm bones from children and adults today. Mata Menge’s bone had many signs that it had stopped growing, suggesting the individual was an adult.
This is surprising because Mata Menge’s humerus was tiny, the smallest of any adult hominin found to date. Dr. Kaifu and his colleagues calculated that the arm’s owner had been just 100 centimeters tall, less than a meter and a half tall.
The fossils found so far at Mata Menge appear to come from at least eight individuals. The newly revealed teeth and humeri make Dr. Kaifu and his colleagues more confident that the Mata Menge hominins were indeed Homo floresiensis.
Matthew Tocheri, a paleoanthropologist at Canada’s Lakehead University who was not involved in the study, agreed. “What else could they be?” he asked. “Any alternative seems incredibly unlikely.”
However, Deborah Argue, a paleoanthropologist at the Australian National University, said she was not convinced. “More skeletal material from this enigmatic hominin will help determine whether this group represents Homo floresiensis,” she said.
Dr. Kaifu and his colleagues argued that Homo floresiensis evolved from a species of tall hominin called Homo erectus. Originally from Africa, Homo erectus arrived in Java about 1.3 million years ago and survived there for more than a million years.
The researchers proposed that Homo erectus traveled 450 miles east from Java to Flores, arriving on the island about a million years ago. That’s the age of the oldest stone tools found there. Once isolated on Flores, Homo erectus shrank to the height of a hobbit 700,000 years ago, the scientists say.
Dr. Kaifu speculated that food shortages on the island may have driven Homo floresiensis’ extraordinary evolution. And in this particular location, its small size did not increase its risk of being killed by predators.
“If you go to an isolated island where there are no lions or tigers, you don’t have to be big,” Dr. Kaifu said.
According to theory, this shrinkage also drastically reduced the brain of Homo floresiensis. And yet, the presence of stone tools on Flores suggests that hobbits still retained a powerful mental capacity.
“I find this quite shocking,” says Dr. Kaifu. “We thought that being smart and having a bigger brain was the destiny of humans. But Floresiensis tells us that this is not necessarily the case.”
Dr. Argue did not accept that evolutionary hypothesis, given the scarcity of direct fossil evidence that Homo erectus migrated to the island. “We cannot assume that this species ever reached Flores,” he said.
Dr. Tocheri also thought the Homo erectus hypothesis was exaggerated. “The evidence for this idea is very weak,” he said.
Until more fossils turn up, both Dr. Tocheri and Dr. Argue said other explanations remain plausible. It is even possible that Homo floresiensis descended from African hominins that were already small when they crossed into Asia.
#Scientists #find #arm #bone #ancient #human #Hobbit
