The discovery of a tiny hand bone suggests that ancient humans known as “hobbits” became smaller and smaller only after they arrived on the Indonesian island a million years ago, scientists said on Tuesday. Much about the diminutive Homo floresiensis has remained a mystery since the first fossils suggesting its existence were found on the island of Flores in 2003.

The tool-using hominins are thought to have lived on the island around 50,000 years ago, when our own species, homo sapiens, walked the Earth, including nearby Australia. Scientists had previously suggested that the hobbits were around 1.06 metres (3.5 feet) tall, based on teeth that are around 60,000 years old and a jawbone found in an island cave.

But the discovery of part of a shoulder bone and some teeth on an open-air island on the island suggests that some hobbits were only three feet tall about 700,000 years ago, according to a study in the journal Nature. Nature Communication.

The bone was so small that an international team initially thought it belonged to a child. Study co-author Adam Brumm, an archaeologist at Griffith University in Australia, told AFP it was the smallest fossil of an adult hominin ever found.

“Truly Epic”

The discovery could tip the balance of a heated debate among scientists over how H. floresiensis became so small. One camp argues that the hobbits, named after minor characters in JRR Tolkien’s fantasy novels, are descended from the already tiny early hominids that arrived on Flores about a million years ago.

Others believe that our ancestor Homo erectus, which was as large as us and spread across Asia, became stranded on an island and evolved into the smaller H. floresiensis over the next 300,000 years. The researchers behind the latest discovery believe it strongly supports the latter theory.

These ancient humans “significantly reduced their body size, consistent with a well-known evolutionary phenomenon known as undulating dwarfism,” Brumm said. This is the process by which larger animals tend to shrink over time to adapt to their limited environments.

The tropical island was home to other smaller mammals, including the elephant’s cow-sized relative. The newly discovered teeth also appear to be smaller versions of Homo erectus teeth, the researchers said.

“If we are right, it seems that Homo erectus was somehow able to overcome difficult deep-sea barriers to reach isolated islands like Flores,” Brumm said.

“We don’t know how they did it,” he said, adding that “accidental ‘raft’ formation on tsunami debris” was a possibility.

Brumm said these ancient humans survived for hundreds of thousands of years while stranded on the island, evolving into “strange new forms.” The discovery means “we can now say with certainty” that the Homo erectus theory is the more likely scenario, said archaeologist Mark Moore of the University of New England in Australia, who was not involved in the research.

Moore, who studied the stone tools used by hobbits, told AFP that the technology “did not protect our cousin species from the forces of biological evolution”.

He added that the extent to which hobbits have changed in just 300,000 years is “a reminder of the power of natural selection.” “The evolutionary history of this hominid group is truly epic.”