This tiny arm bone fossil sheds light on the early human species known as the 'hobbit' (2024)

A 700,000-year-old fragment of arm bone has shed light on the origins of the early human species known as the "hobbit".

The tiny piece of bone is from an early hobbit (hom*o floresiensis) individual, which researchers estimate was just 100 centimetres tall.

This was 6cm smaller than its descendants, which lived 60,000 years ago.

While this change in height was unexpected to archaeologists, the discovery of the bone and some new teeth do solve the long-standing question of where H. floresiensis came from.

The study, published in Nature Communications, found distinctive features of the teeth connect the hobbit's lineage to a taller Javanese hom*o erectus ancestor, rather than the shorter African Australopithecus — also known as Lucy — or hom*o habilis.

Recent hobbit discoveries

H. floresiensis made its first appearance in the archaeological record with the 2003 discovery of a nearly complete, 106-centimetre female skeleton in Liang Bua, a cave on the western side of Flores Island in Indonesia.

That find was dated to around 60,000 years old and, along with subsequent discoveries of more fossils in the same cave, raised questions about where these small early humans came from.

In 2016, archaeologists unearthed more fossils — this time, some teeth and part of a jawbone — in a different part of the island called Mata Menge.

Dated to 700,000 years old, these remains also bore the hallmarks of H. floresiensis, but the absence of bones from elsewhere in the body made it difficult to draw conclusions about the size of these older specimens.

Now the discovery of a partial upper arm bone, the smallest adult human arm bone in the fossil record so far, and two more teeth at Mata Menge has revealed that this H. floresiensis individual was only around 100cm tall when they died.

This came as a surprise to archaeologists.

They had expected earlier specimens of H. floresiensis to be taller than their more recent counterparts, reflecting their H. erectus ancestor, Griffith University archaeologist Adam Brumm said.

"Instead, what we seem to have found is a much older variant of the hobbit itself, of hom*o floresiensis."

The small stature of all H. floresiensis fossils has been explained by what's called "island dwarfism" or "insular dwarfism".

It's an evolutionary pattern evident in island-dwelling life forms that sees typically small species such as birds and insects get much bigger, while larger ones, including humans and elephants, shrink.

But that doesn't explain why the hobbit appears to have shrunk relatively soon after diverging from its larger H. erectus ancestor — which inhabited Java around 800,000 to a million years ago — and then grew slightly larger over the subsequent hundreds of thousands of years isolated on Flores.

"This is what we're still trying to get our head round," Professor Brumm said.

"It could just be some natural size variation within the population. It could be a male and female thing, the males being probably a bit bigger than the females in body size."

He speculates that the environment on the island at the time the older specimens lived might have made smaller size an advantage, and perhaps those conditions had changed slightly by the time the younger fossils were found.

That question is unlikely to be answered until more fossil specimens are found from the period between the 700,000- and 60,000-year-old discoveries, he said: "We just have to keep digging in the hope that we're going to find more complete remains."

Teeth's ancestry clues

Something the new discovery does is tie H. floresiensis more definitively to H. erectus.

When the original younger H. floresiensis fossils were found in Liang Bua in 2003, there were hints that the early human might have been descended from African hominids, such as Australopithecus, said Susan Larson, professor of anatomy at Stony Brook University in New York, who was not involved with the study.

"This was remarkable, because we don't know of any dispersal events out of Africa that early.

"There didn't seem to be many features that really made hom*o erectus a better ancestral form."

But these new findings, specifically the teeth, show clear evidence of the hobbit's H. erectus ancestry.

"It is very fortuitous that teeth and jaws seem to fossilise pretty well, because they are pretty clearly reflective of taxonomy," Professor Larson said.

"Teeth have lots of goofy little grooves and peaks that seem to probably serve some purpose, but also seem to be very species-specific so that you can gather a lot of information about heritage as well as function."

An enduring mystery is how the ancestors of H. floresiensis, whatever their size, made it to the island of Flores in the first place. Huge stretches of water separated the South-East Asian mainland and Flores, Professor Brumm said.

"Somehow, these early humans were able to get across to these islands, whereas most other non-flying land mammals were not."

There's no evidence of any of these early humans made boats or rafts, so, he said, perhaps some individuals were swept out to sea clinging to floating vegetation, "then very, very rarely, some of them survived and ended up on these remote oceanic islands where they effectively became marooned".

There are also questions about if and how H. floresiensis might have interacted with early hom*o sapiens in the region, Professor Brumm added.

"Our species could well have come face to face with these with the late surviving remnants of these early hominins when they first landed on these islands on the way to Australia."

There is evidence in the genetic makeup of modern humans in the region which suggests there may have been some genetic intermingling between these two species.

"It's a fascinating part of the world and it's a very poorly known chapter in the human story," Professor Brumm said.