Smallest Human Limb Bone Ever Sheds New Light on Homo floresiensis, The ‘Hobbits’

In a discovery that rewrites our understanding of human evolution, scientists have unearthed extraordinarily rare fossils on the Indonesian island of Flores, including an adult limb bone so tiny it defies previous theories.

These 700,000-year-old remains offer unprecedented insights into the mysterious lineage of Homo floresiensis, the so-called ‘Hobbits,’ who roamed this island long before modern humans emerged. Homo floresiensis was one of five hominin species that coexisted with Homo sapiens at various points in time.

A new spin on the hobbit story

On a remote Indonesian island, time seemed to have slowed its march. There, nestled in the shadow of a volcano, paleoanthropologists stumbled upon a mystery that would redefine our understanding of human evolution. In 2003, on the island of Flores, they unearthed the skeletal remains of a diminutive hominin, a creature unlike anything ever seen before.

Standing just over three feet tall, Homo floresiensis—or the “Hobbit,” as it was affectionately dubbed—challenged long-held assumptions about human ancestry. Its brain, no larger than a grapefruit, defied expectations for a creature capable of tool manufacturing, hunting, and likely fire-making. Tools found scattered around the Liang Bua cave site, including stone blades and points, indicate they hunted and butchered large animals, like the island’s now-extinct pygmy elephants.

How such a small-brained species could have achieved these cognitive feats remains a puzzle. Some scientists propose that isolation on Flores, with its limited resources, drove the population towards miniaturization—a phenomenon known as insular dwarfism.

What continues to baffle scientists is the origins of Homo floresiensis. Some propose they descended from Homo erectus, an early human ancestor known for migrating out of Africa. Others hypothesize that Homo floresiensis represents a distinct evolutionary lineage, a bizarre offshoot of the human family tree.

This is where the newly reported fossils come in. The fossils, dated to approximately 700,000 years old, come from the Mata Menge site, a location already famous for yielding valuable clues about the enigmatic Homo floresiensis. Previously, scientists discovered a jaw fragment and six teeth belonging to at least three individuals, whose anatomical features were even smaller than those in Homo floresiensis from Liang Bua.

In their new study, researchers led by Professor Yousuke Kaifu of the University of Tokyo, Iwan Kurniawan of the Center for Geological Survey in Indonesia, and Associate Professor Gerrit van den Bergh from the University of Wollongong report the discovery of three additional hominin fossils from Mata Menge dating to 700,000 years ago. These fossils include a keystone fossil, the distal shaft of an adult humerus (lower half of the upper arm bone). 

“When I first saw the small humerus, I thought it was a child’s bone, but I became curious and was surprised when I looked up its developmental stage. The task of estimating the age and length was difficult, but through collaboration with my co-researchers, we were able to solve the problems to produce these results,” Kaifu said in a press statement.

This arm bone fossil is a game changer. It’s the smallest ever found in the human record, belonging to an individual estimated to be only about 3 feet tall (100 cm), 6 cm shorter than the 60,000-year-old Homo floresiensis skeleton from Liang Bua.

This discovery confirms that the ancestors of Homo floresiensis were already incredibly small, even smaller than previously thought.

“We wanted to find out who the ancestor of Homo floresiensis was by finding fossils of humans dating to around about the time of initial colonisation of Flores, who we presumed would be the progenitors of this small-bodied, endemic species. So we started digging extensively at a site called Mata Menge in the So’a Basin where prior work had uncovered fossils of extinct animals alongside stone artifacts in layers of sandstones deposited in a lakeshore environment between roughly 700,000 to 880,000 years ago. Some stone tools in this same part of the island also date back to at least 1,000,000 years ago,” Professor Adam Brumm from Griffith University’s Australian Research Centre for Human Evolution, a co-author of the paper, told ZME Science.

“We were very excited to find the first hominin fossils as they are very rare and it took us over a decade of intensive research to uncover them (however Gerrit van den Bergh’s time at Mata Menge goes back even further, to the early 90s). The big surprise is that the fossils belong to hominins that seem to be a very early form of Homo floresiensis that was actually slightly smaller in body size than these famously diminutive hominins. We weren’t expecting that.”

Moreover, the researchers found additional teeth at Mata Menge, which share similarities with Homo erectus from the nearby island of Java. This evidence strengthens the theory that Homo floresiensis evolved from Homo erectus after becoming isolated on Flores, possibly beginning around one million years ago.

This hypothesis challenges previous theories that Homo floresiensis might have evolved from a smaller, more primitive hominin such as Homo habilis or Australopithecus afarensis.

“It’s clear from the small size of the teeth and humerus we found that extreme body size reduction evolved very early on Flores and that the species we know as Homo floresiensis is also very ancient, having emerged at least 700,000 years ago and possibly earlier than that,” Brumm added.

A Dwarfing Experiment

The island of Flores seems to have been an evolutionary laboratory. Its isolation and limited resources may have favored insular dwarfism. Over hundreds of thousands of years, Homo erectus on Flores may have gradually shrank, giving rise to the extraordinary Homo floresiensis, which also increasingly became smaller according to the latest findings.

A scarcity of predators may have a lot to do with why some island populations get smaller over time. If an animal does not need to be large to flee or defend itself from predators, then predation pressure is relaxed and body size can safely decrease over time. Other factors that may play a role are resource abundance, competition levels, and energetics.

Previously, scientists have documented many species affected by insular dwarfism. For instance, in the Spinagallo caves of Sicily, more than 100 specimens of the smallest elephant that ever lived, Elephas falconeri, were recovered. These tiny elephants were up to 150 times smaller than the Asian or African giant elephants.

On the island of Flores, another proboscidean called Stegodon underwent a similar process of dwarfism—potentially more than once—before eventually going extinct. A population of these pygmy Stegodons may have thrived until about 900,000 years ago, possibly driven to extinction by newly arrived hominins, the ancestors of Homo floresiensis, as evidenced by stone tools from Mata Menge dating back to approximately 950,000 to 810,000 years ago. Another population of pygmy Stegodons, discovered in the more recent deposits of Liang Bua cave, appears to have survived until around 12,000 years ago, when they were likely forced into extinction by a volcanic eruption.

While these new findings offer crucial insights, many questions remain. How did Homo erectus reach Flores in the first place? What environmental pressures drove the dramatic body size reduction? And what ultimately led to the extinction of Homo floresiensis around 50,000 years ago?

As scientists continue to explore this fascinating chapter in human history, one thing is clear: the story of our species is far more complex and intriguing than we ever imagined.

The new findings were reported in the journal Nature Communications.