About 700,000 years ago, the skeletal remains of one of our most diminutive and mysterious ancient relatives were encased in sand and mud in a riverbed on an Indonesian island. Now, scientists have uncovered and analyzed those fossils, shedding light on the most petite known lineage of ancient humans to ever exist.
A team of archeological researchers report and describe a fossilized partial arm bone and two teeth they believe belonged to Homo floresiensis, in a study published August 6 in the journal Nature Communications. The findings add three specimens to the limited collection of fossils thought to be from H. floresiensis, which have only ever been found excavated from two sites on the island of Flores in Indonesia and represent under 20 estimated individuals. These hominins, nicknamed ‘hobbits’ for their small stature, were even smaller than previously thought, according to the new research, which also adds clarity to our tiniest ancient cousin’s likely origins.
Previous analysis of fossils discovered in Liang Bua cave on Flores 20 years ago suggested the H. floresiensis – an entire newly proposed species at the time – stood around 106 centimeters (about 3.5 feet) tall. A skull specimen indicated the lineage had a remarkably small brain, just one-third the size of that of an average modern human, despite being found alongside stone tools, which have mainly been found with larger-brained species. These initial hobbit fossils were dated to about 60,000 to 100,000 years old.
The new fossils, recovered from an archaeological site named Mata Menge, which is about 45 miles away from Liang Bua cave, were found inside a sandstone layer that was once a riverbed. They were collected nearly a decade ago along with seven other fossils described in a 2016 study, but only recently analyzed. All are estimated to be around 700,000 years ago, based on the age of the rock they were contained in; this is much older than the Liang Bua fossils. And, likely because of the age gap, they show slightly different features, offering a glimpse into the potential evolution of H. floresiensis over time.
The two teeth resemble smaller versions of the teeth of Homo erectus, another lineage of ancient humans, more closely than they resemble teeth found at Liang Bua. This supports the controversial hypothesis that H. floresiensis evolved from H. erectus, according to the study authors. The humerus fragment, the lower section of an upper arm bone, suggests that these particular hobbits were even smaller than their relatives found in Liang Bua, standing just 100 centimeters (about 3.3 feet) tall.
“When I first saw the small humerus, I thought it was a child's bone,” said study co-author Yousuke Kaifu, an anthropologist at the University of Tokyo in Japan, in a news statement. Yet despite its particularly tiny size, microscope and feature analysis indicate the bone came from an adult without any apparent skeletal or muscular deformity – a surprise to Kaifu and his colleagues.
“This very rare specimen confirms our hypothesis that the ancestors of Homo floresiensis were extremely small in body size; however, it is now apparent from the tiny proportions of this limb bone that the early progenitors of the ‘Hobbit’ were even smaller than we had previously thought,” said Adam Brumm, a study co-author and an archaeologist at Griffith University in Australia, in a different press release. “It is the smallest upper arm bone known from the hominin fossil record worldwide,” he added.
Putting together all the fossil evidence from Mata Menge and Liang Bua, along with the assemblage of stone tools and other artifacts uncovered at the sites, Brumm, Kaifu, and their co-authors suggest a new story to explain the emergence of H. floresiensis.
Around one million years ago (the age of the oldest tools uncovered at the sites), they hypothesize that the first hominins appeared on Flores, likely H. erectus individuals that made it there by accident after having been swept up in a tsunami or other storm and rafting 450 miles to the island from Java. Living on Flores, natural selection shrank and modified the descendents of those first arrivals over 300,000 years and H. floresiensis emerged. From there, their teeth became more specialized (hence the differences between the teeth found at Mata Menge and Liang Bua) and their size stabilized. The hobbit humans lived on the island up until the arrival of modern humans (Homo sapiens) about 50,000 years ago, which subsequently drove H. floresiensis extinct.
It’s a tidy narrative, that’s possible given current evidence. For instance, it’s well-established that island inhabitants of all species tend to shrink in order to minimize their resource needs in a restricted territory. Yet not all human origins experts are fully convinced. So far, no fossils directly show that H. erectus ever inhabited Flores. “The evidence for this idea is very weak,” Matthew Tocheri, a paleoanthropologist at Lakehead University in Canada, told The New York Times.
And the small hominins may have made their way to Flores through other paths. “Many researchers assume a dwarfing process occurred on Flores itself, but there is currently no way of knowing that at the moment, since the process could have already started on other islands, such as Sumbawa or Sulawesi, prior to the arrival on Flores,” said Chris Stringer, a human origins researcher at the Natural History Museum in the UK, to The Guardian.
Human origins research is often messy and hotly debated, as researchers try to extrapolate tens of thousands of years of history from a small number of incomplete fossil fragments. Yet still, no matter what lineage it represents and no matter how it evolved, the arm bone is proof that we have some surprisingly tiny, distant cousins in the human family tree. Every fossil find brings us one step closer to unraveling the mystery of our hobbit ancestors.
