Evrim Yazgin
Cosmos science journalist
An extremely rare ancient human fossil has been found on the Indonesian island of Flores which could change our understanding of hominin evolution in Southeast Asia.
The 700,000-year-old bone is from an adult. But its total length would have been only a little more than 20 centimetres long and has the smallest minimum circumference of any humerus (upper arm bone) ever found in an ancient human at just 46mm.
This bone and 10 others were found between 2014 and 2016 belonging to at least 4 different individuals including 1 adult, 1 young adult and 2 children.
All the bones were found at the Mata Menge fossil site in the So’a Basin of central Flores.
Of the fossils, 3 – including the diminutive humerus – are described for the first time in a paper published in the journal Nature Communications.
Hobbits, but not like in the books
The new fossils may belong to ancestors of a group of extinct ancient human called Homo floresiensis.
The discovery in 2003 of H. floresiensis shocked the world.
The first H. floresiensis were found 75km west of the Mata Menge site at the Liang Bua cave. These humans died about 60,000 years ago. But one thing about them stuck out. Adults and children alike, they were small.
Their stature earned the ancient Flores people the nickname “Hobbits”.
H. floresiensis stood about 1.1 metres tall. This is as tall, if not shorter, than the first hominins from Africa which lived millions of years ago, diverging the human lineage from that of other apes.
The origin of this tiny population of ancient humans has puzzled archaeologists for more than 2 decades.
Honey, I shrunk the ancient human
Scientists generally agree that H. floresiensis are a separate species of human, rather than a known species like Homo erectus with population-wide birth defects causing dwarfism.
But where they came from and how they got so small has been hotly debated.
One theory is that H. floresiensis is a late-surviving remnant of an ancient small hominin from Africa. Candidate species include Homo habilis or Australopithecus afarensis like the famous ‘Lucy’ who herself would have stood only 1 metre tall when she lived 3.2 million years ago.
Another possibility is that H. floresiensis evolved from a larger hominin, H. erectus, which made it into Asia about 1.8 million years ago.
It is believed that the H. floresiensis population is an example of insular dwarfism – an example of an ecogeographical rule known as “Foster’s rule”. This states that members of a species tend to be smaller or bigger depending on the availability of resources in the environment.
Such a scenario seems likely to have occurred on Flores as H. floresiensis shared the forests with a tiny extinct elephant relative, the 130-cm-tall Stegodon florensis insularis.
“The precise mechanism(s) underlying island dwarfism is still under debate, but it’s probably the case that large-bodied mammals that become isolated on resource-poor islands tend to evolve a smaller body size over time because small bodies require less food than big bodies,” co-author of the new study Adam Brumm tells Cosmos.
Brumm is a professor at Griffith University in Queensland, Australia.
I may be small, but I’m big inside
Mata Menge’s hominin is believed to have been 100cm tall compared to the estimated 106cm-tall “Hobbits” found at Liang Bua cave.
In addition to the humerus, 2 hominin teeth from Mata Menge were also small.
One of the teeth is similar in shape to those of early H. erectus found on the Indonesian island of Java where, coincidently, the H. erectus was first uncovered in 1891.
These finds support the theory that H. floresiensis evolved from Asian H. erectus, rather than from an earlier African hominin.
“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,” Brumm says.
“The evolutionary history of the Flores hominins is still largely unknown. However, the new fossils strongly suggest that the ‘Hobbit’ story did indeed begin when a group of the early Asian hominins known as Homo erectus somehow became isolated on this remote Indonesian island, perhaps one million years ago, and underwent a dramatic body size reduction over time.”
Small steps forward
Brumm notes that there’s more to add to the ancient history of hominins in Southeast Asia.
“‘Wallacea’ in particular (the vast expanse of oceanic islands between continental Asia and Australia) is a fascinating place because early hominins that become isolated on some of these islands underwent remarkable evolutionary changes, resulting in the emergence of strange new species like Homo floresiensis of Flores. No one in our field had predicted the discovery of such a bizarre creature. Who knows what else is out there?”
While the new discoveries build our understanding of the evolution of H. floresiensis, Brumm says more finds will fill in the gaps.
“Ancient DNA would of course be ideal but it’s very unlikely to have survived in the Flores fossils. The discovery of a relatively complete skull or even a partial skeleton of a hominin at Mata Menge would be most welcome; as would be any hominin fossils found elsewhere on the island that span the very substantial time gap between the Mata Menge hominin fossils and the Liang Bua Homo floresiensis fossils.
“I can name other things on my fossil wish list but that would be entering the realm of archaeological fantasy.”
