Where hobbits come from: tracing Homo floresiensis origins
New fossils reveal the tiny species may have had a much taller ancestor
When archaeologists dug up the first Homo floresiensis fossils in Indonesia’s Liang Bua cave in October 2004, nobody knew what to make of them. They were unlike anything previously excavated. The most complete specimen, a woman designated LB1 and later nicknamed ‘the Hobbit,’ was tiny. At 30 years old, she stood at about 3.5 feet (1 meter) in height, and her brain was almost the size of a chimpanzee’s. Still, her skull was unmistakably human-like. Who was she, researchers wondered, and how did she become so small?
Thanks to a recent paleontological discovery in the So’a Basin, another area on the same island as Liang Bua cave, University of Tokyo anthropologist Yosuke Kaifu and his team have shed some light on how LB1 and the other so-called ‘hobbits’ evolved their tiny stature. Their findings finally provide closure to a debate that has persisted ever since those little bones were found in Liang Bua Cave: Where, if at all, does Homo floresiensis fall on the hominid evolutionary tree?
Neither disabled nor dwarf
The Indonesian island of Flores is fairly far away from the mainland, far enough that scientists initially assumed humans hadn’t reached the island during pre-Homo sapiens migration waves. When scientists discovered the tiny bones from Liang Bua cave, some researchers couldn’t believe they were from a new species. They cited LB1’s skull size and asymmetry as a sign of disease. Microcephaly can drastically reduce brain size in modern humans, sometimes to levels similar to that of LB1; the Rampasasa people native to Flores were known to be a pygmy people far shorter than the average Homo sapiens. Some scientists were convinced that these fossils merely belonged to a microcephalic pygmy. This debate raged for nearly a year, with deniers continuing to insist that differences between LB1 and the average modern human woman could be attributed to disease. However, LB1’s skull lacks many features that are characteristic of H. sapiens. Furthermore, while the Rampasasa people are pygmies, they are still much taller than LB1.
In late 2005, archeologists found a new set of fossils in Liang Bua cave, bringing the total number of known ‘hobbits’ to nine. One of them lived 60,000 years later than the rest. Considering that it is highly unlikely that the cave had been a burial site exclusively for people with one specific disease for 60,000 years, scientists concluded that LB1 and the other individuals found in the cave were new evolutionary cousins of H. sapiens.
Undeniably modern
With H. floresiensis established as a distinct species, researchers pivoted their focus toward placing humanity’s new evolutionary cousin onto the hominid family tree. An early idea posited that this new species was a descendant of Homo erectus, the first known hominid species to migrate extensively outside of Africa. Given that H. erectus fossils have been found on other Indonesian islands and that island species often dramatically change in size, most paleoanthropologists accepted this hypothesis, even though many known H. erectus individuals were twice the size of LB1. However, the Liang Bua fossils’ incredibly small brain size doesn’t fit standard evolutionary models that suggest brains generally enlarge over time. Some scientists wondered if earlier species with smaller brains had larger ranges than previously expected, reaching all the way to Southeast Asia. Since those species are more similar to the Flores hobbits than H. erectus in terms of stature and brain size, it isn’t difficult to imagine how the species could’ve become more specialized on an island. Unfortunately, prior to Kaifu and his team’s latest findings, scientists were unable to definitively confirm or deny either of these theories because of the limited number of bones found in Liang Bua cave.
A specialized descendant of Homo erectus
Over a decade after the first H. floresiensis fossils were found in Liang Bua cave, Kaifu and his team unearthed a third set of bones in the So’a Basin, another location on the island of Flores — a handful of teeth much smaller than those of H. erectus, but not entirely dissimilar. Even more surprisingly, they were smaller than the teeth found at the original Liang Bua site. However, by themselves, teeth aren’t enough to determine the size of a hominid or their appearance. For that, scientists needed bones. Recently, the team found key evidence: a piece of an arm bone.
Through geomagnetic and isotopic analysis of surrounding rock layers, Kaifu and his team determined the new fossils were about 700,000 years old. After making casts of the samples, Kaifu and his team examined the proportions and dimensions of the arm fragment to determine the individual’s age and stature: a healthy, full-grown adult even shorter than LB1. Additionally, the arm bone was more structurally similar to that of other members of genus Homo, ruling out the possibility that the Flores hobbits were of the genus Australopithacus. As for the teeth, researchers compared the shape of the So’a teeth with known samples: H. floresiensis teeth from Liang Bua, H. erectus teeth from Java’s Sangiran site, and H. habilis teeth from Africa. They found that the So’a molars were very similar in shape to the Sangiran teeth, but comparable in size to the Liang Bua teeth. These similarities support the hypothesis that H. floresiensis is a direct evolutionary descendant of H. erectus, with the individuals at So’a Basin representing an earlier form of the species.
Although the So’a molars still lack several of the specific features associated with the Liang Bua Cave individuals, the So’a fossils are far older than those from Liang Bua (700,000 years old versus 80,000 years old). Therefore, it is possible that the distinguishing dental characteristics seen in LB1 and LB6 evolved later in the species’ history. This new finding dramatically changes the timeline of H. erectus migration and H. floresiensis evolution: in order for H. erectus to have had enough time to evolve into a new species half as tall, the initial migration to Flores must have taken place around 1 to 1.2 million years ago. Flores’s hobbits are therefore a much longer-lived species than previously thought, which sparks even more questions about the Flores hobbits — where they lived, and how their species managed to survive for so long. While there isn’t enough data to answer these questions yet, Kaifu and his team’s discovery brings hope to some researchers. Perhaps one day, paleoanthropologists will find more answers in new bones.