Flores Hobbits Were Smaller Than Thought

The 2003 discovery of a species of hominin (extinct human ancestor) that lived on the Indonesian island of Flores more than 50,000 years ago created a tremendous amount of interest in the scientific community. This was in part because this species, which was given the scientific name Homo floresiensis, was extraordinarily small. Its skeletal remains suggested the average adult stood just 38 inches (slightly less than one meter) tall, making it much shorter than its modern human cousins living in other parts of the world.

But a new study has just been released showing that these “hobbits,” as the species is referred to colloquially, were even tinier than previously believed. Based on measurements of a newly recovered set of hobbit fossils, which date back far beyond 50,000 BC, it seems the average adult actually reached a height that was 2.4 inches (6 centimeters) shorter than the original estimate.

The Mata Menge humerus fragment (left) shown at the same scale as the humerus of Homo floresiensis from Liang Bua. (Yosuke Kaifu/Nature)

A New Home, a New Species: Human Evolution in Action

In an article just published in the journal Nature Communications, an international team of researchers report the results of their analysis of H. floresiensis teeth and bone samples obtained from an early Middle Pleistocene paleoanthropological site known as Mata Menge.

Located approximately 45 miles (70 kilometers) to the southeast of Liang Bua Cave, where the first hobbit fossils were unearthed in 2003, Mata Menge has produced artifacts and skeletal remains that date far back into the past.

The cache of ‘hobbit’ bones found there have been dated to 700,000 years before the present, which is 300,000 years or so after the earliest H. floresiensis settlers are believed to have arrived on the island of Flores. The dating of the Mata Menge fossils confirms that H. floresiensis survived on the island for an immensely long period of time, having only gone extinct 50,000 years ago.

Intriguingly, the ancestors of H. floresiensis were not so small when they first reached Flores.

One of the teeth that was found at Mata Menge, Flores Island. (University of Wollongong)

The species is widely believe to be a descendant of Homo erectus, a hominin that lived between two million and 250,000 years ago and was about the same size as modern humans. According to the researchers involved in this new study, it was actually H. erectus that came to the island around one million BC,  and it was H. erectus that began to shrink in size following this migration. Within a couple of hundred thousand years or so those H. erectus settlers had morphed into an entirely new and shockingly diminutive species, one that has only ever been found in this one isolated location.

“Acquiring a large body and large brain and becoming clever is not necessarily our destiny,” lead study author Yosuke Kaifu, a paleoanthropologist affiliated with the University Museum at the University of Tokyo, told Live Science.

“Depending on the natural environment, there were diverse ways of evolution not only for animals in general but also for humans.”

Discovering Mata Menge’s Tiny Inhabitants

The assemblage of hominin bones and teeth recovered during excavations at Mata Menge came from at least four individuals: one adult, one adolescent or young adult, and two children. All the bones and teeth were stunningly small, in comparison to modern humans and to some extent even in comparison to the hobbit fossils recovered from Liang Bua Cave 21 years ago.

“The observation that all four (or more) individuals are extremely diminutive supports the argument that small body size was not an idiosyncratic (individual) character but a population feature of the early Middle Pleistocene hominins of Flores,” the study authors wrote in their Nature Communications article.

One of the bones recovered was a partial section of a humerus or upper arm bone. At first glance it looked like the bone of a still-developing human, but the researchers quickly concluded couldn’t have come from a child or adolescent despite its tiny size.

“Adult bones leave traces of metabolism (we call it remodeling for bones) more than those of children,” Kaifu explained. “We detected a strong signal of such trace in the Mata Menge humerus, through microscopic observation of a sliced bone sample.”

New fossils from Mata Menge, include extra small humerus. (Yosuke Kaifu/Nature)

This was an incredibly important discovery, because it helped establish an upper limit on how tall an H. floresiensis adult was likely to grow. Just as significantly, it revealed that H. floresiensis attained its hobbit-like size in the extremely distant past.

“The Mata Menge fossils we report here showed that the extremely small body size of Homo floresiensis evolved within the first 300,000 years of their history on the island … and then after that the small body size was maintained for more than 600,000 years,” Kaifu stated. “Why this happened is another difficult question.”

For Homo Floresiensis, Small was Beautiful

The confined territory of the island (Flores covers just 5,500 square miles or 14,250 square kilometers), and the limits this placed on the available resources, could have played a role in the gradual diminishing of H. floresiensis’ height and weight. Individuals that could survive consuming fewer calories may have had a survival advantage in this environment, leading to more breeding success in the long run. A lack of danger from large animal predators may have also contributed to the change, since having greater size and strength and an enhanced ability to fight off animal attackers wouldn’t have mattered on Flores.

“We tend to think that humans are special among animals,” Kaifu said. “But the evidence from Flores indicates that we humans are, like other animals, also under control of natural selection and could evolve toward unexpected directions.”

It is clear that the evolutionary changes H. floresiensis underwent were beneficial. Despite being confined to limited space on just one small Pacific Island, the species survived for one million years before finally going extinct. Their smallness obviously contributed to their success, even though it would have likely led to their demise if they’d lived in just about any other place on the planet.

Top image: A facial reconstruction of Homo floresiensis.           Source: Cicero Moraes et al. / CC BY 4.0

By Nathan Falde