(Image caption: LB1 in three different views to illustrate facial asymmetry. A is the actual specimen, B is the Right side doubled at the midline and mirrored, and C is the left side doubled and mirrored. Differences in left and right side facial architectures are apparent, and illustrate growth abnormalities of LB1. Credit: A, E. Indriati, B and C, D.W. Frayer)

Flores bones show features of Down syndrome, not a new “hobbit” human

In October 2004, excavation of fragmentary skeletal remains from the island of Flores in Indonesia yielded what was called “the most important find in human evolution for 100 years.” Its discoverers dubbed the find Homo floresiensis, a name suggesting a previously unknown species of human.

Now detailed reanalysis by an international team of researchers including Robert B. Eckhardt, professor of developmental genetics and evolution at Penn State, Maciej Henneberg, professor of anatomy and pathology at the University of Adelaide, and Kenneth Hsü, a Chinese geologist and paleoclimatologist, suggests that the single specimen on which the new designation depends, known as LB1, does not represent a new species. Instead, it is the skeleton of a developmentally abnormal human and, according to the researchers, contains important features most consistent with a diagnosis of Down syndrome.

"The skeletal sample from Liang Bua cave contains fragmentary remains of several individuals," Eckhardt said. "LB1 has the only skull and thighbones in the entire sample."

No substantial new bone discoveries have been made in the cave since the finding of LB1.

Initial descriptions of Homo floresiensis focused on LB1’s unusual anatomical characteristics: a cranial volume reported as only 380 milliliters (23.2 cubic inches), suggesting a brain less than one third the size of an average modern human’s and short thighbones, which were used to reconstruct a creature standing 1.06 meters (about 3.5 feet tall). Although LB1 lived only 15,000 years ago, comparisons were made to earlier hominins, including Homo erectus and Australopithecus. Other traits were characterized as unique and therefore indicative of a new species.

A thorough reexamination of the available evidence in the context of clinical studies, the researchers said, suggests a different explanation.

The researchers report their findings in two papers published today (Aug. 4) in the Proceedings of the National Academy of Sciences (1, 2).

In the first place, they write, the original figures for cranial volume and stature are underestimates, “markedly lower than any later attempts to confirm them.” Eckhardt, Henneberg, and other researchers have consistently found a cranial volume of about 430 milliliters (26.2 cubic inches).

"The difference is significant, and the revised figure falls in the range predicted for a modern human with Down syndrome from the same geographic region," Eckhardt said.

The original estimate of 3.5 feet for the creature’s height was based on extrapolation combining the short thighbone with a formula derived from an African pygmy population. But humans with Down syndrome also have diagnostically short thighbones, Eckhardt said.

Though these and other features are unusual, he acknowledged, “unusual does not equal unique. The originally reported traits are not so rare as to have required the invention of a new hominin species.”

Instead, the researchers build the case for an alternative diagnosis: that of Down syndrome, one of the most commonly occurring developmental disorders in modern humans.

"When we first saw these bones, several of us immediately spotted a developmental disturbance," said Eckhardt, "but we did not assign a specific diagnosis because the bones were so fragmentary. Over the years, several lines of evidence have converged on Down syndrome."

The first indicator is craniofacial asymmetry, a left-right mismatch of the skull that is characteristic of this and other disorders. Eckhardt and colleagues noted this asymmetry in LB1 as early as 2006, but it had not been reported by the excavating team and was later dismissed as a result of the skull’s being long buried, he said.

A previously unpublished measurement of LB1’s occipital-frontal circumference — the circumference of the skull taken roughly above the tops of the ears — allowed the researchers to compare LB1 to clinical data routinely collected on patients with developmental disorders. Here too, the brain size they estimate is within the range expected for an Australomelanesian human with Down syndrome.

LB1’s short thighbones not only match the height reduction seen in Down syndrome, Eckhardt said, but when corrected statistically for normal growth, they would yield a stature of about 1.26 meters, or just over four feet, a figure matched by some humans now living on Flores and in surrounding regions.

These and other Down-like characteristics, the researchers state, are present only in LB1, and not in the other Liang Bua skeletal remains, further evidence of LB1’s abnormality.

"This work is not presented in the form of a fanciful story, but to test a hypothesis: Are the skeletons from Liang Bua cave sufficiently unusual to require invention of a new human species?" Eckhardt said.

"Our reanalysis shows that they are not. The less strained explanation is a developmental disorder. Here the signs point rather clearly to Down syndrome, which occurs in more than one per thousand human births around the world."

The Shrinking of the Hobbit’s Brain

Where do Hobbits come from? No, not the little humanoids in the J. R. R. Tolkien books, but Homo floresiensis, the 1-meter-tall human with the chimp-sized brain that lived on the Indonesian island of Flores between 90,000 and 13,000 years ago. There are two main hypotheses: either the creature downsized from H. erectus, a human ancestor that lived in Africa and Asia and that is known to have made it to Flores about 800,000 years ago and may have shrunk when it got there—a case of so-called “insular dwarfism” often seen in other animals that get small when they take up residence on islands. Or it evolved from an even earlier, smaller-brained ancestor, such as the early human H. habilis or an australopithecine like Lucy, that somehow made it to Flores from Africa. The insular dwarfism hypothesis had fallen out of favor recently, however, because many researchers thought that the Hobbit’s brain, often estimated at 400 cubic centimeters in volume, was too small to have evolved from the larger H. erectus brain, which was at least twice as big. But a new study, published online today in the Proceedings of the Royal Society B, finds from CT scans of the Hobbit’s brain that it was actually about 426 cubic centimeters in volume. The team calculates that this is big enough to make the island dwarfism hypothesis considerably more plausible once the body size differences between the Hobbit and H. erectus—which was nearly twice as tall—are adjusted for.

First facial reconstruction of the Indonesian ‘Hobbit’ unveiled

Scientists at this week’s Australian Archaeological Conference have unveiled the face of Homo floresiensis— more commonly referred to as the ‘Hobbit’ — for the first time. Specialist facial anthropologist Dr. Susan Hayes used forensic facial approximation techniques to build out a female skull specimen discovered in 2003 in Flores, Indonesia. Other bones have been found since, revealing that these Hobbits were only about three and a half feet tall— just like the creatures of J.R.R. Tolkien lore that will hit the big screen later this week. Homo floresiensis populated the island of Flores between 95,000 and 17,000 years ago, but it’s not yet clear where the species falls within the human evolutionary tree. Although she’s pleased with the final results, Hayes says that the reconstruction was far from easy— “she’s not what you’d call pretty, but she is definitely distinctive.”