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In October 2004 skeletal remains found on the island of Flores in Indonesia hinted at a previously unknown species of human that existed 15,000 years ago.

Called Homo floresiensis, the species was dubbed a 'hobbit' as it was smaller than any other known species of human.

But reanalysis has revealed that it may not be a new species at all, but rather a human that has features consistent with someone with Down's syndrome.

Reanalysis of bones found in Indonesia suggests they are not from a 'hobbit'. Scientists say the finding on Flores Island can be attributed to Down's syndrome. This image compares the skull of the 'hobbit' LB1 (left) to that of Liang Momer E, another skull from Flores, dated in the range of 3,000 to 5,000 years ago

The latest findings, reported in the Proceedings of the National Academy of Sciences, was conducted by an international team of researchers.

They suggest that the single specimen on which the new designation depends, known as LB1 after the cave it was discovered in - Liang Bua - does not represent a new species.

Indeed, aside from LB1, no substantial new bone discoveries have been made in the cave since this finding.

'The skeletal sample from Liang Bua cave contains fragmentary remains of several individuals,' said Dr Robert Eckhardt, professor of developmental genetics and evolution at Penn State University.

'LB1 has the only skull and thigh bones in the entire sample.'

The first indicator that the finding could be explained by Down's syndrome was craniofacial asymmetry, a left-right mismatch of the skull that is characteristic of the disorder. 

The researchers 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.

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.

The skeleton also had short thigh bones, which were used to reconstruct a creature standing only 3.5 feet (1.06 metres) tall.

Although LB1 lived only 15,000 years ago, comparisons were made to earlier hominins, including Homo erectus and Australopithecus.

Other traits were characterised as unique and therefore indicative of a new species.

But a thorough re-examination of the available evidence in the context of clinical studies, the researchers said, suggests a different explanation.

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.'

The 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's syndrome from the same geographic region,' Dr Eckhardt said.

The latest findings, reported in the Proceedings of the National Academy of Sciences, was conducted by an international team of researchers. They suggest that the single specimen on which the new designation depends, known as LB1 after the cave it was discovered in - Liang Buaon Flores Island - is not a new species

LB1 is shown 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

The original estimate of 3.5 feet (1.06 metres) for the creature's height was based on extrapolation combining the short thigh bone with a formula derived from an African pygmy population. 

But humans with Down's syndrome also have diagnostically short thigh bones, Dr 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's 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's syndrome.'

This reconstruction of what LB1 was once thought to look like was created by researchers in Australia at the University of Woollongong in 2012. Using the skill fragments found in Flores, they added muscle and skin to reveal her face, but the assumption she was a new species of human may now not be true

Here Dr Susan Hayes (right) looks at a replica of Homo floresienses with Penny Williamson from the University of Woollongong's Earth and Environmental Sciences back in 2012. The new research, however, claims the bones have all the markings of an ancient human that suffered from Down's syndrome

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's syndrome.

LB1's short thigh bones not only match the height reduction seen in Down's syndrome, Dr 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?' Dr 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's syndrome, which occurs in more than one per thousand human births around the world.'