10 years of Homo floresiensis

This is the skull of fossil LB1, found in 2003 in the Liang Bua cave of Flores island, Indonesia. Next October 27th it will be 10 years since the discovery was published in Nature in 2004. It belongs to a nearly complete female skeleton, dated 18,000 years B.P.

LB-1 Homo floresiensis

LB1 skull. Photo: Roberto Sáez

Apart from LB1 there are other rests discovered in that cave. They all describe a human with reduced size (around 100 cm tall, so nicknamed ‘The hobbit’) and little brain (around 400 cc, similar to chimps), but they were found together with complex tools dated to 90-13 Ka and evidences of fire.

They were defined by the discoverers (P. Brown, M. Morwood et al) as a new species: Homo floresiensis… Recently a new study has moved the datation of some of the Liang Bua finds back to 200,000 years.

A little background

The island of Flores was a lost world. Regardless of what time period in the Pleistocene, the only way to get to Flores was always crossing open ocean. In this extreme isolation, many archaic animals (which were extinct in the rest of the world), evolved to giant or dwarf forms by allopatric speciation. Example: the dwarf elephant of Flores (Stegodon). And this included the Homo floresiensis specimens (according to the discoverers), who evolved from Homo habilis or erectus or some australophitecines over several thousand years until c. 15,000 years ago.

Homo erectus, floresiensis, sapiens

Left: H.erectus D2700 (Dmanisi). Centre: H.floresiensis LB1. Right: H.sapiens (modern). Photo: Roberto Sáez

How do they look like?

Globular skull, low profile. Very small brain case within australopithecines range, but flat top-to-down similar to early Homo. Reduced, vertical face below the frontal bone. Less prognatism than early Homo:

homo floresiensis cranium

LB1 skull. Photo: Roberto Sáez

Thick bones, nasal cavity close to upper dental line, prominent canine juga, rounded orbits, double superciliary arches (but not joined like in the Indonesian H. erectus), relatively separated eyes:

homo floresiensis

LB1 skull. Photo: Roberto Sáez

Big size of maxillary and teeth, similar to H. erectus, maybe even more primitive:

homo floresiensis

LB1 skull. Photo: Roberto Sáez

Strong lower jaw (more similar to H. habilis than H. erectus), receding chin. Note that there is no big difference in the dentition size vs. other Homo specimens – compared to the difference we can see in the brain cases above:

Homo erectus, floresiensis, sapiens

Left: H.erectus D2735 (Dmanisi). Centre: H.floresiensis LB1. Right: H.sapiens. Photo: Roberto Sáez

The upper skeleton shows robust bones and muscle insertions, long arms and short legs with proportions close to australopithecines or H. habilis. The humerus has modern shape but is very thick like early Homo. The clavicle and the shoulder morphology are primitive, close to H. erectus.

The lower skeleton again shows robust bones. The muscle insertions are oriented differently than in modern humans. The morphology of the hip and the pelvis are smaller and wider than in modern humans. Some studies suggest that they were bad runners and their locomotion differed from ours, but it is uncertain whether this is explained by island dwarfing or by some pathology or…?

The controversy

This population is one of today’s major challenges for the paleoanthropological community. The island dwarfing was a phenomenon that had previously been documented in other mammals, but never in humans. And the Flores findings reversed a trend toward ever larger brain size over the course of human evolution.

Since the definition of Homo floresiensis, we have read several episodes of discussions among 1) scientists defending this population as a separate species, vs. 2) scientists claiming that they are actually modern Homo sapiens with pathologies. The last episode happened only a few days ago, with the publication of a new article suggesting potential symptoms of Down syndrome in some of the fossils.

Rationale for considering them as H. sapiens 

  • Some potential signs of pathologies such as cranium-facial asymmetries and some strange particularities of molars: anomalous rotations and amorphous crowns.
  • Molar size decreasing sequence, which is the norm in H. sapiens and not in early Homo (though with the exception of Dmanisi specimens).
  • Canines are derived, simple and conical as expected in modern humans, different from early Homo (including Dmanisi).
  • Some skeleton characteristics fall within the range of living australomelanesian populations. The form of the superciliary area, nasal floor, subnasal region, orbits, and occipital superstructures are encountered among australomelanesians.
  • The skeleton shows some growth disorders found in modern humans. The remaining traces of muscle attachments, humeral torsion and bone thickness are either asymmetrical or unusually weak.
  • The complex technology associated with these human remains could be manufactured by other Homo populations yet to be found.

Rationale for considering a separate species evolved from primitive hominids

  • A 3D study of the cranium morphology in 2009 was run, comparing it to early Homo as well as H. sapiens and apes. The results support its similarities to early Homo of 1.5 MYA.
  • The wrist of H. floresiensis is primitive, while the modern wrist of H. sapiens evolved at some point between 1.8 and 0.8 million years ago.
  • The humerus lacks the rotation it has in H. sapiens. The shoulder blade is also angled more forwards than in H. sapiens. Both characteristics are similar to H. erectus.
  • Modern people who suffer from Down syndrome typically have shorter, squatter frontol lobes than normal. But H. floresiensis has long frontal lobes.
  • Morphological and statistical comparisons distinguish H. floresiensis from modern humans with other argued pathologies like myxoedematous endemic cretinism.
  • If they were modern humans with mental pathologies, how could they survived for thousands of years in a small island? (Notice that they lived many thousands years after the latest known Homo erectus c. 30K years ago). And how could they produce such quite complex technology?
  • Even if assuming that LB1 skeleton is controversial, the rest of remains could still be considered dwarf ‘non-pathological’ specimens. It is highly improbable that all the members of the Flores population were diseased. Their short stature is a characteristic of the population and not a pathology. The population is diverse enough to consider a separate new species for them.
  • New finds published in 2016 reinforce the theory of an ancestral population present in the area since c. 1 million years ago, probably descendent from a population of Homo erectus that migrated from the continent:
    • A set of tools on the nearby island of Sulawesi dated to 100 Ka.
    • A set of fossils & tools found in Mata Menge, Flores dated to 700 Ka: a partial jaw and some teeth associated with tools. The fossils suggest a small individual, even smaller than the Liang Bua people.

In conclusion, the LB1 specimen seems to show some developmental issues (dentition, asymmetries, locomotion), but these may not imply a general pathology. Unfortunately the genetics do not help because no DNA material could be recovered, due to the hot environmental conditions in the site. LB1 looks not a good specimen on which to base the overall diagnosis of this species. The rest of fossils can provide more partial conclusions but not yet an overall picture. The controversy will likely last long time, until we will find other relevant fossils from H. floresiensis or from other coexisting Homo populations.

 

3 thoughts on “10 years of Homo floresiensis

  1. Pingback: Nuevos hallazgos de homínidos en la isla de Flores – Nutcracker Man

  2. Pingback: El puzle evolutivo humano en el sureste de Asia y Australia – Nutcracker Man

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