A few months after the diminutive hominin fossil Homo floresiensis, which because of its relatively large feet was quickly dubbed the ‘Hobbit’, turned out to be considerably older than previously thought it hit has the headlines again because its ancestors may have colonized the Indonesian island of Flores far earlier still. A pair of articles in the 9 June 2016 issue of Nature consider evidence from another site on the island where fluvial sediments offer more easily interpreted stratigraphy than the complex Liang Bua cave assemblage where the original skeletal remains were unearthed. The site in the So’a Basin became an important target for excavation following the discovery there in the 1950’s of stone artefacts, east of Wallace’s Line – a fundamental faunal and floral divide once thought to be due to the difficulty of crossing a deep, current-plagued channel in the Indonesian archipelago. The unexpected presence of artefacts drew palaeoanthropologists from far afield, but it was almost 50 years later before their exploration yielded hominin remains.
One of the papers reports sparse new finds of hominin material from the So’a Basin, a fragment of mandible and 6 isolated teeth thought to be from at least three individuals (van den Bergh, G.D. et al., 2016. Homo floresiensis-like fossils from the early Middle Pleistocene of Flores. Nature, v. 534, p. 245-248). The other covers newly discovered artefacts, the stratigraphic and palaeoecological setting, and radiometric dates of the finds (Brumm, A. and 22 others, 2016. Age and context of the oldest known hominin fossils from Flores. Nature, v. 534, p. 249-253). The jaw fragment shows signs of having once held a wisdom tooth, showing that it belonged to an adult. Yet although it resembles the dentition of the younger Liang Bua specimens, it seems more primitive and is even smaller. The other dental finds are most likely to be deciduous teeth of juveniles. Fission-track, uranium-series and 40Ar/39Ar dating indicates that the fossils entered the sediments about 700 ka ago. But tools and remains of prey animals in deeper sedimentary layers here and at other Flores sites indicate the presence of hominins back as far as about 1 Ma, before which there are no such signs.
So, at least a million years ago Flores was colonised by hominins. Either the original immigrants were uniquely small compared with other hominins of that vintage in Asia and Africa, or within 300 ka they had decreased in size through the evolutionary influence of limited resources on Flores and the process of island dwarfism. The second may also have been influenced by an initially small population of migrants or a later population ‘bottleneck’ that added a loss of genetic variability – a founder effect. These two alternatives may point respectively to either the even earlier migration out of Africa and across most of Asia of perhaps H. habilis, or the dwarfing of a limited population of H. erectus who made their way there from their known occupation of Java. The authors painstaking analysis of the meagre remains suggest a closer dental resemblance to Asian Homo erectus than to earlier African hominins, so the second alternative seems more likely. However, even that scenario poses palaeoanthropology with a major problem; yet another evolutionary process that helps cryptify the links among our earlier relatives. (See also: Gomez-Robles, A., 2016. The dawn of Homo floresiensis. Nature, v. 534, p. 188-189.)
In 2004 a newly discovered hominin fossil from the Indonesian island of Flores made headlines worldwide. Although an adult, it was tiny – about a metre tall, had a commensurately small brain (the size of a grapefruit), had made tools and hunted small elephants and giant rats. Dates from the cave floor sediments that had entombed it gave ages as young as 13 to 11 thousand years and as far back as 850 ka. So H. floresiensis was regarded as being the last human to share the Earth with us; that is, if it was a different species rather than a product of evolutionary shrinkage of anatomically modern humans stranded and isolated on the island for a very long time. Then there was talk among locals of the legendary Ebo Go-Go, with whom their ancestors had shared the island – they had arrived between 35 to 55 thousand years ago.
Unsurprisingly, a major controversy raged in palaeoanthropology circles, between those who demanded either island dwarfism or congenital deformity of modern humans, and the other camp focused on many anatomical differences that pointed to a bona fide companion to later immigrants who perhaps survived into modern times. The ‘Hobbit’ became a cause celebre, but many of the original protagonists are now left with the proverbial egg on their faces. The cave sediments turn out to have a much more complex stratigraphy than previously thought, following further excavations led by the original discoverer Thomas Sutikna of the Pusat Penelitian Arkeologi Nasional in Jakarta Indonesia (Sutikna, T. and 19 others 2016. Revised stratigraphy and chronology for Homo floresiensis at Liang Bua in Indonesia. Nature, v. 532, p. 366-369.
The delayed appearance of the revision is hardly surprising, given the lengthy political squabbles surrounding access to the site. And neither are the outcomes, for cave sediments are notoriously tricky because of their episodic reworking by cave floods and roof falls, together with the difficulty in finding materials suited to dating in tropical settings. The original charcoal used in radiocarbon dating and sand grains subject to the thermoluminescence method were in fact from a unit that lies unconformably against the stratum that hosted the fossils. More sophisticated luminescence dating of the actual fossil-hosting sediments yield ages between 100 to 60 ka, tool-bearing units range from 190 to 50 ka. The origins of H. floresiensis are thus pushed back beyond the date of supposed colonisation by H. sapiens, and remain an open question.
When they were first discovered in Liang Bua cave on the Indonesian island of Flores diminutive hominin remains sparked off a heated debate. Part of the reason for dispute was the age of the deposit in which they were found (18 to 850 ka), so young that it indicated possible cohabitation on the island with anatomically modern humans. On the one hand, the finders claimed that they represented a previously unknown hominin species. Other specialists considered that the tiny size (adults no taller than about a metre with brain capacity around that of australopithecines) indicated some congenital dwarfism.
In the 9 years since the remains came to light, several anatomically features have been cited to support the view of a distinct hominin species: their lack of a chin and different arm and shoulder anatomy, which H. floresiensis shares with H. erectus and H. georgicus. The fossils are associated with simple stone tools and bones of a variety of prey animals that show cut marks and charring, suggesting that cooking was part of these hominins’ lifestyle; despite having small brains they were not unintelligent.
Substantial remains of nine or more individuals have been unearthed so that anatomical detail is almost complete. In 2007 details were published of three well-preserved wrist bones from the original find. They too were sufficiently different from modern and Neanderthal humans to warrant confirmation that H. floresiensis is indeed a distinct hominin species. Further work on wrist bones from other individuals has now more or less put the seal on this identity (Orr, C.M. et al. 2013. New wrist bones of Homo floresiensis from Liang Bua (Flores, Indonesia). Journal of Human Evolution, v. 64, p. 109-129), the authors concluding that ‘The pattern of morphology … supports H. floresiensis as a valid taxon and refutes the hypothesis that these specimens represent modern humans with some kind of pathology or growth disturbance’. They take matters further by suggesting that their lineage was established before divergence of modern humans and Neanderthals. As with the shoulder morphology that of their wrists would have somewhat hindered tool-making dexterity, but nonetheless they did make tools.