Homo floresiensis

Homo floresiensis is the name given to a possible human species that lived on the Indonesian island of Flores. One largely complete skeleton (LB1) and a complete mandible (LB2) were found in sediment in the Liang Bua Cave in eastern Flores, in 2003 (Brown et al, 2004). The material, dated at 18,000 years old, was not fossilised or covered with calcium carbonate, but was extremely fragile. The discoverers, a team led by anthropologists Peter Brown and Michael Morwood, recovered further material including a second mandible and postcranial material from other individuals, in 2004. In total, the finds represented at least nine individuals. Stone tools were also found, dating to 95,000-75000 years old and 12,000 years old. These comprised high densities of stone cores, flaking debris, retouched tools and anvils, evidencing a flaking technology comparable to that found at African Oldowan and other Lower Palaeolithic sites. The tools were accompanied by faunal remains, indicating that the area was a focus for a range of hominin activities (Morwood et al, 2005; Tocheri et al, 2007).

LB1 was claimed to have been a 30-year-old female. The cranial capacity of LB1 is 380cc and its stature is no more than 3ft6 (106cm), both of which are comparable to or smaller than Australopithecus afarensis (“Lucy”). The discoverers argued, however, that it possessed a variety of both primitive and derived features, and should be placed in genus Homo:

“When considered as a whole, the cranial and postcranial skeleton of LB1 combines a mosaic of primitive, unique and derived features not recorded for any other hominin. Although LB1 has the small endocranial volume and stature evident in early australopithecines, it does not have the great postcanine tooth size, deep and prognathic facial skeleton, and masticatory adaptations common to members of this genus. Instead, the facial and dental proportions, postcranial anatomy consistent with human-like obligate bipedalism and a masticatory apparatus most similar in relative size and function to modern humans all support assignment to the genus Homo—as does the inferred phylogenetic history, which includes endemic dwarfing of H. erectus. For these reasons, we argue that LB1 is best placed in this genus and have named it accordingly.” (Brown et al, 2004).

The diminutive size of Homo floresiensis was, the team claimed, a result of a phenomenon known as insular dwarfism, where animals living on an island where food is relatively scarce and predators are few or absent will “downsize” over many generations in order to reduce calorific requirements. This is of course no more than evolution favouring the smaller offspring in each generation. If predators do not pose a threat, any advantages in being large will be outweighed by poorer fuel-economy. Before Mesolithic humans reached Flores, the island met both conditions in being both relatively faunally-impoverished and lacking any predators other than the Komodo dragon. If early humans such as Homo erectus had reached Flores, then the same thing could have happened, leading to H. floresiensis.

The team claimed that despite its tiny ape-like brain, the encephalization quotient (EQ) or brain to mass ratio was in the range 2.5 to 4.6, compared with 5.8 to 8.1 for modern humans, 3.3 to 4.4 for Homo erectus/ergaster and 3.6 to 4.3 for Homo habilis. The figure was derived from an estimated brain mass of 433.2gm (based on cranial volume) and two estimates of body mass: an estimate based on stature of 106cm gave 16.0-28.7kg; one based on femur cross-sectional area of 525mm2 gave 36kg.

The EQ is a better indication of intelligence than absolute brain size; for example, elephants and whales have larger brains than humans, but are generally considered to be less intelligent than the latter. The team claimed the higher figure of 4.6 was supported by the probability that Homo floresiensis would have the same lean, narrow body shape as a modern Old World tropical-dwelling human. Thus H. floresiensis was capable of complex behaviour and cognition, and was probably the maker of the tools. Oldowan-equivalent technology would be well within its capabilities.

The discovery attracted considerable publicity, and Homo floresiensis was immediately nicknamed the Flores Hobbit, to Brown’s considerable annoyance (quoted in the Observer, 31 October 2004). However doubts as to whether it was genuinely a new human species emerged almost immediately.

The Indonesian anthropologist Prof. Teuku Jacob claimed that LB1 was a modern human suffering from microcephaly, a developmental disorder leading to a smaller brain. Jacob claimed LB1 was a male Homo sapiens aged 25-30 of Australomelanesian extraction.

An unpleasant dispute then followed when, in December 2004, Jacob removed most of the remains from the Jakarta's National Research Centre of Archaeology, where they had been placed for safekeeping, without permission of this institution’s directors. Jacob was widely cited in press reports as having a reputation for preventing access to specimens in his keeping and Brown was quoted in the New Zealand Herald as saying he doubted “if the material will ever be studied again”.

Jacob eventually did return the remains, but the discoverers claimed the bones were extensively damaged in Jacob's lab during attempts to make casts. The alleged damage included long, deep cuts marking the lower edge of the LB1's jaw on both sides, said to be caused by a knife used to cut away the rubber mould. In addition, LB2 was snapped and glued back together. Whoever was responsible misaligned the pieces and put them at an incorrect angle. The pelvis of LB1 was smashed, destroying details that reveal body shape, gait and evolutionary history. Morwood accused Jacob of being greedy and acting irresponsibly. Jacob denied any wrongdoing and published his own findings contra Brown et al in July 2006 (Jacob et al, 2006). Teuku Jacob died in October 2007, aged 77, but his death did not put an end to the controversy.

Although primatologist Robert Martin of the Field Museum, Chicago, IL supported Jacob’s position (Martin et al, 2006), the majority of workers rejected the microcephaly theory and accepted Homo floresiensis as a new human species (e.g. Argue et al, 2006; Falk et al, 2005 & 2007; Lyras et al, 2008 and Tocheri et al, 2007) .

The studies mainly focussed on the cranial and post-cranial metrics of LB1 in comparison to microcephalic humans, pygmies, early human species (Homo erectus, H. ergaster, H. habilis, etc) and australopithecines (A. garhi, A. africanus, P. bosei, etc.). The general conclusion was that H. floresiensis showed a better fit with the various extinct hominins than it did with the microcephalic or normal modern humans, though the studies differed as to its likely phylogeny, with affinities to Homo erectus, Homo habilis and even the later australopithecines all being proposed. LB1’s long low cranial vault is not a feature shared with modern humans, microcephalic or not (Lyras et al, 2008); LB1’s wrist morphology, based on three wrist bones, predates that of modern humans (Tocheri et al, 2007). Other pathological explanations such as Laron syndrome and cretinism were also rejected (Lyras et al, 2008).

Falk et al (2005) noted expansions in the frontal polar region of LB1. This part of the prefrontal cortex in humans and apes consists of Brodmann’s area 10 (BA10), which in humans may be involved in higher cognitive processes such as the undertaking of initiatives and the planning of future activities. The Falk study concluded that LB1’s brain could not have been a miniaturized version of Homo sapiens or H. erectus.

Citing this study, Argue et al (2006) suggested the implication is that LB1 possessed developed cognitive abilities and was able to plan, respond to conditions, use memories, and transfer information between group members.

Brumm et al (2006) considered 880,000 year old artefacts recovered from the Mata Menge site at the Soa Basin, central Flores in comparison to the Liang Bua artefacts and suggested the two show technological continuity. They suggest the hominins responsible for the Liang Bua artefacts were also responsible for those at Mata Menge, though no hominin remains have been recovered from the latter site.

What are we to make of all this? The case for Homo floresiensis being a pathological modern human does not strike me as being very convincing and on the balance of probabilities I would cautiously accept that it is indeed a new species of hominin. Obviously further evidence, in particular evidence that can be tied to the earlier tool finds, would be highly desirable.

Could H. floresiensis be an intermediate between early Homo and late Australopithecus that migrated out of Africa prior to 2 million years ago (Argue et al, 2006)? It’s not impossible that enhanced cognitive function evolved more than once, in Homo habilis and its descendants and in Homo floresiensis (though the latter would have to be transferred to a new genus to avoid paraphyly should this hypothesis become accepted). Nor would it be impossible for such a hominin to diffuse from Africa, given that the ancestors of the orang-utans did millions of years earlier. The main problem is there is absolutely no other evidence supporting dispersal from Africa of any australopithecine species or of Homo habilis, or of anything intermediate between the two. Homo georgicus, the small-brained hominin from Dmanisi, Georgia, has been touted as evidence Homo habilis did migrate from Africa, but it has now been shown to have a derived Homo ergaster (African Homo erectus) body plan.

Early Homo erectus, or something of that grade seems a more plausible ancestor. The tool technology is consistent with that of the first H. erectus dispersal from Africa, which seems to have happened before the invention of the later Mode II Acheulian hand-axe tradition. The cognitive abilities of Homo floresiensis were probably commensurate with such technology, which predates the emergence of modern human behaviour. As such, therefore, H. floresiensis would have lacked the complex language of modern humans, though it probably had language of sorts.

The question of how the forbears of these people reached Flores in the first place has led some to speculate that they must had the ability to build boats, since Flores – unlike many islands in the Indonesian archipelago – was never connected to the mainland, even during the maximum extent of the ices ages, when sea-levels dropped. But they could have been swept out to sea and stranded there by a natural occurrence such as a flash-flood or a tsunami, possibly on a raft of matted vegetation. This is believed to have been the way the ancestors of the New World monkeys reached South America from Africa; nobody is suggesting that they built boats!

Probably the most controversial idea is that Homo floresiensis survived into modern times and is the mythological Ebu Gogo said to have been living on Flores when the Portuguese arrived 400 years ago, and some claim were still being seen as recently as 100 years ago; and that similar people are the basis of similar legends such as the Orang Pendek from Sumatra and even leprechauns in Ireland?

I will admit to being sceptical (decidedly so about leprechauns!), if only because “little people” are so prevalent in world folk traditions that if these were due to actual diminutive hominins, concrete evidence would have emerged by now. However if an endemic dwarf hominin species can arise on Flores, there is certainly no reason to suppose similar species could not arise elsewhere and it is quite possible that evidence from similar genetically-isolated locations might come to light in the future.

References:

Debbie Argue, Denise Donlon, Colin Groves, Richard Wright (2006): Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo? Journal of Human Evolution 51 (2006) 360-374.

P. Brown, T. Sutikna, M. J. Morwood, R. P. Soejono, Jatmiko, E. Wayhu Saptomo & Rokus Awe Due (2004): A new small-bodied hominin from the
Late Pleistocene of Flores, Indonesia, Nature Vol. 431 28 October 2004.

Adam Brumm, Fachroel Aziz, Gert D. van den Bergh, Michael J. Morwood, Mark W. Moore, Iwan Kurniawan, Douglas R. Hobbs & Richard Fullagar (2006): Early stone technology on Flores and its implications for Homo floresiensis, Nature Vol. 441 1 June 2006.

Dean Falk, Charles Hildebolt, Kirk Smith, M. J. Morwood, Thomas Sutikna, Peter Brown, Jatmiko, E. Wayhu Saptomo, Barry Brunsden, Fred Prior (2005): The Brain of LB1, Homo floresiensis, Science Vol. 308 8 April 2005.

Dean Falk, Charles Hildebolt, Kirk Smith, M. J. Morwood, Thomas Sutikna, Jatmiko, E. Wayhu Saptomo, Herwig Imhof, Horst Seidler and Fred Prior (2007): Brain shape in human microcephalics and Homo floresiensis, PNAS February 13, 2007 vol. 104 no. 7 2513–2518.

T. Jacob, E. Indriati, R. P. Soejono, K. Hsu, D. W. Frayer, R. B. Eckhardt, A. J. Kuperavage, A. Thorne and M. Henneberg (2006): Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: Population affinities and pathological abnormalities, PNAS September 5, 2006 vol. 103 no. 36 13421–13426.

G.A. Lyras, M.D. Dermitzakis, A.A.E. Van der Geer, S.B. Van der Geer, J. De Vos (2008): The origin of Homo floresiensis and its relation to evolutionary
processes under isolation, Anthropological Science, 1 August 2008.

R. D. Martin, A. M. MacLarnon, J. L. Phillips, L. Dussubieux,
P. R. Williams, W. B. Dobyns (2006): Comment on ‘‘The Brain of LB1,
Homo floresiensis’’, Science 19 May 2006 Vol. 312.

M. J. Morwood, P. Brown, Jatmiko, T. Sutikna, E. Wahyu Saptomo, K. E. Westaway, Rokus Awe Due, R. G. Roberts, T. Maeda, S. Wasisto & T. Djubiantono (2005): Further evidence for small-bodied hominins from
the Late Pleistocene of Flores, Indonesia, Nature Vol. 437 13 October 2005.

Scarre C (2005) (Ed): “The human past”, Thames & Hudson.

Matthew W. Tocheri, Caley M. Orr, Susan G. Larson, Thomas Sutikna,
Jatmiko, E. Wahyu Saptomo, Rokus Awe Due, Tony Djubiantono,
Michael J. Morwood, William L. Jungers (2007): The Primitive Wrist of Homo floresiensis and Its Implications for Hominin Evolution, Science Vol. 317 21 September 2007.

© Christopher Seddon 2009