Homo floresiensis

2008/9 Schools Wikipedia Selection. Related subjects: Mammals

Homo floresiensis ("Man of Flores", nicknamed Hobbit) is a possible species in the genus Homo, remarkable for its small body and brain, and survival until relatively recent times. It was named after the Indonesian island of Flores on which the remains were found. One largely complete subfossil skeleton (LB1) and a complete jawbone from a second individual (LB2), dated at 18,000 years old, were discovered in deposits in Liang Bua Cave on Flores in 2003. Parts of seven other individuals (LB3 – LB9, the most complete being LB6), all diminutive, have been recovered as well as similarly small stone tools from horizons ranging from 94,000 to 13,000 years ago. The first of these remains was unearthed in 2003 and the publication date of the original description is October 2004.

The discoverers, anthropologists Peter Brown, Michael Morwood and their colleagues have argued that a variety of features, both primitive and derived, identified the skeleton of LB1 as that of a new species of hominin, H. floresiensis. They argued that it was contemporaneous with modern humans (Homo sapiens) on Flores.

Doubts that the discoveries constitute a new species were soon voiced by the Indonesian anthropologist Teuku Jacob, who suggested that the skull of LB1 was a microcephalic modern human. A controversy developed, leading to the publication of a number of studies which supported or rejected claims for species status. In March 2005 scientists who published details of the brain of Flores Man in Science supported species status. Several researchers, including one scientist who worked on the initial study, have disputed the 2005 study, supporting the conclusion that the skull is microcephalic. The original discoverers have argued against these interpretations and maintain that H. floresiensis is a distinct species. This is supported by the most recent study that disputes possibility of microcephaly published by paleoneurologist Dean Falk comparing the H. floresiensis brain to ten microcephalic brains revealing distinct differences that have so far gone unanswered by critics. In addition, a 2007 study of carpal bones of H. floresiensis found similarities to those of a chimpanzee or early hominid such as Australopithecus and were significantly different from the bones of modern humans. Studies of the bones and joints of the arm and shoulder have also suggested that H. floresiensis was more similar to early humans and apes than modern humans. However, critics of the claim to species status continue to suggest alternative explanations. The most recent hypothesis put forward is that the skeletons found were from cretinous individuals who suffered from iodine deficiencies in the womb. This idea has been dismissed by members of the original discovery team as based on a misinterpretation of the data. To date, the only complete cranium is that of LB1.

Discovery

     Flores is the island highlighted in yellow. The territory of Indonesia as a whole is in green.

The first specimens were discovered by a joint Australian-Indonesian team of paleoanthropologists and archaeologists looking on Flores for evidence of the original human migration of H. sapiens from Asia into Australia. They were not expecting to find a new species, and were quite surprised at the recovery of the nearly complete skeleton of a hominid they dubbed LB1 (for the first skeleton recovered at the Liang Bua Cave). Subsequent excavations recovered seven additional skeletons, dating from 38,000 to 13,000 years old, from Liang Bua limestone cave on Flores. An arm bone, provisionally assigned to H. floresiensis, is about 74,000 years old. Also widely present in this cave are sophisticated stone implements of a size considered appropriate to the 1 m tall human: these are at horizons from 95,000 to 13,000 years and are associated with juvenile Stegodon, presumably the prey of LB1.

The specimens are not fossilized, but were described in a Nature news article as having "the consistency of wet blotting paper" (once exposed, the bones had to be left to dry before they could be dug up). Researchers hope to find preserved mitochondrial DNA to compare with samples from similarly unfossilised specimens of Homo neanderthalensis and H. sapiens. It is unlikely that useful DNA specimens exist in the available sample, as DNA degrades rapidly in warm tropical environments, sometimes in as little as a few dozen years. Also, contamination from the surrounding environment seems highly possible given the moist environment in which the specimens were found.

Anatomy

Aspect ratio between homo sapiens (human being, white) and homo floresiensis (pink).

The most important and obvious identifying features of H. floresiensis are its small body and small cranial capacity. Brown and Morwood also identified a number of additional, less obvious features, that might distinguish LB1 from modern H. sapiens, including the form of the teeth, the absence of a chin, and the unusually low twist in the forearm bones. Each of these putative distinguishing features has been heavily scrutinized by the scientific community, with different independent research groups reaching differing conclusions whether these features support the original designation of a new species, or whether they identify LB1 as a severely pathological H. sapiens. The discovery of additional partial skeletons has verified the existence of some features found in LB1, such as the lack of a chin, but Jacob and other research teams argue that these features do not distinguish LB1 from local H. sapiens morphology.

Small bodies

The type specimen for the proposed species is a fairly complete skeleton and near-complete skull proposed to be that of a 30-year-old female (LB1), nicknamed Little Lady of Flores or Flo, about 1.06 m (3 ft 6 in) in height. This short stature is also supported by the height estimates derived from the tibia of a second skeleton (LB8), on the basis of which Morwood and colleagues suggest that LB8 might have stood 1.09 m (3 ft 7 in) high. These estimates are outside the range of normal modern human height and is considerably shorter than the average adult height of even the physically smallest populations of modern humans, such as the African Pygmies (< 1.5 m, or 4 ft 11 in), Twa, Semang (1.37 m, or 4 ft 6 in for adult women), or Andamanese (1.37 m, or 4 ft 6 in for adult women). Mass is generally considered more biophysically significant than a one-dimensional measure of length, and by that measure, due to effects of scaling, differences are even greater. LB1 has been estimated as perhaps about 25 kg (55  lb). This is smaller than not only modern H. sapiens, but also than H. erectus, which Brown and colleagues have suggested is the immediate ancestor of H. floresiensis. LB1 and LB8 are also somewhat smaller than the three million years older ancestor australopithecines, not previously thought to have expanded beyond Africa. Thus, LB1 and LB8 may be the shortest and smallest members of the extended human family discovered thus far.

Despite the size difference, the specimens seem otherwise to resemble in their features H. erectus, known to be living in Southeast Asia at times coinciding with earlier finds purported to be of H. floresiensis. These observed similarities form the basis for the establishment of the suggested phylogenetic relationship. Despite a controversial reported finding by the same team of alleged material evidence, stone tools, of a H. erectus occupation 840,000 years ago, actual remains of H. erectus itself have not been found on Flores, much less transitional forms.

To explain the small stature of H. floresiensis, Brown and colleagues have suggested that in the limited food environment on Flores H. erectus underwent strong insular dwarfism, a form of speciation also seen on Flores in several species, including a dwarf Stegodon (a group of proboscideans that was widespread throughout Asia during the Quaternary), as well as being observed on other small islands. However, the "island dwarfing" theory has been subjected to some criticism from Teuku Jacob and colleagues who argue that LB1 is similar to local Rampasasa H. sapiens populations, and who point out that size can vary substantially in pygmy populations.

Small brains

In addition to a small body size, H. floresiensis had a remarkably small brain. The type specimen, at 380 cm³ (23  in³), is at the lower range of chimpanzees or the ancient australopithecines. The brain is reduced considerably relative to this species' presumed immediate ancestor H. erectus, which at 980 cm³ (60 in³) had more than double the brain volume of its descendant species. Nonetheless, the estimated brain to body mass ratio of LB1 lies between that of Homo erectus and the great apes.

Indeed, the discoverers have associated H. floresiensis with advanced behaviors. There is evidence of the use of fire for cooking in Liang Bua cave, and evidence of cut marks on the Stegodon bones associated with the finds. The species has also been associated with stone tools of the sophisticated Upper Paleolithic tradition typically associated with modern humans, who at 1310–1475 cm³ (80–90 in³) nearly quadruple the brain volume of H. floresiensis (with body mass increased by a factor of 2.6). Some of these tools were apparently used in the necessarily cooperative hunting of local dwarf Stegodon by this small human species.

An indicator of intelligence is the size of region 10 of the dorsomedial prefrontal cortex, which is associated with self-awareness and is about the same size as that of modern humans, despite the much smaller overall size of the brain.

Additional features

Additional features used to argue that the finds come from a population of previously unidentified hominins include the absence of a chin, the relatively low twist of the arm bones, and the width of the leg bones relative to their length. The presence of each of these features has been confirmed by independent investigators but their significance has been disputed. For example, Jacob and colleagues argue that each of these unusual features indicates some form of pathology in the LB1 skeleton.

In September of 2007, Matthew W. Tocheri, of the Smithsonian's National Museum of Natural History, announced that Homo floresiensis was indeed a separate branch on the human evolutionary chain. He and his team found the bones in the Homo floresiensis wrist to be "indistinguishable from an African ape or early hominin-like wrist and nothing at all like that seen in modern humans and Neanderthals". He goes on to explain how while there are pathologies that can affect the wrist, there are none that can effectively turn a modern human wrist into that of an extinct proto-human or a modern day African ape. Once confirmed, this would mean that Neanderthal was not the last homo species to share this planet with Homo sapiens, as Homo floresiensis only died out around 18,000 years ago, or 12,000 years after the last Homo neanderthalensis.

Recent survival

The species is thought to have survived on Flores until at least as recently as 12,000 years ago making it the longest-lasting non-modern human, surviving long past the Neanderthals (H. neanderthalensis) which became extinct about 24,000 years ago.

Due to a deep neighboring strait, Flores remained isolated during the Wisconsin glaciation (the most recent glacial period), despite the low sea levels that united much of the rest of Sundaland. This has led the discoverers of H. floresiensis to conclude the species, or its ancestors, could only have reached the isolated island by water transport, perhaps arriving in bamboo rafts around 100,000 years ago (or, if they are H. erectus, then about 1 million years ago). This idea of Flores using advanced technology and cooperation on a modern human level has prompted the discoverers to hypothesize that H. floresiensis almost certainly had language. These suggestions have been some of the most controversial of the discoverers' findings, despite the probable high intelligence of H. floresiensis.

Local geology suggests that a volcanic eruption on Flores approximately 12,000 years was responsible for the demise of H. floresiensis, along with other local fauna, including the dwarf elephant Stegodon. The discoverers suspect, however, that this species may have survived longer in other parts of Flores to become the source of the Ebu Gogo stories told among the local people. The Ebu Gogo are said to have been small, hairy, language-poor cave dwellers on the scale of H. floresiensis. Believed to be present at the time of the arrival of the first Portuguese ships during the 16th century, these strange creatures have been reported as recently as the late 19th century.

Gerd van den Bergh, a paleontologist working with the fossils, reported hearing of the Ebu Gogo a decade before the fossil discovery.

Similarly, on the island of Sumatra, there are reports of a 1–1.5 m tall humanoid, the Orang Pendek, which a few professional scholars, such as Debbie Martyr and Jeremy Holden, take seriously. Some scientists, including noted paleontologist Henry Gee, have speculated that H. floresiensis might explain the Orang Pendak.

Controversies

Whether the specimens represent a new species is a controversial issue within the scientific community. Professor Teuku Jacob, chief paleontologist of the Indonesian Gadjah Mada University and other scientists reportedly disagree with the placement of the new finds into a new species of Homo, stating instead, "It is a sub-species of Homo sapiens classified under the Austrolomelanesid race". He contends that the find is from a 25–30 year-old omnivorous subspecies of H. sapiens, and not a 30-year-old female of a new species. He is convinced that the small skull is that of a mentally defective modern human, probably a Pygmy, suffering from the genetic disorder microcephaly, which produces a small brain and skull.

In early December 2004, Professor Jacob removed most of the remains from Soejono's institution, Jakarta's National Research Centre of Archaeology, for his own research without the permission of the Centre's directors. Some expressed fears that, like the Dead Sea Scrolls, important scientific evidence would be sequestered by a small group of scientists who neither allowed access by other scientists nor published their own research. Jacob eventually returned the remains with portions severely damaged and missing two leg bones on 23 February 2005 to the worldwide consternation of his peers. Reports noted the condition of the returned remains; "(including) long, deep cuts marking the lower edge of the Hobbit's jaw on both sides, said to be caused by a knife used to cut away the rubber mould"; "the chin of a second Hobbit jaw was snapped off and glued back together. Whoever was responsible misaligned the pieces and put them at an incorrect angle"; and, "The pelvis was smashed, destroying details that reveal body shape, gait and evolutionary history" and causing the discovery team leader Professor Morwood to remark "It's sickening, Jacob was greedy and acted totally irresponsibly." Jacob, however, denied any wrongdoing. He stated that such damages occurred during transport from Yogyakarta back to Jakarta despite the physical evidence to the contrary that the jawbone had been broken while making a mold of the hobbit, and when trying to repair it "rammed the two halves together at the wrong angle, stuck bone fragments in the cracks, and hidden the mess with a thick coating of glue".

However, prior to Jacob's removal of the fossils, a CT scan was taken of the skull and in 2005, a computer-generated model of the skull of H. floresiensis was undertaken, and analysed by a team headed by Dean Falk of Florida State University. The results were published in Science in Feb. 2005. The authors of the study claimed that brainpan was not that of a pygmy nor an individual with a malformed skull and brain, supporting the view that it is a new species. However, in October 2005 Science published an additional study headed by Alfred Czarnetzki, Carsten M. Pusch and Jochen Weber. This disagreed with the findings of the February 2005 study and concluded that the skull of LB1 is consistent with microcephaly.

The results of the Feb. 2005 study were also questioned in the May 19, 2006, issue of the journal Science, in which Robert D. Martin of the Field Museum in Chicago and co-authors argued that the 2005 study had not compared the skull with a typical example of adult microcephaly. Martin and his co-authors concluded that the skull was probably microcephalic. Martin argued that the brain is far too small to be a separate dwarf species; if it were, he wrote, the 400-cubic-centimeter brain would indicate a creature only one foot in height, which would be one-third the size of the discovered skeleton. In the September 5, 2006, issue of the Proceedings of the National Academy of Sciences, a group of scientists from Indonesia, Australia, and the United States came to the same conclusion as Dr. Martin by examining bone and skull structure.

In response, Brown and Morwood have criticized these recent findings by claiming that the scientists came to incorrect conclusions about bone and skull structure and mistakenly attributed the height of Homo floresiensis to microcephaly. They also pointed to studies by other scientists who rejected the argument that the individual was diseased. Falk's team replied to the critics of their Feb. 2005 study, standing by their results and insisting that the skull is very different from microcephalic specimens. Bill Jungers, a morphologist from Stony Brook University, examined the skull and concluded that the skeleton displays "no trace of disease". However, Jochen Weber of the Leopoldina Hospital in Schweinfurt argues that "we can't rule out the possibility that he suffered from microcephaly." Debbie Argue of the Australian National University has also published a study in the Journal of Human Evolution which rejects microcephaly and concludes that the finds are indeed a new species.

Evidence against microcephaly

On January 29, 2007, Falk published a new study supporting the claim to species status offering the most conclusive evidence to date that the claims of a microcephalic Homo sapiens were not credible. In this new study Falk examines 3-D computer generated models of an additional 9 microcephalic brains and 10 normal human brains, revealing the floresiensis skulls having shape more aligned with normal human brains, but also having unique features which is consistent with what one would expect in a new species. Comparing the frontal and temporal lobes, as well as the portion in the back of the skull revealed a brain highly developed, completely unlike the microcephalic brain, and advanced in ways different from human brains. This finding also answered past criticisms that the floresiensis brain was simply too small to be capable of the intelligence required to create the tools found in their proximity. Falk concludes the onus is now upon the critics that continue to claim microcephaly to produce a brain of a microcephalic that bears resemblance to the floresiensis brain.

Laron syndrome

On June 27, 2007, Hershkovitz et al. published a new paper arguing that the morphological features of H. floresiensis are essentially indistinguishable from those of Laron syndrome, casting the species claim once more into doubt.

Bone structure

The bone structure of H. floresiensis' shoulders, arms and wrists have been described as very different from modern humans, much closer to the bone structure of an early hominin or chimpanzees. This supports to the idea of the Hobbit being a separate species of early human rather than a modern human with a physical disorder.