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Homo floresiensis
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Homo floresiensis ("Flores Man", nicknamed Hobbit) is a possible species in the genus Homo, remarkable for its small body and brain and for its 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 (named LB1, because it was the first specimen found in the Liang Bua cave) 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.
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Homo floresiensis ("Flores Man", nicknamed Hobbit) is a possible species in the genus Homo, remarkable for its small body and brain and for its 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 (named LB1, because it was the first specimen found in the Liang Bua cave) 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 is LB6), all diminutive, have been recovered as well as similarly small stone tools from horizons ranging from 94,000 to 13,000 years ago. Descriptions of the remains were first published in October 2004. To date, the only complete cranium is that of LB1.
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 lived contemporaneously with modern humans (Homo sapiens) on Flores.
Doubts that the remains 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 a recent study published by paleoneurologist Dean Falk and his colleagues that disputes the possibility of microcephaly. They compared the H. floresiensis brain to ten microcephalic brains, and revealed 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 hominin such as Australopithecus and significant differences 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. One recent hypothesis is that the individuals were born without a functioning thyroid, resulting from a type of endemic cretinism (myxoedematous, ME). This idea has been dismissed by members of the original discovery team as based on a misinterpretation of the data.
Discovery
The first specimens were discovered by a joint Australian-Indonesian team of paleoanthropologists and archaeologists looking for evidence of the original human migration of H. sapiens from Asia to Australia. They were not expecting to find a new species, and were surprised at the recovery of a nearly complete skeleton of a hominid they dubbed LB1 from the Liang Bua limestone cave on Flores. Subsequent excavations recovered seven additional skeletons, dating from 38,000 to 13,000 years ago. An arm bone, provisionally assigned to H. floresiensis, is about 74,000 years old. Sophisticated stone implements of a size considered appropriate to the 1 m tall human are also widely present in the cave. These are at horizons from 95,000 to 13,000 years ago and are associated with juvenile Stegodon (a group of proboscideans that was widespread throughout Asia during the Quaternary), presumably the prey of LB1.
The specimens are not fossilized, but were described by Richard Roberts of the University of Wollongong, Australia 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. However, it is unlikely that useful DNA specimens exist in the available samples, 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
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. Recent research of Lyras et al., based on 3D-morphometrics, shows that the skull of LB1 differs significantly from all Homo sapiens skulls, including those of small-bodied individuals and microcephalics, and is similar only to the skull of Homo erectus.
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 ancestor australopithecines, from three million years ago, 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 coincident with earlier finds purported to be of H. floresiensis. These observed similarities form the basis for the suggested phylogenetic relationship. Controversially, the same team is reported to have found material evidence, stone tools, of a H. erectus occupation 840,000 years ago, but 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, 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 extinct 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 alleged 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 hominids 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.
In 2007, Susan G. Larson et al. focused on the twist of the nearly complete upper arm bone of the LB1’s skeleton. Modern people have the top of the bone twisted between 145 to 165 degrees, which makes the inner part of the elbow face slightly forward. Larson originally stated that the LB1’s bone was twisted only 110 degrees, but later made a new measurement and found that the torsion was 120 degrees. This could be an advantage when arm-swinging, but complicates activities associated with modern people, such as tool-making. Larson et al. investigated also the pectoral girdle of H. floresiensis. Due to the incomplete material they studied a broken clavicle of LB1 and a shoulder blade of the individual referred to as LB6. The clavicle was relatively short, which in combination with the shape of the shoulder blade and the low twist of the arm bone resulted in the shoulder being moved forwards slightly, as if it was shrugged. Thus H. floresiensis could bend the elbow in the way modern people do and Larson concluded that it could have been able to make tools as well.
In September 2007, Matthew W. Tocheri of the Smithsonian's National Museum of Natural History and his team published a paper on the wrist of Homo floresiensis. They studied three complete carpal bones, a trapezoid, scaphoid and capitate, believed to belong to LB1. Tocheri et al. found that the shapes of these bones differ significantly from the bones of modern human wrist and that they resemble the wrist of great African apes or Australopithecus.
Jungers et al, who published a study on the lower limbs, found that H. floresiensis’ feet were unusually flat and large in comparison with the rest of the body. As a result, when walking, it would have to bend its knees further back than modern people do. According to Jungers, its walk resembled a sort of high stepped gait and it was not able to walk very fast. H. floresiensis also had unusual shape of its toes and its big toe was very short.
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.
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. Gregory Forth hypothesized 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 creatures are claimed to have existed 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.
On the island of Sumatra, there are reports of a 1–1.5 m tall humanoid, the Orang Pendek, which paleontologist Henry Gee has speculated might be related to H. floresiensis.
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 February 23, 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 February 2005. The authors of the study claimed that the 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 earlier study and concluded that the skull of LB1 is consistent with microcephaly.
The results of the February 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.
Evidence against microcephaly
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 study, standing by their results and insisting that the skull is very different from microcephalic specimens. William 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.
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 3D computer generated models of an additional 9 microcephalic brains and 10 normal human brains, and reveals that the floresiensis skulls have a shape more aligned with normal human brains, but also have unique features which are consistent with what one would expect in a new species. Comparing the frontal and temporal lobes, as well as the back of the skull, revealed a brain highly developed, completely unlike the microcephalic brain, and advanced in ways different from modern 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.
The above mentioned study by Lyras et al. (2008) confirms Falk's results in that 3D-morphometric features of the skulls of microcephalic Homo sapiens indeed fall within the range of normal Homo sapiens and that the LB1 skull falls well outside this range. This means that LB1 cannot be attributed to a microcephalic Homo sapiens, neither based on brain morphology nor on skull morphology.
Laron syndrome
The possibility that the skeletons from Flores are the remains of people who suffered from Laron syndrome was first proposed by American anatomist Gary D. Richards in June 2006. A year later, in June 2007, Israel Hershkovitz, Liora Kornreich and Zvi Laron from the Tel Aviv University in Israel published a new paper arguing that the morphological features of H. floresiensis are essentially indistinguishable from those of Laron syndrome. Laron syndrome causes severe pituitary dwarfism. Unlike growth hormone deficiency, growth hormone levels are increased, but the body is unresponsive to it. Its features include underdeveloped skull with small face and mandible and other skeletal changes. The disease is most often reported with Middle East children of consanguineous parents, but it also occurs in some South-East Asian countries.
The Israeli researchers compared X-rays of Israelis affected with Laron syndrome, whose heights ranged between 108 and 128 cm, with data from LB1. They compared 36 features from around the skeleton and concluded that most features were similar, including a pronounced ridge above the eyes, absence of a particular sinus, and short limbs in proportion to the trunk. They declared that Laron syndrome patients also have smaller heads, although not as small as LB1, and that many of the unique anatomical landmarks that Dean Falk had found left by the brain on the inner part of the LB1's skull, could have also been a feature of Laron syndrome. People with Laron syndrome also have a dense mastoid region bone, unlike healthy individuals, whose bone in this part of the skull is spongy and filled with air. Hershkovitz did not make this comparison, because no radiographs of LB1's skull were available. However, Falk examined the CT scans her team had made and found that LB1's mastoid region does not manifest any signs of Laron syndrome.
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 chimpanzees or an early hominin. This adds support to the idea that the Hobbit is a separate species of early human rather than a modern human with a physical disorder.
Susan G. Larson et al. analyzed the upper limb of LB1. They found that LB1’s arm torsion is unusually low, much lower than with modern people. This had been previously studied by G. D. Richards et al., who declared that it is a sign of modern pygmy populations, and T. Jacob et al., who pointed out that muscle attachments on the bone suggest LB1 had weak muscles which resulted in little development of humeral torsion. Larson et al. opposed Richards’ conclusion, arguing that pygmy populations usually have arm bones similarly twisted as average stature peoples. They argued that Richards et al. cited a 1972 paper which had studied a sample of six female Eastern Central African pygmies and this sample was too small to represent the whole population. Larson et al. also looked for some signs of microcephaly on the studied bones, but failed to find any.
William L. Jungers of the Stony Brook University in New York compared the low twist of the arm bone of H. floresiensis to the similarly small humeral torsion of an early hominid from Dmanisi in Georgia, usually designated as Homo georgicus. Larson et al. also studied a relatively short clavicle and unusual formation of the pectoral girdle. They compared their finding with a Homo erectus skeleton, KNM-WT 15000, known as Nariokotome boy, and suggested that the pectoral girdle of H. floresiensis was a transitional stage in human shoulder evolution.
While some specialists, including paleoanthropologist Russell Ciochon of the University of Iowa, supported the conclusion, others, including Eric Delson of Lehman College, City University of New York, pointed out that the recent sample of H. floresiensis individuals is too small and that Larson’s research was based just on one shoulder bone.
Another study supporting the separate species hypothesis was published by Matthew Tocheri et al., who studied H. floresiensis wrist bones. They compared three carpal bones believed to belong to LB1 with carpal bones of modern humans, some earlier hominids and African apes. They concluded that the carpals from the Liang Bua cave resembled ape carpal bones and were significantly different from the bones of Homo sapiens, Homo neanderthalensis or even Homo antecessor, and that they were comparable to carpal bones of Australopithecus. The carpal bones of H. floresiensis lack features that evolved with ancestors of modern humans at least about 800,000 years ago. These features are already formed during embryogenesis and therefore Tocheri et al. argue that it is improbable that the shape of H. floresiensis wrist bones could be a result of a developmental disease.
This conclusion was challenged by Robert Martin of the Field Museum in Chicago, who noted that no research of wrists of microcephalic people had been done. Alan Thorne of the Australian National University stated that the differences were small and similar variation could occur with living modern humans. He also pointed out that the carpal bones had been found scattered in the cave and it was not certain that they all belonged to the same individual. Michael Morwood of the University of Wollongong in Australia, one of the co-authors of the study, opposed Thorne stating that there were also other features, such as the stature, body proportions, brain size, shoulder, pelvis, jaw and teeth which suggested that H. floresiensis is a separate species that evolved in isolation on the island.
Endemic cretinism hypothesis
In 2008 Australian researchers Peter J. Obendorf, Charles E. Oxnard, and Ben J. Kefford suggested that LB1 and LB6 suffered myxoedematous (ME) endemic cretinism resulting from congenital hypothyroidism and that they were part of unaffected population of Homo sapiens on the island. This disease, caused by various environmental factors including iodine deficiency, is a form of dwarfism which can still be found among the local Indonesian population. Affected people, who were born without a functioning thyroid, have both small bodies and reduced brain size but their mental retardation and motor disability is not as severe as with neurological endemic cretins. According to the authors of the study, the critical environment could have been present on Flores approximately 18,000 years ago, the period to which the LB fossils are dated. They wrote that various features found on the fossils, such as enlarged pituitary fossa, unusually straight and untwisted top of the upper arm bone and relatively thick limbs, are a sign of this diagnosis. The double rooted lower premolar and primitive wrist morphology can be explained in this way as well. The oral stories about strange human-like creatures may also be a record of cretinism.
R. D. Martin has expressed his delight that other researchers continue to explore the possibility that the small skull is in fact a pathological specimen, but he still prefers the microcephaly hypothesis. Dean Falk challenged the Australian team's results, studying computer tomography scans of LB1's pituitary fossa and coming to the conclusion that it is not larger than usual. Because the fossa size was the key argument of the study on ME endemic cretinism, Falk dismissed the whole hypothesis. Peter Brown, the discoverer of the fossils, declared that the remains of the pituitary fossa were very poorly preserved and no meaningful measurement was possible. Other measurements of Obendorf et al. were also disputed, since they had neither the bones nor CT scans available and used just captured images from X-ray scans presented in the 2005 BBC show The Mystery of the Human Hobbit.
See also
Further reading
External links
- Virtual Endocasts of the "Hobbit" - Electronic Radiology Laboratory
- 10/27/2004
- A review of the state of debate regarding the status of
H. Floresiensis, from the open access journal Public Library of Science, Biology.
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