Homo floresiensis
2007 Schools Wikipedia Selection. Related subjects: Mammals
| iHomo floresiensis | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Homo floresiensis cranium.
On the cover of Nature. |
||||||||||||||
|
|
||||||||||||||
|
Prehistoric
|
||||||||||||||
| Scientific classification | ||||||||||||||
|
||||||||||||||
|
|
||||||||||||||
| †Homo floresiensis P. Brown et al., 2004 |
Homo floresiensis ("Man of Flores") is the proposed name for a possible species in the genus Homo, remarkable for its small body, small brain, and survival until relatively recent times. It is thought to have been contemporaneous with modern humans (Homo sapiens) on the Indonesian island of Flores. One largely complete sub-fossil skeleton (LB1) and one molar (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 fossils was unearthed in 2003 and the publication date of the original description is October 2004. Confirmation of species status was expected to appear in March 2005, following publication of details of the brain of Flores Man in Science. However, several other researchers have argued that the original specimen does not represent a new species, but rather a modern H. sapiens with microcephaly. The original discoverers and others have argued against these interpretations and maintain that H. floresiensis is a distinct species. To date, the only complete cranium is that of LB1, and additional skeletons may be required to resolve this debate. Regardless, the discovery is widely considered the most important of its kind in recent history, and came as a surprise to the anthropological community.
Discovery
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
In their initial reports, Peter Brown, Michael Morwood, and their colleagues 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. The most important and obvious of these features are the small body and small cranial capacity of LB1. 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 have verified the existence of some features found in LB1, such as the lack of a chin, but Jacobs and colleagues 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 colleauges 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 relative 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.
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 29,000 years ago. Homo floresiensis certainly coexisted for a long time with modern humans, who arrived in the region 35,000–55,000 years ago, but it is unknown how they may have interacted.
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, because of a deep neighboring strait. This has led the discoverers of H. floresiensis to conclude that 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 perceived evidence of 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 was responsible for the demise of H. floresiensis in the part of the island under study at approximately 12,000 years ago, 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. Widely believed to be present at the time of the arrival of the first Portuguese ships during the 16th century, these strange creatures were apparently last spotted as recently as the late 19th century.
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. Footprints and hairs believed to be from the Orang Pendek have been recovered by two amateur explorers. Analysis of these have yielded mixed results; both footprints and hairs are believed to originate from a previously undocumented species of primate but DNA analysis of the hairs found only human DNA. A possible explanation for this is that contamination by people who handled the hairs could have introduced this DNA and the original DNA could have decomposed. Scholars working on the Flores Man have noted that the Orang Pendek may also be surviving Flores men still living on Sumatra.
Controversies
Whether the specimens represent a new species is a controversial issue within the scientific community. In 2005, a computer-generated model of the skull of Homo floresiensis provided further support that the controversial specimens from Indonesia do indeed represent a new species. The study of the creature's brainpan showed that it was neither a pygmy nor an individual with a malformed skull and brain, as some critics contend, lending support to the discovery team's assertion that the metre-tall specimen belongs to a species distinct from Homo erectus. These results continued to be debated.
In the May 19, 2006, issue of the journal Science, Robert D. Martin of the Field Museum in Chicago and some co-authors argued that the fossil of Homo floresiensis appears to be that of a modern human with microencephaly, a disorder resulting in a small brain and other defects. 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, several paleontologists have criticized the findings by claiming that the scientists came to incorrect conclusions about skull structure and mistakenly attributed the height of Homo floresiensis to microencephaly.
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 or nanocephaly (now discounted). Professor Jacob borrowed most of the remains from Soejono's institution, Jakarta's National Research Centre of Archaeology, for his own research (apparently 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. However, Jacob returned the remains to the Centre, with the exception of two leg bones, on 23 February 2005.