Homo floresiensis

Homo floresiensis
Most scholars used to think that the first migration of hominids out of Africa was around one million years ago, with Homo erectus. In 1994, though, new data analysis of the old Java sites in Indonesia have showed new results. Those results testified the existence of Homo erectus more than 1.66 million years ago (Klein 2009). Scholars started to consider the idea that maybe Homo habilis or Homo rudolfensis could be the first to spread out of Africa, since the analysed data are telling that Homo erectus is equally old in Asia, Africa and Europe. With this, even more questions about Homo erectus' origin are adding up; now there is also the hypothesis that this species overlaps in time with Homo sapiens in Southeast Asia (Campbell and Loy 2000). The Javanese sites of Ngandong and Sambungmacan, which are dating respectively 46,000 to 27,000 and 53,000 to 27,000 years B.P., helped archaeologists to enforce this opinion. In those two sites, skulls were found that created problems whether to define them as Homo erectus or not, yet they showed advanced anatomical features compared to typical Asian Homo erectus specimens (Klein 2009). That is what Morwood and Oosterzee (2007), Klein (2009), and also other scholars state: Homo erectus and Homo sapiens had coexisted at the same period.
More questions about the evolution of Homo species and when they started to move out of Africa, arose in 2003 when new human fossils were found in the Liang Bua cave on Flores Island, Indonesia (Brown et al 2004). An almost complete female skeleton was found and nicknamed the "hobbit" because of her particularly small size (Morwood and Oosterzee 2007). The skeleton found was archived as LB1 and assigned to a new species: Homo floresiensis, because of her unique combination of primitive and derived features (Brown et al 2004). Maybe it will be thanks to this new species that we could have a better understanding of how the human gene has evolved, maybe something more about the Homo erectus that lived in Southeast Asia, and weather Homo erectus was the first to leave Africa or not.
Since "hobbit" was discovered, people have divided in two groups: the ones who believe that she is a new species and the ones who think that she is a modern human with microcephaly or dwarfing (Henneberg and Schofield, 2008). If it was a modern human, though, it is necessary to explain how she ended up buried deep in a cave with primitive tools and the bones of a dwarf elephant, apparently the result of hunting and butchering.
In this paper, there will be an examination of some aspects of Homo floresiensis and support of the theory that H. floresiensis is a new species.
In Liang Bua cave, archaeologists excavated the skeleton of LB1 in 2003. Further excavation conducted the next year digged out of the ground other eight individuals in similar strata as LB1 (Vannucci et al. 2011). Among these, only one, LB1, has an almost complete skull and a near-complete skeleton. Of the other eight individuals there are some teeth and skeletal fragments (Morwood et al. 2004), which include the mandibles of LB2 and LB6, and the tibia of LB8 (Lieberman 2005). These skeletal fragments imply comparably small size with LB1 skeleton (Brown et al. 2004).
The "hobbit" is a one-metre-tall hominid, based on the femoral length. Her remains were found in a small area inside the cave and some parts of the skeleton were still articulates, but the tibia instead was flexed under the femur. After looking at the relationship between the stratigraphy and the orientation of the skeleton, it is affirmed that there could be a possibility that the body had moved slightly down before it was covered by sediments (Brown et al. 2004). Since the skeleton is not completely fossilized or covered with calcium carbonate, it is extremely fragile, and because of this, studying its DNA and skull is really difficult without doing any more damage (Vannucci et al. 2011).
What was recovered of LB1's skeleton was an almost perfectly complete skull, right and left leg bones, left coxal bone, and hands (Brown et al 2004). Also the feet were found, which are very important because they give scholars an idea if she was bipedal or not (Jungers et all 2009). There were also fragments of the vertebral column, sacrum, scapulae, clavicles, and ribs. Were found also some teeth and, of the arm bones, the ulna and radius. Based on tooth eruption, epiphyseal union, and tooth wear, it seems that LB1 was an adult at the moment of death, and based on the pelvic anatomy, it is possible to state that it was a female. LB1 estimated body mass was between 16 to 24 kilograms (Brown et al. 2004).
If it is assumed the hypothesis that Homo floresiensis is a new hominid species, one of the biggest problems is to understand in which species it falls: Australopithecus or Homo. Measurements of the endocranial volume were taken: the first took measurements of LB1's endocranial capacity was of about 380 cubic centimeters, and it was measured with mustard seed by Brown and his colleagues. With this result, the "hobbit" will fall in the Australopithecus species, since the volume is equal to the minimum estimation of this species, and it is extremely below the range of the Homo gene (Brown et al 2004). After, Argue et al. (2006) took measurements. They obtained the result of 400 cubic centimeters, just above the lower limit for adult australopiths (Wolpoff 1999). A recent research shows that the H. floresiensis brain was 426 cubic centimeters. This measurement was taken with replicas of H. floresiensis' skull and with a high-resolution computed-tomography scan that made prototypes of LB1's brain. This is the most accurate estimation so far, and it means that H. floresiensis' brain is approximately one-third the volume of a human brain. The researchers, with this outcome, are sure that it is mechanistically possible that H. erectus suffered and went through dwarfism on an isolated island (Daisuke et al. 2013).
Thus, endocranial capacity suggests that H. floresiensis comes from H. erectus, and other features that suggest so are the absence of mental eminence and the long and low shape of the braincase. Instead, the great length of the arms relative to the legs suggest an australopiths-like species. What suggests a Homo sapiens is the size and proportion of the teeth (Klein 2009). New researche about LB1' feet and the leg bones raise the possibility that H. floresiensis' ancestor was a more primitive hominid than H. erectus, whose scattering into southeast Asia is not documented yet (Jungers et al. 2009).
The feet of LB1 are very important because they give an understanding of the evolution of bipedalism and, along with the rest of the skeleton, the spreading of hominids in Asia (Jungers et al. 2009). LB1's foot has typical features of African apes, as the foot is long relative to the femur and tibia, like other pedal features. The metatarsals' robusticity, although, is human-like (Jungers et al. 2009). Also for Brown et al (2004), the postcranial anatomy of H. floresiensis is that of a biped, but anyway, it differs from modern human locomotion because of its lower-limb proportions and pattern of primitive pedal morphology. There are all the necessary features to believe that LB1 was bipedal, such as the pelvis, the lower-limb bones, and feet, but those features are still different from modern humans. Most importantly, the foot lacks the arch that is very important for bipedalism and present in all Homo genes (Jungers et al. 2009). It is most likely that, since the medial longitudinal arch is weakly developed, most of the weight would have felt on the navicular tuberosity, which is in the tarsal bones. This pattern is seen in australopithecines and in the great apes (Harcourt-Smith et al. 2004). Given the conformation of the foot, it is possible to state that the "hobbit" foot is not well-designed for running, and not just because it lacks a developed arch, which gives the foot more flexibility and to distribute the weight better as in modern humans, but also, the hallux is shorter than the other toes, which helps equilibrium and stability. The relative distance between each toe helped with weight-bearing, especially during running (Bramble 2004).
Primitive feature are shown on the foot, as in its cranium, mandible, body proportion, and in almost every other parts of the skeleton (Jungers et al. 2009). It is plausible that in 800 thousand years a few of those traits changed because of insular isolation (Lyras et al. 2008), but the "island dwarfing", insular isolation, alone s have not change all the stature and features. Hence, H. floresiensis should have had an evolutionary reversal in locomotion. An example that Brown et al. (2004) made are the tribes with pygmies modern people. Pygmies are people which body size have reduced significantly through the world. However, even if they sized diminished, they do not show any evidence of evolutionary reversals that could make a part of their skeleton, or habits, look closer to a primitive morphology.
Also in modern medicine, there are still not known skeletal pathologies that effect the skeleton to go back to have primitive body design (Jungers et al. 2009). A study on the mutation on the Pericentrin (PCNT), that cause primordial dwarfism, was conducted, and the results showed that the hypothesis of a complete "island dwarfing" is improbable. This mutation happens if there are dysfunctions on the pathway of the regulation of cell size and cell division, those cells are the regulators of an individual growth. People affect with this disorder reach a growth not usually more than one meter, which is the case of the "hobbit". The body proportions, anyway, remain the same as in other modern humans. Most of the time, also the brain growth is normal, just few individuals have mental retardation (Rauch et al. 2008). Another research conducted by Argue et al. (2006) lead at the same conclusion: people affected with dwarfism will have a reduction in body and brain size, but the final result is that every part of the body is proportionate. If the "hobbit" had the same features of H. erectus or ancient H. sapiens, or of an australopiths, and just the height would have differed, it would have been plausible to say that LB1 could have suffered of a genetic disorder. H. floresiensis has not just the high that differ, but also the skeleton proportions and the traits.
Instead, scholars who do not believe in the new specie theory are sure that LB1 is a small-bodied modern human that suffered of a growth disease called microcephaly that is a heterogeneous disorder (Henneberg and Schofield 2008). This disease reduces the brain growth with or without other abnormalities. Sometimes it can affect both body and brain size and lead also to subnormal function. This still not explain all the primitive traits that are characteristic of H. floresiensis.
The opinion of Homo floresiensis being affected by island dwarfing was initially discarded even because to arrive in Flores there is the necessity of a boat (Klein 2009). Some scholars think that the "hobbit" descend from H. erectus and then dwarfed in response to the small available area of Flores (Morwood and Oosterzee 2007), and almost no researchers believe that Homo erectus had the abilities to navigate, or to construct a boat. However, in other sites in Flores have been discovered rocks that may be Homo erectus artefacts dated about 800 thousands years ago. If they are, it will mean that this specie had a little of ability to navigate, or found another way to arrive in the island (Klein 2009). H. floresiensis inhabited Flores' island since the Late Pleistocene, where there was an ice age. It is necessary to consider that it would have been easier arrive in the island in this period (Meijer et al. 2010). Also Morwood (2005, 2007), in 2001, found artefacts in Ngandong that seem made by Homo erectus together with a Homo erectus radius. Then, in the surrounding area of Liang Bua, he found other "hobbit" bones and evidence of the use of fire. In the overlying deposits of the cave, his team discovered artefacts and remains of Homo sapiens that might be as old as Homo floresiensis. This could imply that these two Homines could have leaved together in the same island and cave; besides radiocarbon dates locate the "hobbit" around 38 thousand years ago to 12 thousand years ago (Klein, 2009). This can have happened because Homo sapiens stopped in Flores while heading to Australia. Evidences of this theory are artefacts located in sites close to Australia, like the one in Timor, Indonesia, which resembles artefacts found in Liang Bua (Veth et al, 2005).
As an alternative to dwarfing in Homo erectus, the discoverers suggested the "hobbit" to be the end point of an unknown ancient lineage of Homo. This could have explained the small size and the other characteristics of Homo floresiensis, but it does seem unlikely that a lineage with these specific characteristics reached Flores while it remained unobserved elsewhere (Klein 2009).
Assuming that Homo floresiensis descends from Homo erectus, even a dwarf form would have had larger brain than LB1 (Klein, 2009). It would be more presumably a microcephaly case because just the skull size would have decreased. But this hypothesis reached its end. Argue et al. (2006) published an article where they analysed every known data about Homo floresiensis. They compared LB1 skull with other skull's species, from australopithecine to modern human, that were affected and not by microcephaly. The final data of their work show that Homo floresiensis is not a modern human with microcephaly. Even Holloway had tried and failed to find directed correspondences between LB1's cranium and those of people with microcephaly (Brown et al 2004). It is even unlikely that it is a microcephaly Homo sapiens. Moreover, from their research "hobbit" showed characteristics that resemble the australopithecine and others that resemble an early Homo. Researchers concluded, from LB1 cranial analysis data, that Homo floresiensis is not descended from Homo erectus (Argue et al. 2006).
The origins of the "hobbit" are still unclear, even because we lack data of the DNA structure (Brown et al 2004). Lab tests on LB1's DNA have failed mostly because DNA is preserved well just in dry conditions, and Liang Bau cave is damp (Klein, 2009). If we can understand Homo floresiensis, we may also understand better the missing link: how Homo erectus became Homo sapiens. It could be possible that Homo floresiensis is a separate evolution of Homo erectus (Morwood and Oosterzee, 2007).


















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