Excavations at Liang Bua Cave exhibit skeletal evidence of a new species named Homo floresiensis; grounded the mosaic of primitive and derived features. Standing at approximately one meter tall, with a cranial capacity of 417cc, scientists argue that this species is the primary outcome of insular dwarfing, resulting from a long period of evolutionary isolation.
Also reviewed in this assessment is that attributes of Homo floresiensis are unlikely to represent microcephaly; a pathological disease resulting in an abnormal size head and mental retardation. Furthermore, Homo floresiensis demonstrates cranial and postcranial attributes congruent with both Homo and Australopithecine specimens, concluding that this new species is from a primitive ancestry that diffused out of Africa earlier than previously documented. Importantly, Homo floresiensis displays that the genus Homo is far more morphologically and behaviourally varied and complex in its adaptive responses than previously recognised.
In October 2004, came the startling announcement of a partial adult skeleton (Liang Bua 1 or LB1) excavated from Liang Bua Cave in Flores (Groves, 2007). Dating to only 18ka, this discovery sought to challenge preconceived notions on global hominin evolution. Standing at approximately one meter tall, with a cranial capacity of 417cc, these remains were found in Late Pleistocene deposits and constitute the smallest hominin ever found (Hanneke, et al., 2010).
Many argue that LB1 is the holotype specimen of a new species named Homo floresiensis (Brown et al., 2004; Falk et al., 2009; Tocheri et al., 2007), although some dispute this, stating LB1 is a pathological modern human (Jacob et al., 2006). A series of anatomical and comparative analyses have been conducted into not only the characteristics of this new species, but the global implications Homo floresiensis has on evolutionary origins.
Additional fragments of LB1 have been subsequently located in 2005, with remnants of eight specimens, some dating as far back as 74 and 95ka (Groves, 2007). At present, there is minimal information on where, when and which hominins appeared in Asia, and the expansion of hominin species from Africa. While there are boundless issues associated with H. floresiensis, the discussion in this report is restricted to the primary findings and their implications to the theories on global hominin evolution.
Evidence of a new species located at Flores
It is unquestionable that the brain size of LB1 is considerably smaller in comparison to other hominins, as values reported for H. floresiensis (380- 417cc.) are smaller than most gorillas and within the cranial capacities of modern day chimpanzees (Martin et al. 2006). Speculation persisted into the origins of the uniqueness of the Flores hominin, where cranial morphology was assessed in conjunction with limb proportions. Despite the small size, H. floresienisis brain morphology was founded to be completely re-organised, with an expansion of the temporal lobe; considered to be a derived trait (Falk, et al. 2009). Falk, et al. (2009) argues that there are many attributes within the brain that are distinctive of derivative characteristics that are indicative of conceptual abilities.
This is consistent with postcranial analysis, implying that ancestors of H. floresienisis diffused from Africa and survived in Flores, at least until 12kya. Subsequent investigations by Argue et al. (2006) further analysed the cranium and post cranium of LB1, where preliminary findings dismiss Brown’s conclusion that H. floresienisis evolved from H. erectus. This is due to variation in cranial shape, degree of prognathism and in particular, limb proportions (Argue, et al., 2006). Additional multivariate cranial variates analysis (CVA) of several cranial measurements for LB1, modern humans, two microcephalic modern humans, chimpanzees and fossil hominins, surmised that LB1 was distinct from all individuals within the genus Homo; with the closest similarities being with H. ergaster (Gordon, et al., 2008; Argue, et al, 2006). The postcranial analyses of LB1 consist of A. garhi attributes with primitive limb proportions and a long radius relative to the femur (Argue, et al. 2006). Therefore, it may be argued through the postcranial and cranial analyses that H. floresienisis evolved from a species that migrated out of Africa between the evolution of Australopithecus and Homo, prior to 2Ma.
The mandibular remains play a vital role in the interpretation of the remains at Liang Bua Cave, where the morphological specifics of the mandible and teeth strongly support the hypothesis that this is the remnants of a new species (Brown & Maeda, 2009). Respective ages of the LB1 and LB6 specimens can be determined from the exposure of dentine. It was concluded in Brown and Maeda (2009) that LB1 was an older specimen in comparison to LB6, whose age was calculated at approximately 20 years. Further research into the molar wear is congruent with meat eating behaviouristics, where the vegetable component in their diet is unknown.
Morphological comparisons of LB1: partially full skeleton, LB2: isolated left mandibular tooth and LB6: mandible; can all be interpreted in order to make a fluid interpretation of the origins of H. floresienisis.
Both mandibles exhibit characteristics of Australopithecus and early Homo specimens, however particular features (inc. morphology of the symphyseal region, corpus, ascending ramus, and premolars), found in the mandible are uncommon or non-existent in H. erectus or H. sapiens (Brown & Maeda, 2009).
These findings are congruent with the previously discussed cranial morphological analyses of Argue, et al, 2006, supporting the conclusion that H. floresienisis evolved from a species migrating out of Africa between the evolution of Australopithecus and Homo.
Postcranial elements of the early hominin species are rare within the archaeological record, where relatively complete feet are even scarcer (Richmond & Jungers, 2008; Lungers, W., et al., 2009). As LB1’s foot lacks a distinct longitudinal arch, the utilisation of stored elastic energy would have been limited ( Lungers et al, 2009). These vital pieces of information reveal that the foot of H. floresienisis was not designed for high speed or efficient endurance running, which is once again, dissimilar to modern humans (Bramble, & Lieberman, 2004). The length of the metatarsals (bones located between in bones of the hind and mid foot) is within the range characteristic of chimpanzees and the forefoot of LB1 is disproportionately longer than modern humans (Lungers, W., et al., 2009).
Furthermore, the robustness of the bases and midshafts in pedal phalanges are not congruent with characteristics associated with modern humans; the curvature indicative of some Australopithecines (Susman, Stern, & Jungers, 1984; Lungers, W., et al., 2009). Lungers, W., et al (2009) analysis of LB1’s talus is intermediate in shape, falling outside the norms of both modern humans and apes. Concerning ancestry, these features of the bones within the feet of LB1 all show dissimilarities with H. sapiens, showing numerous primitive features not seen in modern humans or late homo species of any size. These same characteristics show association with australopithecines, changing the scientific notion that H.etectus was the first hominin to diffuse out of Africa.
Three carpals recovered from the left wrist consists of a trapezoid, schaphoid and a capitate, that were recovered along with the previously discussed postcranial and cranial elements of LB1, during the September 2003 excavations (Brown, et al., 2004; Tocheri et al., 2007). These wrist bones were analysed and compared through the investigations outlined in Tocheri, et al. (2007) in a range of species including LB1, a gorilla and H. sapiens. Each of these samples were well preserved exhibiting no pathological or developmental abnormalities, nor any characteristics congruent with modern humans, or Neanderthals (Tocheri et al., 2007).
Alternatively, carpals of H. floresiensis accommodate a variety of features that are considered primitive traits. More specifically, LB1’s carpals express symplesiomorphic patterns including a wedge-shaped trapezoid and a triangular articular surface of the scaphoid; all of which associated with African ape species and hominins dating before 1.7Ma (Tocheri et al., 2007). In addition, carpal morphology is formed during embryogenesis (Durand, et al., 2006).
This makes it improbable that pathology resulted in the formation of primitive characteristics; as genes resulting in dysplasia are expressed post the formation of the preliminary shape (Jurgen, et al., 2004). Tocheri’s et al (2007) analysis supports the hypothesis that H. floresiensis evolved from a primitive ancestor that diffused from Africa before the evolution of the derived carpal morphology, evolving between 1.8-0.8Ma. These derived traits represent the adaption to distribute forces radio-ulnarly across the wrist to facilitate the production of lithic technologies apparent in Neanderthal and H. sapien populations (Tocheri et al., 2007). It can therefore be inferred, that the evolution resulting in H. floresiensis, began with an ancestor that migrated out of Africa substantially earlier than previously believed.
Stone tools found give indication into the complexity of the individual who utilised and constructed them, suggesting complexity and behavioural adeptness. Meta Menge is situated within the Ola Bua Formation, which has been dated to 960- 700ka (O’Sullivan, et al., 2001) and can be compared to the remnants located at Liang Bua. Despite these two locations being separated by over 50km and 700ka, there are undeniable similarities between the stone tool technologies of both these sites (Moore, 2005).
Core reduction strategies are also suggested to be similar, with reference to the free hand reduction of cores; both bifacially and radially, where radial cores from the two sites are indistinguishable (Brumm, et al., 2006). Brumm et al. (2006) further states that both of these sites contain similar assemblages, including ‘truncated’ flakes, cores with ‘burination’ scars and additional parallels in the maximum dimensions of flake scars. Disparities are also apparent in the record, as Liang Bua tools contain heat-fractured artefacts which are not apparent in Mata Menge assemblages (Brumm, et al., 2006). These preliminary findings indicate a long term reduction of cores bifacially and radially, producing distinctive stone technologies evident on Flores from 840ka to the disappearance of H. floresiensis 12ka (Morwood, et al, 2004). When interpreting these findings it is likely that the evidence from these two sites characterise an uninterrupted technology from an identical hominin linkage.
Pleistocene stone tool technologies from Flores have been suggested to show morphological similarities to the 1.2-1.9Ma Oldowan tool technologies from Africa (Moore & Brumm, 2008). The suite of tool production at both these sites were reduced by direct hard hammer production; considered to be a relatively uncomplicated approach in conjuncture with modern hominin ability (Moore & Brumm, 2008). It has been hypothesised that H. floresiensis are the remnants of a population of pathological H. sapiens, arguing that lithic technologies located on Flores are far too advanced to be manufactured by a non-modern hominin (Henneburg & Thorne, 2004).
This is challenged through the comparison of these specimens from Flores and Africa, which concludes that the stone artefact assemblage resembles those made from a community of hominins with a smaller cranial capacity and developmental abilities than modern humans (Moore & Brumm, 2008). Through these findings, lithic technologies dismiss the notion that the Flores hominin is a pathological H. sapien, where the tools once again show congruencies with very early hominin species. In addition, although the origins of Oldowan technologies are unknown, it is commonly associated with A. garhi, and flourishing early species of H. ergaster and H. erectus. Similarities within tool technologies of these hominins and H. floresiensis may give further insight into the origin of these unique species.
Global implications concluded from the evidence for H. floresiensis
It was proposed, post the initial discovery that these remains were of a microcephalic modern H. sapien, which result in mental retardation of adults. This is the commonly accepted conclusion of doubtful scientists that do not consider the Flores hominin to be a new species. In modern humans, the cranial capacity is approximately 1200-1700cc; a person suffering with microcephaly is usually short in stature and has a brain size of 700cc. although few have been recorded to be under 400cc. (Groves, 2007).
A number of arguments have been made by Jacob et al (2006), stating that there is insufficient evidence for a new species on Flores. Jacob et al (2006) further states that the attributes of the Flores hominin are indicative of a shared environment that are ‘not primitive but instead regional, not unique but found in other modern populations, and not derived but [disordered developmentally]’ (Jacob, et al., 2006 p. 13426). In addition, comparison of Rampasasa people, who are short stature and have a receding chin, are currently living on Flores today.
Was the Flores hominin really just a pathological modern human? Although microcephaly explains cranial proportions and derivative features in Flores specimens, many scientific investigations have dismissed pathological diseases through comparing samples of microcephalic human records to LB1. Brown et al. (2004), likened LB1 to a specimen from Tanzania, dated to 3.5-3.75Ma. A key paper by Argue et al. (2006) compares features of LB1 to known microcephalic skulls, presenting many attributes that differ unequivocally. Furthermore, the comparison of Bulbeck & Oxenham discussed in Groves (2007), shows no similarities between microcephalic skulls to LB1, beyond the fact that there is a reduction in brain size. These conclusions are supported by additional research on morphology by Tocheri et al. (2007), Brown & Maeda (2009), Lungers, W., et al (2009), as previously discussed in this paper.
After discrediting microcephalic morphologies, Brown et al. (2004) suggests insular dwarfing, proposing H. floresiensis is the product of evolutionary isolation. Insular dwarfing in response to specific ecological changes on smaller island communities, are well documented for animals larger than a rabbit (Lomolino, 1985). An example of this is the Stegodon; a dwarfed endemic species found in association with H. floresiensis (Morwood, et al., 2004). However there is unexplained variation as the evolutionary dwarfism is not applicable in all cases; there is a tendency for large ungulates to become smaller (Hanneke, et al., 2010).
A major argument that has been raised for insular dwarfing is that its small brain size cannot be accommodated in predicted mammalian dwarfing scaling models (Martin, et al., 2006). Evidence to the contrary is beginning to compile, which includes the assessment of the recently extinct Malagasy dwarf hippos displaying insular dwarfing resulting in unique brain sizes, smaller than predicted scaling techniques (Hanneke, et al, 2010).
In addition, Brown et al (2004), suggests that the first hominin immigrants that arrived in this part of the word may have been similar in size to early Homo species, including H. erectus. Henneke et al. (2010) supports this theory, further stating that H. erectus is a prime candidate for the role of ancestor for H. floresiensis. This is because it is the only hominin found to be present in South East Asia in the Pleistocene. Furthermore, having already reached Java by the early Pleistocene, H. erectus has been suggested to have inhabited Flores by the Middle Pleistocene, concluded by the lithic technologies located at Meta Menge.
It is therefore surmised that once H. erectus inhabited Flores, evolutionary dwarfism resulted in selection favouring the reduced energy requirements of smaller individuals (Hanneke, et al, 2010; Bailey & Headland, 1991). In addition, many of the morphological analyses display congruencies with more primitive hominins, including many Australopithecine species. As there are no remnants of Australopithecines outside of Africa, there is insufficient evidence to state that H. floresiensis derived from a more primitive species then H. erectus.
These findings of a new species located in Flores are not easily reconciled with the scientific notions of human evolution. Two chiefly hypothesized theories: the multiregional hypothesis, suggesting independent multiple origins; and the ‘Out of Africa’ theory, which infers that modern humans of African origin conquered the world, completely replacing former hominin species (Jin & Su, 2000). The discovery of H. floresiensis discredits the multiregional theory in a substantial way, as this is a new species with several distinctive features that could not have evolved into modern H.sapiens. In addition, dates of findings in Asia also deliberate the ‘Out of Africa’ theory, suggesting that hominins expanded from Africa earlier than previously surmised. Although there will be doubtless reluctance to abandon the “Out of Africa theory, which is an accepted postulation explaining the small amounts of data from Asia; there are benefits to be gained for broadening our knowledge, subsequently forming new and improved hypotheses. Additionally, the inability to establish the inexistence of a hominin in a particular area, merit the right to judge as to when, if ever, the species inhabited the area.
The archaeological discovery of H. floresiensis challenges our modern day scientific community; perplexing pre conceived notions and creating a further complex evolutionary family tree. Miniscule cranial morphology and postcranial elements resemble both shape and size of our distant ancestors, which were previously supposed to have never left Africa. Furthermore, the complexity of the brain is considered a derived trait, with conceptual and cognitive capabilities.
This mosaic of primitive and derived features proves to be confounded in the evolutionary record, suggesting that the evolution of H. floresiensis is unique. In addition, it could be argued that a more primitive ancestor dispersed out of Africa, resulting in the development of morphological complexities that has yet to be recognised in the archaeological record. This compels scientists to evaluate whether or not this is the result of the absence of taxonomic circumstances or the lack of appropriate fieldwork. Similar to many unresolved scientific theories, no viable conclusions into the complexity of hominin evolution can be made without the validity of additional research and investigation.
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