The Peculiar Case of Homo floresiensis: A New Perspective on Hominin Migrations

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1 The Peculiar Case of Homo floresiensis: A New Perspective on Hominin Migrations Kaitlynn Rachelle Alarie University of Winnipeg Key Words: Homo floresiensis, Hominin Migration, Human Evolution Abstract In 2004 a paleoanthropology team discovered the remains of an extinct and curiously unique hominin species on the isolated Indonesian island of Flores. This find has proven to be among the most compelling hominin specimens since the discovery of Lucy, an iconic early australopithecine. Homo floresiensis, nicknamed the hobbit due to its extremely small stature has shaken the typically accepted evolutionary paradigms. The holotype specimen LB1 has been subject to intense research in efforts to determine its true taxonomic relationship within the hominin family tree. This little species exhibits an extremely small brain size and body stature which parallels that of our distant australopithecine ancestors such as Lucy, however unlikely Homo floresiensis persisted until the recent past and likely lived contemporaneously with Homo sapiens and Homo neanderthalensis. More compelling than its late survival is its small cranial capacity and its curious mix of primitive and independently derived characters. Some researchers have attempted to reconcile LB1 as a pathologically microcephalic or pygmoid Homo sapiens or Homo erectus individual, while others believe it represents an isolated, newly identified, early Homo species. The cranial and limb morphology of the holotype LB1 and subsequent specimens on Flores proves that Homo floresiensis is a unique species and not a biologically anomalous modern human. Homo floresiensis demonstrates the true morphological and adaptive range of our genus. With its small brain, comparable in size to an australopithecine, Homo floresiensis was capable of producing a tool technology which demonstrates sophisticated cognitive abilities. Traditionally, brain size has been at the core of arguments regarding behavioural output. This hobbit may force us to reexamine our view of early hominins and the biological requirements for modern behaviour and cognition. Introduction In 2004 a team of archaeologists published an article in Nature describing their highly controversial fossil discovery from the island of Flores in Indonesia (Cela- Conde and Ayala 2007: ). The team had recovered multiple hominin fossil specimens at their Liang Bua site (Cela- Conde and Ayala 2007: ) that would proceed to shake the paleoanthropological world. The specimens were identified as fully bipedal hominins dating to the late Pleistocene with an adult stature of only one

2 meter and an estimated cranial volume of 380cmᶾ, within the range of the smallest identified African australopithecines (Brown et al. 2004: 1055). The specimens were initially judged to be a newly identified hominin species, and were assigned the taxonomic classification of Homo floresiensis (Brown et al. 2004: 1055). At the time of the discovery of the Flores specimens, it was believed that only two hominin species, Homo erectus and Homo sapiens, had ever inhabited Asia (Cela-Conde and Ayala 2007: 265). Both Homo erectus and Homo sapiens exhibit much larger crania and full body stature than their African australopithecine predecessors (Brown et al. 2004: 1055). It is commonly understood that following Homo habilis the genus Homo developed larger brains, larger stature, and smaller post-canine dentition (Cela-Conde and Ayala 2007: 265). The Flores specimens demonstrate the unexpected existence of a small-bodied small-brained hominin that lived in near isolation surviving into the late Pleistocene. The Flores hominins are truly in opposition to the current theoretical framework of human evolution. I will discuss the unique morphological characters of Homo floresiensis and the various evolutionary interpretations that have been drawn from them. I will also explore the possible taxonomic relationship between Homo floresiensis and other known members of the genus Homo. Holotype Fossil Description The taxonomic identification of Homo floresiensis was initially based upon the single holotype specimen LB1, which was recovered in 2004 (Brown et al. 2004: 1055). The skeleton of LB1 was discovered in a remarkable context; though extremely fragile, it was still partially articulated, which enables a confident comprehension of the specimen s skeletal posture and skeletal morphology (Brown et al. 2004: 1055). LB1 was determined to be a partial adult skeleton consisting of a cranium, mandible, femora, tibiae, fibulae, patellae, partial os coxae, partial hands and feet, and fragments of vertebrae, sacrum, ribs, scapulae, and clavicles (Brown et al. 2004: 1055). The 2004 research team determined that the specimen lacked a covering of calcium carbonate typical of fossils, and later discovered that LB1 had not, in fact, been fossilized (Brown et al. 2004: 1055). The lack of fossilization raises questions, which will be addressed in a further section, of the true age of the specimen and its potentially late survival. Based on dental eruption, the degree of tooth wear, and epiphyseal union the specimen was determined to be an adult individual (Brown et al. 2004: 1055). LB1 was identified by pelvic and cranial morphology as a probable female (Brown et al. 2004: 1055). LB1 displays an endocranial volume and body height similar and possibly even smaller than Australopithecus afarensis (Brown et al. 2004: 1055). However the Flores specimens do not possess the same masticatory adaptations as Paranthropus or any known Australopithecus species (Brown et al. 2004: 1055). When compared to australopithecines, the cranium of LB1 exhibits reduced prognathism, facial height, and post-canine dentition (Brown et al.

3 2004: 1055). The specimen s superior cranial vault bone is significantly thicker than in australopithecines, and Brown et al. (2004: 1055) feel that this trait more closely resembles the state found in Homo erectus and Homo sapiens. The cranial vault is long and low and the cranial size is far below any species of the erectus grade (Brown et al. 2004: 1056).According to this research team, when cranial size is discounted, the cranial indices of LB1 closely resemble the pattern evident in Homo erectus (Brown et al. 2004: 1056). A CT scan of the reconstructed endocranium of LB1 was completed by the Liang Bua team. The results demonstrate that, when compared to Homo sapiens, the brain of LB1 had a flattened platycephalic shape with reduced parietal regions, and its greatest width occurred at the temporal lobes (Brown et al. 2004: 1056). The cranial base angle of LB1 was determined to be 130, which is similar to but still less than the flexion exhibited in Homo sapiens ( ) and Asian Homo erectus (141 ) (Brown et al. 2004: 1056). The cranial base angle of LB1 is much more flexed than in the African small brained hominins; demonstrating that a low-flexed angle is the more primitive condition (Brown et al. 2004: 1056). The face of LB1 displays prominent maxillary juga that form pillars which are laterally separated from the nasal aperture (Brown et al. 2004: 1055). The specimen possesses a continuous supraorbital torus which arches over each orbit; this is not the case is the Asian Homo erectus specimens, where the supraorbital torus forms a flat unarcuated bar (Brown et al. 2004: 1055). The mandible of LB1 does not present a boney chin and the mandibular coronoid process is higher than the condyle (Brown et al. 2004: 1055). The mastoid process is thickened and resembles the state observed in Homo erectus (Brown et al. 2004: 1057). The ilium displays a marked lateral flare, the femoral neck is long relative to the heads diameter, and there was a high bicondylar angle, all indicating that Homo floresiensis was fully bipedal (Brown et al. 2004: 1055). In 2005, Morwood et al. published an article in Nature describing subsequent Homo floresiensis discoveries from the Liang Bua site. The new specimens consist of multiple post-cranial elements which facilitate the confident estimation of stature and cranial volume within the population (Morwood et al. 2005: 1012). The researchers have recovered at least nine individuals, all exhibiting the same unexpected small bodies and crania as the LB1 Homo floresiensis holotype specimen (Morwood et al. 2005: 1012). As stated above the cranial volume of these specimens was similar to that of the smallest australopithecines and the estimated stature was one meter (Mowood et al. 2005: 1012). These new specimens have ruled out the possibility that LB1 was a unique or pathological individual. The Flores hominins are a mosaic of primitive and derived characters, whose significance will be discussed in greater depth later. Brown et al. (2004:1060) concluded that the small size of Homo floresiensis was likely due to insular dwarfing, and that negating the size

4 difference the morphology of the Flores specimens appear to be closely related to Homo erectus. LB1 and the new Homo floresiensis specimens recovered from Liang Bua have demonstrated that a sustainable and unique population of small-bodied hominins lived recently in near insular isolation, and were arguably contemporaneous with Homo sapiens. The emergence of Homo floresiensis and its late survival are at odds with all current hominin evolutionary models. The true date of these specimens may force us to greatly alter our preconceived notions of the timing of the emergence and migration of our genus across the old world. Dating at the Liang Bua Site The LB1 holotype specimen was recovered at a depth of 5.9m and was subject to various radiometric dating techniques (Brown et al. 2004: 1055). The specimen is associated with calibrated accelerator mass spectrometry dates of 18 kyr and the fossil bearing strata is bracketed by luminescence dates of 35 ±4 kyr and 14 ±2 kyr (Brown et al. 2004: 1055). Two 14 C samples were recovered from LB1, yielding dates of 18,700/17,900 and 18,200/17,400 years BP (Cela-Conde and Ayala 2007: 265). These dates place the LB1 specimen in the relatively recent past and the lack of fossilization means that LB1 and the other Flores specimens cannot be considered fossils in the truest sense (Cela-Conde and Ayala 2007: 265). The subsequent finds at Liang Bua have yielded dates that span from kya to 12 kya (Morwood et al. 2005: 1012). These findings support the notion that Homo floresiensis existed contemporaneously with Homo sapiens and that they had survived as the dominant hominin species on Flores for a significant temporal interval. Location and Migration to Flores The Liang Bua site is located on the western side of the island of Flores in Indonesia (Morwood et al. 2005: 1012), in a dolomitic cave within the Wae Racang Valley (Cela-Conde and Ayala 2007: 265). Flores is part of the Wallacea island chain located southeast of the Asian (Sunda) and Australian (Sahul) continental areas (Morwood et al. 1998: 173). Flores is considered to be a small island of 14,000 km² and is located east of the Wallace Line (Brown et al. 2004: 1060). Flores is located east of Java and Bali, which were both connected to mainland Asia periodically throughout the Plio-Pleistocene, though Flores and the other islands in the Wallacea chain were never connected to any of these areas (Morwood et al. 1998: 173). Islands in this chain could have only been accessed by sea-crossings or by flying (Morwood et al. 1998: 173). Even at times of extreme glaciation, when sea levels were at their lowest, water crossing was still necessary to reach Flores from Southeast Asia (Morwood et al. 1998: 173). It has been stated that, consequently, before human intervention all these islands had impoverished faunas comprising of only species that were capable of crossing water by swimming, rafting on flotsam, or by flying in sufficient numbers to establish biologically viable populations, (Morwood

5 et al. 1998: 173). Morwood et al. (1998:173) assert that the very presence of Homo erectus fossils and tools on islands in the Wallacea chain proves that Homo erectus, and by extension Homo floresiensis, was capable of repeat water crossings using rudimentary watercraft. This supports the view that the ancestors of Homo floresiensis, whoever they were, arrived on Flores by watercraft technology rather than via a land bridge. This has significant implications for human evolution and the emergence of fully modern behaviours. It is commonly accepted that only anatomically modern humans possessed the ability to create complex technology such as water crafts. The earliest confirmed case of watercraft travel was by anatomically modern Homo sapiens around 40 kya from the Indonesian/Malaysian archipelago to Sahul (New Guinea and Australia) (Derricourt 2005: 120). The presence of Homo floresiensis on an isolated island may warrant a new approach to the generally accepted views of behavioural modernity. If it is proven that Homo floresiensis is not a taxonomic out-group of Homo sapiens or Homo erectus, but rather a parallel hominin lineage this could have significant implications for the course of development of higher mental faculties within the genus Homo. In his article Getting Out-of-Africa : Sea Crossings, Land Crossings, and Culture in the Hominin Migrations, Robin Derricourt states, It is not biology that allows the crossing of water, it is culture, and that is the province of the archaeologist. Water is crossed by technology and technology is created by culture as reflected by social organization, social need and language (or at least, complex communication). The question of water crossings is inextricably linked to cultural capability (2005: 122). If the presence of Homo floresiensis can be established on Flores earlier than the late Pleistocene, paleoanthropologists would have to consider alternative patterns to hominin migration than the typical Out-of- Africa, land-based travel model.. Tools and Homo floresiensis During the 2004 excavation at Liang Bua, a high density of stone core tools, flaking debitage, retouched lithics, anvils, and manipulated faunal remains were uncovered in stratigraphic association with Homo floresiensis (Morwood et al. 2005: 1012). The team at Liang Bua recovered many points, perforators, blades, and microblades that may have been hafted (Morwood et al. 2004: 1087). The archaeologists identified a well-defined occupational floor, which provided cut animal bones and remains of charred bone and fire cracked rock (Morwood et al. 2005: 1012). Among the cut and burnt faunal remains were dwarfed Stegodon floresiensis elephants, giant rat, rabbit, and bats (Morwood et al. 2005: 1012). Moreover, five fired rocks in a circular hearth shape were discovered (Morwood et al. 2005: 1012). These tools, faunal remains, and evidence of habitation, found in association with the Flores specimens, demonstrate that

6 these hominins, though small-bodied and small-brained, could hunt and control fire domestically. The Liang Bua team believes that the finds of the 2004 excavations illustrate that Homo floresiensis was capable of complex behaviour and advanced humanlike cognition (Morwood et al. 2005: 1012). All lithic tools found in association with the Flores specimens have yielded dates between 95 to 12 kya (Morwood et al. 2005: 1012). The cultural remains of the Pleistocene Homo floresiensis occupation differed from artifacts recovered in a later Holocene occupation, which contained pigments and a high concentration of symbolic artifacts (Morwood et al. 2005: 1012). These later sites are attributed to the migration of modern humans to Flores. Two other sites on Flores have yielded artifacts with highly contentious dates. The artifacts at the Tangi Talo and Mata Menge sites were dated to be much older than those that were associated with the Flores specimens (Morwood et al. 1998: 173). The Tangi Talo lithics were found in association with endemic dwarfed faunal remains, and yielded a zircon fission track date of 900 ± 7 ky (Morwood et al. 1998:173). The Mata Menge lithics were found in association with faunal remains of continental Southeast Asian species, and yielding zircon fission-track dates of 880 ± 7 ky and 800 ± 7 ky (Morwood et al. 1998: 173). These lithic assemblages are at least 700 ky older than the tools in direct association with the Homo floresiensis remains and occupational layer. When did the ancestors of Homo floresiensis first appear on the island of Flores? Presently, there is no way of supporting the claim that these older lithics were created by Homo floresiensis. It is evident that there was an intelligent hominin species on Flores 800,000 years ago. Whether that species evolved into Homo floresiensis or died out is still unclear. The lithics discovered at the Tangi Talo site were in association with endemic dwarfed faunal remains, which may suggest that the restricted environment had already affected the body size of various inhabiting species. Were these early hominins likewise affected? Homo floresiensis within the Homo Family Tree The hominin remains at Flores have been attributed to the new species Homo floresiensis based upon their unique mosaic of primitive and derived traits, gaining widespread interest in the paleoanthropological community (Argue et al. 2006: 360). Attention quickly focused on the affinities of the LB1 specimen, most notably its extremely short stature of one meter, small endocranial volume of cm 3, and very young geological age of 18,000 years (Argue et al. 2006: 360). In 2004, Brown et al. (2004: 1055) stated that Homo floresiensis was likely a descendant from an ancestral Homo erectus population that was subject to insular dwarfing on Flores. In contrast, Morwood et al. (2004: 1012) believed that the species was not likely to be of direct descent from an isolated Homo erectus population; indeed, they left the taxonomic association of the species uncertain, but were inclined to suggest that another early emerging Homo

7 species may have been the progenitor of the Flores specimens. With the taxonomic affiliation of Homo floresiensis left unclear by its initial discoverers, many subsequent researchers have suggested alternative conclusions for the taxonomic relationship of the Flores specimens within the genus Homo. Microcephaly and Pygmoid Conditions The most common hypothesis for the small body and cranial size of Homo floresiensis is that the Flores specimens represent a pathological population of pygmies or microcephalic individuals (Argue et al. 2006: 360). Supporters of these theories believe that Homo floresiensis, and in particular the LB1 specimen with its nearly complete cranium, are microcephalic or dwarfed members of nearly modern Homo sapiens (Argue et al. 2006: 361). Researchers have often compared the traits of small body and cranial size of LB1 with the reduced height of human dwarfs and pygmies caused by many congenital defects and malnutrition during childhood (Argue et al, 2006: 361). In 2006, Argue at al. published a study entitled, Homo floresiensis: Microcephalic, Pygmoid, Australopithecus, or Homo? in which they set out to disprove the theories that attribute LB1 s size to congenital dwarfism, microcephaly, and pygmoidism. The team compared the cranium and post-cranial elements of LB1 against the crania and limb ratios of two known microcephalic Homo sapiens, a pygmoid Homo sapiens excavated from Flores, Homo sapiens African pygmies and Andaman Islanders, Australopithecus, Paranthropus, and early Homo representatives (Argue et al. 2006: 360). Microcephaly can be defined by as, a heterogeneous disorder which is characterized by a marked reduction in brain growth with or without other abnormalities (Argue et al. 2006: 361). A microcephalic condition is problematic to classify, as there are over 400 conditions both congenital/genetic and traumatic, which may result in varying degrees of microcephaly (Argue at al. 2006: 361). Afflicted individuals can incur a range of mental impairments and are usually clinically classified as either having primary or secondary conditions; primary microcephalic individuals may be mentally high functioning, while secondary microcephalic individuals may be extremely mentally low functioning (Argue et al. 2006: 361). Microcephaly is typically identified by a cranial (occipitofrontal) circumference that is two standard deviations below the mean for that individual s age and sex, with very severe cases occurring three standard deviations below the mean (Argue et al. 2006: 361). Primary microcephaly is present at birth and may be characterized by a narrow sloping forehead, pointed vertex, and no intrauterine or postnatal growth defects (Argue et al. 2006: 361). Secondary microcephaly develops postnatally and is characterised by a reduced number and shallow appearance of convolutions of the cerebral hemispheres (gyri), very shallow sulci, diminished frontal lobes, and thinning

8 of the cortex (Argue et al. 2006: 361). Most individuals with secondary microcephaly have extreme mental impairments and often die at a young age (Argue et al. 2006: 361). Only one microcephalic condition, referred to as primordial dwarfism, was identified by Argue et al. (2006: 361) as possibly producing an individual with proportionate dwarfism of the cranium and body and having a relative stature and brain size comparable to that of LB1. However, individuals with this condition have other associated deformities of the skeleton that are not found on LB1, including clubbed feet, an extended beak-like nose, missing teeth, enlarged orbits, small jaws, extremely narrowed face, urogenital malformations, and joint dysplasia (Argue et al. 2006: 361). There have been a number of human crania recovered from archaeological settings which show evidence of microcephalic conditions that do not cause extreme bodily dwarfism; in all cases the crania show a visible narrowing of the skull, large rounded orbits, alveolar prognathism, and reduced cranial size but with relatively normal sized faces (Argue et al. 2006: 362). The cranial morphometric and morphological comparison of LB1 and microcephalic individuals suggests that LB1 is not a microcephalic Homo sapiens (Argue at al. 2006: 371). LB1 has a nonpathological post-cranial skeleton, which is not congruent with the case of primordial dwarfs, and in no way does the morphology of LB1 correspond with any pygmoid or microcephalic conditions that would produce the same stature as LB1 (Argue et al. 2006: 371). Pygmoid conditions are caused by chronic nutritional stress during growth (Argue et al. 2006: 371). Individuals suffering from this condition have stunted growth of the body and limbs, but have a normal sized cranium and face (Argue et al. 2006: 371). In these circumstances proportional growth of the body is sacrificed to enable full development of the brain and cranium. LB1 s cranium and body size are proportionately small, and LB1 cannot be a pygmoid Homo sapiens or Homo erectus (Argue et al. 2006: 371). A virtual endocast of the LB1 specimen was conducted by Falk and colleagues in 2005 (Falk et al. 2005: 242). The team concluded that LB1 possessed an expanded prefrontal cortex and widened temporal lobes, comparable in organisation to other fossil hominins (Argue et al. 2006: 372). LB1 did not display any evidence of decreased brain organisation or lower degrees of convolutions that would indicate microcephaly (Argue et al. 2006: 372). The expanded prefrontal cortex and widened temporal lobes of LB1 were identified by Falk as a derived character set apart from the cases in Homo erectus and Homo sapiens, therefore the brain of LB1 was not a miniaturised or dwarfed version of Homo erectus or Homo sapiens, but an independent yet similar brain organization pattern (Argue et al. 2006: 372). LB1has the smallest cranial capacity of any known member of Homo to date but displays complex endocranial morphology, which supports the argument that Homo floresiensis possessed high cognitive capabilities (Argue et al. 2006: 372). Since Homo floresiensis displays proportionate

9 stature to brain size without any evidence of mental impairment, it is unlikely to be a pathological population (Argue et al. 2006: 372). The question of whether the specimens at Flores represent an endemically dwarfed population or members of an inherently small-bodied and small-brained Homo species remains unanswered. Endemic Populations The specimens discovered on Flores are diminutive in regards to their stature and brain size relative to other contemporaneous hominins. If their dwarfism is not pathological than what is the explanation for their small stature? The Liang Bua team believes that the uniquely small stature of the Flores specimens was likely due to long term isolation on the island, and not congenital malformation or childhood nutritional impairment (Brown et al. 2004: 1055). Homo floresiensis was subject to insular dwarfism or in layman s terms the island rule (Brown et al. 2004: 1060). The observation that when isolated on a resource-limited island, small-bodied species tend to evolve towards gigantism, while large-bodied species tend to evolve towards dwarfism (Bromham and Cardillo 2007: 398). The dwarfing of the Flores hominins was likely the result of a long and gradual selection for smaller body size in a low caloric environment (Brown et al. 2004: 1060). The island of Flores became a restricted environment, and with limited outside access, contemporary faunal communities became impoverished (Brown et al. 2004: 1060). There would have been low interspecific competition; resultantly mammals like hominins would have enjoyed low predation risks (Brown et al. 2004: 1060). With the absence of agriculture or fishing technology, an insular tropical rainforest island would provide a limited supply of calories for a hominin population (Brown et al. 2004: 1060). Population size of all species would have been limited, and under these conditions natural selection would have gradually favoured the low energy requirements of smaller individuals (Brown et al. 2004: 1060). The effects of the island rule can be observed within the other faunal populations of Flores. The fauna of Flores appear to follow the trend of dwarfism in those species which are larger than a rabbit and gigantism in those which are smaller than a rabbit (Brown et al. 2004: 1060). This has led to the evolution of a giant Flores rat, which may have been hunted by Homo floresiensis (Brown et al. 2004: 1060). The Stegadon floresiensis dwarf elephant of Flores is one tenth the size of a regular Asian elephant, and a prime exemplar of endemic dwarfing on the island (Bromham and Cardillo 2007: 398). Superficially, these observations may appear to support the case for the endemic dwarfing of all large-bodied animals on Flores; however there are some large-bodied species not affected. The Komodo dragon and one other large Varanid lizard species are present in a non-diminutive condition on the island (Brown et al. 2004: 1060); however the island rule tends to be limited to mammals and can sometimes cease to extend into other taxonomic groups (Bromham and Cardillo 2007: 398). In light of this circumstance, can we confidently

10 assume that the diminutive nature of Homo floresiensis is due to endemic dwarfing and not reflective of the original species condition? In 2007, Bromham and Cardillo published an article entitled Primates follow the Island Rule : Implications for Interpreting Homo floresiensis. The two authors felt that many in the scientific community had accepted the insular dwarfism hypothesis for the explanation the Flores specimens without any compelling research (Bromham and Cardillo 2007: 398). The pair searched through anthropological literature in search of any records of island primates that differed significantly in size from their mainland counterparts (Bromham and Cardillo 2007: 398). Since the island hypothesis is only true of calorie restricted small islands, the authors only looked at islands smaller than 100,000 km², excluding some islands such as Madagascar, Borneo, and Java, which were treated as mainland sites (Bromham and Cardillo 2007: 398). Most of the islands that met their criteria were at some point in time connected via a land bridge to the mainland, and were not isolated until after the last glaciation event (Broham and Cardillo 2007: 398). They felt that strong morphological differences between the endemic species and their closest mainland relatives would indicate that a significant degree of genetic isolation occurred (Bromham and Cardillo 2007: 398). Their results supported the hypothesis that primates did follow the island rule ; primates smaller than 5 kg tended to develop gigantism when compared to mainland populations, and that those larger than 5 kg tended to develop dwarfism (Bromham and Cardillo 2007: 398). The authors also concluded that larger primates underwent a greater proportional full body reduction which included their skulls (Bromham and Cardillo 2007: 398). Therefore, primates do undergo predictable shifts in body size when isolated in restricted island environments. The presence of Homo floresiensis has been confirmed between 80,000 to 20,000 years, sufficient amount of time to produce endemic dwarfing (Bromham and Cardillo 2007: 399). The largest island primates identified by Bromham and Cardillo (2007: 399) were 52%, 61%, and 80% of the size of their mainland counterparts. Based on these values, the size of Homo floresiensis falls within the expected range if we consider Homo erectus and Homo sapiens to be the progenerate mainland population (Bromham and Cardillo 2007: 399). A body mass estimate of Homo floresiensis would place it at 55% of Homo sapiens and 52% of that estimated for Homo erectus (Bromham and Cardillo 2007: 399). In contrast, the small encephalization quotient calculated for Homo floresiensis based on LB1 is problematic (Bromham and Cardillo 2007: 400). The size of the skull is within the range of dwarfed primates but is not consistent with any other known Homo species even when size reduction is considered (Bromham and Cardillo 2007: 400). It is apparent that the Flores specimens are not microcephalic or pygmies because their craniums are in proportion to their small stature (Bromham and Cardillo 2007:

11 400). Nonetheless, Brown et al. (2004: 1060) believe that anatomical and physiological changes associated with insular dwarfism can be extensive, and may include dramatic changes to brain size and sensory systems; modifications to the brain may likely exceed what changes would be predicted by the allometric effects of body size reduction alone (Brown et al. 2004: 1060). While there is evidence for hominin occupation at Flores from lithic tools dating to 840,000 years ago, there is unfortunately no current hominin skeletal evidence from this period, and the producers of these tools cannot be confidently identified (Brown et al. 2004: 1060). The first hominin remains are the Flores specimens which date to 94 kya in the Late Pleistocene (Brown et al. 2004: 1060). The first hominin inhabitants of Flores may have been similar in size to Homo erectus (Brown et al. 2004: 1060). They may have been subject to insular dwarfing to produce the later Flores specimens, or an unknown small-brained and small-bodied hominin may have arrived at Flores independently (Brown et al. 2004: 1060). Limb Proportions and Allometry The stature of LB1 is often perceived to be similar to that of earlier Homo species such as Homo habilis (Argue et al. 2006: 372), though the stature estimates of LB1 and any early fossil Homo species are difficult to assess with complete confidence. The stature of LB1 has been commonly estimated at 1m, with Homo habilis in the range of 1.04 m, while a female Australopithecus afarensis is estimated at around 1.05 m (Argue et al. 2006: 372). The radius of LB1 is shorter than its femur; however, its radial-femoral index is much larger then in Homo ergaster, Homo erectus, or Homo sapiens (Argue et al. 2006: 370). The radial-femoral proportions of LB1 are nearly identical to Australopithecus garhi (Argue at al. 2006: 372). This means that, physically, LB1 s upper limbs were only slightly shorter than its lower limbs. This is similar to the primitive condition in australopithecines that have less disparity between limb lengths. In Homo erectus and Homo sapiens, the lower limbs are markedly longer then the upper limbs, while African apes have radii nearly the same length as their femora (Argue et al. 2007: 370). The femur length of LB1 has been identified as being slightly shorter than its humeral length (Holliday and Franciscus 2009: 226). In general, apes and early hominins have femur lengths shorter than their humeri (subisometric allometry), while humans have femur lengths equal or longer than their humeri (isometric to positively allometric) (Holliday and Franciscus 2009: 226). Holliday and Franciscus (2009) theorized that an adult member of the genus Homo approximately as small as Lucy should possess a femur of roughly Lucy s length. Body mass estimates proposed by Holliday and Franciscus place the LB1 specimen at approximately 33 kg, which is similar to the body mass estimate of Lucy at 30 kg (Holliday and Franciscus 1998: 226). Furthermore, the femur length of LB1 is 281 mm, while the femur length of Lucy is 280 mm (Holliday and Franciscus 1998: 226). It is reasonable to state that LB1

12 was of a similar stature and body size as Lucy. LB1 and Lucy only exhibit a minor deviation from the African ape femur length:body mass allometry (Holliday and Franciscus 1998: 226). In a study of allometric relationships of LB1 conducted by Holliday and Franciscus, LB1 was only 2.7-4% outside of the Pan regression line for predicted femur length:body mass allometry (Holliday and Franciscus 1998: 226). This study demonstrates that the small limb length of Homo floresiensis is directly correlated to its small stature and is not directly indicative of its taxonomic relationship. Homo erectus and Homo sapiens are very large and have developed the derived character of longer lower limbs. This trait would not be expected of a member of Homo in the size range of Homo floresiensis, and cannot be effectively used to contest the Flores specimen s current taxonomic classification to the genus Homo. This study leaves two possible evolutionary scenarios for the allometry of Homo floresiensis: (1) the Flores specimens represent a new Homo species that retained the small stature and limb ratios of their australopithecine ancestors, or (2) the Flores specimens are descendants evolved from a larger Homo species, such as Homo erectus, that has been subject to insular dwarfism and that subsequently incurred femoral shortening (Holliday and Franciscus 1998: ). The holotype specimen LB1 included a relatively complete left foot and parts of the right foot (Jungers et al. 2009: 81). The feet of LB1 were exceptionally long considering the specimens femur and tibia length (Jungers et al. 2009: 81). Similar foot to leg proportions are common in other African apes, but have never been documented in hominins (Jungers et al. 2009: 81). The robusticity of the metatarsals and the fully adducted hallux is consistent with human-like bipedalism, while other features of the foot and the overall proportions are more ape-like (Jungers et al. 2009: 81). Marked differences can be seen in the position of articular surfaces and shape of the navicular and cuboid bones of Homo floresiensis and Homo erectus (Jungers et al. 2009: 83). The post-cranial anatomy of Homo floresiensis is that of an obvious biped, though with biomechanical differences to a more derived species like Homo erectus (Jungers et al. 2009: 81). The foot of Homo floresiensis was relatively flat and not welldeveloped for high speed or efficient endurance running (Jungers et al. 2009: 83). The feet of LB1 also lack the full set of derived characters found in Homo sapiens (Jungers et al. 2009: 81). The pedal morphology of Homo floresiensis supports the hypothesis that it is not a descendant of the relatively biomechanically-derived Homo erectus, but is from a more primitive Homo possessing a mosaic of primitive and incompletely developed derived traits (Jungers et al. 2009: 81). Taxonomic Implications In cranial volume and stature, Homo floresiensis most closely resembles australopithecines. Moreover, the limb ratios of Homo floresiensis most resemble those of Australopithecus garhi. Homo floresiensis is

13 not likely not a dwarfed Homo erectus population, because a similar, but diminished brain structure would be evident. The endocranial casts of LB1 demonstrate that Homo floresiensis was not a microcephalic or pygmoid Homo erectus or Homo sapiens, but that the Flores specimens display a unique brain organisation. The combination of primitive australopithecine and early Homo morphology, coupled with its unique derived morphology argue against the notion that Homo floresiensis was an endemically dwarfed genetically isolated Homo erectus population. Instead there are two alternative scenarios: The unique morphology of Homo floresiensis may have evolved from a founder population of early Homo, with australopithecine-like stature, that possessed or developed a more advanced cerebral anatomy in relation to its primitive postcranial morphology (Argue et al. 2006: 373). Homo floresiensis represents a transitional form between Australopithecus and Homo that diffused from Africa before the development of fully derived Homo morphology (Argue et al. 2006: 373). Both scenarios imply that Homo floresiensis was of African origin and had not developed from an ancestral Asian hominin population. In addition, both scenarios imply a relatively early expansion out of Africa before or around the time of the development of fully derived Homo morphology around 2 mya (Argue et al. 2006: 373). It is widely accepted that Homo ergaster and Homo erectus were the first hominin species to expand out of Africa; the possibility that Homo floresiensis or other earlier species may have diffused earlier challenges the paradigms of human evolution. Conclusions The peculiar case of Homo floresiensis has many major implications for our understanding of human evolution. Homo floresiensis demonstrates that there is a great degree of encephalization and bodysize variation within the genus Homo. Homo floresiensis survived to live contemporaneously with Homo sapiens and Homo neanderthalensis. The existence of a distinct hominin species on Flores from 94,000-12,000 ya establishes that Homo sapiens did not achieve global dominance until very recently in terms of our presence on earth. The scenario of hominin coexistence becomes even more shocking if we accept the notion that Homo floresiensis was a descendant from an earlier Homo species emerging around the time of Homo habilis and Homo rudolfensis. Homo floresiensis possessed a high cognitive capability; they created complex stone tools, hunted, domestically controlled fire, and likely arrived on Flores via watercraft. Homo floresiensis completed all these actions with a surprisingly low encephalization quotient. The cognitive and behavioural abilities of Homo floresiensis force us to look back at our assumptions of australopithecine cognition. Homo floresiensis could make tools and use fire with a brain size equal to that of the smallest australopithecine. We must challenge long held ideas of the emergence of high reasoning and ask again of what behaviours australopithecines and early Homo may have

14 been capable? We have assumed that only highly derived hominins had expanded from Africa (Argue et al. 2009: 623). The peculiar case of Homo floresiensis may eventually prove that early Homo and possibly australopithecines possessed the level of mental and technological sophistication to expand out of Africa and flourish. It may hold true that brain organisation is indeed more indicative of intelligence than brain size. References Cited Argue, D., Donlon, D., Groves, C., and Wright, R Homo floresiensis: Microcephalic, Pygmoid, Australopithecus, or Homo? Journal of Human Evolution 51: Argue, D., Morwood, M., Sutikna, T., Jatmiko, and Saptomo, E.W Homo floresiensis: A Cladistic Analysis. Journal of Human Evolution 57: Bromham, L. and Cardillo, M Primates Follow the Island Rule : Implications for Interpreting Homo floresiensis. Biology Letters 3: Brown, P., Sutikna, T., Morwood, M.J., and Soejono, R.P A New Small-Bodied Hominin from the Late Pleistocene of Flores, Indonesia. Nature 413 (7012): Cela-Conde, C.J. and Ayla, F.J Human Evolution: Trails from the Past. Oxford: Oxford University Press. Derricourt, R Getting Out of Africa : Sea Crossings, Land Crossings, and Culture in the Hominin Migrations. Journal of World Prehistory 19: Falk, D., Hildebolt, C., Smith, K., Morwood, MJ., Sutikna, T., Brown, P., Jatmiko, Saptomo, EW., Brunsden, B., and Prior, F. (2005) The Brain of LB1, Homo floresiensis. Science 308: Holliday, T.W., and Franciscus, R.G Body Size and Its Consequence: Allometry and the Lower Limb Length of Liang Bua 1 (Homo floresiensis). Journal of Human Evolution 57: Jungers, W., Harcourt-Smith, R., Wunderlich, M., Tocheri, S., Larson, G., Sutikna, T., Rhokus Awe Due, and Morwood, M The Foot of Homo floresiensis. Nature 459: Morwood, M., O Sullivan, P., Aziz, F., and Raza, A Fission-Track Ages of Stone Tools and Fossils on the East Indonesian Island of Flores. Nature 392: Morwood, M., Soejono, R., Roberts, R., Sutikna, T., Turney, C., Westaway, K., Rink, W., Zhao, J., Van den Berg, G., and Due, R. (2004) Archaeology and Age of a New Hominin from Flores. Nature 431: Morwood, M., Brown, P., Jatmiko, Sutikna, T., Saptomo, E., Westaway, K., Due, R., Roberts, R., Maeda, T., Wasisto, S., and Djubiantono, T Further Evidence for Small-Bodied Hominins from the Late Pleistocene of Flores, Indonesia. Nature 437: