Homo Erectus and the Colonization of Asia - Essay Example

Table of Contents Table of Contents 1 Introduction 2 2 Immigration 2 3 The Asian Homo erectus 4 4 The African Connection 8 5 Conclusion 10 References 12 1 Introduction In the study of human evolution the importance of understanding the paleoanthropological evidence from Asia cannot be overemphasized. This is true not only because a substantial part of the total evidence derives from Asia, but also because the Asian evidence has figured prominently in previous and current arguments about the nature of organic evolution in general and hominid evolution specifically. Renewed research efforts in China, Indonesia and other Asian localities also underscores the importance of placing new finds in a chronologic and phylogenetic framework which logically and consistently accommodates all Asian hominid finds. 2 Immigration The presence of Homo erectus has been identified from fossils from the Trinil and Kedung Brubus sites as well as the correlated deposits from Sangiran. These early hominids experienced the interpreted environmental changes. These changes, however, probably had little negative affect on this hominid. In fact, the adaptations that permitted Homo erectus to leave Africa were most likely well suited to the open woodland environments subsequently encountered. These adaptations include larger body size compared to earlier hominids, bipedality, linear body proportions, and a more sophisticated tool kit (Spencer, 1997). Specifically, bipedality would have permitted foraging in open environments (Rodman and McHenry, 1980), whereas large body size would have been useful for surviving interactions with large predators also found in these habitats (Walker, 1993). Others (Anton et al., 2002) have suggested that the maintenance of this large body size, as well as increased brain size, may have resulted from greater nutritional dependence on animal fat and protein. This may have necessitated the increase in tool sophistication for acquiring this additional component of the diet. Finally, the long, linear body proportions found in Homo erectus might have been an advantage for heat dissipation in tropical, open grasslands, like those found in Java during this time (Ruff, 1994). Anton et al. (2002) have proposed a model for the initial hominid dispersal from Africa. They suggest that ecological change provided an increase in niches within grassland and wooded grassland environments for terrestrial herbivores. Hominids of relatively larger brain and body size, in turn, took advantage of these animal resources and ultimately increased their own reproductive success (Leonard and Robertson, 1997; Anton et al., 2002). As foraging strategy and the ecosystem structure changed, the home range of these hominids increased leading to greater dispersal capability. Additionally, the dispersing herbivores not only provided a subsistence resource but may have also served as an impetus for hominid dispersal (Anton et al., 2002). It has been shown that the Middle Pleistocene faunas of Java are closely related to the faunas of India and Burma (de Vos, 1995). Thus, based on the model of Anton et al. (2002), it can be inferred that as these species migrated southward, they began to occupy the open grasslands, densely vegetated river valleys, and upland forests of Java during the Early to Middle Pleistocene. As the hominids followed the migrating herbivores, they too would have taken advantage of the resources afforded by the landscape at this time. The Sunda Shelf then became exposed approximately 800,000 years ago, grasslands expanded, and more species began to enter Java. This increased resource base may have lead to increased reproductive success of Homo erectus. 3 The Asian Homo erectus The relationship of Asian Homo erectus to Asian Homo sapiens has long been a source of discussion. In the simplest terms this problem takes the form of whether or not modern and recent Asian populations show morphological affinities to earlier populations attributed to Homo erectus. Again the currently unresolved question of the genetic significance of observed morphological differences is of crucial importance. Wishing to avoid this difficulty, Thorne and Wolpoff (1981), proposed the concept of morphological clade. While this approach seems to beg the object of taxonomic and phylogenetic studies, it has heuristic value since the reconstruction of phylogeny must be based to a large extent on morphology. Nonetheless, Thorne and Wolpoff note that many authors (Weidenreich, 1939a & b, 1945, Coon, 1963, Howells, 1973, Sartono, 1975, Jacob 1976a) have indicated the morphological similarities which characterize extinct and recent Asian hominids. Weidenreich (1939, cited in Thorne and Wolpoff, 1981) believed that there were not enough preserved parts of the Upper Cave individuals to definitely indicate a relationship with Sinanthropus. Although he believed that the presence of a mandibular torus, shovel shaped incisors, Inca bone and a sagittal torus indicated an affinity between Sinanthropus and Mongois, only a slight mandibular torus (Upper Cave 101) and a sagittal torus (Upper Cave 103) were present in the Upper Cave population. Weidenreich merely stated that the relationship between Sinanthropus and the Upper Cave hominids cannot be ignored. Although he perceived affinities between some of the Upper Cave specimens and Melanesian, Eskimo populations and Upper Palaeolithic populations in Europe; he saw no specific affinities with modern Chinese populations. Weidenreich (1945a, cited in Thorne and Wolpoff, 1981), like Dubois (1921, cited in Thorne and Wolpoff, 1981), also recognized a close similarity between Wadjak and Australian populations. Weidenreich believed that the similarities between the Keilor and Wadjak crania were remarkable. However, he also recognized differences. According to him the Wadjak specimen represented a different phylogenetic level. Weidenreich definitely felt that earlier Javanese populations were ancestral to Australian populations. Coon (1962) adopted basically the same viewpoint as Weidenreich and emphasized what he perceived as racial differences in Zhoukoudian and Javanese Homo erectus (cited in Thorne and Wolpoff, 1981). As mentioned previously, Thorne and Wolpoff (1981) have dealt with this problem from a non-taxonomic viewpoint which seeks to explain the perceived morphological homogeneity of Asian hominids. Like other authors, they feel that the vault and face provide the best evidence for morphological continuity. They feel that a flattened frontal (in the sagittal view), a relatively posterior position of minimal frontal breadth, a relatively horizontal inferior border of the supraorbital tori, a distinct prebregmatic eminence and the relatively low position of the maximum parietal breadth demonstrate local morphological continuity . The extent to which dental and facial reduction characterizes Asian hominids (including Chinese hominids) and sets them apart from others is not clear. This may also be an apt characterization of later populations in other parts of the world. If this reduction is particularly Asian, it should not be used to link specific populations within Asia (e.g. Sangiran 17) and Australian aborigines. Thorne and Wolpoff have also pointed to other features (a ridge on the inferior margin of the nasal aperture) which supposedly unite Sangiran and Australians. All these features are variable and some of them may show phenotypic convergence as a result of masticatory and other stresses encountered in a hunting and gathering adaptation. Recently some authors, such as Anton et al. (2002) have suggested that cultural practices (artificial deformation) may also be responsible for the cranial morphology of at least some of the Australian fossil crania. By far the most important revision results from a critical appraisal of absolute ages which have been recognized for early Asian hominids. Specifically, none of the Javanese hominids which supposedly derive from the Pucangan Formation can be shown to definitely derive from this stratigraphic horizon. With the exception of Perning 1, most of the hominids represent surface or shallow sub-surface finds which were collected by scientifically untrained collectors who apparently had very little incentive to reveal the actual locality of their discoveries. Indeed, many reports have been contradictory. The detailed provenience of most recent finds of supposedly Pucangan hominids has not been published and is therefore not available for critical analysis (Anton et al., 2002). To these considerations may be added the fact that the Sangiran area is a geologically complex exposure of sediments, where similar lithological facies exhibit a great degree of vertical and horizontal variation. Dark clays, conglomerates, and volcanic breccias occur at widely separated horizons in both the overlying Kabuh Formation and the stratigraphically lower Pucangan Formation. It is highly likely that many fossils attributed to the Pucangan Formation may have actually been eroded out of the Kabuh Formation and redeposited on or in the Pucangan sediments. The age of the Ngandong hominid assemblage is extremely difficult to assess. Santa Luca (1980) has cited evidence which may indicate that the crania were redeposited. He has also noted that hominid crania of comparable cranial capacity also derive from stratigraphically lower levels. In any case, it is currently impossible to determine the age of the Ngangdong hominids. Other evidence indicates that an earlier age is possible, but no current evidence compels acceptance of an early date. In light of apparent morphological and size diversity of African Pliocene hominids (Johanson and White, 1979) and Pleistocene African hominids, there is no difficulty in attributing the diversity of the Sangiran sample to a relatively short span of time. By far the most meaningful subdivision of Asian hominids should recognize a distinction between earlier (early Pleistocene or early middle Pleistocene) forms with relatively smaller cranial capacities, lower cranial vaults, and robust mandibles and later (upper middle Pleistocene and upper Pleistocene) forms with larger cranial capacities, higher vaults, less robust mandibles and smaller teeth. The taxonomic rank which should be accorded to this distinction should be no greater than sub specific (Kaifu et al., 2002). Geographic differences among the Asian hominids are recognizable, but they are few. Whether or not these few differences are indicative of subspecies is extremely difficult to determine. Logic suggests that subspecies surely existed in Asia during the Pleistocene, but no large body of morphological evidence supports this. Chinese hominids are quite possibly broadly contemporaneous with the earlier Javanese hominids (Kaifu et al., 2002). Indeed, the only major gradational differences between Asian hominids are discernable between the larger-brained Homo sapiens and smaller brained Homo erectus populations. In spite of the doubtful strato-chronological position of the Asian hominids, there is not surprisingly a clear increase in cranial capacity which is consistent with the order in which most paleoanthropologists have placed these groups. This trend is especially notable if upon, according to Holloway (1981), the exclusion of Perning 1 and Lantian crania. Although cranial capacity is not the ultimate determinant in hominid taxonomy, it is almost always included as an important characterization of hominid taxa. In regard only to cranial capacity, a clear gap separates all species of Australopithecus from Homo habilis. An even larger gap separates Homo habilis from the Sangiran-Trinil group. The largest gap occurs between Ngandong and modern humans. If the early Chinese and Javanese hominids, including Ngandong, are entered into the same taxon (Homo erectus), then Asian members of this taxon would range in cranial capacity from about 69% - 82%. Australopithecus species would range from about 32% - 40%. The range of Asian Homo erectus would be on the order of fifty percent greater than Homo habilis. In spite of this, Holloway (1981) argues that this difference does not necessitate the placement of either the Ngandong hominids or the Pucangan hominids in their separate species. Palaeontologists expect to find transitional forms. Other morphological features discussed previously also suggest the inclusion of the early Asian hominids in a single taxon. 4 The African Connection In general, Van den Bergh, Vos and Sondaag (2001), contend that the tendency to taxonomically link early Asian hominids (primarily Pucangan hominids) and Plio-Pleistocene hominids in Africa has been heavily influenced by the acceptance of the dates of Asian specimens. The belief in the general synchronicity of these two groups has fostered the acceptance of the admittedly logical hypotheses that synchronic tropical hominids are probably taxonomically synonymous, and that similar taxonomic groups existed sympatrically in both Asia and Africa. Such a view expects to find both australopithicines and early species of Homo in both places. Even if one rejects the idea that australopithicines have been recovered from Asia, the problem of whether similar grades of early Homo were spread across the lower Pleistocene tropics still remains (Van den Bergh, Vos and Sondaag, 2001). If the difficulty of demonstrating similar grades of Homo in both places can be overcome, there is still scarcely any justification for recognizing the formal synonymy of Homo modjokertensis and Homo habilis (Walker, 1993; De Vos, 1995). The type specimen of this former taxon cannot be meaningfully compared with either African or other Indonesian specimens. Similarly it is difficult to recognize other taxa of Javanese hominids such as Meganthropus palaeojavanicus or Pithecanthropus dubius since these are also based on fragmentary type specimens which preclude definitive taxonomic and morphological comparisons with other hominids. Those morphological distinctions which have been recognized for these specimens have not been shown to be taxonomically significant (Walker, 1993; De Vos, 1995). According to this view, very little precludes the inclusion of all the Javanese hominids (with the exception of modern Homo sapiens forms) in Homo erectus. It is primarily size (cranial capacity) which distinguishes the Ngandong hominids from the Sangiran hominids and even in this they are close to the earlier hominids than to modern hominids (Walker, 1993; De Vos, 1995). The phylogenetic relationships of the Asian hominids are more difficult to determine. At all levels one is faced with the problem of determining which morphological features are indicative of phylogeny. Within the context of the stated, it seems best to accept the view that Asian hominids are descended from some of the earlier African hominids which evidence a general morphology which is plesiomorphic for the genus Homo (Walker, 993; De Vos, 1995). This view is based on the theoretical assumption that earlier hominids are less derived than later hominids. In the case of Homo erectus it means that thin supraorbital tori, an angular occipital, thin cranial bones, more vertical frontals and small cranial capacities are plesiomorphic for Homo erectus. 5 Conclusion In conclusion it needs to be emphasized that whether or not Asian members of Homo erectus were directly ancestral to Asian Homo sapiens is still uncertain. Again nothing precludes such a relationship. It is fair to say that there is no reason not to expect the morphological features which have been used to link local populations of Homo erectus and Homo sapiens to also be present in invading allopatric populations. That Australian populations are descendent from Southeast Asian populations remains the most logical and parsimonious hypothesis. It may be that we can never develop adequate morphological parameters which will settle this question. It should also be noted that the situation which characterized the appearance of modern Homo sapiens in other parts of the world, such as Europe (whatever that situation is finally adjudged to be), need not also apply to Asia. All Homo sapiens need not have originated in one area, but they may have colonized some places in the Old World last. The relatively small frigid peninsula of Europe may have been one of those places. References Anton, S.C., Leonard, W.R. and Robertson, M.L. (2002) An ecomorphological model of the initial hominid dispersal from Africa. Journal of Human Evolution, 43: 773-785. de Vos, J (1995) The migration of Homo erectus and Homo sapiens in Southeast Asia and the Indonesian Archipelago. In (Bower, JRF and Sartono, S, Eds) Evolution and Ecology of Homo erectus, Pithecanthropus Centennial Foundation. Leiden University, The Netherlands. Pgs. 239-304. Holloway, R.L. (1981) The Indonesian Homo erectus brain endocasts revisited. American Journal of Physical Anthropology, 55: 503-522. Johanson, D.C. and White, T.D. (1979) A systematic assessment of early African hominids. Science, 203, 321-330. Kaifu Y, Baba H, and Aziz F (2002) On the coexistence of Homo erectus and Pongo in the Early/Middle Pleistocene of Java. Anthropological Science 110(1): D26. Leonard, W.R. and Robertson, M.L. (1997) Comparative primate energetics and hominid evolution. American Journal of Physical Anthropology, 102: 265-281. Rodman, P.S. and McHenry, H. (1980) Bioenergetics and the origin of hominoid bipedalism. American Journal of Physical Anthropology, 52: 103-106. Ruff, C.B. (1994) Morphological adaptation to climate in modern and fossil hominids. Yearbook of Physical Anthropology, 37: 65-107. Santa Luca, A.P. (1980) The Ngangdong fossil hominids: A comparative study of a far eastern Homo erectus group. Yale University Publications in Anthropology, 78. Spencer, L.M. (1997) Dietary adaptations of Plio-Pleistocene Bovidae: implications for hominid habitat use. Journal of Human Evolution, 32: 210-228. Thorne, A. and M. Wolpoff (1981) Regional continuity in Australasian Pleistocene hominid evolution. American Journal of Physical Anthropology, 55: 337-349. Van den Bergh, G.D., de Vos, J., and Sondaar, P.Y. (2001) The Late Quaternary paleogeography of mammal evolution in the Indonesian Archipelago. Palaeogeography, Palaeoclimatology, and Palaeoecology 171: 385-408. Walker, A. (1993) The origin of the genus Homo. In (Rasmussen, DT, Ed.) The Origin and Evolution of Humans and Humaness. Jones and Bartlett, Boston. Pgs. 29-47. Read More