Complex Evolutionary History of East Asians

Australia: The Land Where Time Began

Complex Evolutionary History of East Asians

Europe and Africa, and the Levantine corridor connecting them, have historically been the main focus of the known fossil record of the evolutionary history of modern humans, the parts of the evolutionary history that took place on the Asian continent therefore remained largely unknown. The result of the lack of archaeological research in the vast expanses of Asia has been that all the knowledge of human remains from the Upper Pleistocene are concentrated on 2 sites in South Asia possibly dating to between 33,000 and 25,000 BP. More human fossils are known from East Asia (Wu & Poirier, 1995) but as a result of the poor knowledge of the geological context and inadequate dating (Trinkaus E, 2005; Wu & Poirier, 1995; Kaifu Y. & Fujita M, 2012) of the sites their significance has been difficult to assess. In this paper the authors¹ consider East Asia to be bounded by the Ural Mountains in the west, in the southwest by the Himalayan Plateau, in the northeast by Bering Strait and extending to the islands of Southeast Asia (Wu & Poirier, 1995). The fossils of this individual was discovered in 1958 and its geological age has been disputed ever since as there is no documentation indicating the exact stratigraphic position of the human remains (Bräuer & Mímisson, 2004, p.62).

A skeleton found at Liujang in southern China is widely thought to be the earliest known modern human in East Asia, its age being estimated as being greater than 153,000-30,000 BP (Kaifu & Fujita (2012; Bräuer & Mímisson, 2004) A similar age problem exists for the remains in the Upper Cave (Zhoukoudian), discovered in the 1930s, the age estimates ranging from 33,000-10,000 BP (Wu & Poirier, 1995; Bräuer & Mímisson, 2004). There is also a problem with the provenience of the Niah Cave child found in East Malaysia (Barker G, et al., 2007), though an age of about 45,000 BP has been proposed for this cranium based on a recent field and lab program with the aim of assessing the stratigraphy and dating of the deposits the remains were found in (Barker G, et al., 2007).

There are similar problems with other modern human remains from East Asia that could contend the title of the earliest modern human. The only specimen recover from the Tabon Cave in the Philippines that is of taxonomic diagnostic value is the frontal bone that has been assigned to H. sapiens, that has been dated to 16.5 ± 2 thousand years BP (Dètroit F, 2004). The authors¹ suggest the oldest specimen from the site that have been dated to 47+11/10 thousand BP (Dètroit F, 2004), could possibly be from an orangutan. A hominin metatarsal from Callao Cave on the Philippine island of Luzon has been directly dated to an estimated 66.7 ± 1thousand years (Mijares A.M. et at., 2010), but the assignment of this specimen to H. sapiens is unreliable as it proved to be difficult to classify reliably. The remains of an individual have been recovered from Tianyuan Cave near the town of Zhoukoudian in the northeast part of China that has been estimated to be about 42,000-39,000 BP (Shang H, et al., 2007), the partial skeleton was composed of 34 pieces of bone that are apparently from a single individual, including the femur that was dated directly to 40,328 ± 816 cal. yr. BP (Shang H, et al., 2007). According to the authors¹ this specimen appears to be the most likely candidate for the earliest known modern human in East Asia, though it is significantly younger by more than 20,000 years than the colonisation of the region based on genetic clock estimates. A mandibular fragment has been recovered from Zhirendong in southern China that has been dated stratigraphically to more than 100,000 BP (Liu W. et al., 2010), though this specimen is fragmentary and its taxonomic status is uncertain as it is comprised of a mosaic of archaic and modern characters (Liu W. et al., 2010; Dennell R, 2010).

Genetic sequencing of samples taken from living populations have, of necessity, been relied upon by palaeoanthropologists to reconstruct modern human origins in East Asia, as there is still great uncertainty concerning the fossil record of humans. About 70-60 thousand years ago the earliest humans crossed from Africa to Eurasia, and after this time rapidly colonised Southeast Asia and Australasia, at some point soon after this time, according to the results of the genetic research (Zhong et al., 2011; Kong et al., 2011; Stoneking & Delfin, 2010; Rasmussen et al., 2011). It is suggested by the authors¹ that after about 40,000-30,000 BP there appears to have been another migration within Eurasia that added the population lineages of modern Northeast Asians and Europeans. There appears to have been several later migrations within this region, some of which may possibly have been associated with the Neolithic (Zhong et al., 2011; Kong et al., 2011; Stoneking & Delfin, 2010). It has been found that DNA, that was extracted from a hominin fossil found in Denisova Cave, Central Asia, that was more than 50,000 BP, that were in the Neanderthal lineage, have features they share with Aboriginals from Southeast Asia and Australasians (Reich er al., 2010; Reich et al., 2011; Abi-Rached et al., 2011). This has led to a number of interpretations. One is that interbreeding occurred between the Denisovans and the earliest modern humans who had previously colonised the region. Another suggestion is that the same evidence implies that during the Upper Pleistocene this archaic population occupied Southeast Asia (Reich et al., 2010; Reich et al., 2011).

According to the authors¹ in 2008 they began a collaborative research project aimed at human remains, possibly from the Pleistocene of Southwest China, and providing detailed comparisons of the remains, as they suggest the East Asian fossil record is of central importance to the ability to test scenarios of human evolution, both regionally and globally. According to the authors¹ the human remains in Longlin Cave (LL or Longlin) and Malu Cave (Maludong or MLDG) are the focus of this paper.

Longlin

In1979 human remains were found in a cave near De'e, Longlin County, Guangxi Zhuang Autonomous Region, Guangxi Province, by a petroleum geologist, Li Changquing. A block of fine-grained sediment that contained the human remains, as well as animal bones that were not identified, and charcoal and fragments of burnt clay were taken to Kunming, Yunnan Province, not long after its discovery. In 2010 study of the contents produced a partial mandible and fragments of postcranial bone. The authors¹ discovered a thin flowstone adhering to the vault of the LL 1 skeleton and fragments of charcoal were found in sediment inside the endocranial cavity. The authors¹ suggest that as the cranium, mandible and elements of the postcranial skeleton were associated, all with similar levels of preservation, within a small block of sediment less than 1 m³ in volume suggests there that post-depositional there was limited if any disturbance.

Maludong

Situated near the city of Mengzi, Honghe Prefecture, Hani and Yi Autonomous Region, southeast Yunnan Province, the cave fill of Maludong Cave, had been partially mined (Wu & Poirier, 1995; Zhang X et al., 1991). In 1989 the original excavation at this site took place, most of the material, fossil and archaeological material, being recovered. at that time. In 2008 further excavations were carried out at the site, at which time the remaining stratigraphic section were re-evaluated. A large number of samples for dating and archaeomagnetic analysis were taken. During the current study more human remains were recovered from stratigraphic analysis, as well as from fossil collections that were recovered in the 1989 excavation but had remained unsorted and unstudied.

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Discussion

There are a range of individual features, as well as a composite of characters that have not been demonstrated among H. sapiens from the Pleistocene or the present, that are present in the partial human skull that was recovered from Longlin Cave, and the human calotte, partial mandibles and teeth from Maludong. According to the authors¹ they do not share any particular affinity with East Asians from the Pleistocene, such as those recovered from Liujiang or Upper Cave 101, or with East Asians from the present. The range of individual features present form complexes of multiple developmental-functional features (Enlow & Hand, 2008) of the neurocranial vault. These features include the endocranium, cranial base, facial skeleton, mandible and dentition. Metrical dimensions involved, where they can be assessed, are characterised by heritability that is mostly moderate to high (Sjøvold, T., 1984; Carson, A.E., 2006; Sherwood et al., 2008; Townsend & Brown, 2008). The authors¹ suggest that samples from both locations are from the same population, based on their morphological similarity, geographically close proximity, the sites being less than 300 km from each other, and the geologically young age, transition from Pleistocene to Holocene.

Multivariate analysis, used to track neutral genetic distances (Weaver, T.D., Roseman. C.C. & Stringer, C.B., 2007), was carried out on the shape of the vault indicating that with regards to the phenetic affinities between LL 1 and MLDG 1704 the picture is to some degree mixed. The first principal component, that accounted for 45-46 % of the total variance, indicated the dominant phenetic signal in these analyses showed LL 1 and MLDG 1704 to be on the edge of the variation with H. sapiens from the Pleistocene, and in some analyses they are also shown to be on the edge of H. erectus variability. They were indicated to possess a cranial shape that was unique among all later hominins from the Pleistocene. A weaker phenetic signal, that was revealed particularly by principal component 3, about 12-14 % of the total variance, indicates they had a cranial shape that was unique among all later hominins from the Pleistcene

The conclusion that remains from both sites display affinities to H. sapiens is supported by a range of features:

Neurocranium

Projects moderately and the supraorbital part is thin laterally with a bipartite form in MLDG 1704; the chord and arc length of the frontal bone are moderate, though it has a broad maximum width; and the endocast is long, broad and has tall frontal lobes.

Viscerocranium

Narrow superior facial breadth; facial skeleton that is vertically short (superior facial height, orbital height and nasal height); and the nasal breadth is moderate relative to height.

Mandible

The mental foramen has a mesial position; and a medial pterygoid process is absent.

Dentition

Anterior dental crowns that are small (narrow).

There are many features that are either rare or completely absent in H. sapiens from the Pleistocene and recent times in the fossils from Longlin and Maludong, many of them plesiomorphies of later Homo, including:

Neurocranium

Endocranial volume is moderate; the frontal squama is highly arched; the parietal bones are short; the parietal lobes of the endocast are short; the post orbital region is short; and in Longlin 1 there is no bipartite supraorbital morphology.

Cranial Base

In Longlin 1 the mandibular fossa is long (A-P), broad (M-L) and deep (S-I).

Viscerocranium - Only the Longlin site

A flat mid-face with strong alveolar prognathism at the nasal root and aperture and the zygomatic process of the maxilla; a broad facial skeleton - interorbital, bizygomatic and bimaxillary; broad piriform aperture; no canine fossa and a deep sulcus maxillaris is present; laterally flared zygomatic arch; strongly arched zygomatic angled, its inferior margin sitting well lateral to the superior part; small zygomatic tubercle, lateral to a line projected from the orbital pillar (anterior aspect); a broad, deep sulcus marks the attachment area of the anterior masseter attachment; lateral orbital pillar (later aspect) strongly transversely curved; anterior wall of the zygomaticoalveolar root situated anteriorly - above P⁴/M¹

Mandible

The mental foramen is medial and there is no medial pterygoid tubercle. No sagittal keel and distinct lateral tubercles; chin is small (MLDG 1706 Rank 3, LL 1 ?3); mandibular foramen bridging (MLDG 1706); transverse tori is thickened; mandibular notch is symmetrical (MLDG 1679); there is a retromolar space; mandibular notch crest positioned laterally (MLDG 1679); anterior symphyseal angle is low (MLDG 1706).

Dentition

Taurodont molars are present as are broad post-canine crowns (large BL diameters).

The authors¹ say it is unusual to find this combination of characters of modern, H. sapiens, and archaic (putative pleisomorphic) populations, especially in Eurasia. Several remains that are known from the Pleistocene of Africa have been found to possess such a combination of modern features with putative Homo plesiomorphies. These include Klasies River Mouth Cave (Smith, F.H., 1992; Lam, Y.M., 1998) and Hofmeyr (Crevecoeur et al., 2009) (South Africa), Iwo Eleru (Nigeria)(Harvati, K. et al., 2011), Nazlet Khater (Egypt), and Dar-es-Soltane and Témara (Morocco)(Trinkaus, E., 2005; Trinkaus E., 2007; Crevecoeur et al., 2009). Most are much older than Longlin and Maludong. Dar-es-Soltane and Témara have not been dated, though they have been associated with Aterian lithic assemblages, and these hand been dated to 107,000 ± 3,000 and 96,000 ± 4,000 years at another site, La Grotte des Contrebandiers in Morocco (Jacob, Z. et al., 2007). The remains found at Klasies River Mouth Cave are 2 units that have been dated to more than 101,000 BP and more than 64,000-104,000 BP (Millard, A.R., 2008); Nazlet Khater 2 is possibly about 42,000 BP (Trinkaus, E., 2007); and Hofmeyr is 36.2 ± 3.3 thousand years BP (Grine, F.E. et al., 2007). At about 16.3-11.7 thousand years BP (Harvati, K. et al., 2011) it is similar to the remains from China.

Outside of Africa a number of fossils from then Upper Pleistocene have been described that possess an unusual mosaic of characters (e.g., Trinkaus, E., 2007). Remains from such places as Skhul, and Qafzeh, in Israel, and in Romania, Pestera cu Oase, were included in the analyses, the authors¹ suggest that overall they appear to be well within the range for H. sapiens from the Pleistocene. Some similarities are displayed with the LL 1 and MLDG 1704 in univariate comparisons by samples from the Levantine.

The authors¹ have attempted to explain the presence of such an unusual morphology during the transition from the Pleistocene to the Holocene in East Asia, suggesting the Longlin and Maludong remains could be from individuals that were very robust within an Epipalaeolithic population in southwest China that was previously unknown. Based on the presence of several features that are apparently unique, combined with a mixture of modern and archaic features that are unusual, are present in several specimens, as well as spanning developmental and functional complexes, the authors¹ consider that their explanation to be unsatisfactory. According to the authors¹ this hypothesis could also be used as an explanation of the morphology of remains at Klasies River Mouth Cave, Hofmeyr, Iwo Eleru, Nazlet Khater, Dar-es-Soltane, Témara, and Zhirendong, but as many of the archaic features are rare or lacking in H. sapiens it has not been used. This also applies to the Longlin and Maludong remains.

Another possible explanation that has been proposed by the authors¹ is that the remains at Longlin and Maludong are from an archaic population athat were late-surviving, that are possibly similar to those from Dar-es-Soltane and Témara (Trinkaus, E., 2005; Trinkaus, E., 2007; Crevecoeur, I., Trinkaus E., 2004). The morphology of the remains from North Africa is not well known, and the affinities and taxonomy of them is unclear, (Trinkaus, E., 2005; Trinkaus, E., 2007; Crevecoeur, I., Trinkaus E., 2004). The mandibular fragment from Zhirendong, from within East Asia, has been described and has been found to have a mosaic of archaic and pleisomorphic characters, which renders its taxonomic status problematic (Kaifu, Y., & Fujita, M., 2012; Liu, W., et al., 2010; Dennell, R., 2010). The authors¹ used stratigraphy to date this specimen to more than 100,000 BP, making it of a similar age to the assemblage from North Africa, though much older than Longlin and Maludong. A specimen from Salkhit, Mongolia, has recently been described and has been suggested to be from an unspecified archaic taxon (Coppens, Y., 2008). A preliminary date of about 20,000 BP has apparently been reported (Kaifu Y., & Fujita, M., 2012), though dating is considered by the authors¹ to be uncertain. The authors¹ say that as a result of measurement errors in this specimen, as well as others in Table 1 of Coppens et al., 2008), they were unable to use it in their analyses.

The retention of many ancestral polymorphisms in a H. sapiens population has been proposed by the authors¹ as another possible explanation of the unusual morphology of the remains from Longlin and Maludong. According to the authors¹ a concept that has commonly been resorted to as an explanation of groups that are morphologically mixed, where particular features are also present in allopatric populations of the same taxon, is the concept of incomplete lineage sorting (Mavárez & Linares, 2008). Pleistocene age H. sapiens in Africa have been suggested by recent morphological studies to have been deeply subdivided geographically prior to their dispersal to Eurasia (Gunz, P., et al., 2009). The same explanation has been used in the case of the unusual morphology of the calvarias from Iwo and Eleru (Harvati, K., et al., 2011). The authors¹ suggest that the morphology of the remains from Longlin and Maludong might be interpreted as being consistent with this hypothesis, and they also suggest that samples from the Chinese sites could be from a human population (or migration?) that was not known previously, and that may have not contributed to the East Asians of the present. This idea could be tested by the extraction of ancient DNA from a specimen from Maludong, but this has so far not been possible as a result of the lack of genetic material that has been found to be recoverable.

The presence of unusual morphology at Longlin and Maludong during the transition from the Pleistocene to the Holocene makes it obvious that the human evolutionary history of East Asians is more complex than was previously believed.

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