现代人起源的多地区进化学说在中国的实证

关于现代人起源主要有两种学说:多地区进化说和近期出自非洲说。文章介绍了中国人类进化的假说:'连续进化附带杂交’。构成这个假说的基础的中国资料为多地区进化说提供实证。其直接证据来自人类化石,包括中国人类化石具有一系列共同特征,直立人与智人之间有形态学上的镶嵌,中国化石中有表现西方基因的形态学证据。另外,本文还简略介绍了用DNA研究中国现代人起源目前达到的结论,并从体质人类学、旧石器时代考古学、古环境研究和分子生物学研究等诸方面的资料对这个结论进行检验。

EVIDENCE OF MULTIREGIONAL HUMAN EVOLUTION HYPOTHESIS FROM CHINA

There are two main hypotheses on the origin of modern humans, the Multiregional Evolution versus the Recent Out-of-Africa. The former was proposed in 1984 by Wolpoff and others. It is supported by the following three-fold evidence of Continuity with Hybridization in China. (1) There are a series of common morphological features among human fossils of China. They are: the flatness of the face, the low nasal saddle, the more or less quadrangular shape of the orbit with rounded infero-lateral margin, the antero-lateral surface of the fronto-sphenoidal process of zygomatic bone facing more forward, the curved margin of the lower border of zygomatic process of maxilla, the sutures between frontal bone and the nasal and maxillary bones forming a more or less horizontal curve, the most prominent point of the midsagittal line of the frontal bone locating at the lower half of this line, the broadest part locating at the posterior part of the middle third of the vault, the sagittal keeling of different degrees, the shovel-shaped upper incisor etc. (2) There is a morphological mosaic between Homo erectus and Homo sapiens in China. In Hexian Homo erectus skull, there are several characteristics such as the high cranial index, the weak post-orbital constriction, and the high length-height index of temporal squama, which are generally present in Homo sapiens, but not in Homo erectus. In a few Homo sapiens skulls there are a few characteristics thought to be unique characters of Homo erectus. The examples of such kind include the exaggerated post-orbital constriction in Maba skull, the thick cranial wall and brow ridges of Dali skull, the angular transition between occipital and nuchal planes of the occipital bone in Dali and Jinniushan skulls, the angular torus in Dali and Ziyang skulls, and the thick cranial wall in Xujiayao parietal bones.(3) In a few fossil skulls of China there are a few characters which are different from those seen in most Chinese fossils, but are similar to those usually existing in European skulls. The examples include the bulge between the orbit and anterior nasal aperture in the skull from Dali, the protruding nasal saddle of Nanjing skull No.1, the spherical orbit of Maba skull, the bun-like structure in the skulls from Liujiang, Lijiang, and Ziyang, the orientation of the antero-lateral surface of the bony pillar lateral to the orbit in Upper Cave skull No.102, and the Carabellis cusp in Lijiang skull. Another example is that the frontal nasal suture is at a higher level than the fronto-maxillary suture shown in the frontal bone from Salawusu region.The above mentioned common features and morphological mosaic indicate the continuity of human evolution in China. The dissimilar characters existing in a few fossils of China might be the results of gene flow from Europe to China.The hypothesis of Continuity with Hybridization is supported by the context of Paleolithic technique in China. In Africa and Europe, the Paleolithic technique developed in a sequence from Mode Ⅰ through Mode Ⅴ; while in China Mode Ⅰ technique persisted in the whole course of Paleolithic period, with only a few sites showing other modes of Paleolithic technique, such as Mode Ⅱ at Baise of Guangsi, Taishanmiao of Hubei and Mode Ⅲ at Shuidonggou of Ningxia, Longtanshan of Yunnan, Mode Ⅳ at the Upper Cave of Zhoukoudian, and Mode Ⅴ at Xiachuan, Shanxi etc. Baise and Taishanmiao sites are of Middle Pleistocene; the other sites are of Late Pleistocene. The Paleolithic technique thus shows a continuous development accompanied by some cultural exchange with that of Europe. This development history is quite different from that in Africa and Europe.Since 1998 some studies based on the analysis of genes of Y-chromosome of modern populations have been published. Their main conclusion is that modern humans of China originated from Africa. It suggested that the immigrants entered China around 60000 years before present during the Last Ice Age and totally replaced the indigenous populations in China. However, such a conclusion has not got any support from data available in other related disciplines but is in contradiction with the context of Paleolithic archeology of both China and the Near East. The study of fauna has shown that in Late Pleistocene a large area of East China south to 40° was not so cold that mammals could survive even in Ice Age. There are at least five sites which have yielded human fossils and/or Paleolithic artifacts and have been dated with chronometric dating. These data strongly indicate the human existence in China between 50000~100000 years ago. In the Near East there are Mousterian sites of about 100000 years ago. If the Recent Out-of-Africa hypothesis were correct the artifacts of these sites should be made by the first anatomically modern immigrants migrated from Africa, which is in conflict with the Y-chromosome analysis conclusion that immigrants entered China around 60000 years ago, an age which should be associated with Paleolithic technique of Mode Ⅲ. If immigrants had thoroughly replaced the indigenous people in China, their technique or technique developed from it should replace technique of Mode Ⅰ which had been prevalent in China for long time. However, the ModeⅠ technique kept prevalent in China till after 60000 years ago. In recent years, chronometric dates have been obtained from 29 Paleolithic sites from 60000aB.P. through 10000aB.P., among which only 2 show the Mode Ⅲ technique, 3 show the Mode Ⅳ, and 5 show the Mode Ⅴ. The Mode I is the only mode being demonstrated in all other sites.The recent anatomy of East Asians is also favourable to the Multiregional Hypothesis. According to the investigation of Lahr (1994) the mid-sagittal keeling, the mandibular torus, the pinched nasal saddle, and the congenital agenesis of the third molar are present in recent East Asian skulls in different frequencies but absent in recent African skulls. The mid-sagittal keeling and mandibular torus are commonly seen in Homo erectus found at Zhoukoudian; the pinched nasal saddle exists in Middle Pleistocene skull from Maba and Upper Paleolithic skull from the Upper Cave; the congenital agenesis of the third molar is shown in Middle Pleistocene mandible from Lantian and Late Pleistocene skull from Liujiang. According to the Multiregional Evolution hypothesis, these features in recent East Asians might be inherited from the human fossils mentioned above. The combination of the presence of these features in East Asians and their absence in recent Africans is difficult to be explained with the Recent Out-of-Africa hypothesis.It is furthermore worthy of mentioning that as molecular biologists have indicated, "it is important to recognize that each locus in human genome can capture only a fraction of the human history, and different loci can have rather different generalogies. Thus, some conclusions from different loci are necessarily conflicting. Only after a sufficient number of studies have been conducted, can we gradually reach a consensus about the history of modern humans." In respect of the origin of modern humans in China, the total replacement conclusion based on some genes of Y-chromosome thus needs to be more carefully considered.