中国人从哪里来的
遗传学者宣称,实验室的DNA测试表明,中国人的祖先不是四五十万年前的北京人,而是在6万至10万年前来自非洲。而考古学家的证据却言之凿凿地说,中国人是在自己的土地上长大成人的。
全世界同宗?
复旦大学遗传学研究所、美国得克萨斯大学人类基因研究中心教授金力说:“我们从基因变异中发现,10万至20万年前,现代人的共同祖先出现在非洲,而各地男人之间的差别不超过14. 4万年,大约在6万至10万年前,走出非洲的后代向东沿印度洋迁入东南亚和中国。”
这在中国古人类学界引起轩然大波。关于“现代人的起源”已争论了几十年,遗传学者的加入使争议变得空前激烈。
该研究结果为“夏娃假说”提供了证据。1987年,美国加州大学威尔逊实验室做了一项实验,从不同人种的148个胎盘中提取DNA研究,从而提出“夏娃假说”:所有的现代人都有一个共同祖先————20万年前的一位非洲妇女,她的后代在13万年前走出非洲,扩散到各大洲取代了当代居民。
反对“取代论”的代表人物是中国科学院古人类研究所研究员吴新智。他认为:“人类的进化是多样性的,我相信欧洲的大部分‘原住民’被来自非洲的人取代了,这在化石上得到证实,但不能因此认为亚洲也发生了同样的事。”“中国人的进化是以连续进化为主,附带与境外人类的杂交。”
在中国发现的最早的化石是170万年前的元谋人牙化石。吴新智说,不同时期的化石有共同特征,如铲形门齿、长方形眼眶、脸较为扁平等,这表明至少170万年以来,中国人的进化过程是连续不断的。
80%——90%中国人门牙的背面是铲形的,在中国发现了很多门齿化石,它们的背面全部是铲形的,而在非洲,这种情况只有百分之十几,在欧洲还不到10%。而在发现北京人头盖骨时,美国专家魏敦瑞便提出,头骨特征显示,北京猿人和现代黄种人有密切的联系。
冰川时代冻死了北京人的后代?
金力说:“遗传学没有发现这种连续性,因为不可能拿到古代的DNA,无法做比较,但如果当地智人更接近现代人,现在看到的进化谱系的结构将会完全不一样。我们在东亚和东南亚采集了1500——2000份样本,基因研究表明,没有一例可能是由当地古老人种进化的,即使有,对现代群体的基因贡献也不大。”
吴新智说,基因测试是通过比较基因变异的多少,来判断人种进化历史的长短,这种方法本身就有缺陷,现代人基因变异的多少,不等于历史积累基因变异的总量。
“例如,种族分支灭绝造成积累的基因变异丢失,谁能知道进化中丢失了多少?而且代代相传越多,积累的基因变异越多,而热带地区和寒带地区繁衍后代的周期不一样,不能从现代人的基因变异中简单推算进化历程的长短。”
1998年11月,金力让学生仔细搜索300多页的《中国人类的进化》,没有查到5万至10万年前的中国人类化石,12月1日,他当面请教作者吴新智,得到了证实。
金力感到豁然开朗,相信抓住了问题的关键——这从化石上印证了中国智人和现代人之间的断层,北京人的后代在1. 5万至7. 5万年前的冰川时代就灭绝了,继而6万至10万年前,非洲来客顺理成章地成为主人。
对此,吴新智反驳说:“没有发现并不等于不存在,而且全球冰川期不等于全球皆冰,中国东、南部低海拔地区就没有形成大冰盖,在华南发现了1万至100万年前的几十个化石地点,发掘出很多猩猩、大象、犀牛、貘等热带动物化石,说明这期间的气候一直是温暖甚至炎热的,人类也可以生存。”吴新智提出一个旁证————西奈半岛是走出非洲进入亚洲的必经之路,10万年前,以色列的石器十分精致,而中国石器的制作工艺直到3万年前仍比较粗放,如果6万至10万年前经以色列登陆中国,这些“技术移民”怎么没把手艺带来?
民族情绪还是学术之争?
金力表示,石器问题确实不好解释,而且无法证实。他猜测:“可能途经东南亚时多用竹子、木头,如果没有原材料,手艺就会失传。”
金力说:“尽管我出于个人感情,希望看到中国人独立起源的证据,但结论恰恰相反,绝大部分现代人的基因来自非洲,尤其男性Y染色体全部支持我们的观点,感情必须尊重科学发现。”
对此,吴新智也强调:“搞科学要按证据说话,是就是,不是就不是。1991年巫山号称发现200万年前的‘巫山人’,我认为那不是人类化石,还写了1万字的文章提出反对意见,如果出于民族主义感情,我应该很赞同。”
100年来,古生物学家锲而不舍地在化石记录中追寻物种的起源。吴新智十分怀疑基因研究的科学性,称:“用基因研究的结果推测人类进化过程是间接的,化石才是直接的证据。”
金力针锋相对:“考古学的方法是把看到的东西综合起来讲故事,是演绎。遗传学是先做假设,再拿到实验室验证,如不正确就否定假设,进行归纳。”
尽管双方的观点针锋相对,但一致认为,两大学科的证据都不会错,基因与化石都是事实。然而,人类进化的历史事实只有一个,还需要双方继续进行科学探索。
----辽宁日报
- Re: 中国人从哪里来的posted on 03/25/2005
80%——90%中国人门牙的背面是铲形的,在中国发现了很多门齿化石,它们的背面全部是铲形的,而在非洲,这种情况只有百分之十几,在欧洲还不到10%。而在发现北京人头盖骨时,美国专家魏敦瑞便提出,头骨特征显示,北京猿人和现代黄种人有密切的联系。
其他没想法,但这个反驳不成立,当初非洲原始人里百分之十几的铲形门牙者只有有那么几个到达了中国,那么在中国生产80~90%的后代就不是没有可能了压。 - Re: 中国人从哪里来的posted on 03/26/2005
我看这左右双方都是空中筑幻,没有多少名堂。
能混这样一碗饭吃真是不简单啊,不简单!
不喜欢把世界搞得那么简单,实证或逻辑思维都太单一化,是一种贫
血的标志。
有时我想童年听到的野人的故事更有意思,高行健对探访野人有兴趣
。李白有诗:两岸猿声啼不住。《水经注》有:猿啼三声泪沾裳。
- Re: 中国人从哪里来的posted on 03/26/2005
不知基因测试的可靠性多高, 是否有一些理所当然的假设混在推断中 - 结论的准确性要经得住其他证据的考验.
说句外行话, 什么可以在化石中找到基因呢? There are too many missing links in mankink's evolution.
- Re: 中国人从哪里来的posted on 03/27/2005
我以为现今世界各地种族皆源于非洲智人在古人类学界已是个大家都接受的假说了(如进化论在生物界,相对论在物理界),没想到在中国还有争执。 - posted on 03/27/2005
报纸和这位吴研炒冷饭而已。即便是化石证据也已证明中国人来自非洲。见英国《自然》杂志此文:
http://online6.hsls.pitt.edu:2147/cgi-taf/DynaPage.taf?file=/nature/journal/v431/n7012/full/4311043a_fs.html
Figure 1 Homo floresiensis in the context of the evolution and dispersal of the genus Homo. a, The new species as part of the Asian dispersals of the descendants of H. ergaster and H. erectus, with an outline of the descent of other Homo species provided for context. b, The evolutionary history of Homo is becoming increasingly complex as new species are discovered. Homo floresiensis (left) is believed1 to be a long-term, isolated descendant of Javanese H. erectus, but it could be a recent divergence. 1, H. ergaster/African erectus; 2, georgicus; 3, Javanese and Chinese erectus; 4, antecessor; 5, cepranensis; 6, heidelbergensis; 7, helmei; 8, neanderthalensis; 9, sapiens; 10, floresiensis. Solid lines show probable evolutionary relationships; dashed lines, possible alternatives.
我对此图的理解,现代智人的化石遍布全世界,最早的在非洲。直立人最早的化石也在非洲,大约二百万年。中国直立人跟非洲直立人有进化关系。
另外,包括周口店人在内的这些化石应该是已经灭绝的直立人(Homo erectus),不是智人(Homo sapiens)(现代人是智人)。见这篇中国学者的文章:
http://www3.interscience.wiley.com/cgi-bin/abstract/109805329/ABSTRACT - Re: 中国人从哪里来的posted on 03/27/2005
假设当时地球大陆版块还没进行漂移的话,那么非洲妇女可以通过各种途径到达任何一个可以生存的陆地上繁衍生息,问题在于如果她和同族男性的后代那必将是黑色人种,基因决定人体性状,那后来怎么会演变为黄色人种,白色人种了呢?那就不难理解了,如果和当地人类杂交的话,也许会成立.既然当地已经有了人类的迹象,那这非洲妇女也只能算外来移民者.难道只有她的后代在人类漫长的进化中生存下来了吗?毕竟哺乳动物是有性繁殖而非无性繁殖啊. - posted on 03/27/2005
I thought so too. This Mr. Wu is kind of living behind the time.
Wanted to read the article in Nuture magazine, but can't access it. It asked for password.
报纸和这位吴研炒冷饭而已。即便是化石证据也已证明中国人来自非洲。见英国《自然》杂志此文:http://online6.hsls.pitt.edu:2147/cgi-taf/DynaPage.taf?file=/nature/journal/v431/n7012/full/4311043a_fs.html - posted on 03/27/2005
here we go.. I already put in the key figure (see above).
Nature 431, 1043 - 1044 (28 October 2004); doi:10.1038/4311043a
Palaeoanthropology: Human evolution writ small
MARTA?MIRAZ?N?LAHR AND ROBERT?FOLEY
Marta Mirazón Lahr and Robert Foley are in the Leverhulme Centre for Human Evolutionary Studies, Department of Biological Anthropology, University of Cambridge, Downing Street, Cambridge, CB2 3DZ, UK.
e-mail: m.mirazon-lahr@human-evol.cam.ac.uk e-mail: r.foley@human-evol.cam.ac.uk
We are the only living species of the genus Homo. Given the startling results of a cave excavation in Southeast Asia, it seems that we coexisted with another species until much more recently than had been thought.
The fossils described elsewhere in this issue probably left no descendants, are not very old, and were found on a remote island. Despite this, they are among the most outstanding discoveries in palaeoanthropology for half a century. The two papers concerned — by Brown et al.1 and Morwood et al.2 — appear on pages 1055 and 1087 of this issue, and respectively describe the fossils and their archaeological context. The find is startling. It is of a pygmy-sized, small-brained hominin, which lived as recently as 18,000 years ago, and which was found on the island of Flores together with stone tools, dwarf elephants and Komodo dragons. Discoveries don't get better than that.
The Flores fossils add a new and surprising twig to the hominin family tree, which diverged from the chimpanzee lineage about 7 million years ago. The first African hominins existed 7–1.2 million years ago, were 1–1.5 metres tall, walked upright on two legs (that is, were bipedal), and had chimpanzee-size brains. These early forms comprised as many as six genera and fourteen species, of which the australopithecines are the best known. By 2.5 million years ago, our own genus, Homo, had emerged, with its different body shape, slower growth, greater reliance on meat in the diet, and 'encephalization' — larger brains than expected for body size. These were the first hominins to make stone tools systematically and to colonize Eurasia. They include the familiar names of H. habilis, H. erectus, H. neanderthalensis and, finally, H. sapiens, which put in an appearance about 160,000 years ago. The new fossil is part of this Homo group (Fig. 1).
Figure 1 Homo floresiensis in the context of the evolution and dispersal of the genus Homo. ??Full?legend
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High resolution image and legend (42k)
Flores lies to the east of Java, and was probably never connected to the mainland. The presence of 800,000-year-old simple stone tools first attracted attention in 1998 (ref. 3), raising the controversial possibility that H. erectus had produced them and had crossed major sea barriers to reach Flores. Now we have the announcement of the discovery of an 18,000-year-old hominin skeleton from a cave, Liang Bua, on Flores. Although this date is more than 140,000 years after modern humans evolved in Africa, more than 25,000 years after H. sapiens reached Australia, and about 10,000 years after the last known Neanderthal, the skeleton is that of a new species — Homo floresiensis. Its most remarkable features are its diminutive body (about a metre in height) and brain size (at 380 cm3, the smallest of any known hominin).
Homo floresiensis is a challenge — it is the most extreme hominin ever discovered. An archaic hominin at that date changes our understanding of late human evolutionary geography, biology and culture. Likewise, a pygmy and small-brained member of the genus Homo questions our understanding of morphological variability and allometry — the relation between the size of an organism and the size of any of its parts. Brown et al.1 claim that the skeleton, designated LB1, represents a new species within the genus Homo. They believe that it may have been a female. They also conclude that it was a dwarfed descendant of Javanese H. erectus, and part of an endemic island fauna. But what other taxonomic assignments are possible?
Convergence — a process through which two species become more similar to each other than their ancestors were — is a strong evolutionary force4, and LB1, with its minute brain, could be a convergent Southeast Asian ape. But it evidently was an obligatory biped and had small canine teeth, key hominin traits that, with the rest of its morphology, firmly place it within the hominin group5. Given its body and brain size, as well as some other features, could the remains be those of an australopithecine? Those features include bony reinforcements along the sides of the nose, thigh bones that were less obliquely aligned than ours (a trait essential for the way we walk and deal with gravity), and pelvic bones that were very wide, giving it a different overall body shape from ours. But the answer is again no. Most of LB1's other characteristics, such as the thickness and proportions of the skull, the flexion evident at the skull base, and the shape of the teeth, are derived traits of the genus Homo.
Could LB1 be a pygmy H. sapiens? Again, no. Compared with a human skull scaled to less than a third of full size, the LB1 skull differs in shape, robusticity and key features of the base. Furthermore, although human pygmies are short (1.4–1.5 m), they show very little reduction in brain size, probably because their small size is attained through mechanisms that curtail growth during puberty, when brains are already fully grown6.
In general terms, LB1's morphology groups it with H. erectus7. The name includes African and non-African hominins with brains smaller than 1,250 cm3, which may be one species (H. erectus), or several (antecessor, cepranensis, erectus, ergaster, georgicus, mauritanicus and soloensis). Height among these 'erectines' is considered8 to range between 1.55 m and 1.78 m, and brain size between 650 cm3 and 1,260 cm3. The body and brain size of LB1 (about 1 m and 380 cm3) clearly indicate a major departure from the erectine extremes, while its peculiar combination of primitive and derived traits points towards the complex effects of dwarfism and its allometric consequences.
Island dwarfism is well known among mammals9. Released from predation pressure or constrained by restricted resources, and limited by population size, the phenomenon can be dramatic. Some examples can be truly extreme — for example, the one-metre-high fossil elephants, found on Sicily and Malta, which may have become dwarfed from a 4-metre ancestor in less than 5,000 years10. Indeed, remains of now-extinct primitive elephants (Stegodon), which had become dwarfed in relation to their mainland relatives, were found in the same deposits as LB1.
The dwarfism of H. floresiensis is also dramatic, resulting in the shortest adult Homo, and possibly hominin, known. Most significantly, the relative proportions of LB1's brain and body size (Fig. 2) indicate that the size reduction was more pronounced in the brain than the body, so a non-encephalized descendant evidently arose from an encephalized ancestor. This raises many questions about encephalization and hominin behaviour. Such questions aside, H. floresiensis is clear evidence that, in spite of their 'cultural niche', hominins were subject to the same evolutionary rules as other widespread mammals, with local isolation and small population sizes producing differentiation in size and form. This find strengthens the view that the genus Homo was probably much subdivided, resulting in a bushy human evolutionary tree. That view is itself consistent with the idea that the extreme climatic shifts of the past million years promoted population dispersal and isolation, and potentially resulted in instances of local evolution11.
Figure 2 The relative brain and body size of H. floresiensis. ??Full?legend
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High resolution image and legend (35k)
Necessarily, the discovery of H. floresiensis bears on the debate over the origins of modern humans — whether H. sapiens evolved in various regions throughout the world from H. erectus populations, or as a distinct and recent African species. Multiregional evolution requires the existence of large populations for long periods, with isolation being rare or absent so that the global species could evolve in a single direction. Palaeoanthropological and genetic studies have already done much to discredit this model, and H. floresiensis puts yet another (the last?) nail in the multiregional coffin. Not only did H. floresiensis evolve in the absence of gene exchange with other hominins, but no one can argue that LB1 contributed to our own species' genetic make-up.
Finally, accomplishing the sea-crossing that must have been necessary for the founding population to reach Flores adds to the baffling evidence for complex, supposedly 'sapient', behaviours among archaic hominins12. And the behaviour of H. floresiensis itself, of course, remains elusive. Are the 800,000-year-old stones really artefacts? If so, does their date indicate when the taller ancestors of the dwarfed form arrived?
The archaeological evidence is controversial. The 800,000-year-old artefacts are simple, crudely flaked pebbles, similar to those found with Javanese H. erectus, as are some found at Liang Bua dating to more than 100,000 years ago. Only a few tools are associated with LB1. But thousands were found with the Stegodon skeleton in another sector of the cave: some are small flakes struck from radial cores; others consist of points, perforators, blades and possibly hafted microblades. Although Morwood et al.2 attribute the production of all of these tools to H. floresiensis, elsewhere such implements are associated with H. sapiens, and their contrast with tools found anywhere with H. erectus is very striking. One could speculate that modern humans, who were dispersing across southern Asia between 100,000 and 50,000 years ago, may have made the tools, and come across these creatures. They may also have had a part in their ultimate extinction.
It is breathtaking to think that such a different species of hominin existed so recently. Brown et al.1 point to the probability of similarly unexpected fossils being found in other isolated areas. For most of its 160,000-year history, H. sapiens seems to have shared the planet with other bipedal and cultural beings — our global dominance may be far more recent than we thought.
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- Re: 中国人从哪里来的posted on 03/28/2005
我是学文的,要是说了外行话,请纠正。我理解进化论说人演变自类人猿,不仅有外因,也有内因,即突变(mutation)。一次突变只能产生一个新物种,好像没有两次突变产生同一物种的情况。因此,人不可能从两群猿猴中经由两次突变产生。我们的祖先必定是同一个。现在发现的人类祖母是东非的Lucy.
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