考满分网

AA Study of the origins and distribution of human populations used to be based on archaeological and fossil evidence. A number of techniques developed since the 1950s, however, have placed the study of these subjects on a sounder and more objective footing. The best information on early population movements is now being obtained from the 'archaeology of the living body', the clues to be found in genetic material.

A 过去人们对人类起源与人口分布的研究一直是在考古发现和化石证据的基础上进行的。然而，从20世纪50年代起发明的不少新技术使得此项研究拥有更充分、更客观的立足点。关于人口迁移活动的最早信息是从“活体考古”中获得的，专家们可从遗传物质中发现一些线索。

BB Recent work on the problem of when people first entered the Americas is an example of the value of these new techniques. North-east Asia and Siberia have long been accepted as thelaunching ground for the first human colonisers of the New World1. But was there one major wave of migration across the Bering Strait into the Americas, or several? And when did this event, or events, take place? In recent years, new clues have come from research into genetics, including the distribution of genetic markers in modern Native Americans2.

B 近来对人类何时初次踏上美洲大陆问题的研究便是体现这些新技术价值的最好范例。很久以来，东北亚和西伯利亚就一直被视为人类首次向“北美新世界”迁移的发源地。但是，跨越白令海峡进入美洲大陆的移民浪潮是一次还是几次?这次移民事件，或者这几次事件又是何时发生的呢?近些年来，通过对遗传学的研究，专家们找到遗传标记在现代美国本土居民中分布情况的新线索。

CC An important project, led by the biological anthropologist Robert Williams, focused on the variants (called Gm allotypes) of one particular protein immunoglobin G - found in the fluid portion of human blood. All proteins ‘drift’, or produce variants, over the generations, and members of an interbreeding human population will share a set of such variants. Thus, by comparing the Gm allotypes of two different populations (e.g. two Indian tribes), one can establish their genetic 'distance', which itself can be calibrated to give an indication of the length of time since these populations last interbred.

C 由生物人类学家罗伯特·威廉姆斯领导的一项重要工程把研究点聚焦在了免疫球蛋白G变体(又叫做免疫球蛋白同种异型Gm)上。在人类血液流体中可以找到这种变体。所有的蛋白质都处于漂流状态，或者在生产新变体，那么数代之后，通过通婚形成的家族成员们将会拥有一套共同的变体。所以，通过对比两类不同人群的Gm同种异型(比如两个印第安人部落)人们可以建立各自的“遗传距离”，距离本身可以调整，从而可以给出一些信息，提示此族群自从最后一次通婚混血以来经过了多长时间。

　　1 New World: the American continent, as opposed to the so-called Old World of Europe, Asia and Africa

D 威廉姆斯和他的同事们花费20年时间在北美西部地区采集了5，000名美洲印第安人的血液标本。通过研究发现，这些印第安人的Gm同种异型可以划分为两组，其中一组也和中部、南部的印第安人基因类型相区配。其他测试显示因纽特人(又叫爱斯基摩人)和阿留申人形成另一个族群。据此证据可推断出，跨越白令海峡的大规模移民浪潮共有三次。第一次移民浪潮发生在15．000年前，其中的古印第安人是今天美国中部和南部印第安人的祖先。约14．000到12．000年前的第二次移民浪潮带来了纳迪尼狩猎者，他们是纳瓦乔人和阿帕切人(他们在约600或700年前从加拿大南部移民到美国)的祖先。第三次浪潮发生在约10．000或9．000年前，从东北亚移民至北美大陆的这批人是现代爱斯基摩人和阿留申人的祖先。

　　2 modern Native American: an American descended from the groups that were native to America

E 那么，其他研究对此项结论的支持力度又有多大呢?遗传学专家道格拉斯·华莱士通过研究三大彼此远离的本土美洲人(亚利桑那州的皮马-帕帕戈人、墨西哥尤卡坦半岛的玛雅印第安人、巴西亚马逊河上游流域的迪甫拿印第安人)血液样本中的线粒体DNA发现：就像罗们特·威康姆斯的著作预测的那样，三个族群其实源于同一个祖先。

　　3 Inuit and Aleut: two of the ethnic groups native to the northern regions of North America (i.e. northern Canada and Greenland)

F 此外，还有两种研究进一步阐明了本土美洲人的起源问题。它们涉及牙齿研究和语言研究。生物人类学家克里斯蒂·特纳是一位从事人类牙齿生理特征变化研究的专家。他认为齿冠和齿根包含极高的遗传因素，受环境和其他因素影响最小。根据对数千来自新旧世界的样本进行分析，特纳发现，大多数史前美洲人在齿冠和齿根特点上和皿洲北部人口有所联系，如铲形门齿(牙齿单侧或双侧边缘??隆起而中部呈凹窝状)，单重根上齿第一前磨牙和三重根下前第一磨牙。据特纳称，这一特点和古印第安从北亚向外移民有所关联，特纳通过研究牙齿微进化速度得出这次移民发生在14．000年前。通过对牙齿的研究也发现了后面还有纳迪尼和爱斯基摩-阿留申这两次移民浪潮。

　　4 DNA: the substance in which genetic information is stored

G 自从20世纪50年代，语言学家约瑟夫·格林伯格就认为，所有的本土美国语言同属于唯一的一个印第安语系(除纳迪尼和爱斯基摩-阿留申以外)，此种观点对三大主要移民浪潮的说法提供了凭证。格林们格是同时代语言学家中的少数派，而大多数语文学家都赞成这样一种观点：一波又一波的移民浪潮是解释那一时期北美印第安人讲1000多种语文的唯一依据。但是毫无疑问，新的遗传学和牙齿证据为格林伯格的观点提供了强有力的支持。当然，关于移民的具体时间问题了也要谨慎对待，除非这些信息有确凿的考古证据的支撑。

　　

DD Williams and his colleagues sampled the blood of over 5,000 American Indians in western North America during a twenty-year period. They found that their Gm allotypes could be divided into two groups, one of which also corresponded to the genetic typing of Central and South American Indians. Other tests showed that the Inuit (or Eskimo) and Aleut3 formed a third group. From this evidence it was deduced that there had been three major waves of migration across the Bering Strait. The first, Paleo-Indian, wave more than 15,000 years ago wasancestral to all Central and South American Indians. The second wave, about 14,000-12,000 years ago, brought Na-Dene hunters, ancestors of the Navajo and Apache (who only migrated south from Canada about 600or 700 years ago). The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia ofgroups ancestral to the modern Eskimo and Aleut.

　　

EE How far does other research support these conclusions? Geneticist DouglasWallace has studied mitochondrial DNA4 in blood samples from three widely separated Native American groups: Pima-Papago Indians in Arizona, Maya Indians on the Yucatán peninsula, Mexico, and Ticuna Indians in the Upper Amazon region of Brazil. As would have been predicted by Robert Williams's work, all three groups appear to be descended from the same ancestral (Paleo-Indian)population.

　

FF There are two other kinds of research that have thrown some light on the origins of the Native American population; they involve the study of teeth and of languages. The biological anthropologist Christy Turner is an expert in the analysis of changing physical characteristics in human teeth. He argues that tooth crowns and roots5 have a high genetic component, minimally affected by environmental and other factors. Studies carried out by Turner of many thousands of New and Old World specimens, both ancient and modern, suggest that the majority of prehistoric Americans are linked to Northern Asian populations by crown and root traits such as incisor6shoveling (a scooping out on one or both surfaces of the tooth), single-rooted upper first premolars6 and triple-rooted lower first molars6.

　　According to Turner, this ties in with the idea of a single Paleo-lndian migration out of North Asia, which he sets at before 14,000 years ago by calibrating rates of dental micro-evolution. Tooth analyses also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.

　　GG The linguist Joseph Greenberg has, since the 1950s, argued that all Native American languages belong to a single 'Amerind' family, except for Na-Dene and Eskimo-Aleut - a view that gives credence to the idea of three main migrations. Greenberg is in a minority among fellow linguists, most of whom favour the notion of a great many waves of migration toaccount for the more than 1,000 languages spoken at one time byAmerican Indians. But there is no doubt that the new genetic and dental evidence provides strong backing for Greenberg's view. Dates given for the migrations should nevertheless be treated with caution, except where supported by hard archaeological evidence.

　　5 crown/root: parts of the tooth

　　6 incisor/premolar/molar: kinds of teeth