段落A

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.

段落A：

人类群体的起源和分布的研究过去通常基于考古和化石证据。然而，自20世纪50年代以来，一些技术的发展使得对这些领域的研究更加牢靠和客观。关于早期人口迁移的最佳信息现在是从"活体考古学"中获取的，即遗传物质中的线索。

段落B

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 the launching ground for the first human colonisers of the New World. 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 Americans.

段落B：

最近有关人们何时首次进入美洲的问题的研究是这些新技术价值的一个例子。长期以来，东北亚和西伯利亚被认为是新世界第一批人类殖民者的出发地。但是穿越白令海峡进入美洲的是一个主要的移民浪潮，还是多个浪潮？这个事件或事件发生在什么时候？近年来，从基因研究中获得了新的线索，包括现代美洲土著人群中遗传标记的分布。

段落C

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.

段落C：

由生物人类学家罗伯特·威廉姆斯领导的一个重要项目，重点研究了一种特定蛋白质免疫球蛋白G的变异体（称为Gm全型）-这种蛋白质存在于人类血液的液体部分。所有蛋白质都会在世代间发生“漂变”或产生变异体，一个亲缘交配的人类群体将共享一组这样的变异体。因此，通过比较两个不同人群（例如两个印第安部落）的Gm全型，可以确定它们的遗传"距离"，这本身可以被校准以提供它们上次互相交配以来的时间长度的指示。

段落D

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 Aleut 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 was ancestral 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 600 or 700 years ago). The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia of groups ancestral to the modern Eskimo and Aleut.

段落D：

威廉姆斯及其同事在20年的时间内对西北美洲的5000多名美洲印第安人进行了血液采样。他们发现他们的Gm全型可以分为两组，其中一组也与中南美洲印第安人的遗传类型相对应。其他测试表明，因纽特人和阿留申人形成了第三组。根据这些证据推断，穿越白令海峡的主要移民浪潮有三个。第一个是古印第安人的浪潮，距今超过15000年，是所有中南美洲印第安人的祖先。第二个浪潮约在14000-12000年前，带来了纳-德内猎人，是纳瓦霍族和阿帕奇族的祖先（他们从加拿大南迁约600或700年前）。第三个浪潮可能是在10000或9000年前，这一浪潮看到了从东北亚迁徙来的群体，是现代因纽特人和阿留申人的祖先。

段落E

How far does other research support these conclusions? Geneticist Douglas Wallace has studied mitochondrial DNA 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.

段落E：

其他的研究是否支持这些结论？遗传学家道格拉斯·华莱士对来自三个相距较远的美洲土著群体的线粒体DNA进行了研究，其中包括亚利桑那州的皮马-帕帕戈印第安人，墨西哥尤卡坦半岛的玛雅印第安人，以及巴西亚马逊上游地区的蒂库纳印第安人。正如罗伯特·威廉姆斯的研究所预测的那样，这三个群体似乎都是源自同一个祖先（古印第安人）群体。

段落F

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 roots 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 molars.

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.

段落F：

还有另外两种研究方法为了解美洲土著人口的起源提供了一些线索，它们涉及对牙齿和语言的研究。生物人类学家克里斯蒂·特纳是分析人类牙齿变化特征的专家。他认为牙冠和牙根具有很高的遗传成分，几乎不受环境和其他因素的影响。特纳对许多新旧世界的标本进行的研究，包括古代和现代标本，表明大多数史前美洲人的牙齿特征与北亚人群有关，如切牙铲形（牙齿表面的一个或两个凹陷区域）、单根上颌第一前磨牙和三根下颌第一臼齿。

特纳认为，这与从北亚迁出的单一古印第安人移民的观点是一致的，他通过校准牙齿微进化的速率将其设定为在14000年前以前。牙齿分析还表明，后来还有两次纳-德内斯族和因纽特-阿留申族的迁徙。

段落G

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 to account for the more than 1,000 languages spoken at one time by American 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.

段落G：

语言学家约瑟夫·格林伯格自20世纪50年代以来一直主张所有美洲土著语言属于一个"美洲印第安"语系，除了纳-德内斯语和因纽特-阿留申语-这一观点支持了三个主要迁徙的想法。在其他语言学家中，格林伯格是少数派，他们中的大多数支持许多次迁徙的观点，以解释美洲土著人一度使用的1000多种语言。但毫无疑问，新的遗传和牙齿证据为格林伯格的观点提供了有力支持。然而，对迁移日期的给出应予谨慎，除非有硬性考古证据支持。