You should spend about 20 minutes on Questions 1-13, which are bad on “Population movements and genetics”.
Questions 1-6
This reading passage has ven ctions, A-G. Choo the correct headings for ctions A-F from the list of headings below.
简单的商务英语口语Population movements and genetics
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A Study of the origins and distribution of human populations ud to be bad on archaeological and fossil evidence. A number of techniques developed since the 1950s, however, have placed the study of the 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.
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B Recent work on the problem of when people first entered the Americas is an example of the value of the new techniques. North-east Asia and Siberia have long been accepted as the launching ground for the first human colonirs of the New World1. But was there one major wave of migration across the Bering Strait into the Americas, or veral? And when did this event, or events, take place? In recent years, new clues have come from rearch into genetics, including the distribution of genetic markers in modern Native Americans2.
C An important project, led by the biological anthropologist Robert Williams, focud 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 t 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 itlf can be calibrated to give an indication of the length of time since the populations last interbred.
my boo什么意思 1 New World: the American continent, as oppod to the so-called Old World of Europe, Asia and Africa
如何培养学生的学习兴趣整洁的英文 2 modern Native American: an American descended from the groups that were native to America
3 Inuit and Aleut: two of the ethnic groups native to the northern regions of North America (i.e. northern Canada and Greenland)
4 DNA: the substance in which genetic information is stored
holyshit 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 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 was ancestral to all Central and South American Indians. The cond 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 of groups ancestral to the modern Eskimo and Aleut.
E How far does other rearch support the conclusions? Geneticist Douglas Wallace has studied mitochondrial DNA4 in blood samples from three widely parated 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.
F There are two other kinds of rearch 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 ar
gues 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 ts at before 14,000 years ago by calibrating rates of dental micro-evolution. Tooth analys also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.
G The linguist Joph 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 evide
nce 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
Questions 7 and 8
The discussion of Williams's rearch indicates the periods at which early people are thought to have migrated along certain routes. There are six routes, A-F, marked on the map below. Complete the table below.
Questions 9-12
This passage refers to the three-wave theory of early migration to the Americas. It also suggests in which of the three waves the ancestors of various groups of modern native Americans first reached the continent.2020年中小学开学时间
Classify the groups named in the table below as originating from
A the first wave
B the cond wave
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C the third wave
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