首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
"Migration from Asia" The Asian migration hypothesis is today supported by most of the scientific evidence. The first "hard"
"Migration from Asia" The Asian migration hypothesis is today supported by most of the scientific evidence. The first "hard"
admin
2018-07-24
103
问题
"Migration from Asia"
The Asian migration hypothesis is today supported by most of the scientific evidence. The first "hard" data linking American Indians with Asians appeared in the 1980s with the finding that Indians and northeast Asians share a common and distinctive pattern in the arrangement of the teeth. But perhaps the most compelling support for the hypothesis comes from genetic research. Studies comparing the DNA variation of populations around the world consistently demonstrate the close genetic relationship of the two populations, and recently geneticists studying a virus sequestered in the kidneys of all humans found that the strain of virus carried by Navajos and Japanese is nearly identical, while that carried by Europeans and Africans is quite different.
The migration could have begun over a land bridge connecting the continents. During the last Ice Age 70,000 to 10,000 years ago, huge glaciers locked up massive volumes of water and sea levels were as much as 300 feet lower than today. Asia and North America were joined by a huge subcontinent of ice-free, treeless grassland, 750 miles wide. Geologists have named this area Beringia, from the Bering Straits. Summers there were warm, winters were cold, dry and almost snow-free. This was a perfect environment for large mammals—mammoth and mastodon, bison, horse, reindeer, camel, and saiga (a goatlike antelope). Small bands of Stone Age hunter-gatherers were attracted by these animal populations, which provided them not only with food but with hides for clothing and shelter, dung for fuel, and bones for tools and weapons. Accompanied by a husky-like species of dog, hunting bands gradually moved as far east as the Yukon River basin of northern Canada, where field excavations have uncovered the fossilized jawbones of several dogs and bone tools estimated to be about 27,000 years old.
Other evidence suggests that the migration from Asia began about 30,000 years ago—around the same time that Japan and Scandinavia were being settled. This evidence is based on blood type. The vast majority of modern Native Americans have type O blood and a few have type A, but almost none have type B. Because modern Asian populations include all three blood types, however, the migrations must have begun before the evolution of type B, which geneticists believe occurred about 30,000 years ago.
By 25,000 years ago human communities were established in western Beringia, which is present-day Alaska. A But access to the south was blocked by a huge glacial sheet covering much of what is today Canada. How did the hunters get over those 2,000 miles of deep ice? The argument is that the climate began to warm with the passing of the Ice Age, and about 13,000 b.c.e. glacial melting created an ice-free corridor along the eastern front range of the Rocky Mountains. B Soon hunters of big game had reached the Great Plains.
In the past several years, however, new archaeological finds along the Pacific coast of North and South America have thrown this theory into question. C The most spectacular find, at Monte Verde in southern Chile, produced striking evidence of tool making, house building, rock painting, and human footprints conservatively dated long before the highway had been cleared of ice. D Many archaeologists now believe that migrants moved south in boats along a coastal route rather than overland. These people were probably gatherers and fishers rather than hunters of big game.
There were two later migrations into North America. About 5000 b.c.e. the Athapascan or Na-Dene people began to settle the forests in the northwestern area of the continent. Eventually Athapascan speakers, the ancestors of the Navajos and Apaches, migrated across the Great Plains to the Southwest.
The final migration began about 3000 B.C.E after Beringa had been sub merged, when a maritime hunting people crossed the Bering Straits in small boats. The Inuits (also known as the Eskimos) colonized the polar coasts of the Arctic, the Yupiks the coast of southwestern Alaska, and the Aleuts the Aleutian Islands.
While scientists debate the timing and mapping of these migrations, many Indian people hold to oral traditions that include a long journey from a distant place of origin to a new homeland.
The word which in the passage refers to
选项
A、migrations
B、evolution
C、geneticists
D、populations
答案
B
解析
"Because modern Asian populations include all three blood types, however, the migrations must have begun before the evolution of type B, which [evolution] geneticists believe occurred." The pronoun "which" does not refer to Choices A, C, or D.
转载请注明原文地址:https://kaotiyun.com/show/f3fO777K
0
托福(TOEFL)
相关试题推荐
Completetheflowchartbelow.WriteNOMORETHANTWOWORDSforeachanswer.ExpertiseincreativewritingB
Completethesentencesbelow.WriteONEWORDAND/ORANUMBERforeachanswer.Atthebeginningofthereport,thehypothesisan
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrom
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrom
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrompra
Completethenotesbelow.WriteONEWORDONLYforeachanswer.DevelopmentStudiesDevelopmentStudiesattemptstounderstand-
Completethenotesbelow.WriteONEWORDONLYforeachanswer.DevelopmentStudiesDevelopmentStudiesattemptstounderstand-
Manyantsforageacrossthecountrysideinlargenumbersandundertakemassmigrations;theseactivitiesproceedbecauseone
"MigrationfromAsia"TheAsianmigrationhypothesisistodaysupportedbymostofthescientificevidence.Thefirst"hard"
PatentsandInventionsWhenaninventionismade,theinventorhasthreepossiblecoursesofactionopentohim:first,hec
随机试题
我国现行的《中华人民共和国食品卫生法》自________起正式施行。
A、先天性铁储存不足B、铁摄入不足C、铁丢失过多D、铁吸收减少E、生长发育快婴幼儿长期偏食可导致()
单位专用停车场常采用的车辆停发方式是()。
热力管网试运行的时间为:应在设计参数下连续热运行()h。
_________决定着教育的领导权和受教育的权利。
现有一种预防禽流感药物配置成的甲、乙两种不同浓度的消毒溶液。若从甲中取2100克,乙中取700克混合而成的消毒浓度为3%:若从甲中取900克,乙中取2700克,则混合而成的溶液的浓度为5%。则甲、乙两种消毒溶液的浓度分别为()。
①中医认为,人的泪液“由五脏六腑所生.由肝肾所主”②人体是一个有机的整体,脏腑是人体生命活动的中心③眼睛作为人体的一个器官与五脏六腑有着密切的联系,身体各方面的疲劳都会表现为眼睛不舒服④因此,中医治疗眼干燥症需要综合调理,从调节全身阴阳入手,最终达到
葛雷制
A、 B、 C、 D、 A
CD-ROM是
最新回复
(
0
)