托福考试易错题（2019/10/22）

Migration fromAsia
TheAsian migration hypothesis is today supported by most of the scientific evidence. The first "hard" data linkingAmerican Indians withAsians appeared in the 1980s with the finding that Indians and northeastAsians 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 theDNA、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 byEuropeans andAfricans is quite different.
The migration could have begun over a land bridge connecting the continents.During the last IceAge 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 NorthAmerica were joined by a huge subcontinent of ice-free, treeless grassland,750 miles wide. Geologists have named this areaBeringia, from theBering 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 StoneAge 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 northernCanada, 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 fromAsia 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 nativeAmericans have type O blood and a few have typeA, but almost none have typeB、Because modernAsian populations include all three blood types, however, the migrations must have begun before the evolution of typeB, which geneticists believe occurred about 30,000 years ago.
By 25,000 years ago human communities were established in westernBeringia, which is present-dayAlask
A、
But access to the south was blocked by a huge glacial sheet covering much of what is todayCanadA、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 IceAge, and about 13,000B、C、
E、glacial melting created an ice-free corridor along the eastern front range of the Rocky Mountains.
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 SouthAmerica have thrown this theory into question.
The most spectacular find, at Monte Verde in southernChile, produced striking evidence of tool making, house building, rock painting, and human foot-prints conservatively dated at 12,500 years ago, long before the highway had been cleared of ice.
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 NorthAmericA、About 5000B、C、
E、theAthapascan or Na-Dene people began to settle the forest

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