单选题：History of American ImmigrationA．Ancient peoples only loosel

History of American Immigration
A．Ancient peoples only loosely related to modern Asians crossed the Arctic land bridge tosettle in America about 15,000 years ago, according to a study offering new evidencethat the Western Hemisphere had a more genetically diverse population at a muchearlier time than previously thought. The early immigrants most closely resembled theprehistoric Jomon people of Japan and their closest modern descendants, the Ainu， fromthe Japanese island of Hokkaido, the study said. Both the Jomon and Ainu have skulland facial characteristics more genetically similar to those of Europeans than those ofmainland Asians.
B．The immigrants settled throughout the hemisphere, and were in place when a secondmigration -- from mainland Asia -- came across the Bering Strait beginning 5,000years ago and swept southward as far as modern-day Arizona and New Mexico, thestudy said. The second migration is the genetic origin of today's Eskimos, Aleuts andthe Navajo of the US southwest. The study in today's edition of Proceedings of theNational Academy of Sciences adds new evidence to help settle one of anthropology's(人类学) most controversial debates: Who were the first Americans? And when didthey come?
C．"When this has been done before, it's been done from one point of view," saidUniversity of Michigan physical anthropologist C. Loring Brace, who led the team ofresearchers from the United States, China and Mongolia who wrote the new report. "Wetry to put together more aspects." For decades, anthropologists held that the Americaswere populated by a single migration from Asia about 11,200 years ago -- the supposedage of the earliest of the elegantly crafted, grooved arrowheads first found in the 1930sin Clovis, N.M. By the end of the 1990s, however, the weight of evidence had pushedback the date of the first arrivals several thousand years. A site at Cactus Hill, nearRichmond, may be 17,000 years old. In Chile, scientists discovering a 12,500-year-oldsettlement at Monte Verde have found evidence of a human presence that may extend asfar as 30,000 years. But as the migration timetable went on, additional questions havearisen. The 1996 discovery in Kennewick, Washington, of the nearly complete skeletonof a 9,300-year-old man with "apparently Caucasoid" features stimulated interest in thepossibility of two or more migrations -- including the possible incoming from Europe.
D．The new study attempted to answer this question by comparing 21 skull and facialcharacteristics from more than 10,000 ancient and modern populations in the WesternHemisphere and the Old World. The findings provide strong evidence supporting earlierwork suggesting that ancient Americans, like Kennewick Man, were descended fromthe Jomon, who walked from Japan to the Asian mainland and eventually to the WesternHemisphere on land bridges as the Earth began to warm up about 15,000 years ago atthe end of the last Ice Age.
E. Brace described these early immigrants as "hunters and gatherers" following herdsof mastodon (乳齿象) first into North America, and eventually spreading throughoutthe hemisphere. Because the North -- in both Siberia and Canada -- was stillextremely cold, only a limited number of people could make the trek (长途跋涉)and survive. So immigration slowed, Brace said, for about 10 millennia (一千年).
Then, about 5,000 years ago, agriculture developed on mainland Asia, enablingpeople to grow, store and carry food in more lonely areas. Movement resumed, butthe newcomers were genetically Asians -- "distinct racially" from the first wave,Brace added.
F. The second wave spread across what is now Canada and came southward, cohabiting (同居) with the earlier settlers and eventually creating the mixed population found by theSpaniards in the 15th century. While many researchers agree on the likelihood of twomigrations, both their timing and origin are matters of dispute. Brace's team suggeststhat both movements occurred after the last Ice Age began to moderate between 14,000and 15,000 years ago.
G. But University of Pennsylvania molecular anthropologist Theodore Schurr said geneticdata in American populations suggest that humans may have been in the WesternHemisphere much earlier -- 25,000 to 30,000 years ago. This would mean that thefirst wave came before the "glacial maximum" between 14,000 and 20,000 years ago,when the Ice Age was at its fiercest and "human movement was practically impossible,"Schurr said. "Were there people here before the last glacial maximum?" he asked. "Thesuggestion is 'Yes'".
H. The third wave arose in the American continent around the year 1000, when a smallnumber of Vikings arrived. Five hundred years later, the great European migrationbegan. In some cases, the co-existence of Europeans and Native Americans waspeaceful. In other cases, there were cultural clashes, leading to violence and disease.
Many people from Africa, however, were bought here against their will to work asforced labourers in the building of a new nation. As early as 1619, slaves from Africaand the Caribbean were brought forcibly to America. Later,102 English colonists(later referred to as the "Pilgrims") set sail in 1620 on the Mayflower. They landed inPlymouth, Massachusetts. This is generally considered by many to be the "start" ofplanned European migration! In 1638, just 18 years after the Mayflower, the Swedesbegan their migration to America. Unlike the Pilgrim Fathers, the Swedes were notreligious opponents -- they were an organised group of colonizers sent by the SwedishGovernment to establish a colony in Delaware. In 1655, the colony was lost to theDutch. In the mid-1840s, a wave of Swedish migration began with the landing of agroup of migrant farmers in New York and continued up to World War I.
I.During the colonial era most of the immigrants to the US came from NorthernEurope. Their numbers declined during the 1770s, but picked up during the mid-1800s. New arrivals came from several countries, but mostly from Germany andIreland where crop failures caused many to leave their homelands. Other groups alsoarrived from the Netherlands, Spain, Italy, the Scandinavian countries, and EasternEurope.
The anthropologists' earlier work believes that the Jomon are the ancestors of Kennewick Man.