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  3. A six-week old infant who died some 11,500 years ago in central Alaska is now providing clues about how the Americas first came

A six-week old infant who died some 11,500 years ago in central Alaska is now providing clues about how the Americas first came

admin2021-12-15  48
问题     A six-week old infant who died some 11,500 years ago in central Alaska is now providing clues about how the Americas first came to be populated.
    Genomic data from remains of the girl—named "Xach’itee’aanenhT’eedeGaay" (Sunrise Girl-Child) by the local indigenous community—broadly support a migration model that scientists have long argued for, while also revealing the existence of an ancient population previously unknown to science. The girl was a member of an ancient population that the report authors have named "Ancient Beringians. " Beringia is the name given to Alaska, Eastern Siberia, and the land bridge that periodically connected the two during the last ice age.
    The findings suggest a revised family tree: a single ancestral Native American group split from East Asians about 35,000 years ago, before later splitting, some 20,000 years ago, into two distinct groups. One was the Ancient Beringians, and the other constituted the ancestors of modern-day Native Americans, who later split into northern and southern populations about 15,700 years ago.
    "Trying to integrate these findings with what we know from archaeology (考古学) and paleoecology (古生态学) presents exciting new puzzles," says Ben Potter, an anthropologist (人类学家) at the University of Alaska. "The peopling has been shown now to be more complex than we thought previously. " Scientists have sought ancient human remains from Beringia at the end of the last ice age, but Xach’itee’aanenhT’eedeGaay’s genome held a surprise: it was clearly Native American, but not from either of the two major modern Native American groups. It represented a population that diverged from that common ancestor.
    All of this helps narrow down and strengthen the theories of just how those populations arrived in the Americas. But mysteries remain, including definitive answers about where and when some of these population splits occurred and which migration routes were used.
    Researchers outline two possible models. In one scenario, which Dr. Potter favors since it matches well with archaeological data and paleoecological data, the split occurred in Northeast Asia, and the two separate populations later crossed over the land bridge prior to 15,700 years ago, when the Native American ancestors split again. In the other theory, the ancestral population had already arrived in Alaska or eastern Beringia by 20,000 years ago, and the split occurred there, with the second split into North and South American populations occurring south of the ice sheets. What happened to the Ancient Beringians? They might have died out, says Potter, or they could have been absorbed by Northern Native Americans who migrated back to the far North.
    Researchers liken the puzzle to a murder mystery. "You read the book, and the author reveals new clues over the course of the book. Every time a new genome is analyzed and reported, it provides a new clue that’s making the pathway to uncover the real story that much clearer. "
What can we infer from the two possible migration models?
选项 A、The first model seems to have acquired more supports from research data.
B、The first split occurred about 15,700 years ago according to the first model.
C、The split of ancient Native Americans happened on the ice sheets in the second model.
D、The second model can explain the ending of the Ancient Beringians.
答案A
解析 由题干中的the two possible migration models定位到原文第六段。推理判断题。本题考查对研究人员提出的两种迁徙模式的理解。由定位段第二句可知，波特尔偏爱第一种模式，原因是它与考古学和古生态学的数据契合得比较好。由此推断，第一种模式的研究数据更充足，故A)为答案。B)“根据第一种模式，首次分裂发生在大约15，700年前”，原文是指15，700年前种群越过了大陆桥发生了再次分裂，而首次分裂在此前发生，故排除；C)“根据第二种模式，古印第安人的分裂发生在冰原上”，定位段第三句介绍第二种迁徙模式时，提到两次分裂的地点是不同的，第二次分裂为南北两支则发生在冰原的南部，因此C)项属于以偏概全，故排除；D)“第二种模式可以解释古白令人的结局”，从定位段最后两句可知，古白令人最后结局如何对两种模式都是个谜题，第二种模式也无法解答，故排除。
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