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  3. A six-week old infant who died some 11,500 years ago in central Alaska is no

A six-week old infant who died some 11,500 years ago in central Alaska is no

游客2023-08-05  28
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. " [br] What can be the best title of this passage?
选项 A、Debates Aroused by the Remains of Sunrise Girl-Child
B、New Puzzles about the Ancient Beringia to Be Solved
C、Two Possible Models of Native American Migration
D、Native American Family Tree Sprouts a New Branch
答案 D
解析 本题解答需综合全文信息。主旨大意题。本文开门见山，一开篇就指出美洲最初如何进行人口繁衍出现了新线索，而这个新线索说明了什么呢?随后的第二、三段给出了具体说明，提出了印第安人族谱存在一个从前不为人知的分支，第四段至文末也是围绕这个新分支浮出水面后提出的一些论题展开的，可知文章的核心主题就是介绍印第安种群族谱出现了新分支，故D)为答案。
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