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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2024-03-08  19
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] Which of following is mentioned by Ben Potter as the "exciting new puzzles"?
选项 A、Whether Xach’itee’aanenhT’eedeGaay belonged to Native American groups.
B、How Xach’itee’aanenhT’eedeGaay’s population separated from major groups.
C、Why the two major Native American groups diverged from the common ancestor.
D、When the populations crossed over the land bridge and arrived in the Americas.
答案 B
解析 由题干中的Ben Potter和exciting new puzzles定位到原文第四段。语义理解题。本题考查对波特尔所说语句具体内涵的理解。对这句话的理解应着重看波特尔这句话之后的分析。定位段最后两句指出，卡奇娌安妮.媞狄戈伊的基因说明她属于印第安人，可又不属于两个主要的现代印第安人种群分支当中的任何一个；第五段最后一句说，谜题依然存在，包括其中一些种群的分裂是何时何地出现的，他们采用的迁徙路线如何，等等。由此可知，波特尔所说的谜题之一就是卡奇媞安妮.娓狄戈伊的种群究竟是如何从主要群体中分离出来的，故答案为B)。A)“卡奇娌安妮.媞狄戈伊是否属于印第安人种群”这在原文中已经给出了肯定的答案，不存在疑问，故排除；C)“为什么两个主要印第安人种群会从共同的祖先中分离出来”，从原文可知，种群分裂的原因并不在波特尔所说的谜题范围内，因此排除；D)“这些种群是何时越过大陆桥到达美洲大陆的”也不在波特尔所说的谜题范围内，故排除。
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