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  3. Tens of thousands of years ago modern humans crossed paths with the group of hominins known as the Neandertals. Researchers now

Tens of thousands of years ago modern humans crossed paths with the group of hominins known as the Neandertals. Researchers now

admin2015-03-25  31
问题     Tens of thousands of years ago modern humans crossed paths with the group of hominins known as the Neandertals. Researchers now think they also met another, less-known group called the Denisovans. The only trace that we have found, however, is a single finger bone and two teeth, but those fragments have been enough to cradle packets of Denisovan DNA across thousands of years inside a Siberian cave. Now a team of scientists has been able to reconstruct their entire genome from these deficient fragments. The analysis adds new twists to prevailing notions about ancient human history.
    "Denisova is a big surprise," says John Hawks, a biological anthropologist at the University of Wisconsin-Madison who was not involved in the new research. On its own, a simple finger bone in a cave would have been assumed to belong to a human, Neandertal or other hominin. But when researchers first sequenced a small section of DNA in 2010—a section that covered about 1.9 percent of the genome—they were able to tell that the specimen was neither. " It was the first time a new group of distinct humans was discovered" via genetic analysis rather than by anatomical description, said Svante paabo, a researcher at the Max Planck Institute(M. P. I.)for Evolutionary Anthropology in Germany, in a conference call with reporters.
    Now paabo and his colleagues have devised a new method of genetic analysis that allowed them to reconstruct the entire Denisovan genome with nearly all of the genome sequenced approximately 30 times over akin to what we can do for modern humans. Within this genome, researchers have found clues into not only this group of mysterious hominins, but also our own evolutionary past. Denisovans appear to have been more closely related to Neandertals than to humans, but the evidence also suggests that Denisovans and humans interbred. The new analysis also suggests new ways that early humans may have spread across the globe.
    Unfortunately, the Denisovan genome doesn’t provide many more clues about what this hominin looked like than a pinky bone does. The researchers will only conclude that Denisovans likely had dark skin. They also note that there are alleles "consistent" with those known to call for brown hair and brown eyes. Other than that, they cannot say.
    Yet the new genetic analysis does support the hypothesis that Neandertals and Denisovans were more closely related to one another than either was to modern humans. The analysis suggests that the modern human line diverged from what would become the Denisovan line as long as 700,000 years ago—but possibly as recently as 170,000 years ago.
According to the passage, which of the following is TRUE?
选项 A、Modern humans, Neandertals and Denisovans lived completely separated.
B、Denisovans and modern humans were more closely related.
C、Modern humans and Neandertals were more closely related.
D、There were exchanges between Denisovans and modern humans.
答案D
解析 事实细节题。根据第三段第三句…but the evidence also suggests that Denisovans and humansinterbred可知，古人类与丹尼索瓦人杂交，可见他们之间是有交往的，因此选[D]，同时，也可排除[A]。另外，这句话还说明，丹尼索瓦人似乎与尼安德特人的关系比与人类的关系更加密切，故排除[B]和[C]。
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