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  3. One method of dating the emergence of species is to compare the genetic material

One method of dating the emergence of species is to compare the genetic material

游客2024-01-13  62
问题 One method of dating the emergence of species is to compare the genetic material of related species. Scientists theorize that the more genetically similar two species are to each other, the more recently they diverged from a common ancestor. After comparing genetic material from giant pandas, red pandas, raccoons, coatis, and all seven bear species, scientists concluded that bears and raccoons diverged 30 to 50 million years ago. They further concluded that red pandas separated from the ancestor of today’s raccoons and coatis a few million years later, some 10 million years before giant pandas diverged from the other bears. Which one of the following can be properly inferred from the passage?
选项 A、Giant pandas and red pandas are more closely related than scientists originally thought they were.
B、Scientists now count the giant panda as the eighth species of bear.
C、It is possible to determine, within a margin of just a few years, the timing of divergence of various species.
D、Scientists have found that giant pandas are more similar genetically to bears than to raccoons.
E、There is substantial consensus among scientists that giant pandas and red pandas are equally related to raccoons.
答案 D
解析 本题首先提出一普遍性的理论，然后把这一理论应用于一具体的例子。由例子中所描述的几种熊从它们的祖先中分离开的时间可知，大熊猫从熊中分离开的时间比熊和浣熊从同一种祖先中分开时间晚一千零几百万年。因此，根据本题开始提出的两个物种在遗传上越相似，两个物种从同一祖先中分出的日期距今就越接近的理论，可知大熊猫与熊和浣熊相比，在遗传上与熊更为相似，也即(D)为正确答案；(A)、(B)都不能从题干中得出；(C)、(E)是很明显的错误选项。
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