2. 外语
  3. Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted def

Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted def

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问题 Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted definition of the term exists. One approach, called the biological species concept, bases the definition on reproductive compatibility. According to this view, a species is a group of animals that can mate with one another to produce fertile offspring but cannot mate successfully with members of a different group. Yet this idea can be too restrictive. First, mating between groups labeled as different species (hybridization), as often occurs in the canine family, is quite common in nature. Second, sometimes the differences between two populations might not prevent them from interbreeding, even though they are dissimilar in traits unrelated to reproduction; some biologists question whether such disparate groups should be considered a single species. A third problem with the biological species concept is that investigators cannot always determine whether two groups that live in different places are capable of interbreeding.
When the biological species concept is difficult to apply, some investigators use phenotype, an organism’s observable characteristics, instead. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species.
The author of the passage mentions "groups that ive in different places" (line 21) most probably in ordef to
选项 A、point out a theoretical inconsistency in the biological species concept
B、offer evidence in support of the biological species concept
C、identify an obstacle to the application of the biological species concept
D、note an instance in which phenotype classification is customarily used
E、describe an alternative to the biological species concept
答案C
解析 Evaluation
The author’s mention of groups that live in different places comes at the end of the first paragraph, in the context of discussing a third problem with the biological species concept: that investigators may not know whether animals in such groups are able to interbreed.
A The author does not address theoretical inconsistencies in the biological species concept.
B The author mentions groups that live in different places in order to address a problem with the biological species concept, not to support it.
C Correct. One obstacle to applying the biological species concept is that those attempting to distinguish among species may not be able to determine whether geographically separated groups of animals can interbreed.
D The passage does mention that some investigators use phenotype classification when the biological species concept is difficult to apply, but it does not mention specifically that a situation in which groups live in different places is an instance in which phenotype classification is customarily used.
E Animal groups that live in different places pose a problem for the application of the biological species concept, according to the author. The author does not mention these groups in order to describe an alternative to that concept.
The correct answer is C.
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