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  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.
Which of the following best describes the function of lines 10-13?
选项 A、It elaborates the definition of the biological species concept given in a previous sentence.
B、It develops a point about the biological species concept made in the previous sentence.
C、It states the author’s central point about the biological species concept.
D、It identifies a central assumption underlying the biological species concept.
E、It demonstrates why the biological species concept is invalid.
答案B
解析 Evaluation
The sentence in question discusses hybridization as a first factor complicating the applicability of the biological species concept. Thus its function is to help explain why, as the previous sentence states, that concept is too restrictive.
A The sentence in question brings up a problem with the biological species concept; it does not elaborate the definition of that concept.
B Correct. According to the sentence that precedes the sentence in question, the biological species concept can be too restrictive. The author offers three reasons to develop this point, and the first reason is given in the sentence in question.
C The sentence in question could be said to support the author’s central point about the biological species concept—that it is one (flawed) way of determining whether a population is a species—but it does not state that central point.
D The sentence in question expresses a problem with the biological species concept, not a central assumption of it.
E The sentence in question serves to indicate a problem with the biological species concept, but it does not go so far as to demonstrate that it is invalid.
The correct answer is B.
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