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 passage is primarily concerned with
选项 A、describing the development of the biologica species concept
B、responding to a critique of reproductive compatibility as a criterion for defining a species
C、considering two different approaches to identifying biological species
D、pointing out the advantage of one method of distinguishing related species
E、identifying an obstacle to the classification of biological species
答案C
解析 Main idea
This question depends on understanding the passage as a whole. The passage begins by explaining that identifying a species can be difficult, because there are different ways of defining the term. The biological species concept is one approach, but it has problems. Phenotype is another approach that can be used when the biological species concept proves difficult.
A The first paragraph defines the biological species concept and identifies some problems with its application, but it does not explain how that concept developed.
B The passage presents some critiques of reproductive compatibility as a way of identifying a biological species; it does not concern itself with responding to those critiques.
C Correct. The passage considers the biological species concept and the idea of phenotype as ways of identifying biological species.
D While the passage identifies two ways of distinguishing species and states that some investigators use one of those methods- -the phenotype method—when the biological method is difficult to apply, the passage is not primarily concerned with pointing out that either one is better than the other.
E The passage does discuss certain obstacles to the classification of species. First, it points out that there is no single accepted definition of distinct species. Second, it points out obstacles related to one particular approach to the classificatior of species. However, the passage consider: these obstacles in service of its primary concern, namely considering two different approaches to identifying biological species.
The correct answer is C.
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