Over the years, biologists have suggested two main pathways by which sexual selection may have shaped the evolution of male birdsong.
这是本文的主题句，告诉我们一下的信息：
1.本文探讨的是一个现象，是关于鸟的歌曲的性选择问题。
2.本文是一个新老观点对比型的文章，关键词在第一段中间或者第二段开头
3.本文谈到了进化论，那么在文章后面很可能会否定这个说法，并且可能会进行批驳。
4.下文会以性内和性间选择分别展开进行论述。
In the first, male competition (这个就是讲性内选择了)and intrasexual selection produce relatively short, simple songs used mainly in territorial behavior. In the second, (不看也知道，这是讲性间选择)female choice and intersexual selection produce longer, more complicated songs used mainly in mate attraction; like such visual ornamentation as the peacock's tail, elaborate vocal characteristics increase the male's chances of being chosen as a mate, and he thus enjoys more reproductive success than his less ostentatious rivals.
(以上到这里结束，做题时需要重点看的就是黑体字标示的字，通常来说，文章里面的极端语言需要记住它们的位置，比如最高级，比较级，表示唯一，单独的意思的词，可能出直接事实题)
The two pathways are not mutually exclusive, and we can expect to find examples that reflect their interaction. (否定词也要记住位置，可能出改善题)Teasing them apart has been an important challenge to evolutionary biologists.(开始要调戏进化论生物学家)
Early research confirmed the role of intrasexual selection. In a variety of experiments in the field, males responded ag
When female cowbirds raised in isolation in sound-proof chambers were exposed to recordings of male song, they responded by exhibiting mating behavior. (对于跟在论点之后的论述或者例子，我们没有必要去记住太多内容，你只要记住这是什么观点的例子，以及这个例子的关键词)
By quantifying the responses, researchers were able to determine what particular features of the song were most important. In further experiments on song sparrows, researchers found that when exposed to a single song type repeated several times or to a repertoire of different song types, females responded more to the latter.(递进关系，处理同上) The beauty of the experimental design is that it effectively rules out confounding variables; acoustic isolation assures that the female can respond only to the song structure itself.(ONLY就是唯一的意思，那么这个地方记住的就是这种方法可以去掉所有可能混淆的因素)
If intersexual selection operates as theorized, males with more complicated songs should not only attract females more readily but should also enjoy GREater reproductive success. At first, however, researchers doing fieldwork with song sparrows found no correlation between larger repertoires and early mating, which has been shown to be one indicator of reproductive success; further, common measures of male quality used to predict reproductive success, such as weight, size, age, and territory, also failed to correlate with song complexity. (看到这里，本段开头的观点似乎是被否定了，黑体标示的词都是非常明显的否定和转折，那么我们所可以做的就是继续往下看，各位记住，这个地方没有必要看太细，就是因为这段虽有转折，可是依然处于文章的中间，后面还有很多可能。)
The confirmation researchers had been seeking was finally achieved in studies involving two varieties of warblers. (看到这里，上一段的观点就被明显的证实了，所以一定要记住，文章还没有结束，出现的转折部分不用细看，因为经常会出现更多的转折，而不管怎么转，最后一次才算数。)
Unlike (千万记住，这个词出现肯定会考!!通常考反面)the song sparrow, which repeats one of its several song types in bouts before switching to another, the warbler(下面出题会问它) continuously composes much longer and more variable songs without repetition. For the first time, researchers found a significant correlation between repertoire size and early mating, and they discovered further that repertoire size had a more significant effect than any other measure of male quality on the number of young produced. The evidence suggests that warblers use their extremely elaborate songs primarily to attract females, clearly confirming the effect of intersexual selection on the evolution of birdsong.(都是重复本段的结论，不看也罢)
请各位记住，读GRE文章不在于读懂全文，你根本没有时间读懂。你只是 “处理 ”文章，主要线索就是论点和论据，论据大部分不用记住，只要知道在那里就是，要做快，还需要非常清楚地对于某些理论的态度，这样才可以不至于恐慌。下面我们看题目：
21. The passage is primarily concerned with
这种题目叫做主题题，一般做法是 “三出现 ”，主题词必须出现，细节，新内容不能出现。细节，指的就是把这个词从文章拿走，文章不会受影响，依然可以存在的东西。新内容，指的是文章完全没有谈到的东西。
(A) showing that intrasexual selection has a GREater effect on birdsong than does intersexual selection
显然性间选择比性内选择重要，此选项错。
(B) contrasting the role of song complexity in several species of birds(无主题词，错)
(C) describing research confirming the suspected relationship between intersexual selection and the complexity of birdsong (就是它啦)
(D) demonstrating the superiority of laboratory work over field studies in evolutionary biology(同B)
(E) illustrating the effectiveness of a particular approach to experimental design in evolutionary biology( 同B)
22.The author mentions the peacock's tail in line 8 most probably in order to ( 这种题叫举例作用题，正确答案标志有两个词：illustrate 和 give an example of 所以别的选项就可以不看)
(A) cite an exception to the theory of the relationship between intrasexual selection and male competition
(B) illustrate the importance of both of the pathways that shaped the evolution of birdsong (没有谈性间选择问题，马上选D，选项业不用看，因为之可能是它)
(C) draw a distinction between competing theories of intersexual selection
(D) give an example of a feature that may have evolved through intersexual selection by female choice
(E) refute a commonly held assumption about the role of song in mate attraction
23.According to the passage, which of the following is specifically related to intrasexual selection? (问的是性内选择，还记得那个段落谈这个主题多写么，就是第一二段，)
(A) Female choice (这个就是性间选择)
(B) Territorial behavior (纯粹的性内选择，就是它)
(C) Complex song types
(D) Large song repertoires
(E) Visual ornamentation
24.Which of the following, if true, would most clearly demonstrate the interaction mentioned in lines 11-13?
(这是最难的题目之一，叫逻辑题，也是07年10月之后的阅读重点，这种题目不用找内容对应，因为它的重点是假设某一观点成立，那一个能够最大支持 或反对这个观点，这些事实不是来自于文章，所以必须先看清楚11-13说了什么。现在做到题目看完全不迟，因为你即使刚才看了，做到这里也可能混淆，现在考了才回去看，非常直接，清晰。11-13行其实就是第二段的开头，不过请记住，GRE为了增加难度，真正的结论通常在上面一句或者下面一句，这种题目的难度就非常大了，因此，真正的要说明的观点是：The two pathways are not mutually exclusive, and we can expect to find examples that reflect their interaction.)
(A) Female larks respond similarly both to short, simple songs and to longer, more complicated songs. (没有性的吸引)
(B) Male canaries use visual ornamentation as well as elaborate song repertoires for mate attraction. (同上)
(C) Both male and female blackbirds develop elaborate visual and vocal characteristics. (同上)
(D) Male jays use songs to compete among themselves and to attract females. (性内性间都有，就是它)
(E) Male robins with elaborate visual ornamentation have as much reproductive success as rivals with elaborate vocal characteristics. (只有性间)
25. The passage indicates that researchers raised female cowbirds in acoustic isolation in order to (这次我们运气不那么好了，不过还是可以做，in order to前面的内容是例子，观点一般在例子的前面，把鸟儿关在隔音室里是为什么呢，当然就是为了隔开别的因素。选A)
(A) eliminate confounding variables
(B) approximate field conditions
(C) measure reproductive success
(D) quantify repertoire complexity
(E) prevent early mating
26. According to the passage, the song sparrow is unlike (这就是UNLIKE出的题目，这叫做强对比，其实只要强对比出现，肯定都会出题。类似的语言标志还有：previously,by contrast等) the warbler in that the song sparrow (主语是the song sparrow，肯定选表示简单的选项)。
(A) uses songs mainly in territorial behavior (没关系)
(B) continuously composes long and complex songs (复杂)
(C) has a much larger song repertoire (复杂)
(D) repeats one song type before switching to another (重复，简单)
(E) responds agGREssively to recorded songs(没关系)
27.The passage suggests that the song sparrow experiments mentioned in lines 37-43 failed to confirm the role of intersexnal selection because (失败的原因就在否定词)At first, however, researchers doing fieldwork with song sparrows found no correlation between larger repertoires and early mating, which has been shown to be one indicator of reproductive success
原因就是没有关系，答案肯定有否定词。
A) females were allowed to respond only to the song structure (没有)
(B) song sparrows are unlike other species of birds (unlike不是否定)
(C) the experiments provided no evidence that elaborate songs increased male reproductive success (就是它)
(D) the experiments included the songs of only a small number of different song sparrows (没有)
(E) the experiments duplicated some of the limitations of previous field studies (没有)