GRE阅读以艰深著称，很多理论讲解使得考生觉得如雾里云中，下面，我带大家来一起做一篇题目

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 aggressively to recorded songs by exhibiting territorial behavior near the speakers. （以上是性内选择 ）The breakthrough for research into intersexual selection came in the development of a new technique for investigating female response in the laboratory. （这里告诉我们出现了新的突破，这是GRE所特别喜欢的东西，很可能就是本文的重点下面就是要进行说明和举例）

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）