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
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 experim.
其实，GRE阅读技巧很简单，只要抓住出题者出题的习惯和规律，就很容易找到突破口，发现做题时的技巧，这样不仅速度提升了，准确率也提高了。