The two pathways are not mutually exclusive, and we can expect to find examples that reflect their interaction. Teasing them apart has been an important challenge to evolutionary biologists.

　　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. The breakthrough for research into intersexual selection came in the development of a new technique for investigating female response in the laboratory.

　　When female cowbirds raised in isolation in sound-proof chambers were exposed to recordings of male song, they responded by exhibiting mating behavior.

　　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。

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