讲解背景：（全文我没有给出，太长咯，打出来太麻烦咯）
Over the years, biologists have suggested two main pathways by which sexual selection may have shaped the evolution of male birdsong. In the first, male competition and intrasexual selection produce relatively short, simple songs used mainly in territorial behavior. In the second, female choice and intersexual selection produce longer, more complicated songs used mainly in mate attraction; like such visual ornamentation as the peacock’ 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 rival. The two pathways are not mutually exclusive, and we can expect to find examples that reflect their interaction.
注：这期结束叻有些冲忙
