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Sometimes it's easy to understand how an evolutionary change took place, but it's more difficult to understand why.
有時(shí)候去理解生物進(jìn)化演變的過程很容易，想知道原因卻很難。
For example, consider the beautiful birds of paradise which live in the forests of New Guinea. The males of many bird-of-paradise species have evolved colorful plumage, used for dramatic courtship displays. How this plumage evolved is no mystery: The healthiest males usually have the most spectacular plumage, so females choose whichever male has the gaudiest feathers. With this criterion, it's not surprising that male plumage would grow more and more elaborate over the generations.
就拿居住在新幾內(nèi)亞森林中的極樂鳥作例子吧。極樂鳥種群中的雄性常常會(huì)利用它們絢麗多彩的羽毛上演一幕又一幕的求愛話劇。這羽毛是怎樣進(jìn)化來的并不神秘：最健壯的雄性往往擁有最絢麗的羽毛，所以雌性往往會(huì)選擇有艷麗羽毛的雄性。在這種標(biāo)準(zhǔn)的要求下，雄性鳥兒拼命想長(zhǎng)出比同類更搶眼，更精致的羽毛，這一點(diǎn)不足為奇。
Understanding why the plumage evolved is a little trickier. After all, there are some bird-of-paradise species that are really quite drab. These birds devote most of their energy to finding food and raising their young, instead of wasting it on courtship. What makes these near neighbors so different?
了解羽毛色澤為什么會(huì)進(jìn)化就有點(diǎn)棘手了。畢竟，有幾種極樂鳥的顏色十分單調(diào)。這些鳥把它們主要的精力都放在尋找食物和撫養(yǎng)后代上了，而不是用于求愛。是什么導(dǎo)致這些近鄰如此不同？
The answer is diet. Those species with the most elaborate plumage also have the most diverse and reliable diet: a variety of insects, and fruits rich in complex nutrients. With this healthy, reliable food supply, females can raise the hatchlings without help from the males. This frees the males for their extravagant courtship behavior, and the complex diet provides them with chemicals to make their brightly colored feathers.
答案就是日常飲食。那些有著最美麗羽毛的鳥兒有各式各樣并且穩(wěn)定的食物：各種昆蟲和富含多種營(yíng)養(yǎng)的水果。有了這種健康的、可靠的食物供應(yīng)，雌性極樂鳥可以完全不依靠雄性而獨(dú)立撫養(yǎng)后代。這樣就使得雄性有閑暇時(shí)間去發(fā)展求愛行為，而且多樣飲食中的化學(xué)物質(zhì)能讓他們的羽毛更鮮亮。
In contrast, the drabber birds have a limited diet of simple figs, which are available more sporadically. They're monogamous, and both parents need to spend most of their time foraging. This means less time for elaborate courtship behavior.
與此相反，擁有單調(diào)毛色的鳥兒的食譜就相對(duì)簡(jiǎn)單，僅限于零星分布的無花果。同時(shí)它們實(shí)行一夫一妻制，父母雙方都需要花費(fèi)大量的時(shí)間尋找食物，這就大大縮短了用于考慮花哨的求愛方式的時(shí)間。
So different diets lead to different behaviors, which results in the evolution of different plumage. These exotic birds show just how complex evolution can be!
所以，不同的食物產(chǎn)生不一樣的生活方式，也是進(jìn)化出不同毛色的原因。這些奇異的鳥兒向我們解釋了進(jìn)化有多么復(fù)雜！
