By Jon Stewart, BBC Science

媒體英語會(huì)帶大家一起學(xué)習(xí)BBC撰稿人在報(bào)道世界大事時(shí)常用到的單詞和短語。

Background: 一項(xiàng)新研究對長期未解的一個(gè)科學(xué)問題提供了答案，這就是睡眠究竟有什么意義。科學(xué)家原來以為睡眠對于大腦修復(fù)，保持長期記憶力和扭轉(zhuǎn)清醒時(shí)候壓力過渡導(dǎo)致的損害都有意義。然而最新的研究之出睡眠主要的作用在于讓各種動(dòng)物更好地適應(yīng)生存環(huán)境。

Pythons, bats and giant armadillos are among the longest sleepers at over 18 hours a day. Human babies need 16 hours, and most of us probably feel we need around eight hours sleep to function well.

Professor Jerry Seigel, from the University of California, Los Angeles, conducted a study of the sleep times of a broad range of animals, and found that they vary widely. Some, like migrating birds, can survive long periods without sleeping at all. He believes that shows sleep evolved to conserve energy:

“It's animals that are needlessly active that will not survive, but animals that are most efficient and use their waking time to do vital functions, and are otherwise asleep that will survive.”

Sleep helps make best use of limited resources. In humans, when we're awake, our brain accounts for 20 percent of the energy we use when just sitting around. Sleeping also makes us less likely to get injured and less likely to be detected by predators.