在大半个世纪里，大多数生物学家都不愿使用这些词，因为他们牢记着一条进化论的原则，即“进化不能倒退”。

For the better part of a century, most biologists have been reluctant to use those words, mindful of a principle of evolution that says "evolution cannot run backwards".

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虽然我们有一大半的人睡不着觉，但是研究已经显示，大多数准更年期的妇女能够入睡，不过她们只是熬不住。

Although more than half of us aren't sleeping, studies have shown that most perimenopausal women can get to sleep, they just can't stay that way.

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今天，大多数老年人都切盼安度晚年，到那个时候，辛勤工作大半辈子的人们终于能够退休并过上轻松满足的生活。

Today, most older people look forward to reaching their golden years. This is when hard-working people can retire to a life of ease and fulfillment.

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