【英语时差8,16】在黑暗中坚挺的向日葵

Anyone who keeps a garden is aware that many flowers actually bend toward the sun, in order to catch as much of its light as they can. This is called "solar tracking," and sunflowers are a well-known example: if you inspect a sunflower in the early morning, you will find it tilted¹ to the east; by twilight² it will be tilted over to the west. So what happens if you take a sunflower out of the garden bed and keep it in a completely dark closet?  Surprisingly, even though there is no light to catch, the sunflower will continue to bend every day just as it did when it was outside. This is a classic example of what scientists call a circadian rhythm -- it's a daily cycle of behavior that is internal to the organism, rather than being solely³ triggered by the environment. The word "circadian" means "around one day" -- it takes roughly twelve hours for the sunflower to follow the light from east to west, and another twelve to automatically reorient itself toward the east again.

Although they do follow the sun, the fact that sunflowers continue to bend in darkness demonstrates that it is a mistake to think too literally⁴ of plants as "seeking" the sunlight. Sunflowers don't bend themselves with any purpose in mind. More accurately⁵, we can say they have evolved over millions of years into the solar tracking rhythm because it helps catch light effectively, and the ones that catch the light best, are the ones most likely to survive. In all living things, natural selection favors those traits that result in survival; and as a result of that, we now have sunflowers that bend automatically.

1 tilted   

v. 倾斜的

参考例句：

• Suddenly the boat tilted to one side. 小船突然倾向一侧。
• She tilted her chin at him defiantly. 她向他翘起下巴表示挑衅。

2 twilight   

n.暮光，黄昏；暮年，晚期，衰落时期

参考例句：

• Twilight merged into darkness.夕阳的光辉融于黑暗中。
• Twilight was sweet with the smell of lilac and freshly turned earth.薄暮充满紫丁香和新翻耕的泥土的香味。

3 solely   

adv.仅仅，唯一地

参考例句：

• Success should not be measured solely by educational achievement.成功与否不应只用学业成绩来衡量。
• The town depends almost solely on the tourist trade.这座城市几乎完全靠旅游业维持。

4 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

5 accurately   

adv.准确地，精确地

参考例句：

• It is hard to hit the ball accurately.准确地击中球很难。
• Now scientists can forecast the weather accurately.现在科学家们能准确地预报天气。