60秒科学:驯鹿的昼夜节律钟

人类按照24小时一循环的作息规律来生活，是因为大脑中有昼夜节律钟的协调。

研究发现，驯鹿等北极动物，在北极持续数周白天或黑夜里生活时，是没有昼夜节律钟的。

How Its Internal Clock Is Read, Knows Reindeer¹

Humans are pegged² to a 24-hour cycle. We're locked into it not just by day and night—there’s the master timepiece in the brain called the circadian clock. But it doesn't make sense to live by a 24-hour clock in the Arctic, where it's dark or light for months at time. The solution? Lose the daily clock. Which is exactly what reindeer seem to have done, according to a study in Current Biology. [See Weiqun Lu et al,

Reindeer don't sleep eight hours like we do, and there's no obvious 24-hour pattern to their lives. They just chomp³ on tundra⁴, nap a few hours and feast again. But they still need to know when to mate, pack on fat or thicken their coats. So they probably rely on an annual clock instead, set by the hormone⁵ melatonin.

In humans melatonin levels rise at night, in response to darkness and cues from the circadian clock. In reindeer, even if they’re missing a circadian clock, melatonin levels still spike⁶ when it's dark and drop when it's light, making the equinoxes an ideal time to synchronize⁷ their annual clocks.

So ask a reindeer what time of year it is, and it may be able to give you the date. Just don't be offended if it won't give you the time of day.
 

1 reindeer   

n.驯鹿

参考例句：

• The herd of reindeer was being trailed by a pack of wolves.那群驯鹿被一只狼群寻踪追赶上来。
• The life of the Reindeer men was a frontier life.驯鹿时代人的生活是一种边区生活。

2 pegged   

v.用夹子或钉子固定( peg的过去式和过去分词 )；使固定在某水平

参考例句：

• They pegged their tent down. 他们钉好了账篷。 来自《简明英汉词典》
• She pegged down the stairs. 她急忙下楼。 来自《现代英汉综合大词典》

3 chomp   

v. （人、动物进食时）大声地咬，嚼得很响

参考例句：

• I lost a tooth while chomping on a French baguette!我啃法棍面包时，崩掉了一颗牙！
• They just chomp on tundra, nap a few hours and feast again.它们只是在苔原上大嚼特嚼，睡上几小时，接着再吃。

4 tundra   

n.苔原，冻土地带

参考例句：

• The arctic tundra is at the top of the world around the North Pole.北极冻原是指北极点周边的地区，是世界最高的地方。
• There is a large amount of methane gas under the Siberian tundra.西伯利亚的冻土地带之下有大量的甲烷气体。

5 hormone   

n.荷尔蒙，激素，内分泌

参考例句：

• Hormone implants are used as growth boosters.激素植入物被用作生长辅助剂。
• This hormone interacts closely with other hormones in the body.这种荷尔蒙与体內其他荷尔蒙紧密地相互作用。

6 spike   

n.长钉，钉鞋；v.以大钉钉牢，使...失效

参考例句：

• The spike pierced the receipts and held them in order.那个钉子穿过那些收据并使之按顺序排列。
• They'll do anything to spike the guns of the opposition.他们会使出各种手段来挫败对手。

7 synchronize   

v.使同步 [=synchronise]

参考例句：

• The sound on a film must synchronize with the action. 影片中的声音必须与动作配合一致。
• You must synchronize your Inbox before selecting additional folders. 在选择其他文件夹前，您必须同步您的收件箱。