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How Its Internal Clock Is Read, Knows Reindeer

Humans are pegged 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.

人类被限制在24小时的循环内，不仅仅是被日夜限制其中，大脑中还有一种叫昼夜节律钟的计时器约束着我们。可在昼夜为好几个月的北极圈里，按照24小时来起居就没什么意义了。有什么解决办法吗？有，就是抛弃白天的钟。据《当代生物学》的一篇研究看来，驯鹿就是一直这么做的。

Reindeer don't sleep eight hours like we do, and there's no obvious 24-hour pattern to their lives. They just chomp on tundra, 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 hormone melatonin.

驯鹿不像我们要睡足八小时，起居活动也没有明显的24小时规律。它们只是在苔原上大嚼特嚼，睡上几小时，接着再吃。即使如此它们也还是得了解何时交配、储存脂肪或是增加皮毛，因此它们依赖的可能是由荷尔蒙褪黑素调节的年钟。

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 spike when it's dark and drop when it's light, making the equinoxes an ideal time to synchronize their annual clocks.

拿人体来说，由于对黑暗作出反应并受昼夜节律钟的影响，褪黑素值会在晚上升高。即使缺少昼夜节律钟，驯鹿的褪黑素值仍会在黑暗时达到顶峰，光亮时就下降，使昼夜平分点成为它们调节年钟的最佳时期。

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.

所以，要问驯鹿这是一年中的什么时段，它可能会给你个准确的日期，可如果它答不上来现在几点的话你就别生气了。


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