为什么树懒没有被自然淘汰

树懒是疯狂动物城中最出彩的形象,它已经在地球上存在了四千万年。既然树懒行动那么迟缓,为什么还没有被自然淘汰。

We humans are obsessed with speed. Busyness is a badge of honor, and convenience trumps quality in our quest for quick. Our addiction to the express life is choking us and the planet. We idolize animals like the cheetah, the "Ferrari of the animal kingdom," capable of doing naught to 60 in three seconds flat. Well, so what? So what? The sloth, on the other hand, can reach a leisurely 17 feet a minute with the wind behind it.

But being fast is costly. The cheetah is speedy, but at the expense of strength. They can't risk getting in a fight, so they lose one in nine kills to tougher predators like hyenas. No wonder they're laughing. The sloth, on the other hand, has taken a more stealthy approach to dinner. They survive by capturing and consuming static leaves.

But you see, leaves don't want to be eaten any more than antelope do, so they're loaded full of toxins and very hard to digest. So in order to consume them, the sloth has also had to become an athlete - a digesting athlete.

The sloth's secret weapon is a four-chambered stomach and plenty of time. They have the slowest digestion rate of any mammal. And it can take up to a month to process a single leaf, which gives their liver plenty of time to process those toxins. So, sloths aren't lazy. No, they're busy. Digesting. Yeah, really busy.

Hard at work, that sloth, very hard at work. And of course, leaves have little calorific value, so sloths have evolved to spend as little energy as possible. They do about 10 percent of the work of a similar-sized mammal and survive on as little as 100 calories a day, thanks to some ingenious adaptations. The Bradypus, three-toed sloths, they've got more neck bones than any other mammal, even a giraffe. Which means they can turn their head through 270 degrees and graze all around them, without having to actually bother with the effort of moving their body.

标签 : 演讲生物树懒

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