【英语时差8，16】深处睡眠2

 In October of 2000, biologists on a research boat off the coast of Chile happened upon what seemed to be a group of sleeping whales.   The sperm¹ whales were completely still and hanging vertically² in the water with their noses up toward the surface, and tails disappearing down into the depths. The researchers had switched off the boat's engines to record the whales' sounds, but ended up drifting silently through the whale pod.

Although the boat passed within a foot of several whales, they didn't seem to notice or respond. But when the boat accidentally brushed against the side of one whale, it suddenly awoke and swam away, rousing its neighbors.

The biologists decided³ to investigate further. They tracked the behavior of fifty-nine more sperm whales across the world. They found that sperm whales in the wild switch off completely for short periods of time, having "cat naps" while performing slow rhythmic⁴ dives.

Biologists had long thought that whales and other air-breathing marine⁵ mammals survived without any sleep at all. But studies of captive dolphins and small whales later revealed that they did sleep, but only with one side of the brain at a time.

Essentially⁶ one half of their brain shuts off while the other half stays alert, with one eye open. This kind of "uni-hemispheric" sleep allows the animals to swim, breathe, avoid predators⁷ and stay in contact with neighbors while still catching⁸ "forty winks⁹."Although more research is needed to know for sure, sperm whales seem to have evolved a different strategy for sleeping at sea -- sleeping with their whole brain more like terrestrial mammals, rather than sleeping with half a brain and one eye open.

1 sperm   

n.精子，精液

参考例句：

• Only one sperm fertilises an egg.只有一个精子使卵子受精。
• In human reproduction,one female egg is usually fertilized by one sperm.在人体生殖过程中，一个精子使一个卵子受精。

2 vertically   

adv.垂直地

参考例句：

• Line the pages for the graph both horizontally and vertically.在这几页上同时画上横线和竖线，以便制作图表。
• The human brain is divided vertically down the middle into two hemispheres.人脑从中央垂直地分为两半球。

3 decided   

adj.决定了的，坚决的；明显的，明确的

参考例句：

• This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
• There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。

4 rhythmic   

adj.有节奏的，有韵律的

参考例句：

• Her breathing became more rhythmic.她的呼吸变得更有规律了。
• Good breathing is slow,rhythmic and deep.健康的呼吸方式缓慢深沉而有节奏。

5 marine   

adj.海的；海生的；航海的；海事的；n.水兵

参考例句：

• Marine creatures are those which live in the sea. 海洋生物是生存在海里的生物。
• When the war broke out,he volunteered for the Marine Corps.战争爆发时，他自愿参加了海军陆战队。

6 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。

7 predators   

n.食肉动物( predator的名词复数 )；奴役他人者（尤指在财务或性关系方面）

参考例句：

• birds and their earthbound predators 鸟和地面上捕食它们的动物
• The eyes of predators are highly sensitive to the slightest movement. 捕食性动物的眼睛能感觉到最细小的动静。 来自《简明英汉词典》

8 catching   

adj.易传染的，有魅力的，迷人的，接住

参考例句：

• There are those who think eczema is catching.有人就是认为湿疹会传染。
• Enthusiasm is very catching.热情非常富有感染力。

9 winks   

v.使眼色( wink的第三人称单数 )；递眼色（表示友好或高兴等）；（指光）闪烁；闪亮

参考例句：

• I'll feel much better when I've had forty winks. 我打个盹就会感到好得多。
• The planes were little silver winks way out to the west. 飞机在西边老远的地方，看上去只是些很小的银色光点。 来自辞典例句