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第1段
1 .<-NARRATOR:->Listen to part of a lecture in a biology class.
旁白：请听一段生物学课的节选片段。
第2段
1 .<-FEMALE PROFESSOR:->So, to review... who remembers how animals are classified, in terms of body temperature? Mike?
教授：我们先复习一下，谁还记得我们是怎么通过体温来划分动物的种类的？Mike？
第3段
1 .<-MALE STUDENT:->[hesitant] Um, endotherms and ectotherms?
学生：嗯，恒温动物和变温动物？
第4段
1 .<-FEMALE PROFESSOR:->Right. All animals are considered either endotherms or ectotherms.
教授：对的！所有的动物都可以被划分成恒温的和变温的。
第5段
1 ."Therm"...that means "heat."
“小卡”...这意味着“热”。
2 .And the main thing that distinguishes endotherms from ectotherms is the source of body heat.
还有，区分恒温动物和变温动物的主要依据之一就是体温的来源。
3 .So an endotherm- "endo" meaning "internal"-an endotherm's body heat mainly comes from inside its body.
所以一个恒温动物，恒温的意思是内部产热的，一个恒温动物的体温主要是来自身体内部。
4 .It can generate its own heat internally, with its metabolism.
它可以通过自己的新陈代谢产热。
5 .And an ectotherm- "ecto" meaning "external"- an ectotherm gets its body heat mainly from outside its own body.
而一个变温动物，变温意味着体温来自于身体外部，一个变温动物从身体之外获得热量。
6 .Meaning, from its environment. Mostly from the sun's radiation.
也就是从环境里获得，大多数是从太阳辐射获得的。
第6段
1 .So we've got endotherms- mammals and birds are the classes that fall under this category-and ectotherms-that's pretty much everything else... including reptiles, amphibians, insects...
我们再来看看恒温动物。哺乳动物和鸟类是恒温动物类别下的两种生物。变温动物就是另一类了，包括爬虫类，两栖动物类，还有昆虫......
第7段
1 .Now, body temperature is important.
所以体温很重要。
2 .And if an animal's environment gets very hot or very cold, something needs to happen in order for the animal to maintain its body temperature within its normal range.
如果动物所处的环境变得太热或者太冷，动物为了保持自己的体温在正常范围内，需要采取一些措施。
3 .In endotherms, this is mostly physiological-the body changes its rate of heat production.
在恒温动物这边，这些措施都是生理性的，它们的身体会改变产热的速率。
4 .OK, well... humans are endotherms.
好的，那么，人类就是恒温动物。
5 .What does your body automatically do when it gets really cold?
当你觉得冷的时候，你的身体会自动做什么呢？
第8段
1 .<-MALE STUDENT:->Shiver?
学生：颤抖？
第9段
1 .<-FEMALE PROFESSOR:->Right. Shivering-in fact, any muscle movement-increases metabolism, the process that produces heat and keeps your body temperature up when your surroundings get cold.
教授：对的，颤抖。实际上，任何肌肉的动作都会增加新陈代谢，新陈代谢这个过程可以产热，在周围环境变冷的时候帮助你保持体温稳定。
2 .And then there's what's known as brown fat. Like other kinds of fat, it stores triglyceride.
有一种叫做褐色脂肪的东西，就像其他的脂肪一样，储存着三碘甲状腺氨酸。
3 .But brown fat is unique because it chemically produces lots of heat even without muscle movement.
但是褐色脂肪很独特，因为它可以不需要肌肉运动也产生大量的热。
4 .That's especially beneficial for small mammals in colder climates.
这就对于寒冷环境里的小哺乳动物很有用。
第10段
1 .And when an animal gets too hot... well, have you ever seen a dog cooling off by taking short, quick breaths?
那么当一个动物很热的时候，你们见到过一只狗通过短促的呼吸来散热吗？
2 .And humans... we sweat, of course... perspire, which also gets rid of body heat.
对于我们人类，当然就是出汗了，出汗可以帮助我们散热。
3 .These are automatic physiological responses too.
这也是自动的、生理上的反应。
4 .Yes, Allie?
怎么了，Allie?
第11段
1 .<-FEMALE STUDENT:->[checking comprehension] So in endotherms, it's not really about behavior... about doing things.
学生：所以，在恒温动物身上，调节体温这件事不仅仅是关于行为的，是关于做什么事情的。
第12段
1 .<-FEMALE PROFESSOR:->Well... a human, you know, might put on a winter coat, or jump in a swimming pool.
教授：一个人类，你知道，可能会穿上冬天的大衣或者跳进游泳池的水里。
2 .Or, elephants... Elephants might splash themselves with cold water when it's warm out.
或者一头大象，可以在热爆了的时候拿凉水撒自己身上。
3 .But, for the most part, no... it's not what we endotherms do that keeps our temperatures within range.
但是对于自然界的大多数动物，这个不是一个普遍的解决办法。
4 .Unlike ectotherms.
变温动物用来把体温维持在正常范围内的手段和我们不同。
第13段
1 .<-FEMALE STUDENT:->Well, what about ectotherms? Like... frogs, they must have metabolism too...
学生：关于变温动物呢？，比如说...青蛙，它们也必须有新陈代谢。
第14段
1 .<-FEMALE PROFESSOR:->Sure they do. It's just that metabolism in ectotherms is so much lower.
教授：那是自然。只是变温动物的新陈代谢速率太低了。
2 .I mean, the metabolic rate of an endotherm-say a mouse- is at least six or seven times that of an ectotherm of a similar size, like a frog or a lizard.
我的意思是，一个恒温动物的新陈代谢速率，比如说一只老鼠的，至少是相同体型的恒温动物像青蛙或蜥蜴的六七倍。
3 .An ectotherm doesn't generate nearly as much heat internally, so its body temperature will tend to equalize with the temperature of its surroundings.
一只变温动物在内部不会产生同样多的热量，所以它们的体温一般是和环境温度持平的。
4 .And that's where behavior comes in.
这就到了动物习性发挥作用的时候了。
第15段
1 .Imagine a lizard, OK? Living in the desert. Now, a desert gets very cold at night and very hot during the day.
想象一只蜥蜴，住在沙漠里。沙漠在夜间变得很冷，在白天变得很热。
2 .So what's the lizard do to maintain its body temperature?
所以蜥蜴要怎么来维持体温呢？
3 .Well, on a cold morning, it can warm itself by going to a sunny spot and lying in the sun.
在寒冷的早晨，蜥蜴可以通过去有阳光的地方晒太阳来温暖自己。
4 .And later, if it gets too hot, it can seek out a cool place in the shade.
晒了一会儿之后，如果它觉得热了，它可以找一个树荫下的阴凉地呆着。
5 .It's by means of such behavior that an ectotherm like this lizard regulates its temperature.
通过这种行为，像这种蜥蜴一样的变温动物可以做到调节自己的体温。
第16段
1 .But you put that same lizard in a temperature-controlled chamber... and gradually drop the temperature, say, twenty degrees... and here, of course, the lizard can't go off to lie in the sun...
但是如果你把同样一只蜥蜴放在一只可控温箱子里，逐渐降温的时候，假设降个20度，当然了， 蜥蜴不能在阳光下躺着...
2 .So, what happens?
所以会发生什么呢？
第17段
1 .<-MALE STUDENT:->Well, the lizard's body temperature drops too.
学生：蜥蜴的体温也会下降。
第18段
1 .<-FEMALE PROFESSOR:->Right. And this really slows down its metabolism- which depends on temperature.
教授：对的。这就降低了它的新陈代谢速率，新陈代谢速率是基于温度的。
2 .Even that twenty-degree drop in body temperature, though... the lizard can survive that, no problem, and come out just fine when it warms up again.
即使降低了20度的气温，蜥蜴也可以活下去，当气温慢慢暖和过来时，蜥蜴还是活的很好的。
3 .Ectotherms can do that.
变温动物可以做到这一点。
第19段
1 .<-MALE STUDENT:->But an ectotherm probably wouldn't survive in a place where the temperatures got too low, right?
学生：但是一个变温动物不大可能在气温非常低的地方生存下来，对吗？
第20段
1 .<-FEMALE PROFESSOR:->[lightly affırming] Ever heard of a frog being chased by a polar bear?
教授：没听说过一只青蛙被北极熊追吧？
第21段
1 .<-MALE STUDENT:->[chuckle, understanding]No.
学生：没有。
第22段
1 .<-FEMALE PROFESSOR:->Well, there you are.
教授：这就对了。
2 .Now, a mouse in the same situation, in the same temperature chamber... it's just the opposite of the lizard.
假设现在是一只老鼠在相同的境地下，在相同的可控温箱子里，它和蜥蜴的情况相反。
3 .When the temperature goes down, the mouse's metabolism goes up.
当气温下降的时候，老鼠的新陈代谢变快了。
4 .Like any endotherm, it starts producing more heat to keep its body temperature stable.
就像是任何的恒温动物一样，它开始产更多的热量，保证体温不下降。
5 .Same as it would do outside in a field.
就像是老鼠在自然环境中所做的一样。