Evolution Theory托福听力原文翻译及问题答案

Evolution Theory托福听力原文翻译及问题答案

一、Evolution Theory托福听力原文：

NARRATOR Listen to part of a lecture in a biology class.

FEMALE PROFESSOR Probably back in some previous biology course,you learned that snakes evolved from lizards.And?that the first snakes weren't venomous.And then along came more advanced snakes,the venomous snakes?OK,venomous snakes are the ones that secrete poisonous substances,or venom—like the snakes of the viper family,or of cobras...Then there's nonvenomous snakes,like constrictors and pythons...

Another family of snakes,the colubrids,don't really fit neatly into either category,though.Colubrids—and you probably learned this,too—although they're often classified with venomous snakes,they're actually generally nonvenomous.They're classified with venomous snakes because they resemble them,their advanced features,more than the other nonvenomous snakes.Now...what if I told you that there's a good chance that most everything I just said is wrong?Well...everything except the part about snakes evolving from lizards.See,the basic theory about snake evolution has been challenged by a recent study that revealed a whole new understanding of evolutionary relationships for reptiles—y'know,which reptiles descended from which ancestors?

The researchers studied the proteins in the venom genes of various species of colubrids.Um?snake venom is a mixture of proteins...some toxic—poisonous—and some not.By analyzing the DNA—the genetic material—of the proteins,the researchers could focus on the toxic genes,and use them to trace the evolution of snake venom...and,from this,the evolution of snakes.Traditionally,to understand evolutionary relationships,we looked at various easily observed physical characteristics of animals—their skeleton,the size of their brain...and then classified them based on similarities and differences.The problem with this method is that characteristics that appear similar may actually have developed in quite different ways.For example,some venoms are chemical based,and others are bacteria based,so they clearly had to have developed along different routes and may not be as closely related as we thought...

Now—and not everyone will agree about this, but classification based on DNA seems to be much more reliable. OK,back to the research. The researchers found that venom evolved before snakes even existed?about a hundred million years before.Now,a couple of venomous lizards were included in this study,and the researchers found some of the same DNA in their venom as in the snake's venom. 

This suggested that the common ancestor of ALL snakes was actually a venomous lizard.Which means that,actually,according to this research,anyway,in terms of the snake's ancestry,there's no such thing as a nonvenomous snake!Not even colubrids.What separates colubrids from other snakes we've been classifying as venomous is not the lack of venom,but the lack of an effective way to deliver the venom into its prey.

In most venomous snakes,like vipers and cobras,the venom is used to catch and immobilize the prey—but in colubrids,venom drips onto the prey only after the prey is in the snake's mouth.So,for colubrids,the venom must serve some other purpose...maybe linked to digesting prey.

As the different families of venomous snakes evolved,the teeth moved forward,becoming larger?and the venom became stronger.So the evolution of the obvious venomous snakes—like cobras and vipers—is about the evolution of an efficient delivery system,not so much the evolution of the venom itself.So if there are no truly nonvenomous snakes,were the so-called nonvenomous snakes—like constrictors and pythons—were they venomous at some point in their evolution?Well—that's not clear at this point.Constrictors have evolved to kill their prey by crushing.But perhaps they once were venomous and then...at some point...their venom-producing apparatus wasn't needed anymore,so it gradually disappeared.There's one species of snake—the brown tree snake—that uses both constriction and venom,depending on its prey...so—well...it is possible...So...we have this new concept of snakes?evolution and a new DNA database—all this information on the genetic makeup of snake venom.And,what we've learned from this has led researchers to believe that venom proteins may have some exciting applications in the field of medical research.

You see,venom alters biological functions in the same way certain drugs do.And the big benefit of drugs made from snake venom would be that they'd target only certain cells—so maybe that's create fewer side effects.Now,it sounds far-fetched—venom as the basis for human drugs?so far,only one protein has been targeted for study as a potential drug?but—who knows,maybe some day...

二、Evolution Theory托福听力中文翻译：

旁白在生物课上听讲座的一部分。

女教授可能早在之前的生物学课程中，你就知道蛇是由蜥蜴进化而来的。和第一批蛇不是有毒的。然后出现了更高级的蛇，毒蛇？好吧，毒蛇是那些分泌有毒物质的蛇，或者像毒蛇家族的蛇或者眼镜蛇一样的毒液。。。还有无毒的蛇，像蟒蛇和蟒蛇。。。

然而，另一类蛇，colubrids，并不完全属于这两类。你可能也了解到了这一点，虽然它们通常被归类为毒蛇，但实际上它们通常是无毒的。它们被归类为毒蛇，因为它们比其他无毒蛇更像毒蛇，更具高级特征。现在如果我告诉你，我刚才说的大部分话都是错的，那会怎么样？好除了关于蛇从蜥蜴进化而来的那一部分以外，其他的都是。瞧，最近的一项研究对蛇进化的基本理论提出了挑战，该研究揭示了爬行动物进化关系的全新理解——你知道，哪些爬行动物是哪些祖先的后代？

研究人员研究了各种脊椎动物毒液基因中的蛋白质。嗯？蛇毒是蛋白质的混合物。。。有些有毒，有些不有毒。通过分析蛋白质的遗传物质DNA，研究人员可以专注于有毒基因，并利用它们追踪蛇毒的进化。。。从这一点来看，蛇的进化。传统上，为了理解进化关系，我们观察了动物的各种容易观察到的身体特征——骨骼、大脑大小。。。然后根据异同对其进行分类。这种方法的问题是，看似相似的特征实际上可能以完全不同的方式发展。例如，一些毒液是化学物质，而另一些是细菌，所以它们显然是沿着不同的途径发展的，可能不像我们想象的那样密切相关。。。

现在，并不是每个人都会同意这一点；但基于DNA的分类似乎更加可靠&nbsp；好的，回到研究上来&nbsp；研究人员发现毒液在蛇存在之前就已经进化了？大约一亿年前。现在，一些有毒蜥蜴被纳入了这项研究，研究人员在它们的毒液中发现了一些与蛇的毒液中相同的DNA&nbsp；

这表明所有蛇的共同祖先实际上是一种有毒的蜥蜴。这意味着，实际上，根据这项研究，无论如何，就蛇的祖先而言，没有无毒蛇这回事！甚至连colubrids都没有。我们一直在分类的毒蛇与其他毒蛇的区别并不是因为它们没有毒液，而是因为它们没有有效的方法将毒液传递给猎物。

在大多数毒蛇（如毒蛇和眼镜蛇）中，毒液用于捕捉和固定猎物，但在短尾蛇中，毒液只有在猎物进入蛇口后才会滴到猎物身上。所以，对于colubrids来说，毒液必须有其他用途。。。可能与消化猎物有关。

随着不同毒蛇家族的进化，牙齿向前移动，变得越来越大？毒液变得更强了。因此，像眼镜蛇和毒蛇这样明显的毒蛇的进化，与其说是毒液本身的进化，不如说是一个高效的输送系统的进化。那么，如果没有真正无毒的蛇，那么所谓的无毒蛇是否像蟒蛇和蟒蛇一样，在进化过程中的某个阶段是有毒的呢？现在还不清楚。巨蟒已经进化成通过挤压来杀死猎物。但也许它们曾经是有毒的然后。。。在某个时候。。。它们的毒液产生装置不再需要了，所以逐渐消失了。有一种蛇，棕色树蛇，根据其猎物的不同，它同时使用收缩和毒液。。。那么好吧。。。有可能。。。所以我们有了蛇的新概念？进化论和一个新的DNA数据库所有这些关于蛇毒基因组成的信息。而且，我们从中了解到的情况使研究人员相信，毒液蛋白可能在医学研究领域有一些令人兴奋的应用。

你看，毒液就像某些药物一样改变生物功能。由蛇毒制成的药物的最大好处是，它们只针对特定的细胞，所以可能会产生较少的副作用。现在，作为人类毒品的基础，这听起来牵强的毒液？到目前为止，只有一种蛋白质作为潜在药物作为研究的靶点？但谁知道呢，也许有一天。。。

三、Evolution Theory托福听力问题：

Q1:1.What is the lecture mainly about?

A.Methods of analyzing toxic proteins in snake venom

B.Insights about snake evolution provided by venom analysis

C.How snake venom differs from lizard venom

D.Why colubrids are considered nonvenomous snakes

Q2:2.Why does the professor review information about the classification of snakes that students probably learned in previous courses?

A.To determine whether the students have enrolled in the appropriate course

B.To stress the usefulness of the classification system for students

C.To present assumptions that have recently been challenged

D.To give an example of a method that she will explain in greater detail

Q3:3.According to the professor,what is a major weakness of the classification system that is based on animals'physical characteristics?

A.It can show the relationships only among a small number of animal species.

B.It requires technology that is not widely available.

C.It cannot account for characteristics that first appeared in the recent geologic past.

D.It cannot determine whether similar characteristics developed in similar ways.

Q4:4.According to the professor,in what way do colubrid snakes differ from other venomous snakes?

A.Colubrids did not evolve from lizards.

B.Colubrids do not use venom to catch their prey.

C.The front teeth of colubrids are much larger than those of other venomous snakes.

D.Colubrids produce a much stronger type of venom than other venomous snakes do.

Q5:5.Why does the professor mention the brown tree snake?

A.To support a hypothesis about the evolution of constrictor snakes

B.To support a hypothesis that venomous snakes evolved from constrictor snakes

C.To give an example of a snake species that was never venomous

D.To give an example of a type of snake that can change its color

Q6:6.What is the professor's attitude toward the result from medical research on snake venom proteins?

A.She is enthusiastic about the drugs that have been tested to date.

B.She is concerned about the side effects of drugs created from snake venom proteins.

C.She doubts that the DNA database will be useful in developing new drugs.

D.She thinks it is too early to tell how successful the research will be.

四、Evolution Theory托福听力答案：

A1:正确答案：B

A2:正确答案：C

A3:正确答案：D

A4:正确答案：B

A5:正确答案：A

A6:正确答案：D

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