Evolution Theory托福聽力原文翻譯及問題答案

Evolution Theory托福聽力原文翻譯及問題答案

一、Evolution Theory托福聽力原文：

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托福聽力中文翻譯：

旁白在生物課上聽講座的一部分。

女教授可能早在之前的生物學課程中，你就知道蛇是由蜥蜴進化而來的。和第一批蛇不是有毒的。然后出現(xiàn)了更高級的蛇，毒蛇？好吧，毒蛇是那些分泌有毒物質的蛇，或者像毒蛇家族的蛇或者眼鏡蛇一樣的毒液。。。還有無毒的蛇，像蟒蛇和蟒蛇。。。

然而，另一類蛇，colubrids，并不完全屬于這兩類。你可能也了解到了這一點，雖然它們通常被歸類為毒蛇，但實際上它們通常是無毒的。它們被歸類為毒蛇，因為它們比其他無毒蛇更像毒蛇，更具高級特征?，F(xiàn)在如果我告訴你，我剛才說的大部分話都是錯的，那會怎么樣？好除了關于蛇從蜥蜴進化而來的那一部分以外，其他的都是。瞧，最近的一項研究對蛇進化的基本理論提出了挑戰(zhàn)，該研究揭示了爬行動物進化關系的全新理解——你知道，哪些爬行動物是哪些祖先的后代？

研究人員研究了各種脊椎動物毒液基因中的蛋白質。嗯？蛇毒是蛋白質的混合物。。。有些有毒，有些不有毒。通過分析蛋白質的遺傳物質DNA，研究人員可以專注于有毒基因，并利用它們追蹤蛇毒的進化。。。從這一點來看，蛇的進化。傳統(tǒng)上，為了理解進化關系，我們觀察了動物的各種容易觀察到的身體特征——骨骼、大腦大小。。。然后根據(jù)異同對其進行分類。這種方法的問題是，看似相似的特征實際上可能以完全不同的方式發(fā)展。例如，一些毒液是化學物質，而另一些是細菌，所以它們顯然是沿著不同的途徑發(fā)展的，可能不像我們想象的那樣密切相關。。。

現(xiàn)在，并不是每個人都會同意這一點；但基于DNA的分類似乎更加可靠&nbsp；好的，回到研究上來&nbsp；研究人員發(fā)現(xiàn)毒液在蛇存在之前就已經(jīng)進化了？大約一億年前?，F(xiàn)在，一些有毒蜥蜴被納入了這項研究，研究人員在它們的毒液中發(fā)現(xiàn)了一些與蛇的毒液中相同的DNA&nbsp；

這表明所有蛇的共同祖先實際上是一種有毒的蜥蜴。這意味著，實際上，根據(jù)這項研究，無論如何，就蛇的祖先而言，沒有無毒蛇這回事！甚至連colubrids都沒有。我們一直在分類的毒蛇與其他毒蛇的區(qū)別并不是因為它們沒有毒液，而是因為它們沒有有效的方法將毒液傳遞給獵物。

在大多數(shù)毒蛇（如毒蛇和眼鏡蛇）中，毒液用于捕捉和固定獵物，但在短尾蛇中，毒液只有在獵物進入蛇口后才會滴到獵物身上。所以，對于colubrids來說，毒液必須有其他用途。。?？赡芘c消化獵物有關。

隨著不同毒蛇家族的進化，牙齒向前移動，變得越來越大？毒液變得更強了。因此，像眼鏡蛇和毒蛇這樣明顯的毒蛇的進化，與其說是毒液本身的進化，不如說是一個高效的輸送系統(tǒng)的進化。那么，如果沒有真正無毒的蛇，那么所謂的無毒蛇是否像蟒蛇和蟒蛇一樣，在進化過程中的某個階段是有毒的呢？現(xiàn)在還不清楚。巨蟒已經(jīng)進化成通過擠壓來殺死獵物。但也許它們曾經(jīng)是有毒的然后。。。在某個時候。。。它們的毒液產生裝置不再需要了，所以逐漸消失了。有一種蛇，棕色樹蛇，根據(jù)其獵物的不同，它同時使用收縮和毒液。。。那么好吧。。。有可能。。。所以我們有了蛇的新概念？進化論和一個新的DNA數(shù)據(jù)庫所有這些關于蛇毒基因組成的信息。而且，我們從中了解到的情況使研究人員相信，毒液蛋白可能在醫(yī)學研究領域有一些令人興奮的應用。

你看，毒液就像某些藥物一樣改變生物功能。由蛇毒制成的藥物的最大好處是，它們只針對特定的細胞，所以可能會產生較少的副作用?，F(xiàn)在，作為人類毒品的基礎，這聽起來牽強的毒液？到目前為止，只有一種蛋白質作為潛在藥物作為研究的靶點？但誰知道呢，也許有一天。。。

三、Evolution Theory托福聽力問題：

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托福聽力答案：

A1:正確答案：B

A2:正確答案：C

A3:正確答案：D

A4:正確答案：B

A5:正確答案：A

A6:正確答案：D

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