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托福TPO听力文本翻译Lecture 3 Biology

2014-04-30 16:52| 来源:环球托福

摘要: 今天,环球托福为备考托福听力的考友们带来托福TPO听力文本翻译Lecture 3 Biology (Snake Evolution) ,请看环球托福分享的托福TPO听力文本:
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经过上文托福TPO听力文本翻译Lecture1Lecture2的阅读,是否意犹未尽呢?环球托福为备考托福听力的考友们继续带来托福TPO听力文本翻译Lecture 3 Biology (Snake Evolution),帮助大家复习托福听力。
 
Lecture 3 Biology (Snake Evolution) 
 
Narrator Listen to part of a lecture in a biology class.  
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 cobras. Then there is non-venomous 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 are often classified as venomous snakes, they are actually generally non-venomous. They are classified as venomous snakes because they resemble them, their advanced features more than the other non-venomous snakes.  
 
托福TPO听力文本翻译Lecture 3 Biology
 
可能你们从先前的生物课上学到的是,蛇是从蜥蜴进化来的,最早的蛇是无毒的,但此后出现了更多的高级蛇类,即毒蛇。毒蛇是指分泌有毒物质或毒液的蛇类,例如蝮蛇族或眼镜蛇族。也有无毒蛇,比如大蟒或蟒蛇。另外一类蛇,colubrid, 却没法归入这两类之中。Colubrid这类蛇,可能你们也知道,虽然经常被归为毒蛇类,但它们实际上却是无毒蛇。它们被归为毒蛇的原因仅仅是外表相似,而其实更高级的特征更接近无毒蛇。  
 
Now, what if I told you that there is 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 relationship for reptiles, you know, which reptiles descended from which ancestors. The researchers study the proteins in the venom genes of various species of colubrids. Emm... 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.  
 
托福TPO听力文本翻译Lecture 3 Biology
 
现在,要是我告诉你们,我刚讲的绝大多数内容都是错的,又会如何?嗯,我指的是除了蛇是由蜥蜴进化来的那部分之外的所有内容。来看下,关于蛇进化的基础理论受到了最近一项研究的挑战,该研究昭示了对爬行动物进化关系的一种全新的理解,即哪一种爬行动物是哪个祖先的后代。科研人员对很多种colubrid毒液基因中的蛋白质进行了研究——嗯,蛇毒液包含很多种蛋白质,有的有毒、有的无毒。通过分析DNA(什么,你不知道DNA是啥?就是蛋白质中的遗传物质),研究人员能够抓出其中的毒性基因,用它们来跟踪蛇毒液的进化,进而追踪蛇本身的进化。  
 
Traditionally, to understanding evolutionary relationships, we looked at various easily observed physical characteristics of animals, their skeleton, the size of their brain, and... And then classify 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 venom 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.  
 
托福TPO听力文本翻译Lecture 3 Biology
 
以传统方式,要了解进化关系,我们就得审视动物身体结构上那些容易观察到的特点,像骨骼、脑容量等,然后根据彼此之间的相似和差异来分类。这一方法的问题在于,看上去相似的特点有可能是由相当不同的方式发展而来的。例如,一些毒液是化学性毒性,而另一些是细菌性毒性,因此它们必然是经由不同的途径发展而来,并且不会像我们以为的那样有很近的联系。  
 
Now, and not everyone will agree about this. The 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 snakes’ venom. This suggested that the common ancestor of all snakes was actually venomous lizard, which means that actually, according to this research, anyway, in terms of the snakes’ ancestry, there is no such thing as a non-venomous snake, not even colubrids. What separates colubrids from other snakes we have been classifying is 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 becoming 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.
 
托福TPO听力文本翻译Lecture 3 Biology
 
现在,并非所有人都会赞成这一点。基于DNA的分类看上去似乎要更可靠些。好,回到研究上来。科研人员发现毒液在蛇类存在之前就开始进化了,时间大概是一亿年以前。目前,若干有毒蜥蜴都已经被包括进这项研究之中。研究人员已经发现,蜥蜴的毒液中含有一些跟蛇类毒液相同的DNA。这昭示了所有蛇类共同的祖先就是毒蜥蜴,也通过该研究表明,就蛇类的祖先而言,没有所谓的无毒蛇,即使colubrid也是如此。Colubrid跟那些被归类为毒蛇的相比,其差别并非是本身无毒,而是缺乏将毒液注入猎物的有效手段。大多数毒蛇,像蝮蛇和眼镜蛇,毒液的作用是抓获并麻痹猎物;而对于colubrid,毒液只有当猎物已经进嘴了,才会滴在猎物身上。因此,colubrid的毒液必然有其它的某些作用,也许跟消化猎物有关。在不同种类的毒蛇进化过程中,其牙齿渐渐向前生长,变得更大,毒液也变得更厉害,因此那些明显的毒蛇——眼镜蛇、蝮蛇等——的进化,实际上就是更有效的注毒系统的进化,而不是毒液本身的进化。  
 
So, if there are no truly non-venomous snakes, were the so-called non-venomous 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 apparatus4 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.  
 
托福TPO听力文本翻译Lecture 3 Biology
 
因此,如果并不存在真正的无毒蛇,那么那些所谓的无毒蛇,像大蟒或蟒蛇,是否会在进化过程中的某个时期是有毒的呢?嗯,在这一点上还不是很清楚。大蟒使用将猎物“绞碎”的方式进行捕猎,但也许它们也曾经有毒过,然而在某个时候,它们不再需要毒液分泌器官,然后这器官就渐渐消失了。有一种蛇,褐色树蛇,既会用缠绞又会用毒液,视不同的猎物而定。所以,嗯,这是有可能的。  
 
So, we have these new concepts of snakes’ evolution and a new DNA database, all these information on the genetic makeup of snake venom. And what we have 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 snakes venom would be that they target only certain cells, so maybe that’ll create fewer side effects. Now, it sounds far-fetched5, venom is the basis for human drugs. So far, only one protein has been targeted for study as a potential drug, but who knows, maybe someday.  
 
托福TPO听力文本翻译Lecture 3 Biology
 
好,我们现在有了关于蛇进化的新的概念和一个新的DNA数据库,即所有的关于蛇毒液的遗传补充信息。我们从中学到的东西让研究人员相信毒液蛋白质可能在医学研究领域有一些让人激动人心的应用。你看,毒液改变生物功能的方式跟某些特定药物是一样的,由蛇的毒液制成的药物的一大好处就是它可以只作用于某些特定的细胞,这样也许就能减少副作用。当然,目前这听上去有点离奇,毒液居然是人类药物的来源。到目前为止,其中只有一种蛋白质被选定为可能的制药对象,但今后,谁说得准呢,说不定哪一天就成为现实了。
 
以上即是本次环球托福为大家带来的托福TPO听力文本翻译Lecture 3 Biology (Snake Evolution) ,环球托福预祝大家托福考试顺利!我们知道托福听力TPO文章是练习托福听力的关键。以后,环球托福会继续发布一些TPO听力文本翻译,供大家学习!