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Narrator:Listen to part of a lecture in a biology class.
獨白:聽下面一段生物課程的講解
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.
教授:可能在之前的生物課上你們學習到蛇是由蜥蜴進化而來，而且起初的蛇是沒有毒的，后來才出現(xiàn)了更高級的蛇，也就是毒蛇。
Ok, venomous snakes are the ones that secrete poisonous substances or venom, like the snakes of the viper family or cobras.
毒蛇就是指那些分泌有毒物質或者毒液的蛇，比如蝰蛇及眼鏡蛇。
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.
還有像蟒蛇、蚺蛇這樣的無毒蛇類。還有一類蛇-黃頜蛇，并不能將其進行嚴格的分類。
Colubrids, and you probably learned this too, although they are often classified as venomous snakes, they are actually generally non-venomous.
黃頜蛇你應該也學習過，雖然通常被分到毒蛇類別中，但事實上它們大致是無毒的。
They are classified as venomous snakes because they resemble them, their advanced features more than the other non-venomous snakes.
之所以將其劃分到毒蛇類，是因為它們更像毒蛇，而且它們具備一些比其他無毒蛇類更先進的一些特點。
Now, what if I told you that there is a good chance that most everything I just said is wrong?
那么現(xiàn)在，假如我告訴你們，我剛才講的多數(shù)的理論很有可能都是錯誤的，那會是怎樣呢？
Well, everything except the part about snakes evolving from lizards.
呃，除了蛇是從蜥蜴演化而來以外，其余部分也許都是錯誤的。
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.
蛇進化的基本理論受到了最近一項研究的動搖。這項研究揭示了一個關于爬行動物進化關系全新的理解，你們知道，就是什么爬行動物由何祖先演變而來。
The researchers study the proteins in the venom genes of various species of colubrids.
研究人員研究了各種黃頜蛇的毒液基因。
Emm... snake venom is a mixture of proteins, some toxic, poisonous, and some not.
恩，蛇毒是由蛋白質構成的混合物，有的有毒，有的則沒有毒。
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.
通過對 DNA 及蛋白質中的基因物質的分析，研究人員就能專注于有毒基因并用其找出蛇毒的進化軌跡，這樣，也就找到了蛇的進化源。
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.
傳統(tǒng)意義來講,為了了解動物的進化關系, 我們要看動物各種各樣容易觀察的體型特征,它們的骨骼, 大腦的大小, 然后, 呃, 然后再根據(jù)其相同點及不同點來進行分類。
The problem with this method is that characteristics that appear similar may actually have developed in quite different ways.
這種方法的弊端就是表面上的相似特點也許實則是以不同的方式進行進化發(fā)展的。
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.
比如, 有些毒液是以化學元素為基礎的, 有些則是以細菌為基礎的, 因此很顯然它們是在以不同的路徑進行進化發(fā)展的, 也許并不如我們所想的那般關系緊密。
Now, and not everyone will agree about this. The classification based on DNA seems to be much more reliable.
而現(xiàn)在不是每個人都同意這個觀點。基于 DNA 進行分類看似是更有說服力的。
Ok, back to the research.
好，那再回到研究的話題上來。
The researchers found that venom evolved before snakes even existed, about a hundred million years before.
研究人員發(fā)現(xiàn)毒液在蛇還未存在的時候就已經進化了, 大約是在一億年前。
Now, a couple of venomous lizards were included in this study.
現(xiàn)在, 兩種毒蜥蜴也已經被囊括到研究中來。
And the researchers found some of the same DNA in their venom as in the snakes' venom.
而且研究人員在毒蜥蜴體內也發(fā)現(xiàn)了一些和毒蛇同樣的毒液。
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.
這就意味著所有蛇類的祖先都是毒蜥蜴, 也就是說, 根據(jù)這項研究, 關于蛇的祖先這個問題來講, 根本就沒有無毒蛇之說, 包括黃頜蛇。
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.
我們將黃頜蛇與其他蛇類鑒別開來是通過它們的毒液, 并不是說它沒有毒液, 而是看它是否用毒液來作為一種有效的方式進行捕獵。
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.
多數(shù)的毒蛇, 像蝰蛇及眼鏡蛇, 都是用毒液來捕捉和削弱其獵物的力量, 而黃頜蛇卻是在獵物已經進入其口中之后才注入毒液。
So for colubrids, the venom must serve some other purpose, maybe linked to digesting prey.
所以對于黃頜蛇來講,毒液一定是有其他的作用, 可能和消化獵物有關聯(lián)。
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.
至于各類別毒蛇的進化, 它們的牙齒更加向前, 變得更大, 毒液也變得越加劇烈, 所以說這些明顯是毒蛇的蛇種, 像眼鏡蛇和蝰蛇, 都是捕捉有效性的進化, 而非毒液的進化。
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?
因此, 如果說沒有真正的無毒蛇類的話, 那么像蟒蛇, 蚺蛇這類所謂的無毒蛇類難道是在進化中由有毒進化為無毒嗎?
Well, that's not clear at this point.
呃， 這點我們還不是很清楚。
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.
蟒蛇是通過纏繞擠壓來進行捕獵，也許它們曾經是有毒蛇類，而它們施放毒液的器官又在某種程度上無關緊要，所以便逐漸消失了。
There's one species of snake, the brown tree snake that uses both constriction and venom, depending on its prey.
還有一種蛇，叫做棕樹蛇，它們即靠纏繞擠壓的方式又靠毒液的方式捕獵，這取決與它們的獵物是什么。
So, well, it is possible.
所以說，這種猜測還是可能的。
So, we have these new concepts of snakes' evolution and a new DNA database, all these information on the genetic makeup of snake venom.
那么，我們就有了關于蛇類進化新的概念以及新的 DNA 數(shù)據(jù)，所有這些都是關于蛇毒基因構成的信息。
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.
我們的這項發(fā)現(xiàn)使研究人員開始相信毒蛋白質也許在醫(yī)學領域會有驚人的應用。
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.
你們看，毒液與一些特定的藥物一樣能改變生物的功能性，而從蛇毒中提取的藥物能針對特定的細胞有巨大的功效，也許就能減少一些副作用。
Now, it sounds far-fetched, venom is the basis for human drugs.
現(xiàn)在來看還很遙遠，毒素僅僅是人類藥品的基礎。
So far, only one protein has been targeted for study as a potential drug, but who knows, maybe someday.
到目前為止，只有一種蛋白質被用來作為潛在的藥品研究，但是誰知道呢，也許將來會有所成就。
