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.
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.
通过对 DNA 及蛋白质中的基因物质的分析，研究人员就能专注于有毒基因并用其找出蛇毒的进化轨迹，这样，也就找到了蛇的进化源。
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.
传统意义来讲,为了了解动物的进化关系, 我们要看动物各种各样容易观察的体型特征,它们的骨骼, 大脑的大小, 然后, 呃, 然后再根据其相同点及不同点来进行分类。
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.
比如, 有些毒液是以化学元素为基础的, 有些则是以细菌为基础的, 因此很显然它们是在以不同的路径进行进化发展的, 也许并不如我们所想的那般关系紧密。
Now, and not everyone will agree about this. The classification based on DNA seems to be much more reliable.
而现在不是每个人都同意这个观点。基于 DNA 进行分类看似是更有说服力的。
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.
这就意味着所有蛇类的祖先都是毒蜥蜴, 也就是说, 根据这项研究, 关于蛇的祖先这个问题来讲, 根本就没有无毒蛇之说, 包括黄颌蛇。
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.
我们将黄颌蛇与其他蛇类鉴别开来是通过它们的毒液, 并不是说它没有毒液, 而是看它是否用毒液来作为一种有效的方式进行捕猎。
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.
多数的毒蛇, 像蝰蛇及眼镜蛇, 都是用毒液来捕捉和削弱其猎物的力量, 而黄颌蛇却是在猎物已经进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.
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.
至于各类别毒蛇的进化, 它们的牙齿更加向前, 变得更大, 毒液也变得越加剧烈, 所以说这些明显是毒蛇的蛇种, 像眼镜蛇和蝰蛇, 都是捕捉有效性的进化, 而非毒液的进化。
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?
因此, 如果说没有真正的无毒蛇类的话, 那么像蟒蛇, 蚺蛇这类所谓的无毒蛇类难道是在进化中由有毒进化为无毒吗?
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 these new concepts of snakes' evolution and a new DNA database, all these information on the genetic makeup of snake venom.
那么，我们就有了关于蛇类进化新的概念以及新的 DNA 数据，所有这些都是关于蛇毒基因构成的信息。
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.
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-fetched, 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.