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NARRATOR:Listen to part of a lecture in a biology class.FEMALE PROFESSOR:Ok. There are two major types of classifiers in the world: people we call "lumpers" and people we call "splitters."A lumper is someone who tries to put as many things as possible in one category.Splitters like to look for the differences and put things in as many different categories as possible.Both lumpers and splitters work in the business of defining biological classifications.
The Greek philosopher Aristotle is generally considered the first person to systematically categorize things.He divided all living things into two groups—they were either animal or vegetable.And these categories are what biologists came to call kingdoms.So if it ran around it was an animal... a member of the animal kingdom, and if it stood still and grew in the soil it was a plant... a member of the plant kingdom.This system—organizing all life into these two kingdoms—worked very well for quite a while, even into the age of the microscope.
With the invention of the microscope in the late 1500s, we discovered the first microorganisms; we saw that some wiggled and moved around and others were green and just sat there.So the ones that moved like animals were classified as animals, and the more plant-like ones as plants.Oh, before I go on, I must mention Carolus Linnaeus...kah-ROE-lus Li-NAY-us
A hundred years or so after the invention of the microscope, Carolus Linnaeus devised a simple and practical system for classifying living things, according to the ranks of categorization still in use today— class, order, family, and so on.And by far the best aspect of Linnaeus' system is the general use of binomial nomenclature—having just two names to describe any living organism.This replaced the use of long descriptive names, as well as common names which vary from place to place and language to language.Binomial nomenclature gives every species a unique and stable two-word name, agreed upon by biologists worldwide.
But not everything about this system remained unchanged.Take, for example, the mushroom... a fungus. It grew up from the ground and looked like a plant.So it was classified as a plant.But using the microscope, we discovered that a fungus contains these microscopic thread-like cells that run all over the place and so it's actually not that plant-like.So in this case, the splitters eventually won, and got a third kingdom just for the fungus.
And as microscopes improved, we discovered some micro-organisms that were incredibly small.I'm talking about bacteria.And we could see that they didn't have what we'd call a nucleus, so they got their own kingdom—a kingdom of very tiny things without nuclei.So then we had separate kingdoms for plants, and for animals. And the different kinds of fungus, like mushrooms. And for these tiny bacteria.But we also had some other micro-organisms that didn't fit anywhere.So biologists gave them their own kingdom, and this fifth kingdom was sort of an anything-that-doesn't-fit-in-the-first-four kingdom, which upset some people.
And then there was the question of viruses.Viruses have some characteristics of life, but don't reproduce on their own or use energy.So we still don't know what to do with them.The lumpers want to keep viruses in the current system.Some of the splitters say to give them a separate kingdom; and the extreme splitters say that viruses have nothing at all to do with living things and "keep them out of my department."
Recent research, though, has moved us in yet another direction.Nowadays when we want to determine the characteristics of something, we look at its biochemistry and its genetic material.And what we've discovered is that some bacteria are not like the others.Many of these are called "extremophiles" EXTREME uh files.They live in very strange places—in polar ice, or in the boiling water of hot springs; or in water so salty other organisms couldn't live there.Extremophiles tend to have a different chemistry from other bacteria, a chemistry that, in some cases, is actually more related to plants and animals than to previously known bacteria.
So, what to do with these strange bacteria?Well, one thing we've done is create a new set of categories—the domains—overarching the different kingdoms.Biologists now recognize three domains.But even as we talk about these new domains, well...come back in a few years and it might all be different.
旁白：请听一个生物课上的讲座片段。教授：在世界上有两种分类派系，一种被我们称为统合派，一种被我们称为分割派。统合派的人会尽力把各种事物都放在一个分类下。分割派的人则会着眼于事物之间的区别，把它们尽力划分出最多的类别。统合派和分割派都致力于确定生物的分类。
伟大的哲学家亚里士多德普遍被认为是系统地为生物分类的第一人。他将所有生物划分为两大类，它们不是动物就是植物。这些分类被生物学家称为“界”。所以如果一个生物可以四处跑来跑去，它就是动物，是动物界中的一员，如果它不动，长在土壤里，就是植物，属于植物界中的一员。这个分类系统把所有的生命体都划分进了这两个界，它在很长一段时间都起着很好的分类作用，甚至在显微镜的时代。
随着十六世纪末期显微镜的发明，我们发现了第一批微生物，我们看到一些会扭动且可以自由移动，另一部分是绿色且不动的。所以那一些像动物一样可以移动的就被归类成了动物，更像植物的生物就被归类成了植物。哦，在我继续讲下去之前我必须先提一下卡罗勒斯•林奈。
大约在显微镜发明的一百年后，卡罗勒斯•林奈发明出了一个给生物分类的简单而实用的系统，这个系统是根据等级编目法来的——涉及的等级有纲，目，科等等，这些等级现在还在使用。至今为止，林奈的分类系统最好的一点是，他普遍使用了双名法，也就是只使用两个名字来命名任何一种生物。这就代替了长长的描述性名字，也代替了地域之间、语言之间各不相同的对物种的俗称。双名法给每一个物种都起了一个独特稳定的双词名字，并且被全世界的生物学家所认同。
但是这个系统也并不是没有变化的。我们拿蘑菇，一种真菌的例子来说，蘑菇从地里长出来，看起来像是植物。它以前也是被分到植物那一类的。但是使用显微镜，我们发现真菌身上有这些微小的线状细胞，它们在真菌体内不断活动，所以它实际上也不那么像植物。所以在这种情况下，分割派取得了最终的胜利，他们为真菌分出了第三个界。
随着显微镜的逐渐改进，我们发现一些微生物是非常之小的。我在说细菌。我们可以看到它们并没有我们称之为的细胞核，所以它们要独立出自己的界，一个没有核仁的非常小的生物的界。所以植物、动物、不同种类的真菌比如蘑菇、还有这些小小的细菌各自属于自己的界。但是我们还有一些别的微生物，它们不属于任何一个界。所以生物学家给它们单独分出了自己的界，几乎所有不适用于前四个界的生物都被归到了第五个界，这使得一些人沮丧。
还有一个问题就是病毒。病毒有一些生命体的特征，但是它们并不能自体繁殖，也不会消耗能量。所以我们仍然不知道该怎么给病毒分类。统合派想把病毒也包含进目前的分类系统里。一些分割派说应该给病毒单独分出一个新的界，极端分割派认为病毒和生物并没有什么干系，应该将其剔出分类中。
然而近期的研究指向了另一个方向。现在，当我们想去决定一些生物的特征的时候，我们会看它的生物化学特征及基因组成。我们发现的是，一些细菌和其他细菌并不一样。很多这种细菌被称为极端微生物。它们居住在非常奇怪的地方，比如在极地冰层里，热温泉沸腾的泉水里或者在其他细菌存活不下去的高盐度的水里。极端微生物和别的细菌结构有差异，它们含有一种某些情况下与动植物联系更加密切的化学物质，这种物质与我们先前知道的细菌的联系倒是没有那么密切。
所以我们该怎么划分这种奇怪的细菌呢？我们已经做了的一件事是创造一系列新的分类，就是生物领域，它横跨不同的界。生物学家现在定下了三个生物领域。但是甚至就是在我们正在谈论这些新的生物领域的时候，几年之后，它们也许会变得和现在很不一样。
如果对题目有疑问，欢迎来提出你的问题，热心的小伙伴会帮你解答。