今天小编为广大
Listen to part of a lecture in a biology class.
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 work 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 great philosopher Aristotle is generally considered the first person to systematicallycategorize 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 thought 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. 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 the 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 microorganisms that were incredibly small. I’m talking about bacteria. And we could see that they didn’t have what we call a nucleus. So they got their own kingdom, a kingdom of very tiny things without nucleoli. So then we had several 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 microorganisms that didn’t fit anywhere.So biologist gave them their own kingdom. And this fifth kingdom was sort of anything that doesn’t fit in the first four kingdom, which upset some people.
And then there was a 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 to see 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. They live in very strange places, in polar ice or in a boiling water of hot springs or in water so salty (that) other organisms couldn’t live there. Extremophiles tend to have a different chemistry from other bacteria, a chemistry that in some case is actually more related to plants and animals than to previously known bacteria. So what to do with this strange bacteria?
Well, one thing we’ve done is creating 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.
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