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.