By Robert Hazen, Ph.D., George Mason University
Before looking at life in detail, it’s important to think about names, the field of taxonomy. Taxonomy is a formalized procedure for classifying and naming life forms. This is not at the forefront of science these days, yet nomenclature always plays a central role in science. This is because scientists can’t talk about objects in nature without naming them.
The Importance of Taxonomy in Science
Scientists not only have to name every kind of organism, but also they have to be able to name all the different parts of organisms. They can’t communicate in a chaotic way, where they have their own set of terms. They have to be able to communicate with other scientists.
Another reason why nomenclature is important is that sometimes you can’t recognize a new phenomenon unless you have a name for it.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
The Linnaean System
The Linnaean system is the way that scientists arrange and describe and catalog living things. It is a hierarchical classification, much like the way an address works. When you write a letter to somebody, you give an address from top to bottom. The Linnaean system works exactly the same way. You define a kingdom, a phylum, a class, an order; then a family, a genus, and a species.
For example, humans are in the kingdom of animals. We’re in the phylum of chordates, the sub-phylum of vertebrates, that is all the animals with bony backbones. We’re in the class of mammals, the order of primates, the family of hominids, the genus Homo, and the species sapiens.
The common shorthand, when dealing with this very complex nomenclature system, is to just cite the genus and species; it’s what’s called binomial nomenclature. So, for example, humans are members of Homo sapiens: Homo being the genus, sapiens being the species.
Learn more about the evolution of life.
A Matter of Species
The matter of species in taxonomy is not a simple one. It’s not always easy to tell what a species is. The simplest definition, that people have used for a long time, is that if two organisms can mate and produce fertile offspring, they’re of the same species.
That sounds simple enough, but what’s a species? How do you define it? Nature does what nature wants to do; it doesn’t conform to our definitions. Nature is much more complex, and that’s why nomenclature can be very complex. Of course, this situation gets even more complex when you look at fossils.
The fossil record is filled with objects that vary one from another in subtle ways. Are they different species? Are they the same? Could they have interbred? Who knows? You have to use taxonomy, various forms of morphology, the shape of those fossils, and make your best guess—and qualify it, because nature is what nature is.
Learn more about the competing theories about how evolution occurs.
Estimating the Number of Species
In terms of living things, all life can, in one way or another, be classified according to the Linnaean system. At present, there are about 1.8 or 1.9 million known species; but how many species are there in the world that haven’t been identified?
It’s difficult to estimate, but one way of doing it is to plot the number of known species versus time. For example, the number of birds in 1800, and 1810, and 1820, and so forth, versus time; you see a gradual increase and a leveling-off. Once you see that leveling-off, you know you’re getting close to the number of total species.
This implies that there’s been a constant looking for birds, mammals, or some other group. But some types of organisms are tremendously underrepresented, because no one’s looked for them; microbes in particular, tiny single-celled organisms, and very small, microscopic, organisms that are multicelled.
People have conducted exhaustive tests on small plots of land, just to see how many species there are; and it turns out, we may not know very much at all about life on Earth.
Common Questions about Taxonomy: How to Name and Classify the Living Things
The Linnaean system is the way that scientists arrange and describe and catalog living things. They define a kingdom, a phylum, a class, an order; then a family, a genus, and a species. Humans are in the kingdom of animals. We’re in the phylum of chordates, the sub-phylum of vertebrates, that is all the animals with bony backbones. We’re in the class of mammals, the order of primates, the family of hominids, the genus Homo, and the species sapiens.
When dealing with very complex nomenclature systems in taxonomy, a shorter naming method is used, which is called binomial nomenclature. In this type of naming, only genus and species are considered. For example, humans are members of Homo sapiens. Homo indicates the genus and sapiens indicates the species.
The simplest definition, that people have used for a long time, is that if two organisms can mate and produce fertile offspring, they’re of the same species. However, the nature and the nomenclature process are much more complex than this simple definition.
