Classification

Classification is a method of organizing plants and animals into categories based on their appearance and the natural relationships between them. Also called scientific classification, it is science's way of identifying and grouping living things. The classification of organisms is a science called taxonomy, or systematics.

The first person to attempt any type of systematic grouping of organisms was the Greek philosopher and scientist, Aristotle (384–322 b.c.) Until his work, most people simply divided all plants and animals into two basic categories: useful and harmful. As a careful observer of the natural world, Aristotle began arranging organisms according to their physical similarities. Since there were only about one thousand organisms known in his time, he classified animals according to those with red blood (vertebrates or having a backbone) and those with no red blood (invertebrates or no backbone). He also classified plants by size and by whether they were herbs, shrubs, or trees. Despite many mistakes and an over-simplified idea, Aristotle's impulse to classify and to categorize organisms was a necessary attempt to make sense of the diversity of life in order to study it better.

THE BENEFITS OF CLASSIFICATION

In the life sciences, the need to organize is very important and extremely useful. Classification helps biologists keep track of living things and to study their differences and similarities. It also shows biologists how living things are related to one another through evolution (the process by which living things change over generations). Classifying also saves time and effort. There are many possible ways to classify life: appearance, behavior, evolutionary history, or life development from fertilization to adulthood. The modern classification system is considered a natural system since it represents genuine relationships between organisms. In this natural system, the more closely organisms are related to each other, the more features they have in common. This system is also hierarchical, meaning that its categories are grouped according to size in a series of successively larger ranks.

CAROLUS LINNAEUS DEVELOPS BINOMIAL SYSTEM OF NOMENCLATURE

The system used today is based on the work of one individual, the Swedish physician and naturalist, Carolus Linnaeus (1707–1778). In his day, it sometimes took as many as ten words to name a particular organism and no standard system existed upon which everyone agreed. Linnaeus traveled throughout Europe compiling lists of the animals and plants he encountered, and in 1735 published a book which tried to make some sense of this great diversity. By 1758 he had completed his huge encyclopedia called System of Nature which described and classified all known organisms by their structure and placed them in one of the seven levels of his hierarchical system. Linnaeus also developed the binomial system of nomenclature, which gave a distinctive two-word name to each species. This system is still followed with the first part being the genus name, and the second part serving as its species name. For example, both the bobcat and the house cat belong to the genus Felis, but the bobcat's species is rufa (Felis rufa) while that of the domestic cat is Felis domestica. The second name is usually descriptive of the particular animal. Among the rules for this system, the two-part name is always used. The species part

CAROLUS LINNAEUS

Swedish botanist (a person specializing in the study of plants) Carolus Linnaeus (1707–1778) devised the first orderly system of classifying living things. He also introduced the binomial system of nomenclature (a two-part naming system) that is still in use today. He is called the father of taxonomy (the science of classifying living things) because his system was able to impose a much-needed order on the study of life itself.

Being able to identify a plant or animal, to tell how it is different from others, and to know how it fits into the entire natural world is something that people simply take for granted in today's world. However, there was a time in the history of the life sciences when naturalists (people specializing in the study of plants and animals in their natural surroundings) used as many as ten words to give something a specific, descriptive name, and even with all that effort, there was no guarantee that it would be used by others or that someone who spoke a different language would know what the name meant. This describes what the life sciences were like before the great classifier, Carolus Linnaeus, gave science a practical way of naming organisms that was based on clear and simple standards upon which everyone could agree.

Linnaeus was born Carl von Linne in South Rashult, Sweden. (Linnaeus is the Latin version of his name.) His father was a clergyman, and the very young Linnaeus was so interested in gardens and growing things that the locals called him "the little botanist." When his father sent him to medical school, Linnaeus was able to combine school with botanical exploring trips that only made him more interested in plants. When he became lecturer in botany at Uppsala University at the age of twenty-three, he was able to go on longer, more extensive excursions to Lapland in 1732. After traveling 4,600 miles (7,407 kilometers) throughout northern Scandinavia discovering new plant species and observing animal life, he began to formulate the details of an idea that he had first expressed in a paper some years before. By 1735, Linnaeus had published his System of Nature in which he proposed the idea of classifying plants in the simplest and most clear way that one could. To Linnaeus, that meant a system based on the specimen's external characteristics that were most obvious to the eye. His system would therefore be based on observable characteristics such as structure, or anatomy, or on the details of the way a thing reproduced itself. In his landmark book, he showed how this could be done. First, he created a hierarchical system (in a hierarchy, things are arranged in a certain order) in which the categories above included all of the ones below it. Thus, he created a system in which living things were grouped according to their similarities, with each succeeding level possessing a larger number of shared traits. He named these levels class, order, genus, and species. He also popularized what is called binomial nomenclature, which gave every living thing a Latin name consisting of its genus and species. For example, this would distinguish two very different species, like a lion and a cougar, simply by their Latin names. The lion belongs to Panthera leo and the cougar belongs to Felis concolor. Thus each organism has a generic name, telling which group it belongs to, and a specific name for itself.

Although classification might not seem to be as important a subject to science as some others, it proved absolutely essential to such a broad and diverse field as the life sciences. In fact, only after Linnaeus's system was accepted and regularly used did biology and botany begin to make real progress. The advantages of his system are numerous. For example, his use of Latin allows scientists to communicate worldwide about organisms without having to understand different languages. Since each type of organism can fit into his system in a logical and orderly way, it can be expanded indefinitely. It is also a great advantage that the levels of his hierarchical system provide a framework for seeing and understanding the relationships among different organisms or groups of organisms. His system is also flexible and adaptable. Since it was first introduced, the number of levels have grown, with phylum being inserted above class and kingdom being placed at the very top. Finally, although his system was introduced before the theory of evolution (the process by which gradual genetic change occurs over time to a group of living things), it always has been able to accommodate any new discoveries or modifications which that theory has made. Linnaeus was said to have been an almost obsessive classifier, yet he was a person who turned his passion for an idea into a truly great scientific contribution.

is never used alone. The generic name always begins with a capital letter but the species name is always lowercase. Both names are written in italics or are underlined. Latin is used to avoid any confusion in translating different languages. Altogether, this system allows everyone in the world to use the same name for the same organism and to immediately understand each other.

CLASSIFICATION GROUPS

Seven major groups or categories make up the scientific classification system. The groups or categories themselves are called taxons (from taxonomy, which is the science of naming and classifying organisms). These groups range in order of size, so from the largest or most general to the smallest and most specific, they are: kingdom, phylum, class, order family, genus, and species. Each kingdom is divided into smaller and smaller groups until each type of organism is placed in a unique category. One way of remembering this general-to-specific scheme is the rhyme or formula, "King Philip Came Over From Great Spain."

Kingdom is the largest unit and is composed of five separate kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. Beginning with Linnaeus and for a long time afterward, there were only two kingdoms, Plantae and Animalia. But with the improvement of the microscope and the discovery of microorganisms, the number was expanded to five. From kingdom on down to species, organisms are grouped together with increasing similarity. Besides these seven major groups, biologists are able to use various subgroups to deal with minor differences among organisms when those differences are not large enough to form a new group. For example, species may be divided up into subspecies.

Classifying a dog and a wolf offers a good example of how two animals would fit into these seven categories. Both are in the kingdom Animalia since they cannot make their own food. Next, they would both be in the phylum Chordata since they have a notochord (like a vertebrae or backbone). Both also belong to the class Mammalia since they have fur and feed milk to their young. Both are members of the order carnivora since they are meat eaters. They also both belong to the family canidae because they cannot retract their claws and they hunt and stalk their prey. However, while both are similar enough to be in the same genus, canis, they are different enough to be in separate species. Therefore, the wolf's scientific name is Canis lupus and the dog's is Canis familiaris.

A classification system provides a method that best represents genuine relationships between organisms. It is a natural system that is based on overall resemblances and which reflects how each organism is related from an evolutionary standpoint.

[See alsoClass; Family; Genus; Kingdom; Order; Phylum; Species ]