Lesson
BIOLOGICAL CLASSIFICATION
Over 200 years ago Carolus Linnaeus established the first system for classifying species of plants and animals. He developed a categorical way of naming species and a formal hierarchy for establishing larger categories consisting of groups of species.
Linnaeus labeled each species with a Latin double-name. The species name for the brown trout, for example, is Salmo trutta. The first word (with initial letter always capitalized) designates the genus (pl. genera). Every species belongs to a genus that may also include other species. We can see from its name that the trout belongs to the genus Salmo. So does the closely related species Salmo Salar (Atlantic Salmon).. The second word (which always begins with a small letter) designates the species. A third word, indicating a sub-species may also be used, e.g. Salmo trutta caspius - the Caspian Sea Brown Trout.
The principle of gathering categories into more specific groups is a fundamental aspect of Linnaean classification. The basic building block of classification is the species. A genus is a group of related species. Genera are grouped in families, families into orders, and so on.
Linnaean Nomenclature
The standard nomenclature for species is attributed to Carolus LINNAEUS (1707-1778).
The Linnaean method for classification of living things groups organisms together based on presumed similarities in structures. The assumption is that the more structural similarities the organisms in question share, the closer they must be in terms of evolutionary distance. The larger, more inclusive divisions of the Linnaean system (beyond species) are created by including together closely related groups of the immediately lower divisions. The result is a hierarchy of classification with the highest category consisting of all living things. The lowest category consists of a single species. Each of the categories above species can have numerous subcategories.
Linnaeus arranged classification categories as a series of nested groups. His sequence from broadest to smallest category is: Kingdom, Phylum, Class, Order, Family, Genus, and Species. To remember this order you need only to remember the following:
King (Kingdom) Philip (Phylum) Came (Class) Over (Order) For (Family) Good (Genus) Soup (Species)
Related groups of organisms were determined by the many shared characteristics; especially those having to do with maintenance, feeding, and digestion.
The basic unit in the Linnaean classification of living forms is the species. Each species is given a unique, two part Latin name; the name is always underlined or italicized in print. The name consists of the genus, which is a group of species more closely related to one another than to any other group, followed by the specific name, which identifies a particular species within a genus. The first letter of the genus is capitalized, while the specific name is in lowercase, as in Felis domesticus (House Cat) and Salmo salar (Atlantic Salmon). The binomial species name replaced the much longer descriptions of earlier classifications.
Linnaeus named groups of organisms for the defining characters that he noticed. For example, the name Mammalia to the group of animals that possess mammary glands and secrete milk to feed their young. He also recognized that monkeys are most nearly like humans, and as a logical consequence of strictly biological classification, humans would be grouped not only in the class Mammalia but in the same representative group as the monkeys and apes.
Today, the decision of which species to group in a single genus is based on evolutionary relationships - that is, a genus should be a group of species all descended from a single ancestral species. Many biologists also consider overall anatomical resemblance in addition to strict evolutionary relatedness in making their classifications.
Black Bear
Kingdom: Animals
Phylum: Chordates
Subphylum: Vertebrates
Class: Mammals
Order: Carnivores
Family: Ursidae
Genus: Ursus
Species: Americanus
DEFINITION OF A SPECIES:
A Species is a group of populations that are capable of successfully breeding and producing fertile offspring. Animals of one species, in other words, cannot mate successfully with animals of another species (or if they do mate and have offspring the offspring are sterile) — and it is this fact of "reproductive isolation" that establishes them as members of a separate species
Binomial Nomenclature
In biology, binomial nomenclature is a standard convention used for naming species. As the word 'binomial' suggests, the scientific name of a species is formed by the combination of two terms: the genus name and the species epithet or descriptor. The first term (generic name) is always capitalized, while the specific epithet (trivial "name") is not; both are to be typeset in italics, e.g. Homo sapiens. The genus name can be abbreviated to its initial letter, but never omitted, (as H. sapiens) when repeated or when several species from the same genus are being listed or discussed in the same paper or report. In rare cases this abbreviation form has spread to more general use—for example the bacterium, Escherichia coli, is often referred to as just E. coli.
The importance of a standard method of naming living organisms becomes evident when you consider the multitude of names that are used for a single species as you move from locality to locality. Depending on where you live the term Green Pepper, Bell Pepper, Sweet Pepper or Mango are all used to describe the fruit Capsicum frutescens. In Placentia Bay the term "Grepe" is often used to refer to the Bald Eagle. It is necessary that a common system be in place so as to avoid confusion.
For a more detailed examination of the role that Linnaeus played in the development of Taxonomy as a discipline consult the following web links. You will find many others through a general search using the search engine of your choice.
THE WORKS OF CARL LINNAEUS (1707-1778)
Activity
Using a word processor (Word, Wordperfect) prepare a 250 word essay on the contribution of Linnaeus to the classification of living things. Use Internet and/or library sources for information. Submit your paper to your instructor through email.
Test Yourself
There is no self test for this lesson.