Species

There are many different groupings beginning with species and ending with kingdom. Thus, you and all other human beings belong to the species Homo sapiens. In addition, you and all other animals belong to the group Kingdom Animalia.

A system for classifying organisms has developed gradually over the past 300 years. It was not until the late seventeenth century that an Englishman, John Ray (1627-1705), developed a clear concept of species. To him a species consisted of offspring of similar parents. The concept has been modified since the time of Ray. We now look upon a species as a group of individuals that can breed with one another. At the same time individuals of one species do not usually breed with individuals of other species in nature. We must emphasize the “in nature” because many species can crossbreed under artificial conditions even though they do not under natural conditions.

It was left to the eighteenth-century Swedish biologist Carolus Linnaeus to establish the rules that are used for naming organisms. Linnaeus gave every species that he knew a name of two words. Hence his system is known as binomial nomenclature. The first word of the species name is the name of the genus to which it belongs. The second name is the so-called descriptive or trivial name. Both words are Latin or Latinized Greek (later systematists have not always used classical words in naming organisms). The genus and descriptive name together constitute the species name of the organism concerned. For example, the large group of cats was given the generic (genus) name Felis. A particular group of cats was given the trivial name Leo. These words together, Felis Leo, are used for the lion, one species of cat. The scientific name of the common house cat is Felis domesticus; of the tiger, Felis tigris. All are cats, but each is a different species of cat.

Linnaeus listed 4,236 species of animals in his Systems Naturae of 1758. The total today is almost a million known species. We are sure there are just as many, and possibly more, that have not been named.

To ensure that no two groups of animals get the same specific name, a very elaborate system has been set up for classifying animals. There is even an international court of biologists that will decide any disputed cases of naming that occasionally occur.