species, inbiology,classificationcomprising related organisms that share common characteristics and are capable ofinterbreeding. This biological species concept is widely used in biology and related fields of study. There are more than 20 other different species concepts, however. Some examples include the ecological species concept, which describes a species as a group of organisms framed by the resources they depend on (in other words, theirecological niche), and the genetic species concept, which considers all organisms capable of inheritingtraits from one another within a commongene pool and the amount of genetic difference betweenpopulations of that species. Like the biological species concept, the genetic species concept considers which individuals are capable of interbreeding, as well as the amount of genetic difference between populations of that species, but it may also be used to estimate when the species originated.

Taxonomy

1 of 3

2 of 3

3 of 3

Thedesignation of species originates intaxonomy, where the species is the fundamental unit of classification recognized by the International Commission of ZoologicalNomenclature. Every species is assigned a standard two-part name ofgenus and species. The genus is the generic name that includes closely related species; the graywolf, for example, is classified asCanis lupus and is a close relative of thecoyote found inNorth America and designated asCanis latrans, their systematic relation indicated by their sharing the same genus name,Canis. Similarly, genera that have sharedcharacters (or traits) are classified in the same taxonomic family; related families are placed in the same order; related orders are placed in the same class; and related classes are placed in the same phylum. This classification system is ahierarchy applied to all animals and plants, as originally set forth by the Swedish naturalistCarolus Linnaeus in the 18th century.

Organisms are grouped into species partly according to theirmorphological, or external, similarities, but more important in classifying sexually reproducing organisms is the organisms’ ability to successfully interbreed. Individuals of a single species can mate and produce viable offspring with one another but almost never with members of other species. Separate species have been known to produce hybrid offspring (for example, thehorse and thedonkey producing themule), but, because theoffspring are almost always inviable or sterile, the interbreeding is not considered successful.

Interbreeding only within the species is of great importance for evolution in that individuals of one species share a commongenepool that members of other species do not. Within a single pool there is always a certain amount ofvariation among individuals, and those whose genetic variations leave them at a disadvantage in a particularenvironment tend to be eliminated in favour of those with advantageous variations. This process ofnatural selection results in the gene pool’s evolving in such a way that the advantageous variations become the norm. Because genetic variations originate in individuals of a species and because those individuals pass on their variations only within the species, then it is at the species level that evolution takes place. Theevolution of one species into others is calledspeciation.