Biologists do not think of species simply as a long alphabetical list.

Since Linnaeus, the father of modern taxonomy, species have been arranged in a taxonomic hierarchy:

• Species are grouped in genera. The gray wolf species Canis lupus and the golden jackal Canis aureus , for example, are grouped in the genus Canis .

• Genera are grouped into families; the genus containing dogs and wolves combines with several other genera, such as the fox genus Vulpes , to make up the family Canidae.

• Several families combine to make up an Order (Carnivora, in this example).

• Orders make a Class (Mammalia).

• Classes make a Phylum (Chordata).

• Phyla make up one of the five Kingdoms (Animalia).

Each species, therefore, is a member of a genus, a family, an order, and so on. The problem is how to group species into higher categories. This is an important theoretical issue with conflicting taxonomic schools of classification.

Figure: shown here is a fairly complete classification of the gray wolf Canis lupus. This way of classifying living things was invented in the eighteenth century by the Swedish biologist Carolus Linnaeus.