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As an example, the classification levels for the domestic dog are shown in [link] . The group at each level is called a taxon    (plural: taxa). In other words, for the dog, Carnivora is the taxon at the order level, Canidae is the taxon at the family level, and so forth. Organisms also have a common name that people typically use, such as domestic dog, or wolf. Each taxon name is capitalized except for species, and the genus and species names are italicized. Scientists refer to an organism by its genus and species names together, commonly called a scientific name, or Latin name. This two-name system is called binomial nomenclature    . The scientific name of the wolf is therefore Canis lupus . Recent study of the DNA of domestic dogs and wolves suggest that the domestic dog is a subspecies of the wolf, not its own species, thus it is given an extra name to indicate its subspecies status, Canis lupus familiaris .

[link] also shows how taxonomic levels move toward specificity. Notice how within the domain we find the dog grouped with the widest diversity of organisms. These include plants and other organisms not pictured, such as fungi and protists. At each sublevel, the organisms become more similar because they are more closely related. Before Darwin’s theory of evolution was developed, naturalists sometimes classified organisms using arbitrary similarities, but since the theory of evolution was proposed in the 19 th century, biologists work to make the classification system reflect evolutionary relationships. This means that all of the members of a taxon should have a common ancestor and be more closely related to each other than to members of other taxa.

Recent genetic analysis and other advancements have found that some earlier taxonomic classifications do not reflect actual evolutionary relationships, and therefore, changes and updates must be made as new discoveries take place. One dramatic and recent example was the breaking apart of prokaryotic species, which until the 1970s were all classified as bacteria. Their division into Archaea and Bacteria came about after the recognition that their large genetic differences warranted their separation into two of three fundamental branches of life.

Art connection

Illustration shows the taxonomic groups shared by various species. All the organisms shown, plants, insects, fish, rabbits, cats, foxes, jackals, wolves and dogs, are in the domain Eukarya. Of these, insects, fish, rabbits, cats, foxes, jackals, wolves and dogs are in the kingdom Animalia. Within the kingdom Animalia, fish, rabbits, cats foxes, jackals, wolves and dogs are in the phylum Chordata. Rabbits, cats, foxes, jackals, wolves, and dogs are in the class Mammalia. Cats, foxes, jackals, wolves and dogs are in the order Carnivora. Foxes, jackals, wolves and dogs are in the family Canidae. Jackals, wolves and dogs are in the Genus Canis. Wolves and dogs have the species name Canis Lupus. Dogs have the subspecies name Canis lupus familiaris.
At each sublevel in the taxonomic classification system, organisms become more similar. Dogs and wolves are the same species because they can breed and produce viable offspring, but they are different enough to be classified as different subspecies. (credit “plant”: modification of work by "berduchwal"/Flickr; credit “insect”: modification of work by Jon Sullivan; credit “fish”: modification of work by Christian Mehlführer; credit “rabbit”: modification of work by Aidan Wojtas; credit “cat”: modification of work by Jonathan Lidbeck; credit “fox”: modification of work by Kevin Bacher, NPS; credit “jackal”: modification of work by Thomas A. Hermann, NBII, USGS; credit “wolf” modification of work by Robert Dewar; credit “dog”: modification of work by "digital_image_fan"/Flickr)

In what levels are cats and dogs considered to be part of the same group?

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Source:  OpenStax, Concepts of biology for slcc biol 1010. OpenStax CNX. Aug 13, 2013 Download for free at https://legacy.cnx.org/content/col11555/1.1
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