English for

phylum
, 
class
, 
order
, 
family
, 
genus
, and 
species
. 
As an example, the classification levels for the domestic dog are shown in Figure 70. The 
group at each level is called a 
taxon
(plural: taxa). In other words, for the dog, The taxon at the order 
level is Carnivora, the taxon at the family level is Canidae, and so on. Additionally, each organism 
has a common name that is commonly used by people, such as domestic dog or wolf. Except for 
species, all taxon names are capitalized; 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
. 
Figure 70 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.
Some earlier taxonomic classifications have been found to not accurately reflect evolutionary 
relationships by recent genetic analysis and other advancements; as a result, changes and updates 

---

115 
must be made as new discoveries are made. 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. 
Figure 70.
Organisms are more similar between each sublevel of the taxonomic classification system. 
Because they can breed and produce offspring, dogs and wolves are the same species, but they differ enough 
to be categorized 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) 

---

116 
At what levels are dogs and cats regarded as belonging to the same group?
46