species-

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring.

two different species

dog
external image complete-dog-food.bmp

cat
external image cat2.jpg


Species that are believed to have the same ancestors are grouped together, and this group is called a genus. A species can only belong to one genus that it was grouped into. The belief is best checked by a similarity of their DNA, but for practical reasons, other similar properties are used.