taxonomic group of organisms composed of individuals of the same genus that can reproduce among themselves and have similar offspring.
In biology, a species (abbreviated sp., with the plural form species abbreviated spp.) is the basic unit of biological classification and a taxonomic rank. A species is often defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. While this definition is often adequate, looked at more closely it is often problematic. For example, in a species complex, the boundaries between closely related species become unclear or disappear altogether. Other ways of defining species include similarity of DNA, morphology, or ecological niche. The presence of locally adaptive traits may further subdivide species into infraspecific taxa such as subspecies.
Species are grouped into genera (singular: genus) by taxonomists, genera are grouped into families, families into larger groups. Taxonomists use scientific hypotheses that species in the same genus have the same ancestors. The hypotheses are first based on observed similarity of physical attributes and behaviour, and where available, the DNA sequences of individuals and of species.
All species are given a two-part name, a "binomial". The first part of a binomial is the genus to which the species belongs. The second part is called the specific name (zoology) or the specific epithet (in botany, also sometimes in zoology). For example, Boa constrictor is one of four species of the Boa genus.
A usable definition of "species" and reliable methods of identifying particular species are important for stating and testing biological theories and for measuring biodiversity, though other taxonomic levels such as families can form the basis of broad-scale studies. Extinct species known only from fossils are generally difficult to assign precise taxonomic rankings, which is why higher taxonomic levels such as families are often used for fossil-based studies.