A species is defined as a group of individuals that, in nature, are able to mate and produce viable, fertile offspring.
Speciation is an event in which a single species may branch to form two or more new species.
Allopatric speciation occurs when a single species becomes geographically separated; each group evolves new and distinctive traits.
Sympatric speciation occurs when two individual populations diverge from an ancestral species without being separated geographically.
Reproductive isolation, through mechanical, behavioral, and physiological barriers, is an important component of speciation.