The sixth great extinction episode has been precipitated by human activities, and it appears to be happening very quickly. Most of the world's extinctions have been true extinctions, when a species completely dies out and leaves no descendants. A few have been pseudoextinctions, when the original or ancestral species has become transformed by evolution into another species. All species living today, including ourselves, evolved from another species. True extinctions and pseudoextinctions are both a type of global extinction.
Global extinction is the complete elimination of a particular species everywhere in the world.
Many endemic species have a limited georgraphic range, such as a single island. No matter how small that area is, their disappearance from it is a global extinction if the species is not found anywhere else. A local extinction is the extirpation of a species from a portion of its geographic range . Local extinctions mean the loss of the genetic diversity represented by that population and the removal of that species' contribution to the local ecosystem. Because members of the species still exist in other locations, local extinctions can be reversed if the original causes are addressed, and the species can recolonize or can be reintroduced into the area.