The distribution of species around the globe is not a random process but an outcome resulting from several evolutionary mechanisms as well as past and current environmental limitations. As a result, since the mid-19th century, biologists have identified several main regions, called biogeographic realms, that depict these large ensembles of species around the world. These biogeographic realms represent one of the most fundamental descriptions of biodiversity on Earth and are commonly used in various fields of biology.
