Bos is the genus of wild and domestic cattle. Bos can be divided into four subgenera: Bos, Bibos, Novibos, and Poephagus, but these divisions are controversial. The genus has five extant species. However, this may rise to seven if the domesticated varieties are counted as separate species, and nine if the closely related genus Bison is also included. Modern species of cattle are believed to have originated from the extinct aurochs.