Bos (from Latin bōs: cow, ox, bull) is the genus of wild and domestic cattle. Bos is often divided into four subgenera: Bos, Bibos, Novibos, and Poephagus, but including these last three divisions within the genus Bos without including Bison in the genus is believed to be polyphyletic by many workers on the classification of the genus since the 1980s. The genus as traditionally defined has five extant species but this rises to eight when the domesticated varieties are counted as separate species, and 10 when the closely related genus Bison is also included. Most but not all modern breeds of domesticated cattle are believed to have originated from the extinct aurochs. Many ancient breeds are thought to have originated from other species. Zebus and taurine cattle are thought to descend from ancient Indian and Middle Eastern aurochs, respectively.