Cattle were originally identified by Carl Linnaeus as three separate species. These were Bos taurus, the European or "taurine" cattle (including similar types from Africa and Asia); Bos indicus, the zebu; and the extinct Bos primigenius, the aurochs. The aurochs is ancestral to both zebu and taurine cattle. Recently these three have increasingly been grouped as one species, with Bos primigenius taurus, Bos primigenius indicus and Bos primigenius primigenius as the subspecies.
Complicating the matter is the ability of cattle to interbreed with other closely related species. Hybrid individuals and even breeds exist, not only between taurine cattle and zebu (including the sanga cattle breeds, Bos taurus africanus) but also between one or both of these and some other members of the genus Bos: yak (called a dzo or "yattle"), banteng and gaur. Hybrids can also occur between taurine cattle and either species of bison (for example, the beefalo breed), which some authors consider to be in the genus Bos as well. The hybrid origin of some types may not be obvious – for example, genetic testing of the Dwarf Lulu breed, the only humpless taurine-type cattle in Nepal, found them to be a mix of taurine cattle, zebu and yak. Cattle cannot successfully be hybridized with more distantly related bovines such as water buffalo or African buffalo.
The aurochs originally ranged throughout Europe, North Africa, and much of Asia. In historical times its range became restricted to Europe, and the last known individual died in Masovia, Poland, in about 1627. Breeders have attempted to recreate cattle of similar appearance to aurochs by crossing traditional types of domesticated cattle, creating the Heck cattle breed.