History of the domestic sheep exact line of descent between domestic sheep and their wild ancestors is unclear. The most common hypothesis states that "Ovis aries" is descended from the Asiatic ("O. orientalis") species of mouflon. A few breeds of sheep, such as the Castlemilk Moorit from Scotland, were formed through crossbreeding with wild European mouflon. The urial ("O. vignei") was once thought to have been a forebear of domestic sheep, as they occasionally interbreed with mouflon in the Iranian part of their range. However, the urial, argali ("O. ammon"), and snow sheep ("O. nivicola") have a different number of chromosomes than other Ovis species,
Purebred an acceptance of natural selection to weed out undesirable traits, created many ancient domesticated breeds or types now known as landraces. Many times, domesticated species live in or near areas which also still hold naturally evolved, region-specific wild ancestor species and subspecies. In some cases, a domesticated species of plant or animal may become feral, living wild. Other times, a wild species will come into an area inhabited by a domesticated species. Some of these situations lead to the creation of hybridized plants or animals, a cross between the native species and a domesticated one. This type of crossbreeding, termed