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,
Species homogeneity calories. 95% of world consumption of protein derives from a few domesticated species, i.e. poultry, cattle and pigs. There are about 1,000 commercial fish species, but in aquaculture fewer than 10 species dominate global production. Human food production therefore rests on the tips of pyramids of biodiversity, leaving the majority of species not utilised and not domesticated. Species naturally migrate and expand their ranges, utilising new habitats and resources, e.g. the cattle egret. These natural invasions, an incursion in the absence of anthropogenic influences, occur "when an intervening barrier is removed, or through the development of biotic or abiotic transportation