 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 , making a direct relationship implausible , and phylogenetic studies show no evidence of urial ancestry . Further studies comparing European and Asian breeds of sheep showed significant genetic differences between the two . Two explanations for this phenomenon have been posited . The first explanation is that a currently unknown species or subspecies of wild sheep that contributed to the formation of domestic sheep . The second explanation is that this variation is the result of multiple waves of capture from wild mouflon , similar to the known development of other livestock . 
