Talk:Bellwether/@comment-27997791-20160327121322/@comment-6032121-20160418183423

Ignoring Superwritermaniac's Doylist answer, here's a possible Watsonian (in-universe) one: it's conceivable that as sheeps becam anthropomorphic, fair wool became a beauty criteria among them. Since sheeps with white abundant wool began to mostly mate with similarly "beautiful" sheeps, and in time the "white abundant wool" criteria came to be present in all of the sheep population.