The Clydesdale is a breed of horse that has been bred for farm work. It is taller, more muscular, and has a longer mane than that of the tarpan (the extinct wild ancestor of domestic horses). The Clydesdale traits most likely arose by . artificial selection, because changes in these traits likely occurred because of human breeding for taller stature and long falling manes on horses natural selection, because these traits were unconsciously selected by humans natural selection, because these traits must have randomly evolved in their population over time artificial selection, because these traits differ from their common ancestor