Evidence suggests that the genus Cygnus evolved in Europe or western Eurasia during the Miocene, spreading all over the Northern Hemisphere until the Pliocene. When the southern species branched off is not known. The mute swan apparently is closest to the Southern Hemisphere Cygnus; its habits of carrying the neck curved (not straight) and the wings fluffed (not flush) as well as its bill color and knob indicate that its closest living relative is the black swan. Given the biogeography and appearance of the subgenus Olor it seems likely that these are of a more recent origin, as evidence shows by their modern ranges (which were mostly uninhabitable during the last ice age) and great similarity between the taxa.
