It was long accepted that the three southeastern species—which all have bright white wing-bands of a type not found in any close relative and differ little except in the amount and concentration of eumelanins in their plumage—form a clade.

[1] Reeves's pheasant (S. reevesi) is probably derived from ancestral stock that remained in the general area of the genus' origin, adapting to the local conditions and evolving numerous peculiar male apomorphies, such as the lack of facial wattles (which judging from their presence in Phasianus were present in the ancestral Syrmaticus too), the golden body plumage, the conspicuous head stripes or the immensely long tail.

Around the Miocene-Pliocene boundary, roughly 5.4 mya or so, the ancestors of the copper pheasant (S. soemmerringii) separated from the mainland lineage and probably settled Japan at that time or soon thereafter.

[1] Perhaps the white wing-band was already present by that time; as the copper pheasant has a highly apomorphic coloration with reduced sexual dimorphism, it may well have lost such a trait after it settled Japan.

However that may be, the minor plumage differences of the wing-banded species suggest that their last common ancestor looked almost identical to the living Mrs. Hume's pheasant (S. humiae).

This divergence was probably in some way connected to climate changes at the Günz-Mindel interglacial to Mindel[2] boundary, when mountains in the region became dry and at times icebound.