The adjacent mainland population split into the subtropical and partially leucistic Elliot's pheasant (S. ellioti) and the tropical Mrs. Hume's pheasant only in the Middle Pleistocene, around half a million years ago.
The geographical separation of the mainland population led to the divergence of two distinct species, the Elliot's pheasant and the Mrs. Hume's pheasant, around half a million years ago during the Middle Pleistocene.