There has never been a reference, in the either series or by any producers, that indicates that the ancients evolved on Earth. They apparently lived on Earth for a time, but left after 'seeding' the planet with life that would evolve into humans. The series seems to indicate that the ancients were a galactic civilization that had colonies all over the Milky Way Galaxy. Then a plague struck them, and their population was decimated. The remaining ancients set out to repopulate their kind by 'seeding' worlds that could support life. Earth was the last of these worlds in the Milky Way galaxy that was 'seeded' before the ancients left for the Pegasus galaxy to continue their work. 