Thousands of worlds in the Galaxy, or at least our region of the Galaxy, have been seeded over the past few millennia, mostly by the Galen and the Elders, with humans abducted from various parts of Earth.
Even before they created the Velorians, the Galen had been planting human colonies on a number of worlds, sometimes "futzing" the settlers in whole or in part with superhuman powers. These First Generation worlds, as they later came to be called, were quite varied in their ethnic makeup. Abductees settled on Olympia, for example, came from ancient Greece, while those on Tanzrobi originated in East Africa. Like later seeded worlds, they were open to trade with the Scalantrans. While the Galen themselves were the original Seeders, they later assigned that task to their Surrogates, inhabitants of the First Generation worlds. Second Generations worlds, like First Generation worlds, were settled by abductees from Earth, with behind-the-scenes cooperation by the Galen and the Scalantrans, but without any genetic engineering of the settlers. Again, the ethnic roots of the abductees were varied; on Andros, for example, they were Greeks from the Byzantine Empire; on Nova Iberia, medieval Spaniards.
Third Generation worlds are those settled by emigrants from Second Generation worlds that have achieved interstellar spaceflight capability or can hire transport. The best known but least typical example is Kelsor 7, where the first settlers were from Belside -- a world destroyed by the Arions despite its neutrality in the Enlightenment-Arion Empire conflict. Beyond that there are some really odd worlds like Rostran, settled by fugitives from the Empire who went to great lengths to conceal their origin. The Empire itself established a few seeded worlds, notably Novo Recife (with abductees from northeastern Brazil) and Westfold (a combination of British and West Africans).
Although the Elders were outpaced by the Galen in the number of their seeded worlds, and likewise their rebellious Diaboli surrogates, their influence is still felt in the Diaboli presence on worlds originally seeded by the Galen or their surrogates -- notably Reigel 5. Though worlds primarily or totally populated by Diaboli are small in number compared to other worlds they do exist and the basis for many a tall tale among explorers. Among the Elder seeded worlds in our stories are New Atlantis and Velvet.