The question of whether the Old and New Worlds constituted a whole or were distinct cosmographical entities was already antiquated by the end of the sixteenth century. The notion of multiple worlds propounded by Plato, Aristotle, and other writers of classical antiquity had been rejected as heretical by the Fathers of the Church. Throughout the Middle Ages there were differences of opinion as to the exact distribution of land to water on the globe, but there was unanimity among Christian writers on the unity of the habitable world, in keeping with biblical teaching that God had given mankind all the earth to inhabit. The discovery of America and the subsequent realization that it was a previously unknown, distinct, and inhabited part of the world gave rise to doubts about its nature and that of its peoples. But by the end of the sixteenth century it was clear to Christian Europe that the American Indians were human beings, descendants of Adam and Eve like themselves, and that mankind's domain was not restricted to Europe, Africa, and Asia, as previously thought. The explanations of how people had come to inhabit America were varied, but Acosta's conjecture that the indigenes must have migrated across an as yet undiscovered connection between Asia and North America is indicative of the acceptance that the idea of the unity of the New World with the rest of the world had gained among European thinkers.