Aristotle's model of the geocentric ("earth-centered") universe and his categorization of all the earth's objects provided a hierarchical vision of the universe.
This model was adopted in the middle ages and used by Christians to explain man's relationship with God, laying out the pecking order of all entities, from rocks, to humans, to celestial beings.
Called "The Great Chain of Being" (scala naturae), it persisted through the Renaissance into the Age of Enlightenment. The astronomical perspective of the Earth as the center of the universe finally gave way to the heliocentric universe (sun-centered) when scientists, following the work of those like Copernicus, found Aristotle's views no long tenable in light of more current research. This shift from geo-to heliocentricity has been described by some, like Thomas Kuhn, as a mighty philosophical change. Despite the realization that the cosmos was not laid out hierarchically, it has been well accepted that there are indeed earthly ones. Herein lies one of the issues that we are studying in this course: diversity and difference.