The early human occupation of South America was favored by an unusual set of geological and climatic factors which channeled population movements in a north to south direction. Because of the exposure of the continental shelf and the ameliorating effect of the oceanic climate, the area between 30[degree] and 50[degree] south latitude may have featured favorable environmental zones for human habitation. Therefore, it is no accident that the earliest dated cultures are known from the southern end of the continent. This factor is a logical result of the climatic and geographic factors influencing human migrations in South America, influences which may have resulted in this north to south migration requiring only a brief span of time. The exact chronology of this migration is inadequately known. However, comparison of the geographical location of the early sites with the presumed location of the late Pleistocene ice masses suggests that a majority of these sites are of post-glacial age. The presence of any sites of glacial age is yet to be demonstrated.