Examples from late glacial and early and mid-Holocene archaeological sites in southern South America provide information about the human dimensions of past climate changes. Particularly in semiarid areas with marginal food and water resources (e.g., central and northern Chile), changes from humid to arid conditions coincided with major changes in human occupational and cultural patterns. The end of the first period of human occupation in central Chile (Paleo-Indian period between ca. 11,400 and 9700 ¹⁴C B.P.) coincided with rapidly increasing aridity, when trees were replaced by shrubs and herbs, the Pleistocene paleolakes disappeared, and, finally, the Pleistocene megafauna became extinct. The Paleo-Indian hunters occupied ecological refuges around lakes, where the resources were concentrated in an environment under general water stress. A similar process was observed 2000 years later in the Atacama Desert and Altiplano of northern Chile, when the first period of human occupation (Early Archaic, between 10,800 and 8000 ¹⁴C B.P.) came to an abrupt end, synchronously with the rapid desiccation of early Holocene paleolakes and the disappearance of abundant water, vegetation, and animal resources. The subsequent extremely arid mid-Holocene environments resulted in a general hiatus of human occupation in the Atacama basin, whereas widespread resettlement (Tilocalar phase with agriculture and pastoralism, 3200 14C B.P.) coincided again with a rise of the paleolake levels to modern levels.