Once upon a time, at the end of the Pleistocene (between 13,000 and 11,700 years ago), cold conditions in the North Atlantic pushed the Intertropical Convergence Zone southward over the central Andes. The South American Summer Monsoon, which brings precipitation to the Andean highlands, was strengthened. Rainfall increased, lake levels rose, and biotic productivity was boosted, just as the first people were setting foot on the last major continent where no human had gone before. Archaeological sites between 2500 and 4500 meters above sea level in Colombia, Ecuador, Peru, Bolivia, Chile, and Argentina attest to extensive human presence in the mountains by 12,000 years ago, soon after, or perhaps at the same time as, the earliest sites in adjacent lowlands.

How and why did people choose to engage with the high Andes so soon after initial arrival to South America? The answer may lie in deep-time cultural knowledge of mountain systems, their challenges, resources, and opportunities. In this talk I will examine some probable reasons why people chose to explore and reside in the Andes, drawing on geographic, ecological, and archaeological lines of evidence. Early transfers of obsidian from many geologic sources in the Andes provide a temporal baseline for thorough knowledge of the topographically complex highlands by early South Americans. How this knowledge was acquired so quickly currently confounds explanation, although I will suggest some possibilities.