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Human subsistence systems in the Pampa and Patagonia regions evolved from generalists during the Late Pleistocene/Early Holocene to specialists during the Middle Holocene, according to diversity and relative taxonomic richness counts. The general hypothesis is summarized as follows: 1) at the end of the Pleistocene and beginning of the Holocene (interval between 13.0 and 8.5 ka), the Pampean and Patagonian landscape was different from the present one, with a mammal biodiversity larger than in the Middle Holocene; 2) during the Middle Holocene, the highest mammal taxonomic richness corresponds to one species, Lama guanicoe . Although available biomass was the same for the hunter-gatherers, it was due to the larger abundance of individuals of that single species; 3) the emerged continental surface during the Late Pleistocene/Early Holocene was more extensive than during the Middle Holocene. In ecological terms, this greater land mass is reflected in an equally larger biodiversity, even assuming that populations of Pleistocenic megafauna were diminishing in number since ca. 13,500 years BP. Based on the analysis of our own information and published data, we state that the human groups which colonized the Pampean and Patagonian regions towards the end of the Pleistocene and beginning of the Holocene used generalist strategies encompassing a wide range of faunal resources (birds and mammals, especially of terrestrial habitats). Plasticity of hunter-gatherer societies, plus a complex technology, a higher social mobility and unfilled territories, allowed them to rapidly replace one resource for another in conditions of environmental stress. This lifestyle resulted in the occupation of different ecological zones (niches) and the evolution to specialized systems, based on one or a few mammal species, once the colonization and support in the different environments were successful and the resources of the Late Pleistocene/Early Holocene disappeared.

Environmental conditions in Southernmost South America (the Patagonian Andes and the extra-Andean plains) during the early peopling of the region in Late Glacial/Early Holocene times are herein described. Different glacial advances or stabilization phases in valley glaciers occurred several millennia after the Last Glacial Maximum (LGM), as a consequence of regional cold climatic episodes. According to Clapperton (1993), two advances during the Late Glacial took place, ca. 15-14 14 C ka and 12-10 14 C ka B.P. A cold event during this last period, probably correlative with the “Younger Dryas” episode in the Northern Hemisphere, has been observed in the palynological record. A tundra environment dominated until ca. 13-10 14 C ka B.P.; afterwards, a gramineous steppe with forest refuges developed. The transition steppe-forest lasted to the Middle Holocene, when the Nothofagus forest took over. The arrival of man in Southernmost South America (ca. 13 14 C ka B.P. or even before) probably took place while glaciers were still present in most Andean valleys, sea level was much lower than today, and tundra environments dominated the extra-Andean plains. Moreover, peopling in the Isla Grande de Tierra del Fuego would have occurred not later than 11.8 14 C ka B.P., when the present Magellan Straits valley was still occupied by a meltwater discharge, braided stream, fed by the receding “Magellan Glacier”.