Neo-Environmental Determinism and Agrarian 'Collapse' in Andean Prehistory

Article excerpt

Introduction: neo-environmentalism in Andean archaeology

In early anthropology, environmental determinism was used to explain race, human demography, material culture, cultural variation and cultural change. As anthropological interpretation evolved, simplistic reductionist thinking was replaced with more complex socio-cultural explanations. Despite these theoretical advances, environmental determinism continues to be invoked to explain Andean prehistory. The rise and fall of Andean civilizations are 'mapped onto' sediment cores, pollen diagrams and ice cores and somehow this 'explains' cultural change. In the extreme incarnations of neoenvironmental determinism, humans are considered passive pawns at the mercy of droughts and floods. I will evaluate a recent hypothesis proposed to explain the collapse of the Tiwanaku State and raised-field agriculture from a landscape perspective informed by a 'bottom-up approach' to Pre-Columbian farming systems, the ethnography of wetland peoples and insights from the New Ecology.

The collapse hypothesis

Andean archaeologists have long been infatuated with the idea that cultural change could be explained by climatic shifts in rainfall and temperature (e.g. Shimada et al. 1991; Cardich 1985). These ideas appear and disappear in regular cycles of about 20 years for the south central Andes. The 'collapse hypothesis' recently proposed by Kolata, Binford and Ortloff (Kolata 1993; Kolata 1996; Binford et al. 1997) for the collapse of the Tiwanaku civilization bears a striking resemblance to that proposed by Puleson (1976) for the explanation of the 'horizon/intermediate period' phenomena in Andean prehistory, and that proposed by Posnansky (1945) for the collapse of Tiwanaku. Since much of the world is still recovering from a major El Nino event, a critical examination of neo-environmental determinist explanation is relevant.

According to Kolata and colleagues (1997: 235), 'Environmental thresholds vary through time as climate changes, populations grow, cultures and their technologies evolve, and resources are depleted and substituted'. They define an environmental threshold as 'climatic extremes that limit the complexity of cultural development'. In this perspective (Binford et al. 1997: 246),

Human cultures adapt to changing environmental conditions within a range of normal variation. 'Normal' is usually defined by recent and short-time scales, rather than by long-term variability during which thresholds at environmental extremes can significantly affect cultural adaptability. In commonly defined normal periods, thresholds can be exceeded for short periods without seriously affecting a civilization. However, in the long term, lower frequency variation with larger amplitudes may exceed the limits of human adaptability.

According to the collapse hypothesis for Tiwanaku, the threshold was exceeded when 'chronic drought' conditions prevailed in the South Central Andes after AD 1150.

Kolata and colleagues have marshalled impressive evidence from the Quelccaya ice cores, sediment cores from Lake Titicaca, water budget modelling and archaeological excavations in raised fields. The scenario of Tiwanaku collapse can be summarized as follows: a drastic rainfall deficit beginning at AD 1150 caused a 'chronic drought' of 300 years. The water level of Lake Titicaca dropped between 12 and 17 m and much of the lake was reduced to a saline swamp surrounded by a bleak arid landscape. The raised-field system was abruptly abandoned because it became impossible to maintain due to drought conditions, higher labour costs and salinization. Because Tiwanaku's food production was based on intensive agriculture, the collapse of the regional raised-field system brought on the collapse of the Tiwanaku urban centre and state administration. Populations dispersed and migrated out of the region. According to Kolata and colleagues, this resulted in a total 'cultural collapse', plunging the Lake Titicaca basin into a post-Tiwanaku 'Dark Ages' lasting until the conquest of the region by the Inka in the late 15th century. …