People and environment in pre-Columbian Amazonia: two new proxies

What was the extent of human occupation and environmental impact in the pre-Columbian Amazonia?

This question has been at the center of much of the research on pre-Columbian Amazonia since Betty Meggers published her paper ‘Environmental Limitation on the Development of Culture’ (1). The reconstruction of the Amazon’s past is based on evidence obtained from the study of the present landscape, sediments and archaeological remains. These ‘evidences’ are called proxies. Pollen is a proxy for past vegetation, tree rings are proxies for past climate variability, CO2 stored in the ice cores is a proxy for past levels of atmospheric CO2 and so on.

Paleo-ecologists, geographers, archaeologists etc. trying to understand the region’s past have first to look for proxies (this means going to the field and taking samples of lacustrine sediments and/or soils, or going into the mountains after morains and other glacial deposits); then they have to interpret the data gathered and assess their significance (to what extent does this data represent a local or regional event?): we can say that past values of CO2 inferred from ice cores are proxies for past global concentrations of CO2 because the atmosphere is well mixed, but we cannot say that the extent of a moraine in a particular valley indicates past global temperature or precipitations, because local conditions in that valley could have been (and very likely were) different from the conditions of a similar valley in the other hemisphere. As the process involves different stages, datasets and interpretations, it is not uncommon for researchers to disagree on the conclusions. This has often been the case with regards to Amazonia.

In this post, I will try to provide a brief overview of the proxies (and their interpretations and significance) that have been used to infer the extent of the impact pre-Columbian populations had on Amazonia and the contribution of a recent paper published in Science (2) to our understanding of the region’s past.

The first proxies

When Betty Meggers wrote ‘Environmental Limitation on the Development of Culture’ in the fifties (1), there was not much data on Amazonia. At that time scientists relied considerably on anthropological studies of modern indigenous communities and on written documentation left by the first explorers. The fact that the ‘modern’ indigenous population in Amazonia was limited to small nomadic and semi-nomadic groups was attributed to environmental constraints: unfertile soils and frequent floods. As Amazonian soils cannot support large and stable populations in modern times, it was thought that, also in the past, Amazonia was inhabited by small groups of hunters and gatherers. In contrast, written reports from the first explorers described large and rich societies with plenty of food and gold. Myths such as El Dorado arose on the basis of these reports. However, as the written reports contained some statements that were clearly false, such as the existence of blond women warriors with only one breast (the “Amazonas” from whom the river and the region took their names), these historical documents were often disregarded and the consensus within the scientific community was that Amazonia in the past only hosted small nomadic groups that did not have a significant impact on the environment. 

The discovery of the “lost cities”

In the last 30 years, when more funding, interest and technology became available to spur archaeological research, scholars started to find new evidence of pre-Columbian complex societies in those very places where Megger’s model of environmental determinism predicted that they shouldn’t be. The discovery of raised fields and monumental mounds in the Bolivian Amazon (3,4), the geometric ditches in the Acre (5), the terra preta sites, the earthworks in the upper Xingù (6), the mounds in the Marajo islands, were far more reliable proxies than ‘modern indigenous communities’ and ‘old written reports’. More importantly, these discoveries suggested that Betty Meggers’ model was wrong. Archaeologists (actually, in most cases, North American Anthropologists) started speculating about the significance of these discoveries and how they challenged the theory of environmental determinism. Archaeological evidence showed that environmental constrains did not limited cultural evolution in Amazonia because human intelligence overcame them. People built highly productive raised fields that were able to produce tons of Maize per hectare on a continuous basis (without fallow periods); people transformed infertile oxisols in extremely rich terra preta allowing the production of food surpluses that permitted the rise of large and complex societies all over Amazonia. Pre-Columbian Amazonia was now seen by many as a “cultural parkland” (6) and an “anthropogenic cornucopia” (7). Pre-Columbians practiced agroforestry to such an extent that they contributed to the modern patterns of Amazonian biodiversity. Some geographers, paleoecologists and climatologists speculated about the large impact that pre-Columbians had on world climate: As Amazonia was densely populated, then it was also extensively de-forested. Following the discovery of the Americas in 1492, 95% of the original population died because of the spread of the diseases brought by the Europeans. The sharp decrease in population meant the abandonment of the agricultural fields and the re-growth of the rainforest. The forest absorbed huge amounts of CO2 from the atmosphere and, because of this, contributed to trigger the Little Ice Age…

The latest paradigm shift

The above reconstructions, although exciting, have been considered too extreme by some scholars, including myself (4,8); because there is insufficient paleoecological data or archaeological evidence to support them. The main problems with the reconstructions of pre-Columbian Amazonia as an “anthropogenic cornucopia” are related to the interpretation and significance of the proxies taken into account. Although it is a fact that there are thousand of hectares of raised fields in the Bolivian Amazon (the proxy) it is not clear how they were used and how productive they were (the interpretation). Moreover, there is no basis for assuming that similar levels of landscape modification took place elsewhere in Amazonia (the significance or scope). The same is true for other proxies. For instance, terra preta. On what basis do we interpret terra preta as an improved agricultural soil? We all agree that within the Amazon basin there is evidence of past complex society, but can we extrapolate from a few sites to the whole of Amazonia? Till now, the most important argument against the “anthropogenic cornucopia” theory has been the lack of data supporting it. As Betty Meggers said, it is all about wishful thinking. But, a few days ago, a new paper by McMichael et al. (2) added two new proxies to the debate: charcoal and phytoliths. They are actually not new at all, but, for the first time, extensive parts of the Amazonian rain forest have been sampled for the presence of these two proxies. Charcoal is a proxy for fire and phytoliths are a proxy similar to pollen, phytoliths tell us which kinds of plants were cultivated (if any). Both of them have local significance because you can find them only in the very place were the fire or the plants were. But, as McMichael et al. sampled many spots in the Amazon rain forest (247 soil cores collected from 55 locations) , their results are now of regional significance. This is the first time that we have a dataset obtained from the random sampling of an extensive part of Amazonia, rather than mere generalizations of data obtained from small and selected archaeological sites. Based on the analysis of charcoal and phytoliths, McMichael et al. concluded that most of Amazonia was “predominantly occupied by relatively small and shifting human populations during the pre-Columbian era”. This opens up a great and fascinating perspective for future studies. If, as Meggers said more than half a century ago, environment matters: what are the environmental opportunities that allowed the rise of complex societies in some sites such as the Llanos de Moxos in the Bolivian Amazon?

There is still much to be learnt about human-environment interactions in pre-Columbian Amazonia. The Llanos de Moxos, with its great amount, diversity and spatial variability of earthworks, is a promising site for future research.

1) B. J. Meggers (1954). Environmental Limitation on the Development of Culture American Anthropologist  
2) McMichael CH, Piperno DR, Bush MB, Silman MR, Zimmerman AR, Raczka MF, & Lobato LC (2012). Sparse pre-Columbian human habitation in western Amazonia. Science (New York, N.Y.), 336 (6087), 1429-31 PMID: 22700926  
3) Lombardo, U., Prümers, H. (2010). Pre-Columbian human occupation patterns in the eastern plains of the Llanos de Moxos, Bolivian Amazonia Journal of Archaeological Science, 37 (8), 1875-1885  
4) Lombardo, U., Canal-Beeby, E., Fehr, S. and Veit (2011). Raised fields in the Bolivian Amazonia: a prehistoric green revolution or a flood risk mitigation strategy? Journal of Archaeological Science, 38 (3) 5) Pärssinen, M., Schaan, D., and Ranzi (2009). Pre-Columbian geometric earthworks in the upper Purús: a complex society in western Amazonia Antiquity, 83  
6) Heckenberger MJ, Kuikuro A, Kuikuro UT, Russell JC, Schmidt M, Fausto C, & Franchetto B (2003). Amazonia 1492: pristine forest or cultural parkland? Science (New York, N.Y.), 301 (5640), 1710-4 PMID: 14500979  
7) Erickson, C. L (2008). Amazonia: the historical ecology of a domesticated landscape in Handbook of South American archaeology, edited by H. Silverman and W. H. Isbell  
8) Lombardo, U., May, J-H. and Veit, H. (2012). Mid- to late Holocene fluvial activity behind pre-Columbian social complexity in the south-western Amazon basin The Holocene