Ever since Darwin, history and evolution—the twin theoretical “engines” for tracking change—continue their uneasy, if not (falsely) antagonistic, relationship in framing and addressing the questions posed in this paper’s Introduction. On the one hand, evolutionary
Figure 12.6. An evolutionary model of plant food-yielding systems and their corresponding exploitative activities, as proposed by David Harris (1989, 1991). The triangles with Roman numerals indicate key thresholds (transitions) of increased efficiency in the output of food procurement and production. A schematic historical sequence for Amazonia is added to the model, marking the appearance and intensification (increasingly darker shade) of key food products and agricultural landscapes along a time line. The two arrows at the bottom track the socio-demographic trends that are linked to increased food production efficiency. (adapted from D. Harris 1989, 1991 by Jose Oliver)
Ecological models grounded on optimal foraging theory have been invoked to explain the shift from food procurement to food production strategies that ensued in the Neotropics during the critical transition from late Pleistocene to early Holocene climatic conditions (Figure 12.6). On the other hand, explanatory models based on historical contingency are invoked by historical ecologists to address the same kind of questions. While both allow for human agency and intentionality (see Lathrap 1984; Piperno and Pearsall 1998:17), their premises are certainly different. The former focuses on co-evolutionary processes in nature, within which human communities are a part of the biotic system, whereas the latter focuses on the role of human history, rather than nature, in creating and remodeling the landscape.
Optimal Foraging Evolutionary Theory
As discussed by Piperno and Pearsall (1998:16-18, 324-327) optimal foraging theory is articulated through the “Broad Spectrum Diet Revolution” model and addresses the question of why it would be advantageous to shift from a proven foraging system to the untested, thus risky practice of agricultural production. Succinctly, the model proposes that food plant resources forming the diet of a foraging group are not those most abundant in a given area, but those that are most efficient to procure in terms of effort expended for calorific return. As the abundance of these high-ranked plant resources in a given area declined
At the close of the Pleistocene, efficient foraging would have required investing less time in searching for high-ranked plants and more time searching and handling a wider range of lower-ranked resources. As high-ranking plant resources declined, efficient foragers would choose a broader, more diversified diet because they would obtain a higher return rate than could be achieved by searching for the depleted, dispersed high-ranked resources. A reduction in search time would allow foragers to invest time in food processing and storage, adding to the nutritional value and use-life of the food resources. The increased diet breadth and the decreased search time lead to a smaller foraging range and thus to increased residential stability and sedentism (Piperno and Pearsall 1998:17-8), the context that promoted the development of house gardens.
Such changes in diet-breadth may well result in socio-demographic changes, depending on the nature and characteristics of the food resources entering the diet. But it is important not to view changes deterministically. If the development of sedentism, domestication and agriculture were inevitable, modern foragers like the Nukak (Politis 2001; Politis and Saunders 2002) would simply not exist (Figure 12.7). Nor would formerly sedentary agricultural groups, like the Gorotire Kayapo, have reverted to “nomadic agriculture” in the early twentieth century. One possible direction a given group can take is, of course, toward sedentism, house gardening and, eventually, agriculture. As the opportunity arises to concentrate an increasing number of high-ranked food plants within the home area, while still
Figure 12.7. A cultivated field created by the disturbances of a previous Nukak (Maku) encampment. This field includes root crops (manioc plus others unidentified) and Seje palms. Once created, the Nukak foragers will not reuse this locus as a camp site so as not to interfere with plant growth. The unusually high density distribution of palms in the Guaviare territory in Amazonian Colombia is largely the product of foraging and itinerant gardening activities going back to at least 9000 BP. (photo by Gustavo Politis)
Foraging for a broad suite of low-ranked food sources, it would be expected that at some point in time the optimal efficiency in terms of effort invested will shift to bringing high-yield plants under increasing human dependency and control for their reproduction.
Historical Ecology: Humans and Their Landscapes
In the last twenty-five years or so, there has been a growing disenchantment with the explanations arising from strictly neo-Darwinian (co-) evolutionary approaches, such as optimal foraging theory, to the question of origins and development of agriculture (Balee 1998; Erickson 2003; Politis and Saunders 2002). Historical ecology has emerged as a challenge to the dominant theoretical perspectives of the 1980s emanating from cultural and human ecology, ecological anthropology, sociobiology and evolutionary biology. The basic premise is that Native Amazonians did not adapt to nature, but rather created the world that they wanted through human creativity, technology and engineering, and cultural institutions (Balee 1998; Denevan 2001). “The focus is on human history rather natural history of the environment contextualized within a historical and cultural tradition” (Erickson 2004: 456).
Balee (1994), one of its key exponents, presented a model of “agricultural regression” where the patterns of food quest by modern hunter-gatherers and farmers occur in landscapes that are the result of, and were created by, hundreds of generations of previous occupants. Present-day native societies, hence, do not adapt to nature or a given natural environment. Instead, as Erickson (2003:456) noted, they are “exploiting the past, complex human history of the landscape capital created by their ancestors.” Native Amazonians are therefore not passive entities adapting to given natural environments, but are instead proactive, rational actors, in their interaction (ecology) with nature and in promoting change and continuity through culture. In short, the goal of historical ecology is to understand the long-term history of human behaviors in creating the diverse landscapes that are known today (Erickson 2003: 459).
In assessing breadth-diet evolutionary theory, I suspect that historical ecologists would be weary of how food procurement/production efficiency is measured, in contrast to how it would be valued by Native Amazonians. They would likely insist that the resulting food-yielding (anthropogenic) landscapes cannot merely be reduced to those behaviors that select for food procurement efficiency in terms of effort expended for calorific return. Other value judgments that depend on native perceptions of the cosmos are likely to enter in the decisions that produce particular kinds of anthropogenic landscapes and make “efficient” use of specific suites of food-yielding resources (Arhem 1993; Reichel-Dolmatoff 1996). Thus, for example, the Nukak foragers of the Guaviare observe animal taboos and various gender-based food restrictions that preclude their inclusion into their diet, even when selecting for these would be the optimal efficient thing to do, and indeed would enhance the breadth of diet (Politis and Saunders 2002). Food prohibitions and other dietary restrictions are culturally instituted (valued); their efficiency has everything to do with the emic understanding (beliefs, ideology) of body-and-soul health and very little to do with calorific returns.
For a long time it was believed that agriculture was invented rather quickly, leading to the domestication of plants and, in due course, to settled life and civilization (see Harris 1972, 1989, 1991). This idea no longer holds for anywhere in the world, Amazonia included. Rather, agriculture followed domestication and settled life. Domestication is the long-term result of predator-prey (human-plant/animal) relationships where both populations stand to benefit, while agriculture, in its broadest sense refers to human behaviors that create a new kind of ecological succession (an agroecology), and hence a particular kind of landscape,
Where the life-cycle of the cultivars are under human control (Pipemo and Pearsall 1998: 17-18), and where food-yielding landscapes are created by human action. But before food production based on domesticated crops (agriculture) emerged, there was a long and protracted period of mutually beneficial human-plant interactions (Rindos 1980, 1984, 1989; Lathrap 1984; Pearsall 1995: 159-160). In procuring food and other plant resources by foraging, human beings began to alter the landscape well before any systematic cultivation took place, while creating the necessary opportunities for sedentism and domestication to develop. Such opportunities might arise from activities such as clearing land around campsites or setting fires in grasslands to hunt animals.
Over ten millennia of human activities in the quest for food in Amazonia have left a vast array of signatures on and “inside” the landscape, some of which are still legible and decodable today and many others that have been distorted, rearranged and even erased by the passage of time. The geometric growth of human activities—intentional and unintentional—over ten-thousand years, and the different, variable scales of impact on the landscape, have blurred and altered the boundaries between what is natural and cultural in Amazonia. Perhaps this conceptual, analytical dichotomy made sense only in that fleeting moment, when a human group first stepped into an environment, a niche, a landscape and ecology devoid of humanity.