People, Plants, and Landscapes: Studies in Paleoethnobotany

7. An Evolutionary Ecology Perspective on Djet Choice, Risk, and Plant Domestication

CHAPTER 7 An Evolutionary Ecology Perspective on Diet Choice, Risk, and Plant Domestication BRUCE WINTERHALDER AND CAROL GOLAND Most models of plant domestication and the origins of agriculture assign causal primacy to one or more generalized, normative1 variables (or "prime movers"; summary in Redding 1988:57-60). Examples are population, climate change affecting resource abundance or distribution , technological innovation, and energy-extraction efficiency. Typically these variables describe system-level properties and they are characterized by weH:-behaved mathematical averages. Population grows, climate shifts, technological proficiency improves, or energy use expands . Processes of change are removed from the daily decisions of individual ecological actors, and they are continuous and gradual. The agroecological and socioeconomic consequences cited in these models are the result of broad adaptive responses to steady changes in material conditions as the population moves from food gathering to food production .2 In this chapter we shift perspective and use evolutionary ecology models to examine the possible consequences for agricultural origins of localized decisions about resource selection. We approach the question of domestication through foraging models, beginning with a brief description of some key assumptions and concepts of that approach. We use the diet-choice model to show how resource selection decisions could bring foragers into contact with potential domesticates and how this might affect population density and subsistence risk. We turn to hunter-gatherers and show that sharing and regional exchange have evolved as highly effective responses to unpredictable day-to-day success in the food quest. We then show that the field dispersion common 123 124 B. Winterhalder & C. Goland to nonindustrial farmers functions to reduce risk in the same manner as does sharing among hunter-gatherers. The heart of the argument is more speculative. We try to envision the evolutionary transformation from foragers who buffer risk primarily by sharing to farmers who mitigate it by field dispersion. To provide empirical moorings to this exercise, we review the record of agricultural origins in eastern North America in terms of our scenario. Next, we briefly compare aspects of our approach with several other recent models. Our summary highlights some strengths of microecological analysis of prehistoric economies and their transformations (Winterhalder 1993). Domestication as an Evolutionary Question In the usual approach to domestication a change in the key variable (e.g., population growth) poses an adaptive opportunity or challenge (e.g., food stress). One or more of the properties of agriculture known to result from domestication (e.g., greater productivity per area) are posited as a response to the opportunity or as a solution to the problem. We believe that this' manner of conceptualizing the issues has three liabilities that can be mitigated using evolutionary ecology models: (a) it engages an adaptationist-functionalist form of argument that is less powerful than a more direct selectionist approach; (b) it focuses attention on the particular variable (e.g., climate) to the neglect of its adaptively salient properties (e.g., unpredictable variability); and (c) it tends to focus on highly generalized variables, deflecting attention from the actual subsistence choices faced by foragers-becoming-farmers. Our alternative perspective (a) adopts evolutionary ecology models, (b) encompasses nonnormative properties of the environmental variables affecting subsistence adaptations, and (c) locates the key processes in the immediate and localized decisions routine to the economic lives of the actors. Because of their importance, we state each of these points as a principle, followed by brief elaboration and the references containing the fuller justification. PRINCIPLE 1: Selection-based explanations are more powerful than functionalist (or the closely related adaptationist) explanations. In most accounts the domestication ofplants or animals is explained as an adaptive response to an environmental challenge (e.g., resource 125 Diet Choice, Risk, and Plant Domestication shortages caused by overpopulation or climate change). The advantages of cultivating plants or husbanding animals (e.g., increased yield) thus account for the origins of the practice. In general, the form is that of a functionalist argument: a benefit of the feature is presumed to explain its origin. Although widespread in the biological and social sciences , functionalist analyses are fraught with logical and empirical pitfalls (Elster 1983). In particular, they usually are not subject to a causal theory explaining how benefits act to produce the trait. Many of these pitfalls can be avoided by paying careful attention to theoretical or methodological underpinnings. In Elster's (1985) terms this means using aspects of methodological individualism to illuminate system microfoundations. In evolutionary ecology...