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State of the Art: Rational Choice Models of Mobility

The mobility of hunter-gatherers is not a new field, so this chapter begins with a brief review of some of the existing anthropological models so as to prepare the ground for my theoretical argument. Probably the best known anthropological model in this respect is optimal foraging theory (Martin, 1983). It is particularly interesting because its application has not been limited to living hunters and gatherers but broadened to cover human behavior more generally. For instance, this theory has served to model human behavior in western-style museum exhibitions (Rounds, 2004). The assumption is that visitors to an exhibition optimize their visit by matching elements of high-interest value with low search costs and that there are some do’s and don’ts that result in rules for deciding how long and in what order one should view the items at an exhibition. These rules (search rules, attention rules, quitting rules) are aimed not at the best possible solution but at one that is satisfactory given the environment as it is (p. 404).

The original version of optimal foraging theory consists of theorems intended to explain when and how foragers move from one resource to another (see Kelly, 1995, for an overview). For example, the theorem of diminishing returns, a central feature of optimal foraging theory, holds that staying in a given patch, say a grove or a small forest of nut trees that foragers exploit, requires increasing work in the form of walking to nut trees that are ever further away within the patch. At a certain point the additional work generates ever fewer returns. The rational choice solution to the problem, namely, moving camp to another grove, is an initial extra investment, but there is a point at which that investment is compensated for by the decreasing returns of the original patch. On the basis of several assumptions about caloric requirements and caloric expenditure (Kelly, 1995, pp. 133-134), the optimal foraging theory predicts that hunter-gatherers will make a move to another patch when a one-way foraging distance reaches 3 km (1.9 miles) on average. This calculation matches what many reports say about the way in which foragers move. Foragers do not stay in a forest until the last nut has been consumed. They walk off much earlier, and the model can show that this strategy complies with rationality in terms of getting the best deal given a number of available patches. When the gathering of the same amount of nuts requires ever more effort, the point at which foragers will leave a given patch of resources will be earlier than the point at which approaching starvation would necessitate a move. Optimal foraging theory also goes beyond this scenario, for it takes into account more complicated ones as well. Indeed it must because many factors are involved (e.g., the number of foragers, the size of a group that shares foraging returns, the variety of storage possibilities, increases or decreases in the desired quantity to forage, and the nature of what is foraged). One could even say that it will eventually be very difficult to disentangle causes and effects in such a model. What appears to be a given patch may turn out to be the variable outcomes of a combined set of practices.

According to optimal foraging theory, forager movements are rational because they follow calculable thresholds. Of course, foragers do not perform this calculation abstractly with graphs. Instead, they are driven by the logic inherent in the environmental conditions and the ways in which human exploitation interacts with these conditions. Other proximate reasons, such as social tensions, may also be considered, but they are thought to boil down to the ultimate causes inherent in the logic of resource exploitation (Kelly, 1995, p. 140). In other words, in this model rationality (as exhibited in the way foragers use scarce resources) is completely contained in the environmental action and ultimately dictated by environmental conditions. It is still a sort of rationality but one that mandates certain cultural practices by ecological necessity instead of being mandated by cultural rules.

Nonetheless, caution is needed to avoid succumbing to the “fallacy of the rule” (Bourdieu, 1977, p. 29), which establishes a likely outcome and reinstills it in the minds of the agents as something that has caused the outcome. Optimal foraging theory exemplifies a strongly deductive notion of rationality. It is usually seen as adhering a strict, nomothetic, deductive approach. The conditions of a patch and the characteristics of the forager group exploiting it (e.g., the number of people and their caloric intake) are defined as premises allowing one to derive what the rational behavior in that situation will be, for that behavior necessarily follows. If real-life foragers depart from what is predicted, either they are mistaken (and will eventually die out from maladaptation) or the observers are mistaken in their premises and need to adapt the formula (the values making up the graph), but the deductive logic of the model at large is not questioned. However, optimal foraging theory may be more productive in combination with abductive reasoning (see below). After all, the assumption that foragers move (or shall move) after three days because of the inherent rationality of patch depletion holds only until there are alternative explanations that are more plausible.

A need for alternative explanations seems evident from a close examination of the ethnographic record that describes the life of foraging groups. As formulated in a study on Canadian Unuk (Eskimo) hunter-gatherers,

In the spring.. .the spirit of impermanence seemed to infect people, so that, from my point of view, they seemed to make the maximum rather than the minimum necessary number of moves. When the flooding river forced us uphill, the retreat was always made foot by foot as the river rose. For several days we moved camp at least once a day and sometimes oftener, and always when the water had arrived within inches of our doorsteps....It sometimes seemed as though moving—rearranging the environment—were a form of play for the Eskimos, a pleasure in itself. Whatever the explanation, I never completely shared the Eskimo spirit....Moves were a nuisance that disrupted my work and, worse, shifted my world as a kaleidoscope shifts its bits of glass, making me uncomfortably aware of the pattern’s fragility. (Briggs, 1970, p. 32)

This account is but one of the many that have shed doubt on the universal applicability of optimal foraging theory. As pointed out above, residential moves are not guided only by subsistence efficiency. The acquisition of other raw materials or the attraction of other places may also be important (e.g., for finding a spouse or for joining a ritual). A place’s adverse conditions (e.g., a plague of insects) may be a crucial factor, too. All these aspects are possible social motivations for residential moves (Kelly, 1995, p. 147). The model of diminishing returns is not a law of diminishing returns. One cannot assume (or deduce) that moves are ultimately due to foraging efficiency. It is possible only to abduct that this foraging efficiency for food resources is a factor that is part of the rationality at work, more in some cases and less in others. The implication is not, however, that the aforementioned Unuk Eskimos (and the other known groups) are acting irrationally. Should one assume instead that they have a kind of primitive rationality, now politically more correctly called a forager mode of thought? What else may lie behind formulations such as “spirit of impermanence” or “the Eskimo spirit” in the quotation above?

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