There is a small HBE literature on agricultural origins. Keegan (1986, 92) made an early and prescient argument that foraging models could be extended to the study of horticultural production. He highlighted horticulture because it represents a mixed subsistence system, transitional between the economies of hunter-gatherers and agriculturalists. Using data from the Machiguenga of Peru, Keegan argued that the key variables of the diet breadth and patch-use models have direct analogs in food production, facilitating the use of these cost-benefit models in analysis of this system and the evolutionary transitions that gave rise to it. His calculations showed that the Machiguenga generally were stocking their gardens with optimal combinations of cultigens and, with allowance for seasonal and nutritional constraints, making efficient trade-offs among fishing, forest hunting, and gardening.
In a 1991 paper, Layton et al. (1991) described a "complete break" from the standard, evolutionary progression theories of agricultural origins. They proposed instead an approach that sees hunting, gathering, herding, and cultivation as alternative strategies of subsistence that may be taken up alone or in various, stable combinations, depending on socio-ecological circumstances, and without any implication of irreversible directionality to transitions among them. For instance, there is nothing to prevent food producers from evolving into foragers. Various conceptual elements from foraging theory, such as the ranking of resources by pursuit and handling costs, cost-benefit analysis of subsistence trade-offs, boundary defense, and risk minimization are found throughout their argument. In support of their interpretation they summarized numerous ethnographic cases in which these strategies are mixed in shifting and sometimes stable balances, reminiscent of Smith's (2001a) concept of low-level food production.
Layton et al. stimulated two follow-up papers, both of them making more explicit use of foraging theory to critique or amend specific predictions from their article. Hawkes and O'-Connell (1992; cf. Layton and Foley 1992) used a sharper distinction between search, and pursuit, and handling times—the central conceptual distinction of the diet breadth model—to argue that high-ranking resources will not drop out of a forager's diet in response to exploitation and depletion. However rare, they will always be pursued when encountered. Hawkes et al. expand discussion of the circumstances likely to promote subsistence innovation, and argue that "increases in diet breadth result from reduced foraging return rates and so lead to declines in population growth rates" (Hawkes and O'Connell 1992, 64). They also draw attention to HBE arguments for a gendered division of labor (Hawkes 1991) that might have been important in the evolutionary processes underlying subsistence transitions.
In a second follow-up paper, Winterhalder and Goland (1993) addressed the population growth prediction by Hawkes and O'Connell, cited just above. They used a dynamic, population ecology variant of the diet breadth model to show that declining foraging efficiency associated with expanding diet breadth may result in a decrease or an increase in forager population density. The deciding factors are the density and reproductive potential—together, the sustainable yield—of the low-ranking resources that happen to come into the diet.
Subsequently, Winterhalder and Goland (1997) expanded on these arguments for using a HBE form of analysis in agricultural origins research. They cited three advantages that distinguish HBE from other research traditions: (1) it engages selectionist explanations (Smith and Winterhalder 1992b) that are more powerful than the more commonly used functionalist ones; (2) it has tools for non-normative analysis of unpredictable variation in environmental features and the risk-minimizing adaptive tactics they elicit; and (3) it focuses on localized and immediate resource decisions and their consequences for people "on the ground." HBE thus engages the behaviors most likely to be causal to evolutionary change: "The changes we summarize under broad concepts such as domestication and the Neolithic revolution have their origin and form in the ecologically situated choices and actions of individuals" (Winterhalder and Goland 1997, 126; italic in original). Winterhalder and Goland used the diet breadth model to show how foragers might initially come to exploit the organisms that became domesticates, and to speculate on the adaptive consequences of this co-evolutionary engagement. Among the effects examined were the consequences for resource depletion, human population density, and risk management tactics, using evidence from eastern North America to exemplify their arguments.
Working on the prehistoric development of agriculture in eastern North America, Gremillion (1996a) used diet-breadth and risk-minimization models along with opportunity-cost arguments to generate and evaluate predictions about the circumstances in which new cultigens will be adopted by groups already practicing some agriculture, and whether they will replace existing plant resources, as did maize following a significant delay from its first appearance, or become a supplement, as in the case of peaches. In a second study, Gremillion (1998) analyzed macrobo-tanical data from the Cold Oak rock shelter in eastern Kentucky to show that increased dependence on cultivation of seed crops around 1000 BC was accompanied by greater anthropogenic disturbance of habitats and a shift in mast resources from acorns to hickory nuts. She developed several HBE hypotheses to address this situation, finding greatest credence for the idea that an increase in the overall abundance of mast resources led to specialization on the most profitable species, in this instance hickory, at the expense of the less highly ranked oak. Alternatively, increases in the ranking of profitability of seed crops such as maygrass, chenopod, and knotweed may have displaced acorns from the diet due to their high processing costs. In each of these applications Gremillion argued that HBE is a fertile source of new and archaeologically testable hypotheses about the subsistence and economic changes associated with the origins of agriculture.
The most thorough existing application of HBE to the question of agricultural origins is Piperno and Peasall's (1998) monograph, The Origins of Agriculture in the Lowland Neotropics. Over half the crop plants domesticated in the Americas are thought to have wild progenitors native to neotropical lowland habitats. Among them are New World staples such as manioc, yams, achira, sweet potato, peanut, gourds, squashes, beans, and perhaps maize. These plants likely were first used by foragers, who cultivated, domesticated, and subsequently incorporated into specialized agricultural production systems, in seasonal, low elevation forested habitats of the neotropics.
Piperno and Pearsall focus their analysis on the climate and vegetation changes occurring at 11,000 to 10,000 radiocarbon years BP and their likely effects on Neotropical foragers. The first inhabitants of the neotropics encountered a salubrious, open-grassland foraging environment that persisted for only a short time. At around 10,500 BP, the transition to a wetter Holocene climate began to produce a seasonal, deciduous forest cover in the lowland tropics. Piperno and Pearsall hypothesize that due to this habitat shift, and perhaps also to human exploitation (1998, 181), the abundance of the high ranking, "open habitat," plant and animals species decreased, along with foraging efficiency. While the new seasonal forests remained relatively hospitable to mobile hunter-gatherers at low population density (1998, 71), the diets of early Holocene foragers expanded to encompass a broader array of dry-forest plants, species that previously had been ignored. For instance, comparative studies of the efficiency of harvesting tubers suggest they likely were outside of the optimal diet in the late Pleistocene (1998: 85), but moved into that diet as a low-ranked but critical resource once early Holocene habitats became more forested.
The low-ranking, newly important species found in seasonally dry forests were subject to human interest and manipulation, either intentional or inadvertent, routed into cultivation and eventually domesticated (1998; 27, 82). Because they were sparsely distributed over the landscape, hence relatively unattractive to human foragers, there arose an immediate advantage for those who manipulated through burning or harvested species from these habitats so as to increase their density and yield of useful energy or materials.
Piperno and Pearsall cite three rationales for using the diet breadth model in this analysis (1998, 236): (1) the archaeological evidence shows that early hunter-gatherer/horticultural residents of the neotropics had an expanding diet breadth followed by increasing subsistence commitment to low-ranked species; (2) the prehistoric changes of concern are evident enough that short-term precision in the use of the model isn't necessary (cf. Smith, this volume); and finally (3) evidence from ethnographic tests shows that this model and an energy currency are commonly successful in predicting the economic response of foragers to changing environmental circumstances. They conclude, "[b]ehavioral ecology seems to us to be the most appropriate way to explain the transition from human foraging to food production" (1998, 16).
Many of the dozen or so early HBE papers on domestication and agricultural origins are fairly general and conjectural. They ask, without too much attention to specific cases or the empirical record of prehistoric findings on this topic, how might the ideas of HBE be used to address the question of agricultural origins? By and large, their authors are ethnographers whose experience is with extant hunter-gatherer societies. And, they generally have been written by people who already placed themselves within the research tradition of HBE. By contrast, most of the papers in this volume are based on empirical case studies, and they are written largely by archaeologists. Most are authored by individuals for whom behavioral ecology is a new analytic tool.
We do not claim that the HBE research tradition is a complete replacement for the other approaches that we have identified and briefly described. We view it rather as a sometimes complementary and sometimes competing form of explanation. It is complementary in two respects: (1) HBE takes up issues rarely or never addressed in these approaches; search and pursuit trade-offs in the harvest of low-ranking resource species; risk-sensitive adaptive tactics; and, (2) it frames these issues in quite a different manner than other, sometimes older, anthropological and archaeological research traditions by focusing on the costs and benefits associated with individual-level subsistence decisions in localized ecological settings. This framing difference is determined largely by the analytical effort of modeling and hypothesis testing within an explicitly selectionist, neo-Darwinian theoretical framework (Smith and Winterhalder 1992b; Winterhalder and Smith 1992). In both respects, HBE provides tools that complement or make other traditions more complete. At the very least, HBE provides a theoretically well-grounded set of tools to begin exploring the transition to agriculture in a variety of environmental and social contexts.
For instance, although Hayden (Hayden 1990; Hayden 2001) presents his competitive feasting model as a sufficient social explanation for the origins of agriculture, in effect as an alternative to models drawing on materialist or ecological explanations, we would prefer a more cooperative form of analytic engagement. We might assume that social stratification and competitive feasting increase the demand for resources and then ask how this source of ecological change would be represented in terms of foraging models—those extant, adapted, or developed specifically for this purpose—and with what consequences for predictions about subsistence choices and the co-evolution of humans and their resources. Taking this a step further, HBE might help us to identify the socio-ecolog-ical circumstances and evolutionary processes that combine to generate a competitive social hierarchy like that expressed in feasting (Boone 1992). A signal strength of HBE is its ability to carry into hypothesis generation a wide variety of postulated sources of causation—global climate change to the aggrandizement of dominant individuals.
Nonetheless, to the extent that HBE is successful in addressing the question of agricultural origins, it will raise doubts about or contradict elements of other research traditions. In the process it will help us sort out, appraise and discard faulty elements of these approaches. Thus, for reasons of parsimony as well as theory, those working in the HBE tradition are skeptical of the adequacy of explanations couched at the level of global prime movers such as climate change. Likewise we doubt the efficacy of explanations made in terms of universal, directional pressures, such as Childe's postulated trend of increasing energy capture (Childe 1965) or ecosystem approaches premised on cybernetic properties such as homeostasis (Flannery 1968).
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