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 . 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 : the archaeological evidence shows that early hunter-gatherer/horticultural residents of the neotropics had an expandingdiet breadth followed by increasing subsistence commitment to low-ranked species; the prehistoric changes of concern are evident enough that short-term precision in the use of the model isn’t necessary ; and finally 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” . 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, growing berries in containers 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: 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, 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 . 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 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-ecological circumstances and evolutionary processes that combine to generate a competitive social hierarchy like that expressed in feasting .

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 or ecosystem approaches premised on cybernetic properties such as homeostasis .Behavioral ecology begins with an optimization premise. As a result of natural and cultural evolutionary processes, behavior will tend toward constrained optimization . This assumption makes operational the long-standing view of anthropologists that hunter-gatherers tend to be skilled and effective in the food quest . Efficiency, say in capturing food energy, is important even if food is not in short supply because it affords hunter gatherers the time and resources to engage fully in other essential or fitness-enhancing activities . We state this premise as constrained optimization because we do not expect behavior to be fully optimal. Temporal lags in adaptation and compromises among conflicting adaptive goals impede this outcome. Optimization likewise must be determined within the cognitive capacities, beliefs and goals of the organism under study. We adopt the assumption of constrained optimization rather than “satisficing” because the latter—while it may lead to superficially similar predictions—is an empirical concept and is therefore not able to generate theoretically robust predictions . Constrained optimization is an analytically powerful starting point that does not entail the belief that behavior is routinely optimal, only that there be a tendency towards optimal forms of behavior.

Behavioral ecology likewise is grounded in the observation, now well confirmed by non-human as well as anthropological studies, that some fundamental economic concepts transcend their scholarly origins in microeconomic attempts to explain the functioning of market-oriented economies. They are useful for studying adaptive decision making whether the questions concern the behavior of capitalists and workers, or the subsistence choices of hunter-gatherers, horticulturalists, and agriculturalists, not to say juncos and bats . At a minimum this list would include marginal valuation, opportunity costs, discounting, and risk sensitivity. marginal value. For most tasks we pursue and things we consume, immediate value changes with quantity, be it duration of the activity or the amount of a good obtained or ingested. The first breakfast sausage is more satisfying than the sixth or seventh; an hour-long bath is a delight, but four hours in the tub makes even insipid alternatives attractive. This would be trivial except for the additional observation that the decision to suspend consuming something like sausage or doing something like taking a bath is based on its marginal rather than initial, average or total value. Because of marginal valuation we move from doing one thing to another even though the intrinsic qualities of the options themselves may be unchanging. The formulation of marginal analysis was fundamental to microeconomics , and the careful reader will find marginal trade-offs in each of the foraging models we discuss below. opportunity costs. The idea of opportunity costs is closely related: the decision to switch from one behavior—a kind of consumption; a work activity—to another depends not only on its marginal value, but on the return to be gained from the available alternatives. Thus, one ceases to consume sausage when it becomes more attractive to sip orange juice; one stops bathing when preparing a ceremony is more compelling. More to the point of our subject, blueberry containers one ceases to forage for mussels when the opportunity and benefits of doing something else take precedence. In each case we assess the current activity, be it consumption or purchase against what we might be doing instead. In technical terms, the opportunity cost of an activity refers to the value of the opportunity that is foregone or displaced by continuing it. For instance, the diet breadth model sets the decision to pursue a particular resource against the opportunity cost of ignoring it in favor of searching for a more profitable resource to pursue. Much of microeconomics is a logical and mathematical elaboration on the workings of marginal valuation and opportunity costs, as they are manifested in the environment of a market economy. Using these ideas, economists ask how a wage earner’s consumption patterns change in response to an increase in her income.

By contrast, the behavioral ecologist analyzes how these two concepts play out as an organism interacts with a natural environment of physical processes and other organisms in the roles of predators, competitors, food resources, potential mates, and offspring. She asks, how might the resource choices of a forager shift as a consequence of a decline in the density of a highly valued resource, or an improvement in the technology used to harvest a particular species? The most basic claim of the papers in this volume is that these same ideas can be adapted to an understanding of decisions faced by humans during the evolutionary transition between foraging and agriculture. discounting. Discounting refers to the situation in which we assign a future reward less value than if it were available immediately and with certainty. For instance, we would pay less at planting time for a corn crop which might after all fail, than for that same crop at harvest time when the yield is certain. We discount in this manner when the cost of an activity such as planting occurs immediately but the reward, the harvest, is delayed and, perhaps because of that delay, uncertain. Delay alone can be important because the opportunity to benefit, even from a completely assured harvest in the most extreme case might diminish or pass, were the cultivator to die in the meantime. Delay also offers opportunities for hailstorms, locust plagues and other unforeseen events to reduce the value of the reward itself. For both reasons, effective behavior will hedge, finding it economical to discount delayed rewards. Use of this concept is fairly recent in behavioral ecology theory . Because the shift from hunting and gathering to agriculture represents a shift from immediate- to delayed reward activities this basic concept likely will be quite important in economic analyses of the transition from foraging to farming. risk-sensitive behavior. Basic behavioral ecology models assume that all environmental variables are constants and that a forager pursuing an optimal set of resources gets the expected reward at all times. By contrast, risk-sensitive models aim to be more realistic by introducing a stochastic element to the relevant environmental variables. All hunters recognize the large role of chance in the discovery and successful capture of game. In a risk-sensitive model the acquisition rate experienced by the forager is expressed by a statistical distribution; outcomes can be assigned probabilities but the actual rate at any time is unpredictable. Therefore, the optimization problem must take into account both the long-term average and the inevitable periods of shortfall. Risk-sensitive models do this. They are generally more realistic and more complicated than deterministic models, sometimes generate like predictions and, given the heuristic nature of the modeling effort, may not always be the preferred option for analysis . There is a well-developed literature regarding the risk-sensitive behavior of foragers and food producers, taken separately , but little has been written about risk sensitive adaptation during the transition from one of these subsistence systems to the other .The concepts just reviewed—marginal valuation, opportunity cost, discounting, and risk sensitive analysis—signal that behavioral ecology is an attempt to assess the costs and benefits of alternative courses of action under a range of environmental conditions. In operational terms, we accomplish this task with models that have in common four features: an alternative set, constraints, some form of currency, and a goal. Within a particular model, the range of possible behavioral actions is known as the alternative set. For instance, the diet breadth model specifies an alternative set of ranked combinations of potential resources . In the marginal value theorem, the alternative set refers to patch residence times. The alternative set is the dependent variable in the analysis; a particular socioenvironmental factor constitutes the independent variable. The model itself does not specify what might cause the independent variable to take on a certain value, or to change. It thus leaves open the opportunity for exploring how diverse influences such as habitat or climate change, seasonal variations in population density, over exploitation, competition from another predator or pressure to extract a surplus might affect a behavior like resource selection.