on the resulting overall context or environment in which the organism must operate.

The context is frequently labeled as economic because it is hypothesized that the organism—the soldier—chooses what, when, and how to eat in order to best balance the costs and benefits of the situation. For example, in a study conducted by Engell et al. (see Engell, Chapter 12 in this volume), subjects given a pitcher of water within reach during a laboratory lunch meal drank approximately twice as much water with their meal as did subjects who were required to walk across the room or a hallway to obtain water. Apparently the extra "cost" of obtaining water outweighed any motivation to drink water for physiological, sensory, or psychological reasons. It is reasonable to hypothesize that subjects in the higher cost conditions recognized that any fluid "deficit" could easily be met shortly after the meal and hence responded to the cost by decreasing fluid consumption while eating. If, however, subjects had reason to expect that they would be unable to drink for several hours after the meal, they might then have chosen to drink similar amounts of water in all conditions regardless of the differences in required effort. Likewise, for most people, ordering a meal in a restaurant is not purely a function of which meal would give the greatest hedonic pleasure, but a balance of pleasure with factors such as meal price, health concerns, occasion, hunger, time available for eating, and who else is present.

Collier's approach, thus, is not confined to the common research question of what organisms do when given the opportunity to eat. Rather it is an effort to capture the entire process of obtaining (or foraging for) food: locating, procuring, preparing, consuming, and metabolizing food in the broader context of the organism's overall existence. Admittedly, at times the situation is fairly simple. People pick one dessert over another for the simple reason that it tastes better, or they do not drink at dinner because they will soon be driving home. Still, the immediately simple, discrete decisions are obviously the product of a complex, ongoing process that takes a great many forces into account. Current models of optimization have yet to fully reflect what happens in actual situations, yet they do at the very least provide a sense of the importance of different viewpoints.

The impact of taking an economic viewpoint of the eating situation is that while any given factor may indeed have an influential role in human food consumption, that role will change with the specifics of the situation. The work of Collier (1989) and others (Hursh, 1984; Lea, 1978), for example, make apparent that the magnitude and type of consequences for specific factors will vary depending on the multiple inputs of the many variables relevant to the eating situation. Soldiers eating in a field scenario provide one instance of a complex physical environment in which accomplishing one's mission, obtaining sufficient nutrients, and meeting other needs or desires requires soldiers (and their commanders) to adopt strategies (preplanned or not) to achieve an acceptable outcome.