the top of the food chain that culminates in the human species. But, as the Christian Bible tells us, “Man does not live by bread alone.”

Modern humans bring into play a more complex requirement for sustenance. As a purely biological organism, the species requires an energy source to support replication and propagation. However, as we’ll consider just a bit later, human requirements for life can extend beyond simple energy requirements and encompass higher order needs as well. Very specifically, the human mind requires sustenance in its own right. The mind can drive the body to seek this additional sustenance in a complex dance of needs and fulfillment. So, how and more to the point, why are these various aspects of sustenance in play?

The acquisition of sustenance in all its varied forms is typically driven by action stimuli that are associated with the particular sustenance needed. We will ascribe the term appetite to this stimulus for action. In essence, appetite provides the feedback to a loop mechanism; when a particular sustenance is missing or is in short supply, then an appetite is created that stimulates action to gain a new supply of the sustenance. Another instance of asymmetry is sometimes found when the feedback loop involves an indirect connection between appetite and sustenance. Consider the appetite for oxygen and the physiological urge to breath that forms the feedback loop to sate that particular appetite. The body senses carbon dioxide levels in determining whether to autonomically stimulate breathing; so a high carbon dioxide level translates into an urge to breath. Sometimes underwater divers, or novice swimmers, will take several deep breaths before setting off to swim some distance underwater. Their perception is that these deep breaths will increase the oxygen in their systems and they can consequently hold their breath longer. In fact, what the deep breaths do is to lower the carbon dioxide levels in the blood. Now, when the diver is underwater and depletes the available oxygen, the carbon dioxide level may still be so low as to not stimulate the urge to breath. The result is that the diver may actually lose consciousness due to a lack of oxygen. This is definitely not a good thing when it happens while a person is under water.

We tend to apply a lot of names to this concept of appetite: a shortage of water creates a thirst, a lack of food creates a hunger, a deficiency of salt creates a craving, and so on. We’ve all alluded to the cravings of a pregnant woman for pickles and ice cream; in fact, the demands of gestation do present extreme demands on certain forms of sustenance and the appetites that are generated as a result can present as relatively innovative stimuli. The feedback mechanisms that we can observe are certainly not limited to humans, or to animalia for that matter. Consider that the need for water stimulates the growth of taproots in many plants, and the sunflower changes the orientation of its bloom during the day in order to track the movement of the sun and thereby gain more light. So, the recurring theme that is far-reaching in its consequence is the feedback loop as a means of stimulus and control of the actions of living things. The lack of sustenance creates an appetite which stimulates action to alleviate the deficiency of sustenance. Another way of saying this is that the need for sustenance effects policies to alleviate the need.

The needs that we’ve considered thus far are basic physiological needs. As we’re going to consider a couple of sections hence, humans exhibit needs at much higher (cognitive) levels. Each need, in turn, has its own appetite signaling when a need is going unfulfilled. For example, we have a need for safety and security. When this need is unfulfilled, we feel apprehension and fear; feelings that provide impetus to stimulate actions to alleviate this need.

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