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8 The Motivation System

In general, animals are in constant battle with many different sources of danger. They must
make sure that they get enough to eat, that they do not become dehydrated, that they do
not overheat or freeze, that they do not fall victim to a predator, and so forth. The animal’s
behavior is beautifully adapted to survive and reproduce in this hostile environment. Early
ethologists used the term motivation to broadly refer to the apparent self-direction of an
animal’s attention and behavior (Tinbergen, 1951; Lorenz, 1973).

8.1 Motivations in Living Systems

In more evolutionary advanced species, the following features appear to become more
prominent: the ability to process more complex stimulus patterns in the environment, the
simultaneous existence of a multitude of motivational tendencies, a highly flexible behav-
ioral repertoire, and social interaction as the basis of social organization. Within an animal
of sufficient complexity, there are multiple motivating factors that contribute to its observed
behavior. Modern ethologists, neuroscientists, and comparative psychologists continue to
discover the underlying physiological mechanisms, such as internal clocks, hormones, and
internal sense organs, that serve to regulate the animal’s interaction with the environment and
promote its survival. For the purposes of this chapter, I focus on two classes of motivation
systems: homeostatic regulation and emotion.
Homeostatic Regulation

To survive, animals must maintain certain critical parameters within a bounded range.
For instance, an animal must regulate its temperature, energy level, amount of fluids, etc.
Maintaining each critical parameter requires that the animal come into contact with the
corresponding satiatory stimulus (shelter, food, water, etc.) at the right time. The process
by which these critical parameters are maintained is generally referred to as homeostatic
regulation (Carver & Scheier, 1998). In a simplified view, each satiatory stimulus can be
thought of as an innately specified need. In broad terms, there is a desired fixed point
of operation for each parameter and an allowable bounds of operation around that point.
As the critical parameter moves away from the desired point of operation, the animal
becomes more strongly motivated to behave in ways that will restore that parameter. The
physiological mechanisms that serve to regulate these needs, driving the animal into contact
with the needed stimulus at the appropriate time, are quite complex and distinct (Gould,
1982; McFarland & Bosser, 1993).

Emotion
Emotions are another important motivation system for complex organisms. They seem to
be centrally involved in determining the behavioral reaction to environmental (often social)

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