Emotion as Homeostasis
Ross Buck proposed a very elegant decomposition of human behavior. In his view, our behavior is the product of several systems of organization which belong to two big families. The first one is the family of innate special-purpose processing systems (reflexes, instincts, etc.). In general their function is "bodily adaptation" to the environment. In general, their approach is not analytic but holistic and syncretic: they don't "reduce" the situation to its details, they treat it as a whole. In Buck's view, these processes are innate, we don't need to learn them. The second family contains acquired general-purpose processing systems. In general their function is to make sense of the environment. Their approach is sequential and analytic. The former family is associated with the right hemisphere of the brain and is responsible for emotional expression; the latter is associated with the left hemisphere and is responsible for symbolic thinking. The two families cooperate in determining the body's behavior.
What is even more interesting about Buck's analysis is actually the advantage of emotions in communication between humans. Communication of emotions turns out to be a biologically shared signal system. It was created through the evolutionary process and it is part of every human being. It means that it is very easy to communicate an emotion: we immediately recognize the meaning of another human's emotion. On the contrary, communicating a theorem is not easy at all, and often requires special skills.
Besides bodily adaptation, therefore, emotions have the important function of speeding up communication of crucial information among members of the same species.
If emotion is, ultimately, a reaction to a situation in the environment, it can be assumed to be a "measure" relative to that situation, and what is communicated is precisely that measure. But a measure of what? Buck thinks that emotions always originate from motives that must be satisfied: the emotion is a measure of how far they have been satisfied. For example, fear is a measure of safety.
A more appropriate way of referring to adaptation is "homeostasis", which is the process of searching for a balance. If something changes in the environment, all the organisms that depend on that environment will react somehow to recreate the equilibrium they need to survive. This process of continuous search for equilibrium is called "homeostasis". Most scientists who have studied emotions agree with Buck that the ultimate function of emotions is homeostasis.