Although I agree with an approach that seeks evolutionary explanations for biological traits in general, and emotions in particular, there are a number of problems with the specific formulation in Nesse's paper that must be addressed.
2. Although I agree with an approach that seeks evolutionary explanations for biological traits in general, and emotions in particular, I have a number of problems with the specific formulation in Nesse's paper. For one thing, the word "mood" is used in a somewhat idiosyncratic way. To illustrate, the unabridged dictionary has three definitions: A conscious feeling or emotion; a fit of anger (archaic); or a prevailing attitude or disposition. In everyday usage "moodiness" is often equated with being temperamental, that is, showing many emotions in somewhat unpredictable ways. The use of the word "mood" to refer to feelings of happiness or sadness exclusively is part of psychiatric jargon and even there it is more likely to refer to states of mania and depression than to states of happiness and sadness. Nesse suggests that "high and low mood (i.e., ordinary happiness and sadness) are opposite sides of the same coin, as demonstrated in manic-depressive illness, and yet he states that he is not concerned with explaining mania, depression and grief. There is obvious confusion about the meaning of these different concepts, and opinions are far from unanimous about how different sadness, grief, and depression are from each other. Surely our explanations should not be limited to particular words; if relevant they should apply to synonymous concepts as well.
3. Second, the impression one receives from reading Nesse's paper is that we need to find one function for the capacity to experience high and low moods, under the assumption that we have a single continuum. This seems to me to be an unnecessarily restrictive assumption. It would imply that we require one explanation for fear and aggression by virtue of the fact that they are on a fight-flight (or approach-avoidance) continuum. The same would apply to such polarities as acceptance-disgust and love-hate. Most theories that have looked at this issue have sought separate explanations for the functions of fear and anger, joy and sadness, acceptance and disgust (Plutchik, 1980; 1991). In the same sense, it seems appropriate to seek separate functional explanations, if possible, for joy and sadness, rather than assuming that they alone, of all emotions, exist on a unique continuum.
4. My third point concerns the implication that happiness and sadness are inner states or feelings whose functions we are to discover. If we accept the evolutionary view of emotions, the feeling aspect of the complex process called an emotion is, from an evolutionary point of view, the most recent development -- and the least important. As Darwin (1872/1965) stated so clearly (and the ethologists have since demonstrated countless times), it is the communicative aspect of emotions that is the most significant for survival. Emotions are complex, homeostatic, behavioral feedback systems; their introspective aspect is the part that is the most variable and the most subject to distortion, defense, and repression (Plutchik, Kellerman and Conte, 1979). It is hardly likely, therefore, that evolution should create a survival mechanism on so variable a base.
5. My fourth and last point concerns the suggestion that mood is regulated by the "propitiousness of current circumstances." This is surely a circular definition, for the dictionary defines "propitious" as "favorably disposed, benevolent, advantageous." Thus, to say that propitiousness regulates mood is equivalent to saying that when things are favorable we feel good, and when they are not favorable, we feel bad. But how do we know what is favorable? The concept of propitiousness must somehow relate to specific classes of events that may influence survival if this explanation is to be based on evolutionary biology. What we need to identify are general universal events found at all evolutionary levels, events whose presence or absence influences survival. Key candidates for such events would be food, contact, and sex -- or their many learned symbolic equivalents. I suggest that the gain or loss of these special survival-related events (or their symbolic equivalents) in human adults are the basis for joy and sadness, just as other significant events are the bases for all emotions.
Nesse, R.M. (1991) What is mood for? PSYCOLOQUY 2.9.2.
Plutchik, R. (1991) The emotions. Lanham, MD: University Press of America.
Plutchik, R. (1980) Emotion: A psychoevolutionary synthesis. New York: Harper and Row.
Plutchik, R., Kellerman, H. and Conte, H.R. (1979) A structural theory of ego defenses and emotions. In C.E. Izard (Ed.) Emotions in personality and psychopathology. New York: Plenum.