What are emotions, and why do we have them?

In just a moment, a physical affront to the face can elicit the emotional response of anger. See more in the emotion photo gallery.

If you're ever hit in the nose hard enough to make your eyes water, you may also notice that your skin will grow hot, your mouth will go a bit dry and your pulse will become elevated. You'll find that your head begins to swim with a strong desire to hit something in return, possibly to shout while you do. Eventually, you'll find that you've overcome this sudden influx of physical and mental stimuli. What you've just experienced -- the basic emotion of anger -- has passed.

Why a slight impact to the nose leads to a series of physiological and mental changes has long been a matter of speculation, but most psychologists agree that a basic emotion like anger exists as an evolutionary trigger. We humans -- and most other animals -- appear to be equipped with a set of predictable responses to situations. We call these the basic emotions: anger, fear, surprise, disgust, joy and sadness, as described in the 1970s by anthropologist Paul Eckman [source: Changing Minds].

Over time, this list of basic emotions has been added to, subtracted from and reshaped based on the idea that human emotions are universal. This notion suggests that for any given situation, like being hit in the nose, any individual in any culture would experience something like anger. This view of emotions as largely objective is widely accepted, although there is an emerging school of thought that believes emotions to be far more subjective: Rather than six or 11 basic emotions, there is an emotion for every possible human experience [source: SCAS].

Under almost every explanation of emotions is the premise that they're a naturally-occurring response to a situation. Whether this response is the result of our own evaluation or an automatic one remains to be seen. In the field of psychology, the view of the nature of emotions can be divided into two camps: Emotions are either the result of a judgment of any current situation or a perception of changes taking place within our bodies [source: Thagard]. In other words, when we experience disgust, it could be the result of a judgment about how we feel when we see vomit. Under the other view, we experience disgust because our body undergoes physiological changes like queasiness and increased skin temperature at the sight of vomit.

Over time, research has also separated other emotions that most in the scientific community believe are only experienced by humans and some other primates. These higher or moral emotions are based on self-awareness, self-consciousness and ability to empathize with others [source: Heery, et al]. The moral emotions are pride, guilt, embarrassment and shame [source: Simons].

Like basic emotions, moral emotions have accompanying physiological changes associated with them. But they diverge from basic emotions in that they tend to emerge after self-reflection, and they support the theory that emotions are results of judgments, rather than simply involuntary reactions to a stimulus.

Whether discussing the origin or nature of basic or higher emotions, one question remains: Why do we experience them in the first place?