Even with many definitions, from Aristotle's 4th century BC definition -- "the emotions are all those feelings that so change men as to affect their judgments, and that are also attended by pain or pleasure" (7) -- to Merriam-Webster's 20th century AD definition -- "the affective aspect of consciousness; feeling"(2) -- emotion, and what causes emotion, can be rather difficult to define, especially in non-scientific terms. Defining the difference between a "true" smile and a "false" smile is almost impossible to put into words, yet most people readily admit that they can distinguish between the two. (4) So what is it that defines emotion?
     Scientists are still trying to understand just what causes us to have emotions, but recent researchers have discovered the center of "emotions" in the brain. "A region at the front of the brain's right hemisphere, the prefrontal cortex, plays a critical role in how the human brain processes emotions," says a 2001 University of Iowa report. (6) Scientists monitored single brain cells—neurons—in the right prefrontal cortex and found

"that these cells responded remarkably rapidly to unpleasant images, which included pictures
of mutilations and scenes of war. Happy or neutral pictures did not cause the same rapid
response from the neurons." (6)

The scientists speculated that the rapid reaction of neurons to "unpleasant images" might be related to the results of other studies, which have shown that the brain is capable of responding very quickly to "potentially dangerous or threatening kinds of stimuli." (6) The study is not conclusive, however, as the experiment was performed on only one patient who had epilepsy, but the experimenters stated that "the tissue being studied was essentially normal, healthy prefrontal cortex." (6)
     Another interesting aspect of studies of emotion is the differences between the right and left hemispheres of the brain. Left-handed people, who are right-brain dominant, tend to be more emotionally and artistically oriented, but left-handed people are a minority of the population. Studies have shown that the left hemisphere of the brain is responsible for "logical thinking, analysis, and accuracy," whereas the right hemisphere is responsible for "aesthetics, feeling, and creativity." (8) The right brain also dominates in producing and recognizing facial and vocal expressions. (3) Unfortunately, most schools emphasize "left-brain modes of thinking, while downplaying the right-brain ones," (8) and society in general emphasizes rational thought over emotional thought. (1) "The classic assumption is that emotion wreaks havoc on human rationality..." (1) It has been argued, however, that emotions actually contribute to and aid rational thought, rather than being purely irrational thought. (5)
     In one study, a businessman, Elliot, suffered from a brain tumor that partially damaged his brain, specifically his prefrontal cortex—the emotional center of the brain. As a result, Elliot "lost the ability to experience emotion; and without emotion, rationality was lost and decision-making was a dangerous game of chance." (1) Without emotions, he could no longer analyze the experiences he had lived through, which left him with nothing to tell him whether a decision would be good or bad. Elliot's lack of emotional response to anything that he experienced led to a lack of understanding what is good and what is bad. This case seems to emphasize the importance of emotions in "rational" decision-making. Emotions "are fundamental building blocks out of which an intelligent and fulfilling life can be constructed." (1)
     Since emotions have been observed to be such an important part of who we are, it is worthwhile to wonder where emotions come from. Why do we have emotions, and how are we able to tell the difference between so many subtly different facial expressions that convey different emotions?
     Language is a very important part of what defines humanity and how we interact with and understand each other, and facial expressions play an important role in interpreting what another person is feeling—someone might say that they are okay, but their facial expressions might indicate that they are lying. The importance of facial expressions is easily seen "when we converse on an important subject with any person whose face is concealed." (4)
     How do we recognize emotions? When you see someone who is happy, do you pause to thoroughly analyze the person's features before determining that the person is indeed happy? Most people are not aware -- at least not consciously aware -- of performing any sort of in-depth analysis to determine what emotion someone else is feeling, so does that mean that emotions are innate? The discovery of an emotional center in the brain would seem to support this idea.
     When Charles Darwin studied emotion in humans and animals in the latter half of the nineteenth century, he hypothesized that emotions are innate, but that humans learned them before they became imbedded in our nature -- that is, after years of practicing and having to learn emotions as part of communication skills, emotions became innate through the process of evolution. (4) Further support of the idea that emotions are innate comes from observing infants and young children, who are definitely capable of conveying emotions, but have not had enough time to actually learn the emotions for themselves.

"I attended to this point in my first-born infant, who could not have learnt anything by associating
with other children, and I was convinced that he understood a smile and received pleasure from
seeing one, answering it by another, at much too early an age to have learnt anything by experience. ...
When five months old, he seemed to understand a compassionate expression and tone of voice. When a
few days over six months old, his nurse pretended to cry, and I saw that his face instantly assumed a
melancholy expression ... [T]his child never [saw] a grown-up person crying, and I should doubt whether
at so early an age he could have reasoned on the subject. Therefore it seems to me that an innate feeling
must have told him that the pretended crying of his nurse expressed grief; and this through the instinct
of sympathy excited grief in him." (4)

This demonstrates the importance of emotional facial expressions in communication—they are a child's first language, the first way a child may communicate with the others around him. (4)
     Scientists still have a lot more research to do before we can truly understand our emotions, but it is clear that emotions are an important part of who we are. Emotions are more than just whims or "following your heart;" emotions are a part of how we think "rationally," as seen in the case of Elliot, the man who lost his emotions. Therefore, it is ridiculous that society frowns on those who think too "emotionally" rather than "rationally" -- they are not two separate ways of thinking, but rather they are interconnected, so that we need both in order to make decisions about ourselves and the world around us. Emotions, and the facial expressions that go with them, are the most truthful aspects of humans—"They reveal the thoughts and intentions of others more truly than do words, which may be falsified." (4) Emotions are the intangible and indefinable elements that make us who we are.

"The joy, and gratitude, and ecstasy! They are all indescribable alike."
~ Charles Dickens (9)

References:

1) "Emotion, Rationality, and Human Potential," John T. Cacioppo (University of Chicago); from Fathom: the source for online learning

2) Merriam-Webster OnLine Dictionary: "emotion"

3) "Emotion and the Human Brain" by Leslie Brothers, MIT Encyclopedia of Cognitive Science

4) "The Expression of the Emotions in Man and Animals" by Charles Darwin (1872); Courtesy of "The Human Nature Review" edited by Ian Pitchford and Robert M. Young

5) "Emotions" by Keith Oatley, MIT Encyclopedia of Cognitive Science

6) "UI study investigates human emotion processing at the level of individual brain cells" (Week of January 8, 2001), University of Iowa Health Care News

7) Aristotle's Rhetoric, Book II, Chapter 1, Translated in 1954 by W. Rhys Roberts; written by Aristotle in 350 B.C.

8) "Right Brain vs. Left Brain"

9) Dickens, Charles. "A Christmas Carol", from The Christmas Books. First published in 1843.