The source of our emotions remains elusive. No one knows exactly where emotions come from, what makes us feel the way we do, or whether we can fully control the way we feel. Emotion is intimately related to cognition and culture, and it affects us physically: our bodies react to different emotional states, and we often show emotion physically. Researchers have proposed many theories about the source, purpose, and expression of emotion.
In many ways, our emotions define our existence—without them, most of us would not feel truly alive. We’ve all felt fear of a lurking stranger, pride at scoring well on a test, love, sadness, and loneliness. And between emotional extremes are the ups and downs of everyday life: frustration in a traffic jam, contentment over a satisfying lunch, amusement at a cartoon. We have much to learn about emotion—but we have also learned simply by being human and feeling things every day.