Scientists disagree about facial expressions of emotion. Lisa Feldman Barrett said that recent evidence challenges the idea that they evolved. Paul Ekman and Dacher Keltner replied that the science shows they are universal. Tests have been done with people from dozens of countries, with significant agreement on which emotion is shown, and recognition was strongest for happiness, sadness and disgust. Ekman and Keltner also say that picking a name for a face from a list of emotion words, in cultures that are very different from each other, has been replicated, or done again, nearly 200 times. The argument has a long history. Charles Darwin claimed only that a specific set of expressions he had observed and studied is universal. In the late 1960s, two people separately showed photographs of facial expressions to people in various cultures and found strong agreement in how the expressions were labeled. To test whether media explained the agreement, Ekman studied people in a New Guinea community who had seen few outsiders and no media portrayals of emotion, and they recognized the same emotions.

Another debate is about what emotions are and how many are basic. Most who study emotions agree that there are at least five core emotions, though experts hold differing views. Basic emotion theory predicts a bodily signature for each basic emotion: correlated changes in facial expression, autonomic nervous system activity and preset and learned actions. One theory says emotion is made of an appraisal, bodily changes, an action tendency, an expression and a subjective feeling. Appraisal theories say that emotions differ from one another because of how a person evaluates the significance of a situation. Scientists also think emotions are made of several parts that work together, involving both the brain and the body. Two people can be in the same situation and feel different emotions because they have different thoughts about it.

How do children come to know emotions? Researchers who study how children learn emotions hypothesize that children learn emotion categories by observing others use the same emotion word to label highly variable events. Research shows that by three to four months of age, infants possess rudimentary concepts for pleasantness and unpleasantness. By about four to six months, a baby's facial expressions consistently reflect anger, joy, interest, fear, disgust or surprise. Infants and young children cannot yet name an emotion or say why they feel it. Regulating emotions and managing behavior are skills that develop slowly over time during childhood. Babies cry to tell people what they need, and around two months old, a baby starts to smile to connect with other people. Because the brain's regulating system is still maturing, young children often feel emotions more intensely and find it harder to regulate their reactions.

Can putting a feeling into words change it? In a 2007 UCLA brain-imaging study, the amygdala, a tiny part of the brain the shape and size of an almond, was less active when people labeled the emotion of a face. The study scanned 30 people, aged 18 to 36, with functional MRI while they viewed pictures of faces. Labeling a face with an emotion word such as "angry" reduced the amygdala response, but labeling it with a name such as "Harry" did not. The lead researcher compared labeling feelings to braking at a yellow light: putting feelings into words seems to hit the brakes on emotional responses, and the effects are likely to be modest, the researcher said. Some people find it harder than others to work out what emotion they are feeling, but with practice, people get better at knowing what they are feeling.

Crying is also argued over. One scientist proposed that crying flushes out chemicals present during strong feelings, but not all scientists agree. Some doubt that crying flushes out enough hormones to explain relief, since even a long bout of sobbing produces only a thimble full of hormone-laden tears. Some studies suggest we cry not because we are upset but because we are trying to get over being upset, so crying may reset the body toward calm. Many scientists say that crying is an involuntary way of calming down. Studies have not been conclusive because genuine grief and crying are hard to cause and measure in a laboratory. People sometimes cry when they feel sad, and emotional tears are one of three kinds of tears. Basal tears bathe the eyes with each blink, and reflex tears well up when onion fumes irritate the eyes.

Deep breathing is a way to calm down, and scientists have tested it. In a Stanford study, one minute of guided slow breathing lowered the heart rates of children about seven years old. Heart rate changed only for children who watched the deep-breathing video, and the control group, the children who did not watch it, showed no change. Stanford researchers said further research should examine deep breathing in this age group after a stressful or challenging experience. One calming breathing exercise is to let the breath flow deep into the belly without forcing it, and to breathe in through the nose and out through the mouth. Pretending to smell a flower and blow out a candle helps children take slow breaths. When you feel afraid, your breathing can speed up.

Scientists also ask what emotions are for. Some researchers say emotions have adaptive value because they quickly mobilize the resources needed for life tasks and communicate socially useful information through bodily expressions. Researchers have argued that sadness may serve useful purposes, including encouraging reflection and signaling the need for social support. Neuroscience has shown that emotion is not an obstacle to reasoning but a necessary part of effective decision making. Whether an emotion is helpful depends on its strength, how long it lasts, how often we feel it, how we express it and when we express it. Moderate emotional arousal tends to improve memory formation, while extremely high levels of stress may impair it. Feelings help the body get ready to act, and emotions have helped people survive. Fear can make a person run from danger, which may save their life, and many emotions probably exist because of challenges humans have faced over time.

Words to know

• universal: the same everywhere
• replicated: done again
• basic: core
• hypothesize: propose an idea
• involuntary: not chosen