Kindness is offered for the sake of the person who receives it, whether or not the giver is attached to that person; altruism is concern for the well-being of others that does not depend on personal benefit or being paid back. Empathy is sensing and sharing what another person is feeling; emotional contagion is the spontaneous spread of emotions between people. Having empathy does not always mean a person will want to help someone in need; research suggests that inequality can reduce empathy, and that people can enhance or restrict their natural empathic abilities.

In one task, an adult hung clothes on a line and dropped a clothes peg that he could not reach. Toddlers who were 18 months old helped a grown-up they had never met. In the 2006 toddler study, virtually all of the children helped at least once, and the adult never asked them for help. Researchers said the 2006 toddler study shows that even infants without much socialization are willing and able to help spontaneously. Helping behavior is seen in humans from about two years old, when a toddler can understand subtle emotional cues. Warneken argued that people have a biological predisposition to be helpful, so not much moral instruction is needed to develop helping. Kindness is most often taught by parents to children and is learned through observation and some direct teaching. Studies at Yale used games with babies to conclude that kindness is inherent to human beings.

Young chimpanzees helped a person who was reaching for something; young chimpanzees helped in easy tasks but not in the harder ones. Nobody asked or rewarded the toddlers and chimpanzees for helping; As of November 2026, in 2006 the researcher Warneken said the chimpanzee study was the first experiment to show helping toward goals in a non-human primate. Bonobos share food with others, even unrelated strangers; after a chimpanzee hunt, the meat is shared with all hunting party members and even bystanders. In a study of chimpanzees, females were more consoling than males overall, and bystanders seemed sensitive to the neglected victims' need for comfort.

A free rat will open the door of a trap to let out a rat from its own cage that is stuck inside. The researchers did not train the rats to free their cagemates. A rat was as likely to free its trapped cagemate first as to open a container of chocolate. A free rat acted more upset when its cagemate was trapped, as if it picked up the cagemate's distress. Alarm calls were rare in the rat study, so the authors judged that the free rat was unlikely to be opening the door just to end the alarm calls. Rats freed trapped cagemates even when the reward of social contact was prevented, so the contact was not the only reason. Studies report that rodents show empathy for cagemates in pain, but not for strangers. Early results from the rat study suggested that females were more likely to become door openers than males.

Wilkinson first reported in 1984 that vampire bats may share regurgitated blood with non-relatives; vampire bats form strong bonds with their colony mates, and some unrelated bats have traveled together for more than ten years. A vampire bat can share some of its blood meal with another bat in its colony; a vampire bat that found no food can beg another bat for blood, and a small amount lets it live and hunt another day. A vampire bat that misses a few nights of feeding in a row can starve; among vampire bats, grooming is mostly associated with food sharing, and in some pairs grooming eventually gave way to it. In captive bats, those that were more generous were fed more when they failed to feed.

Tit for tat copies what the other player did last, starts with cooperation, and won two competitions against other strategies; in the public goods game, each player secretly chooses how many private tokens to put into a shared pot, which is used to study altruism and cooperation. In public goods games with punishment, people punish at a cost, which usually leads to greater group cooperation, and over the long term it seems more efficient.

Reciprocal altruism is helping with the expectation that the other will help back later; Robert Trivers developed the idea to explain cooperation; vampire bats may not yet qualify as an unequivocal example of reciprocal altruism. A commentator wrote that for vampire bats, reciprocity is not a cold tit-for-tat calculation but rests on trust built up over time; scientists find it hard to know a vampire bat's motivation for sharing, so it is not clear whether bats share with a wider network in mind.

Mirror neurons were first found in macaque monkeys: some cells fired when a monkey grasped food and when it watched a person do the same. In macaques, mirror neurons are found in the inferior frontal gyrus (area F5) and the inferior parietal lobule. Scientists still argue about what mirror neurons do in people, including how much they explain reading other minds. The function of mirror neurons in macaques remains unknown, and adult macaques do not seem to learn by imitation. Mirror neurons may furnish a neural basis for predicting another individual's next actions and inferring intention.

In a study, pet dogs went up to a person who was crying; dogs in a study went to a crying stranger, not only to their owner. The dog study used a method first used with human infants, and most dogs responded to the crying person in a submissive way.

Oxytocin is a peptide hormone and neuropeptide normally made in the hypothalamus and released by the posterior pituitary; oxytocin has a role in social behaviors in many species, so it likely also does in humans, and it may play a part in bonding between humans and dogs. Studies of nasal oxytocin have been criticized: evidence suggests nasal sprays may not produce behavioral effects, and results may reflect publication bias; oxytocin sprayed into the nose has been reported to reduce fear, possibly by inhibiting the amygdala.

Doing something kind for another person can make you feel happier. A psychologist's study found that doing kind acts raised people's well-being. In a bonus study, how workers spent the money, not how big the bonus was, changed their happiness. In one experiment, people were handed a $5 or $20 bill and told to spend it by 5 p.m. that day; those who spent it on others reported more happiness. Regular volunteering has been linked to a lower risk of dying and better physical functioning into old age. Most of the evidence that regular volunteering helps health comes from observational studies of people who volunteer regularly. A Harvard researcher said that volunteering or an act of kindness can distract you from problems, and that selfless acts can buffer against stress.

In one experiment, one person's generosity spread to three people and then to nine. In experiments, generous behavior spread through a group, and so did stingy behavior. In a cooperation experiment, a small number of generous people changed how other people in the group behaved. Christakis compared a social network to a matching grant: one person's giving in the first round was ultimately tripled by others. Cooperative behavior in the experiments spread up to three degrees of separation. A science writer noted that Fowler and Christakis report that both cooperative and selfish acts spread, so it is unclear how the ripples affect real networks.

Words to know

• altruism: selfless concern
• reciprocity: giving back
• inherent: built in
• observational: watching-based
• oxytocin: a hormone