Wilkinson first reported in 1984 that vampire bats may share regurgitated blood with non-relatives. Vampire bats form strong bonds with their colony mates. 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 misses a few nights of feeding in a row can starve. A vampire bat that found no food can beg another bat for blood. A small amount lets it live and hunt another day. Among vampire bats, grooming is mostly associated with food sharing. In some pairs, grooming eventually gave way to it.

In one task, an adult hung clothes on a line. He 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. The adult never asked them for help. Toddlers rarely helped in control conditions where the grown-up did not need help. 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.

Young chimpanzees helped a person who was reaching for something. The 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.

A free rat will open the door of a trap. It lets 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. It was as if it picked up the cagemate's distress. Rats freed trapped cagemates even when the reward of social contact was prevented. So the contact was not the only reason.

Empathy is sensing and sharing what another person is feeling. Emotional contagion is the spontaneous spread of emotions between people. Cognitive empathy means understanding another's perspective or mental state. Having empathy does not always mean a person will want to help someone in need. The Interpersonal Reactivity Index is a 28-item self-report test by Mark Davis that measures empathy.

Scientists have also looked at cells and chemicals in the body. 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. Scientists still argue about what mirror neurons do in people, including how much they explain reading other minds. Oxytocin is a peptide hormone and neuropeptide. It is 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. It may play a part in bonding between humans and dogs.

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. Doing a variety of kind acts seems to work better than repeating the same one. 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.

Asian elephants comfort other elephants that are upset. They use touch and sounds. An elephant may put its trunk in another elephant's mouth to calm it. A researcher compared this gesture to a handshake or hug. As of November 2026, a 2014 study gave the first scientific evidence that elephants console one another. 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.

In the public goods game, each player secretly chooses how many private tokens to put into a shared pot. The game is used to study altruism and cooperation. Tit for tat copies what the other player did last. It starts with cooperation. It won two competitions against other strategies.

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.

Words to know

• regurgitated: brought back up
• predisposition: built-in tendency
• cognitive: thinking-based
• oxytocin: a hormone
• altruism: selfless concern