Altruism is unselfish behavior designed to promote others' welfare regardless of harm to self. For example, non-Jewish rescuers of Jews during the Holocaust of World War II behaved altruistically. While prosocial behavior balances own and others' needs, and martyrdom risks death in support of a cause, altruism serves others without expectation of recognition. Altruism requires awareness of one's own needs, empathetic understanding of others' emotions, and action consistent with personal moral standards. At best, children discern their emotions by age three, empathize with others' feelings by age six, understand social interactions simultaneously from their own and others' perspectives by age ten, and base their moral standards on principles they have evaluated rather than on authority by late adolescence. Experiences with parents, siblings, peers, and authority figures who demonstrate, discuss, and reward self-awareness, empathy, and moral reasoning are essential for the development of a sense of altruism.