Friendship has been studied in academic fields such as sociology.
:248:426:5556 In ethnically diverse countries, there is broad evidence that children and adolescents tend to form friendships with others of the same race or ethnicity, beginning in preschool, and peaking in middle or late childhood
 Aristotle wrote of there being three kinds of friendships: those in recognition of pleasure, those in recognition of advantage, and those in recognition of virtue

