henry copeland:

Animals and fairness

At a canine research centre at Eotvos Lorand University in Budapest, for example, dogs frequently chosen to take part in tests are shunned by other dogs. It turns out that all the dogs want to take part in these tests because they receive human attention; those which are chosen too often are seen as having got unfair advantage. Capuchin monkeys taking part in experiments keep track of the rewards they are getting. If one is offered a poor reward (such as a slice of cucumber), while another gets a tasty grape, the first will refuse to continue the test. Chimpanzees do this, too.
- www.economist.com