An experiment with Capuchin monkeys by Dr. Sarah Brosnan
over 10 years ago shows clearly that certain animals take into account both their own and others’ rewards or actions in comparison to their own and that they can make subjective assessments of the outcome and value of certain rewarded behaviours.
The experiment shows the emotional responses as well as the conscious decision making that one monkey made when it clearly thought unfair treatment was taking place. The monkey throws a tantrum when it realises it was receiving cucumbers for its efforts over the preferred fruit - grapes. The experiment has since been replicated using other animals
A further experiment funded through the National Science Foundation that Dr. Sarah Brosnan conducted was to see whether monkeys and humans cooperate at the same levels. Results showed that humans and monkeys cooperate at about the same amount - between 70-80% of the time, a result that suggests "that cooperation runs deep in the nature of primates." The only time that humans reached higher levels of cooperation than monkeys was when they used their language skills.
Instructions of how to play the game were not given before the task started, however, those who discussed the task during the experiment figured out what cooperative interaction was necessary to earn more points and more dollars.