1947: Scientists identify a new virus in rhesus monkeys in Uganda; first human cases detected in Uganda and Tanzania five years later. (discovermagazine.com)
Rachels has described an experiment with rhesus monkeys in which not only did monkeys refrain from eating for many days in order not to shock another monkey, but the willingness to undergo such hunger was correlated with (1) whether or not the monkeys had been cagemates and (2) whether or not the hungry monkey had itself been in the situation of the monkey undergoing the shocks. (religion-online.org)
Earlier studies on rhesus monkeys showed similar success. (discovermagazine.com)