Dog owners have long known that dog jealousy is a real issue. Now we have proof! A group of Austrian scientists has reported that dogs understand the fairness of treats dispensed by humans, and respond accordingly. The researchers took two dogs, both of whom had been taught the same trick (shake hands). They sat the dogs side-by-side, asked them to perform, then gave them treats as a reward. The dogs were fine when they were each given a treat, even when one treat was better than another. However, when the scientists gave only one dog a treat, the other dog stopped performing on command. The technical term for this behavior is inequity aversion, which has previously only been proven in primates like chimpanzees and people. In 2003, scientists in Atlanta demonstrated that capuchin monkeys understand when a situation is unfair, in a scientific article with the wonderful title, Monkeys Reject Unequal Pay. In a test like the one given to the dogs, the capuchins preferred situations where neither monkey got treats to situations where only one monkey got a treat. Interestingly enough, when only one monkey got a treat, the "unpaid" monkey directed its anger at the researcher - not at the other monkey. Thus showing that the capuchins not only understood that the situation was unfair, but were able to correctly place blame for the unfairness. (Which is more than I can say for some coworkers I've had in the past!) The careful reader will note that only the dog who didn't get the treat stopped performing. Presumably both dogs understood that the situation was unfair. However, the dog who did get the treat was happy to keep performing. I expect this finding will also not surprise dog owners.