The first scientific study to find envy in non-primates affirms what many already know: dogs can get jealous.
"Everybody who has a dog at home probably [suspects] that dogs can be very jealous of other dogs and also of people," said lead author Friederike Range of the University of Vienna, Austria.
In experiments with 43 dogs, Range's team showed that the canines reacted to inequity.
The team had one dog watch another dog receive a reward for doing a trick. When the watching dog performed the same trick and was not rewarded, that dog refused to do the trick again, Range said.
The experiments were modeled after recent studies that observed resentment in capuchin monkeys and chimpanzees when the animals weren't compensated equally after performing the same tasks as a partner.
Dogs are not as sensitive to inequality as the primates, Range and her team found. The canines participating in the study didn't seem to mind if a nearby dog got a better reward or didn't work as hard for the reward—but the primates did.
The study was published online today in the journal Proceedings of the National Academy of Sciences.
(Read about animal minds in National Geographic magazine.)
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Range and her team tested the dogs in the presence of partner dogs they were already acquainted with—a playmate, or a pet from the same household.
The dogs were asked to place their paws in the experimenter's hand. The animals were rewarded—or not—with dark bread and sausage.
"If both of them didn't get a reward, they continued working more or less," Range said. "But if one of them didn't get food, the one that didn't get food just said, No."
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