New scientific research proves without a doubt that not only primates are able to sense envy and jealousy, but that dogs can as well. In order to prove this, researchers used only similarly-trained dogs, and asked them to extend their paw under similar circumstances. As soon as the dog "next door" was getting more attention, other canines showed elevated levels of stress, which seems to point at the fact that these animals evolved these feelings in order to survive.
 

The scientists, working from the University of Vienna, in Austria, conducted their study on 33 animals, all very well-trained. The only thing team leader Friederike Range changed when asking each of the dogs to extend its paw were the conditions under which the request occurred. While sometimes the dogs were rewarded, sometimes they were not, but that didn't seem to matter to them, until the couple tests.
 

During these tests, two dogs were placed next to each other, and asked to extend their paws. One of the specimens received a reward – sweets or small sugar cubicles – while the other did not. And the reaction was almost instantaneous, the dog that was neglected started exhibiting higher levels of stress, and some even started crying, to manifest their disappointment in the injustice.
 

The researchers say that this behavior may have been inherited from their wolf ancestors, who developed a high "sense" of justice in order to cope with the harsh conditions that these animals met in the forests during winters, when the pack was only as strong as its weakest member. Range says that, probably, the sense of justice kept them on their toes and helped the pack leader make hard decisions very fast.
 

"The fate of a wolf or coyote pack can really hang on whether an individual pulls its weight. These animals learn not to tolerate unfairness," argues Marc Bekoff, from the University of Colorado, whose theories were confirmed by this new study.