Dogs have been shown to resist discrimination, which animal psychologists call “inequity aversion”. Intuitively, it makes sense that breeds used to working in teams would have a stronger inequity aversion than those bred for more individual pursuits. If so, it would support theories about how this aspect of animal psychology evolved. However, such explanations have been dealt a blow, since a study (admittedly a small one) has found no difference across breeds.
Righteous anger about the injustice of the world is not an exclusively human trait, as studies of monkeys have powerfully demonstrated. Dogs have it too, resenting when others are privileged above them. Many evolutionary psychologists are curious whether or not inequity aversion co-evolved with cooperation. A sense of fairness, according to this theory, helped pack animals work together.
Certainly the species in which inequity aversion has been observed are also those that hunt together and share food. That doesn't necessarily mean, however, that the two are connected. If they are, reasoned Jim McGetrick of the Konrad Lorenz Institute of Ethology, those dogs bred for generations to work closely with each other or humans, for example in herding sheep, would be more averse to inequity than those chosen for their independence. McGetrick tested this by having trainers order two dogs to sit and give them their paw, with only one rewarded while the other got to watch the unfairness unfold.
The test is an old one. Much evidence shows dogs resent others being favored over them and are less likely to present their paw if another is rewarded for doing so and they are not. If denied a reward in isolation, however, they will present their paw more times. Unlike monkeys, dogs do not show the same resentment if another dog gets a better treat than them for the same work.
What has not been studied before is how this behavior varies across breeds. In PLOS One, McGetrick reports that 24 dogs from eight breeds all displayed inequity aversion and there was no significant difference by breed. It's possible a large sample of dogs would find a pattern McGetrick missed, but it seems unlikely to be dramatic enough to meet expectations.
That's not to say different breeds behaved exactly the same. Supposedly independent breeds such as basenjis and shiba inus were less inclined to give the tester a paw on request than the more collectively minded labradors or border collies, as would be expected. The cooperative breeds also lived up to their reputations by being more sociable with their lab partners between rounds of testing.
However, the refutation of the study's key hypothesis suggests we may need an alternative explanation of how inequity aversion evolved.