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Doggone it. When stiffed, canines turn up their wet noses instead of shaking hands.

Friederike Range

Dogs Have a Nose for Inequity

Advice for anyone trying to cheat her dog: He's not so easily fooled. When researchers asked two side-by-side canines to perform a trick--but only rewarded one for his efforts--the other dog soon stopped playing along. The findings show that even dogs can sense inequity, the first time the feeling has been documented in non-primates.

Equal pay for equal work is deeply ingrained in the human psyche and for good reason (even though it doesn't always play itself out in the workplace). Frans de Waal, who studies primate social behavior at Emory University in Atlanta, Georgia, says the belief helps maintain social harmony within groups, a key to early human survival. Primates benefit from cooperation, too, and indeed De Waal has shown that they display what could be a precursor to a sense of fairness. A capuchin monkey will refuse to continue to trade tokens with an experimenter, for example, if a fellow capuchin receives a sweeter food reward for his efforts. But no one had looked at how non-primates react to unfair treatment.

After discussions with De Waal, animal cognition researcher Friederike Range and colleagues at the University of Vienna in Austria's Wolf Science Center turned to domestic dogs, which have a strong track record of cooperation. The researchers selected 29 dogs of various breeds that had each been trained to put their front paws in someone's hand on command, a task called "giving the paw." The dogs were paired and one was randomly chosen to be shortchanged.

When only one dog received the reward, the other's performance dropped significantly: he gave the paw only about 20 times out of 30, the researchers report online today in the Proceedings of the National Academy of Sciences. At first, the short-changed dogs required more prompts before presenting their paws and showed more signs of stress like looking away or scratching themselves, Range says. "You get the sense that they are not happy." Finally, they simply refused to give the paw. (Breed made no difference in the results).

Dogs that were treated unfairly refused to give the paw almost twice as often as frustrated controls (unpartnered dogs who did not receive a reward for their efforts). So the researchers could conclude that the inequity, not simply the food denial, was causing the dogs' distress, Range says.

Overall, the findings support the idea that dogs detect and respond to incentive inequities, says comparative psychologist Mauricio Papini, who studies incentive learning in mammals at Texas Christian University in Fort Worth. That makes sense, Papini, Range, and De Waal all agree, since dogs are such naturally cooperative animals. "If my monkeys can [sense inequity]," says De Waal, any animal with a decent-sized brain should be able to as well.

But it's too soon to say that dogs can balance their food bowls on the scales of justice. The word "fairness" is loaded with ethical connotations, Papini says, and researchers will need additional evidence and more rigorous controls to demonstrate that dogs possess the sophisticated sense of social justice that humans associate with fairness. The next step would be to look at the behavior in other animals in similar situations. Don't expect results on cats any time soon: getting the famously contrary feline to take commands might be a research project in itself.