The sense of fair play is an important human trait, but new research suggests that it's a key behaviour for dogs and wolves as well.
In tests, if one animal was given a more substantial reward when performing a task, the other one downed tools completely.
It had been felt that this aversion to unfairness was something that dogs had learned from humans.
But the tests with wolves suggest that this predates domestication of dogs.
Scientists have long recognised that what they term a "sensitivity to inequity", or a sense of fairness, played an important role in the evolution of co-operation between humans. Basically, if others treated you badly, you quickly learned to stop working with them.