FR and her colleagues asked a group of dogs to do tricks, like give their paw. Then in a second round, they gave treats to some of the dogs when they did the treat, but refused treats to others even when they did the trick. FR says soon the dogs being refused the treats also refused to do the trick: for example, they would lay down and wouldn't sit up anymore, or they wouldn't look at the experimenter. (For those of us close to dogs, this sounds reasonable. But you read something else into this.) We did a control situation and we tested the dogs alone as well, and they continued giving the paw still even though they weren't rewarded. (So what do you think is going on?) I think this is something comparable to envy or a sense of jealousy. (Is there something evolutionary in that?) It makes sense for the evolution of procreation. If you put in an effort, it should be made clear that you also know there's a rewardï¿½this is important for the evolution of cooperation.