Any dog owner would testify that dogs are just as prone to jealousy as humans.
But can one really compare Othello's agony to Roscoe's pique?
The answer, according to Christine Harris, a psychologist at the University of California at San Diego, is that if you are petting another dog, Roscoe is going to show something that Harris thinks is a form of jealousy, even if not as complex and twisted as the adult human form.
Other scientists agree there is something going on, but not all are convinced it is jealousy. And Roscoe and the rest of his tribe were, without exception, unavailable for comment.
Harris had been studying human jealousy for years when she decided to take this question on, inspired partly by the antics of her parents' border collies. When she petted them, "one would take his head and knock the other's head away," she said. It certainly looked like jealousy.
But having studied humans, she was aware that there were different schools of thought about jealousy. Some scientists argue that jealousy requires complex thinking about self and others, which seems beyond the capabilities of dogs. Others think that just because our descriptions of jealousy are complex, that does not mean the emotion itself is that complex.
Dog emotions, as owners perceive them, have been studied before. In one case, Alexandra Horowitz, a cognitive scientist who is an adjunct associate professor at Barnard and author of Inside of a Dog, found that the apparently guilty look that dogs can exhibit seemed to be more related to fear of punishment.
Harris ventured into the tricky turf of dog emotion by devising a test based on work done with infants.
When dog owners petted and talked to a realistic stuffed dog that barked and whined, the people's own dogs came over, pushed the person or the stuffed dog and sometimes barked. After the experiment, many of the dogs sniffed the rear end of the stuffed dog, suggesting, Harris said, that the dogs thought the stuffed animal might be real.
Harris also recorded what happened as the owners petted and talked to a jack-o'-lantern and read a children's book out loud, to see if any old distraction would provoke a reaction. The dogs paid little attention to the jack-o'-lantern and very little to the book.
Harris concluded, in a paper in the journal PLoS One co-written with Caroline Prouvost, also of UC San Diego, that the dogs showed a "primordial" form of jealousy — not as complex as the human emotion, but similar in that there is a social triangle and the dog is trying to make sure it, not the rival, receives the attention.
Other scientists had mixed reactions to the work. Horowitz said she admired the goal of the research but thought that the researchers had not shown that the behaviors observed actually indicated jealousy.
"What can be shown is that dogs seem to want an owner's attention when there is attention being given out; this study confirms that," she said.
Sybil Hart, at Texas Tech, who has studied jealousy in infants, said she thought the research was "very well done and makes a very compelling argument."
If you see jealousy in babies and dogs, Hart said, "to some degree, it's innate," which would be important to know for attempts to manage jealousy in humans.
"Overall, trying to make it go away has not been very successful," she said. "We are trying to eliminate jealousy, and scientists are saying maybe we should try to understand it better."
Jealousy, Harris writes in the study, "is the third-leading cause of nonaccidental homicide across cultures."
Harris compared the jealousy of dogs to somewhat controversial findings by Hart in the 1990s that infants as young as six months exhibited a form of jealousy.
Whatever the dogs' behavior is called, said Brian Hare, a director of the Duke Canine Cognition Center at Duke University, there are practical implications for their owners.
"Attention seeking can lead to jealousy-like behavior in dogs that includes aggression in some cases," Hare said. "So for dogs with suspected aggression problems, it may be important to avoid situations where they feel ignored."