An emotion once thought to be purely human, becoming "green with envy," can also be observed among dogs, according to a researchers at the University of California, San Diego.
In their study, dog owners who showed affection towards other subjects, including a toy dog that made noise and wagged its tail, and an inanimate object, elicited what appeared to be jealous behavior from their dogs.
About a third of the 36 dogs tested tried "to break up the connection between the owner and a seeming rival," says psychology professor Christine Harris, who led the study. Another quarter of the dogs actually "snapped" at the toy dog.
Many scientists believe that jealousy is a learned emotion - too complex of a trait to be inherited like fear and anger are. Harris' study, published in the journal PLOS ONE, may prove that wrong.
"Our results challenge these ideas, showing that animals besides ourselves display strong distress whenever a rival usurps a loved one's affection," she concluded, suggesting that jealousy may also be 'hard-wired'.
A better understanding of jealousy could have an impact on society, the researchers say, as it is the third-leading cause of non-accidental homicide.