Jealousy seems like a pretty human emotion, requiring as it does both some relatively complex cognitive hardware and tangled relationships we don't usually associate with most other species. But a new study in PLOS One suggests that dogs, too, show some signs of jealousy when they feel their relationship with their owner is threatened by another dog — or a stuffed dog that looks and sounds like one.
The study jumps off previous work in humans that showed that babies exhibited "behaviors indicative of jealousy ... when their mothers interacted with what appeared to be another infant (but was actually a realistic looking doll). The infants did not display the same behaviors when their mothers attend[ed] to a nonsocial item (a book)."
The researchers ran a version of the same experiment, only with dogs instead of babies. "Thirty-six dogs were individually tested and videotaped while their owners ignored them and interacted with a series of three different objects," the researchers write. In the jealousy condition, the owners played with a stuffed dog, "which briefly barked and wagged its tail, as if it were a real dog." In the other two conditions, the object was a "jack-o-lantern pail" or a pop-up children's book. Other researchers then evaluated the videos to gauge the dogs' behavior. Neither the owners nor the video viewers were aware of the experiment's purpose, since if they were it could introduce bias in their actions or evaluations. The dogs ranged over a wide variety of breeds.
The idea, then, was to attempt to distinguish whether the dogs were reacting simply to being ignored by their owners, regardless of the source of the distraction, or whether seeing their owners fawn over what appeared, to them, to be another dog would exhibit the canine version of jealousy. Sure enough, the researchers found statistically significant differences in a variety of behaviors between the three objects that suggested the presence of something like jealousy. Most notable, the dogs were way more likely to push or touch either the owner or the object when that object was that stuffed dog. Also, "86% of the dogs sniffed the anal regions of the toy dog during the experiment or post-experiment phases" (I include that detail because it suggests the dogs saw the stuffed dogs as real, and because how could I not?).
"One possibility," the researchers write, "is that jealousy evolved in species that have multiple dependent young that concurrently compete for parental resources such as food, attention, care, and affection." Jealousy, in other words, may be evolutionary selected for — there are cases in which getting whiny can seriously improve your survival odds, whether you're a baby or a puppy.