Are horses the jealous type? Many owners seem to think so, and the researcher who recently found strong evidence of jealousy in dogs suggest research into horses, birds and cats could reveal some intriguing findings.
University of California researchers Christine Harris and Caroline Prouvost said jealousy in humans was an emotion with far-reaching psychological and social consequences. It typically emerges as the third leading cause of non-accidental homicide across cultures.
While the origins and possible function of jealousy have been debated, most theorists agree its one defining feature is the need for a social triangle, arising when an interloper threatens an important relationship.
“It is commonly assumed that jealousy is unique to humans, partially because of the complex cognitions often involved in this emotion,” Harris and Prouvost wrote, in reporting their findings in the open-access journal, PLoS ONE.
“However, from a functional perspective, one might expect that an emotion that evolved to protect social bonds from interlopers might exist in other social species, particularly one as cognitively sophisticated as the dog.”
The pair adapted an experiment used in human infant studies to examine jealousy in dogs.
Thirty-six pet dogs were individually tested and videotaped in their own homes while their owners ignored them and interacted with a series of three different objects.
In one phase, the owners were asked to play with a realistic-looking stuffed dog as if it was a real dog. The toy barked, whined and wagged its tail. In another phase, the owners were asked to interact with a novel object – a jack-o-lantern pail – in the same way as if they were playing with a dog. In the third “control” phase, they were asked to read aloud from a pop-up children’s book.
They found that dogs exhibited significantly more jealous behaviors, such as snapping, getting between the owner and object, pushing/touching the object/owner, when their owners showed affection toward the realistic-looking stuffed dog as compared to non-social objects.
The most common sign of jealousy was attention-seeking, which often took the form of pushing the owner or attempting to get between the owner and the rival.
Did the pets perceive the stuffed dog as real? Aggressive behaviors aimed at the stuffed animal by some of the dogs seemed to suggest that they did. “Perhaps even more compellingly, 86 percent of the dogs sniffed the anal region of the toy dog during the experiment or post-experiment phases.”
Harris and Prouvost said using a fake dog enabled them to maximize the amount of control they had over the experiment.
“The current findings add support to the emerging view that there is a primordial form of jealousy,” they concluded.
They suggested it was possible that jealousy evolved in animals that required cooperation from other group members for survival and in which alliances were formed (and therefore, can be threatened by rivals).
Another possibility was that jealousy evolved in species that have multiple dependent young that compete for parental resources such as food, attention, care, and affection.
It was also possible that the long co-evolution and domestication of dogs, which likely gave rise to many of their remarkable social-communicative skills, created their capacity for jealousy.
“One might speculate that even if several social species have the capacity for jealousy, dogs may be the only species besides humans in which the emotion can be evoked in connection with a member of a different species.
“Future studies that examine the affective and cognitive abilities of a variety of animal species could help tease apart these various intriguing possibilities.
“Such work is particularly warranted given that a large percentage of owners of some other types of domestic animals such as horses, birds, and cats also report signs of jealousy in their animals.
“Moreover, some of these species such as horses have been shown to be highly sensitive to human attentional cues.
“Further research on the neurobiological components of, and influences on, emotions in both humans and other animals may also help disentangle the similarities and differences of emotion and social behavior across species.”
Harris CR, Prouvost C (2014) Jealousy in Dogs. PLoS ONE 9(7): e94597. doi:10.1371/journal.pone.0094597
The full study can be read here.