Volunteers wash a stray dog while another gets agitated at a Nanjing animal shelter. A new study concludes that dogs can feel jealous if they think you pay more attention to other dogs.[Photo by Lang Congliu/China Daily]

About 30 percent of the dogs also tried to get between their owner and the stuffed animal; 25 percent snapped at the "other dog", only one did so at the pail and book.

"Our study suggests not only that dogs do engage in what appear to be jealous behaviors but also that they were seeking to break up the connection between the owner and a seeming rival," says UCSD lead author Christine Harris.

"We can't really speak to the dogs' subjective experiences, of course, but it looks as though they were motivated to protect an important social relationship," Harris says.

These results, published in the US journal PLOS ONE, support the idea that jealousy may have some primordial form that exists in human infants and in at least one other social species: dogs.

The findings also suggest that jealousy evolves to secure resources, not just in the context of sexual relationships, but also in any of a wide range of valued relationships, such as competing for parental resources such as food, attention, care and affection.

"Many people have assumed that jealousy is a social construction of human beings - or that it's an emotion specifically tied to sexual and romantic relationships," Harris says. "Our results challenge these ideas, showing that animals besides ourselves display strong distress whenever a rival usurps a loved one's affection."