Animal behaviour linked to primordial instinct of jealousy similar to that seen in babies when affection is divided

To legions of dog-owners, the finding will come as no surprise: it does not take much to make a dog feel jealous.

Researchers in the US studied 36 dogs and found that most were indifferent when their owners ignored them and read aloud from a children's pop-up book. But when the owners showered their attention on a stuffed dog – or even played with a bucket with a face painted on the side – the dogs' behaviour changed dramatically.

Video footage showed that when owners petted the stuffed toy, which barked and wagged its tail for effect, their dogs growled more and sometimes snapped and forced their way between the toy and their owner. A quarter of the dogs snapped at the stuffed animal, while only one snapped at the book and the bucket.

Christine Harris, who led the study at the University of California in San Diego, said the dogs' reactions might betray a simple form of jealousy that arises from lack of attention and affection being poured on a rival. The dogs touched the stuffed toy, or tried to get between it and their owner, twice as often as they did with the bucket, and far more than with the book.

"It was striking how much more they tried to do things like get between the owner and the stuffed object," Harris said. "Jealousy was very rare with the other two things." The study is published in the journal Plos One.

The research involved 14 breeds of dogs, including daschunds, chihuahuas, pomeranians and Yorkshire terriers, with the rest being mixed breeds. As a precaution, Harris only used small dogs in case they got overly aggressive and had to be subdued.

Harris said that while anecdotal accounts tell of dogs being jealous of partners, cats and babies, the animals' jealousy is thought to be primordial and similar to that seen in babies. Her study was inspired by previous work that suggested six-month-old babies got jealous when their mothers paid attention to a life-like doll, but not when they read a book.

In her study, Harris ran two tests simultaneously. The first looked at jealous behaviour in the dogs, like growling, snapping, and getting between and pushing the owner and object. The second measured the amount of attention the dogs were giving the object and owner.

Giorgio Vallortigara, a neuroscientist at the University of Trento said: "It is an interesting study that provides some empirical support to the idea, quite widespread among dog owners, that these animals possess some sort of equivalent of jealousy behaviour." If the underlying mechanism is ancient as the authors suppose, it could be sparked by anything that seems to be living, he added.