They are regarded as a man's best friend, but scientists say dogs are selfish creatures who will play with owners, but not help them.
Researchers from the University of Portsmouth studied 24 family dogs to see how useful they were to their owners, finding that they were more interested in themselves than coming to the aid of a human.
Scientists concluded that, although dogs sometimes helped their owners, it was "mainly self-interest that was driving the dogs' behaviour".
To test each animal, a notebook a human had been using was hidden in an opaque tub in one corner while the pet watched and the person left the room. When they returned and searched for their notebook, if the dog indicated where it was, they were being helpful.
A toy was placed in another container in a different corner and, if the dog chose this, they were considered selfish. Also hidden in a third corner was a stapler, which was considered neither selfish nor useful.