Dogs Understand Us Better than Our Closest Relatives
Previous studies had shown that dogs can pass a test in which a human points to a container and the dog must look inside it to find food. Human one-year-olds can pass this kind of test too. But chimpanzees have a hard time with it. Researchers at the Max Planck Institute for Evolutionary Anthropology in Germany wondered if these previous tests were unfair to chimpanzees. Would changing the setup of the experiment prove that chimps really do understand our gesturing?
In previous versions of the experiment, chimpanzees had been seated behind a barrier, while dogs were in the same room as the humans. Additionally, the objects that the animals were asked to choose between usually sat between the human experimenter and the chimpanzee--so the human didn't actually need the chimps' help to lift a container and get the food underneath. Perhaps the chimpanzees understood just fine when the human experimenter pointed to a cup, but thought, "Get it yourself, big-brain."
So the German researchers leveled the playing field between the two non-human species. They added a barrier between human and dog to make their setup more like the chimps'. They put the objects they were pointing to on the far side of their animal subjects, so the humans really couldn't reach the objects themselves. They also replaced containers and hidden food with boring, inedible objects, such as a rope or a sponge. Then they gathered 32 dogs and 20 chimps. ("For practical reasons," the authors write, "the studies of the chimpanzees and the dogs were conducted separately.")
First came a warm-up phase in which the experimenter encouraged the animal to fetch a single object (in exchange for a treat) by saying "Give it to me!" This taught the animals to associate the voice command with retrieving an object. But the experimenter didn't point or look at the object she wanted.
For the experiment itself, there were two objects in the room instead of one. The experimenter pointed to the one she wanted and repeated the "Give it to me!" command, moving her eyes between the animal and the desired object to make her point clearer. The dog or chimp had to turn around, retrieve the correct object, and bring it back to the experimenter to get a treat.
The chimpanzees flunked the test. While they consistently picked up one of the two objects and brought it back to the researcher, they only picked the correct object half the time. But the dogs, as a group, performed significantly better than if they were guessing. (And they did even better when the barrier between them and the human experimenter was removed.)
It's not that chimpanzees don't follow other animals' gazes. Previous studies found that great apes will look where a human is looking to check for anything of interest. But they don't seem to understand that gaze as a form of communication. And pointing with a finger--which is really just an exaggerated way to show where you're looking--doesn't help them.
Dogs, on the other hand, have evolved to be highly attuned to what humans want. As long as they pee outside and perform the duties we assign them (sheep herding, duck retrieving, company keeping) we give them food and warm place to stay.
Of course, dogs' understanding of human gestures will depend somewhat on their personal experiences with their owners. In this study, many of the individual dogs did not perform any better than chance. But earlier studies have shown that young puppies can understand human finger-pointing, while young wolves don't understand it as well.
The fact that chimps don't understand pointing as a form of communication suggests this isn't a universal ape gesture. They can follow a gaze and understand that other individuals have different perspectives; and the captive chimps in this study should have been especially used to communicating with people. But, fittingly enough, the gesture that says "go and fetch that thing for me" seems to be specifically human.
Kirchhofer, K., Zimmermann, F., Kaminski, J., & Tomasello, M. (2012). Dogs (Canis familiaris), but Not Chimpanzees (Pan troglodytes), Understand Imperative Pointing PLoS ONE, 7 (2) DOI: 10.1371/journal.pone.0030913
Photo: by me.