That look has been used effectively to ask for another treat, to help calm an upset or angry human down, and to get a home in the case of dogs in animal shelters. And, it turns out, that “puppy dog eyes” look is an evolved trait as a response to dogs’ close relationship with people.
A team of evolutionary psychologists and anatomists have called the look “AU101: inner eyebrow raise” after conducting a study on how humans and other animals communicate by looking at each other. Focusing on domestic animal facial expressions and musculature, the researchers started with horses and cats, and the dog was the next logical step.
They found that horses have facial movements similar to dogs, but cats do not. In fact, cats don’t really move their faces at all. Dogs, however, have perfected – and some would argue, weaponised – facial expressions to communicate with humans.
In an earlier study, one of the researchers, Prof. Bridget Waller, the director of the Centre for Comparative and Evolutionary Psychology at the University of Portsmouth in the UK, found that the puppy dog eyes look has a real impact. She found that the more frequently dogs deployed the expression, the faster they were rehomed from shelters. In that regard, puppy dog eyes were more effective than tail wagging or the speed at which dogs bounded over to visiting humans.
In the latest research, Waller and her colleague Anne Burrows, an anatomist at US university Duquesne in Pittsburgh, found that dogs have a forehead muscle named the levator anguli oculi medialis, or LAOM, that wolves do not.
They looked at six breeds – chihuahua, labrador, bloodhound, German shepherd, Siberian husky and mongrel, and found all had the LAOM muscle. In the four grey wolves studied, the muscle was missing, save for a few muscle fibres. Since all dogs are derived from wolves, the comparison suggests the LAOM arose in the domestication process.
Only one other difference was noticed by the researchers: A muscle called the retractor anguli oculi lateralis (RAOL), which pulls the eyelids out towards the ears, was less prominent in wolves than dogs. Interestingly, the Siberian husky, one of the most ancient breeds, and the closest genetically to wolves, was the only dog found to lack the RAOL muscle.
After establishing that dogs and wolves have different muscles around the eyes, the researchers filmed the animals to see how their expressions varied. They filmed nine wolves in two different animal parks, and 27 dogs, mostly Staffordshire bull terriers, in shelters across the UK. The footage was reviewed by a trained specialist who was not told about the scientists’ hypothesis. The specialist recorded when the animals made the puppy dog eyes expression, and rated its intensity on a five-point scale.
Unsurprisingly, dogs pulled the doleful face far more frequently than wolves. While dogs and wolves both produced “low intensity” expressions, only dogs appear to have achieved what the scientists classified as “high intensity expressions”.
Waller does not believe dogs originally produced the expression to win humans over. What is more likely, she believes, is that animals that happened to deploy puppy dog eyes tapped into a response humans had evolved over millennia of living in large groups, where reading facial expressions was crucial. They have hypothesised that humans have also unconsciously favoured eyebrow-raising dogs during fairly recent selective breeding.
Whether this was the case, or dogs evolved the expression as a result of their proximity to us, it just proves they are smart enough to use all the tools at their disposal to get their way more with their human friends – by training their own bodies.