‘Puppy eyes’ explained
New research suggests dogs have developed new muscles around their eyes to better communicate with humans
New research comparing the anatomy and behavior of dogs and wolves suggests the facial anatomy of dogs has changed over thousands of years to allow them to better communicate with humans.
A key difference between wolves and dogs
In a comprehensive analysis comparing the anatomy and behavior of dogs and wolves, researchers found that the facial musculature of both species was quite similar, except… above the eyes. It turns out dogs have a small muscle, which enables them to thoroughly raise their inner eyebrow. Wolves just do not have such feature.
The authors believe the inner eyebrow raising movement triggers a nurturing response in humans because it makes the dogs’ eyes appear bigger, more juvenile and also resembles a movement humans make when they are sad. The research team, led by comparative psychologist Dr. Juliane Kaminski, at the University of Portsmouth, was composed of a team of behavioral and anatomical experts in the UK and US. It is published in the journal Proceedings of the National Academy of Sciences(PNAS).
Dr. Kaminski stated: “The evidence is compelling that dogs developed a muscle to raise the inner eyebrow after they were domesticated from wolves. We also studied dogs’ and wolves’ behavior, and when exposed to a human for two minutes, dogs raised their inner eyebrows more and at higher intensities than wolves. The findings suggest that expressive eyebrows in dogs may be a result of humans unconscious preferences that influenced selection during domestication. When dogs make the movement, it seems to elicit a strong desire in humans to look after them. This would give dogs, that move their eyebrows more, a selection advantage over others and reinforce the ‘puppy dog eyes’ trait for future generations.”
Dr. Kaminski’s previous research indicated that dogs moved their eyebrows more when humans were looking at them versus when they were not looking at them. “The AU101 movement (inner brow raiser) is significant in the human-dog bond because it might elicit a caring response from humans but also might create the illusion of human-like communication. Our findings show how important faces can be in capturing our attention, and how powerful facial expression can be in social interaction.” she added.
Co-author and anatomist Adam Hartstone-Rose, at North Carolina State University explains that “These muscles are so thin that you can literally see through them — and yet the movement that they allow seems to have such a powerful effect that it appears to have been under substantial evolutionary pressure. It is really remarkable that these simple differences in facial expression may have helped define the relationship between early dogs and humans.”
Co-author Rui Diogo, an anatomist at Howard University stated: “I must admit that I was surprised to see the results myself because the gross anatomy of muscles is normally very slow to change in evolution, and this happened very fast indeed, in just some dozens of thousands of years.”
Soft tissue (including muscle) doesn’t tend to survive in the fossil record, making the study of this type of evolution harder. The only dog species in the study that did not have such muscle was the Siberian husky, which is an ancient dog breed. Another reason for the human-dog bond could well be that humans have a preference for other individuals which have “whites in the eye” and that intense inner brow raiser movements expose the white part of the dogs’ eyes.
This research is interesting because it helps us understand some of the mechanisms behind dog domestication.