Dogs have evolved new muscles around their eyes to better communicate with humans.
New research comparing the anatomy and behavior of dogs and wolves suggests that dogs’ facial anatomy has changed over thousands of years specifically to allow them to better communicate with humans.
In the first detailed analysis comparing the anatomy and behavior of dogs and wolves, researchers found that the facial musculature of both species was similar, except above the eyes. Dogs have a small muscle, which allows them to intensely raise their inner eyebrow, which wolves do not have.
The authors suggest that the inner eyebrow raising movement triggers a nurturing response in humans because it makes the dogs’ eyes appear larger, more infant-like, and also resembles a movement humans produce when they are sad.
The research team, under comparative psychologist Dr. Juliane Kaminski, at the University of Portsmouth, included numerous behavioral and anatomical experts in the UK and United States.
The study is published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).
“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,” Dr. Kaminski said in a statement. “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 showed that dogs moved their eyebrows significantly more when humans were looking at them compared to when they were not looking at them.
“The raised inner eyebrow movement in dogs is driven by a muscle which doesn’t consistently exist in their closest living relative, the wolf,” stated co-author of the paper, Professor Anne Burrows, at Duquesne University in Pittsburgh. “This is a striking difference for species separated only 33,000 years ago and we think that the remarkably fast facial muscular changes can be directly linked to dogs’ enhanced social interaction with humans.”
Dr. Kaminski and co-author, Evolutionary Psychologist, Professor Bridget Waller, also at the University of Portsmouth, previously mapped the facial muscular structure of dogs, naming the movement responsible for a raised inner eyebrow, the Action Unit (AU) 101.
Soft tissue, including muscle, doesn’t tend to survive in the fossil record, making a study of this type much harder.
The only dog species in the study that did not have the muscle was the Siberian Husky, which is among more ancient dog breeds.
An alternative reason for the human-dog bond could be that humans have a preference for individuals which have more white exposed in their eye, and that intense AU 101 movements expose the white part of dogs’ eyes.
It is not known why or precisely when humans first brought wolves in from the cold and the evolution from wolf to dog began, but this research helps us understand some of the likely mechanisms underlying dog domestication.
Co-authors and anatomists Adam Hartstone-Rose, at North Carolina State University, and Rui Diogo, an anatomist at Howard University in Washington DC, also worked on this important study. All the more reason to treat dogs with love and respect and like the family they are.
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