Those sweet doggy eyes are captivating, but did you know that it is we humans that affected their evolution. Positive feedback works wonders!


Puppy Dog Eyes.

"Puppy Dog Eyes" (Credit: Fotyma/Shutterstock)


British and U.S. researchers from four universities have reported on the evolution of "puppy dog eyes," estimated to begin to evolve about 33,000 years ago, around the time that dogs and wolves became distinct species.

As dog owners, most of us don't focus on the exact movements that make our dog's faces so responsive and so hard to resist. It turns out though, according to a study published in the current issue of PNAS (Proceedings of the National Academy of Sciences of The United States of America), it's a group of muscles in the dogs' eyebrows (Action Unit 101) that, when raised, create the look we call "puppy dog eyes," making the eyes appear larger, often showing the whites of a dog's eyes.

It turns out that wolves don't have those muscles. "To determine whether this eyebrow movement is a result of evolution, we compared the facial anatomy and behaviour of these two species and found the muscle that allows for the eyebrow raise in dogs was, in wolves, a scant, irregular cluster of fibres," observed study anatomist Anne Burrows, researcher from Duquesne University.


Facial musculature in the wolf (C. lupus) (animal’s left) and dog (C. familiaris) (right) with differences in anatomy highlighted in red. Image courtesy of Tim D. Smith (Cambridge University Press, Cambridge, UK).

Facial musculature in the wolf (C. lupus) and dog (C. familiaris) with differences in anatomy highlighted in red. Image courtesy of Tim D. Smith (Cambridge University Press, Cambridge, UK) via PNAS


Perhaps this "cluster of fibres" developed into muscles as dogs learned how to communicate with and please their humans.


Dog eyebrow changes

Internal eyebrow muscles at work! (via)


The study involved 5 dogs - a Labrador Retriever, Bloodhound, Chihuahua, German Shepherd, Siberian Husky, and a mix-breed dog - and 4 wolves. The dogs and wolves were each exposed to a human for two minutes. All of the dogs, except the Siberian Husky, responded with the "puppy dog eyes." None of the wolves responded in that way. (Siberian Huskies are one of the oldest breeds of dogs.)

There are two major take-aways from this study. One is that these special muscles developed in less than 33,000 years, which is a remarkably fast evolution, according to anatomists. Co-author Rui Diogo, an anatomist at Howard University, said of this discovery: “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.”

The second observation is that seeing the whites of a person's eyes has an impact on human interaction with other humans. It's part of human facial expression. Perhaps a dog's ability to imitate eye contact and expression helped enable dog and man's connection. It certainly helps dogs get what they want!




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