The Anatomy of Seduction: Raised Brow Puppy Dog Eyes

New research shows that domestication has altered dogs' facial musculature.
By Marc Bekoff, June 2019
Photo by Ryan Walton

Photo by Ryan Walton

Dogs and humans communicate quite well. We're pretty good at reading what they want and what they're feeling, and they're very good at reading us. This reciprocal understanding of shared emotions, many of which function as "social glue," isn't all that surprising given the close association of dogs and humans during the process of domestication. (See "Dogs Mirror Our Stress and We Know More About How and Why," "Dogs Watch Us Carefully and Read Our Faces Very Well," "How Dogs See the World: Some Facts About the Canine Cosmos," "Can Dogs Tell Us We're Angry When We Don't Know We Are?," "Dogs Smell Human Fear and Mirror Our Mood When They Do," and references therein.) 

Researchers and non-researchers alike are very interested in how different behavior patterns have evolved in our canine companions. And now, due to new research by Dr. Juliane Kaminski and her colleagues, we know more about how domestication has altered the facial musculature of dogs so that they, but not wolves, have a unique muscle called AU101  that controls their seductive, sad-looking, puppy dog eyes. In an essay called "Evolution of facial muscle anatomy in dogs," Dr. Kaminski and her colleagues note that humans shaped dog behavior and anatomical features during domestication. They write, "Here we show that domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. A muscle responsible for raising the inner eyebrow intensely is uniformly present in dogs but not in wolves." Their essay, published in the prestigious journal Proceedings of the National Academy of Sciences (PNAS), is available online along with pictures of the facial musculature of dogs and wolves and informative videos. What's especially appealing about this research paper is that it's a pretty easy read, even for people who aren't researchers themselves. There are also a good number of discussions in popular media for those who want more

Dr. Kaminski and her team made their very interesting discovery by dissecting the faces of four gray wolves and six domestic dogs (cadavers, of course) and also by measuring the intensity of facial movements associated with a unique muscle called AU101 during social interactions with humans by nine wolves and 27 dogs. They discovered that dogs had a greater ability than wolves to raise the inner corner of their eyebrows without squinting due to the action of AU101. 

How and why did puppy dog eyes evolve? The anatomy of seduction

The results of this study are very interesting and important. We now have a better understanding of how and why large, sad-looking puppy dog eyes, have evolved, and it's most likely because humans preferred them and selected for them during domestication. We also know from previous research by Dr. Kaminski and her colleagues that dogs display more facial expressions when we pay attention to them. (See "Dogs Are More Expressive When We're Looking at Them.") 

Puppy dog eyes are often referred to as being "paedomorphic" (infant or juvenile-like). These traits are characterized as being "cute" and often attract attention and care from those who see them. So, it's interesting and relevant that another study titled "Paedomorphic facial expressions give dogs a selective advantage" showed that dogs who display these puppy dog eyes are rehomed more quickly from shelters than those who don't. While we really don't know the details, perhaps this is a way that muscle AU101 evolved, because dogs who displayed seductive puppy dog eyes gained a selective advantage over those who didn't do it as frequently because humans were attracted to this facial expression. The data on rehoming support the idea that it's likely that the presence of AU101 is important for forming and maintaining close relationships between dogs and humans, and they also provide an interesting window into how AU101 might have evolved. Consistent with the rehoming pattern of dogs who do and do not display puppy dog eyes, Dr Kaminski and her colleagues conclude, "Overall, the data suggest that selection—perhaps mainly unconscious—during social interactions can create selection pressures on the facial muscle anatomy in dogs strong enough for additional muscles to evolve."

Are puppy dog eyes used to manipulate humans? 

Raised brow eyes often evoke a caregiving response from humans, but there really isn't any solid evidence that dogs use them to manipulate us despite a few catchy headlines that claim they do. That dogs manipulate and "use us" is among many different myths that need to be put to rest once and for all. Suffice it to say, while some dogs might occasionally use puppy dog eyes or other behavior patterns deceptively to get something from us, there's no evidence at all that this is "canine business as usual" and that it would have resulted in the evolution of muscle AU101, other physical or morphological traits, or behavior patterns. (See "Do Dogs Really Manipulate Us? Beware Misleading Headlines," "'If Dogs Truly Were Human They Would Be Jerks'," "Dogs Live in the Present and Other Harmful Myths," "Let's Give Dogs a Break by Distinguishing Myths From Facts," Canine ConfidentialUnleashing Your Dog, and links therein.)

Human, or artificial selection, clearly influences the evolution of a wide variety of canine traits so that they express themselves in certain ways and in a single direction. Some of these traits benefit dogs, whereas others clearly do not. (See "'Why in the World do People Make These Types of Dogs?'" and links therein). The presence of muscle AU101 made me think of the fascinating fact that dogs' ears are controlled by 18 difference muscles, but we don't know much about how wolves' ears are controlled. (See "How Dogs Hear and Speak With the World Around Them.") Perhaps human selection also played a role in the muscles that control dogs' ear movements. 

Where to from here?

I really enjoyed reading Dr. Kaminski and her colleagues' essay and most, but not all, of the popular accounts. Just like cute puppy dogs eyes, some of the discussions were a bit too cute and fast for me given what we know about dogs and the nature of dog-human interactions. There's still a lot to learn about the many ways in which domestication changed wolves as they became dogs, and who would have thought that humans could have played a significant role in the evolution of a single, unique muscle that is used in dog-human social exchanges? (See "Dumping the Dog Domestication Dump Theory Once and For All.") Its extremely important for us to understand just how influential we have been in consciously and unconsciously designing dogs for our preferences, including traits that serve them well or appear to be neutral in terms of their health and survival and those that clearly don't serve them well and severely compromise their well-being, fecundity (ability to reproduce), and longevity. Many ethical questions loom

The discovery of muscle AU101—the anatomy of seduction—shows that we need to go below the surface, dig deeper if you will, to learn about the hidden causes of what happened in the past as wolves became dogs, or, as author Mark Derr aptly puts it, as dogs became dogs, and what happens now when we interact with our canine companions. (See "Dogs Mirror Our Stress and We Know More About How and Why.") Stay tuned for further discussions of dog behavior, dog-human interactions, and the various ways in which we and our canine companions connect in different social situations. I'm sure there will be many fascinating discoveries and conversations in the future. 

This story was originally published by Reprinted with permission.