Even people who are not particularly dog lovers often find puppies adorable. Their facial expressions, especially their eyes, are something that many people find appealing, and their expressions can help them get away with anything from pooping on the carpet to stealing from the trash can. Humans have even coined the phrase ‘puppy dog eyes’ to refer to an expression that people use when they are pleading or trying to get away with something. Now, the results of studies have shown that it is no accident that dogs use their eyes in their facial expressions in this way. It transpires that dogs have evolved new muscles that allow them to communicate with humans better via their facial expressions, says Dogster.
The interesting study, which relates to the evolution of domestic dogs compared to wild dogs, was published in the journal ‘Proceedings of the National Academy of Sciences’ in June 2019. It notes that domestic dogs have a small muscle above their eye that wolves do not, and this allows domestic dogs to use different expressions, including the sweet look that dog owners have come to love. This study was conducted by a team of researchers at the University of Portsmouth, and Bridget Waller is a co-author of the study. According to Waller, dogs have the power to capture the hearts of humans, and humans pay a lot of attention to a dog’s face. Their expressions can often make them look juvenile or sad, which is a cute factor that induces a nurturing response in humans.
The authors of the study hypothesized that the inner eyebrow-raising movement can trigger human responses because it makes the eyes look bigger and like those of an infant, says Earth Sky. The movement also resembles an expression made by humans when they are feeling sad. Juliane Kaminski is the lead author of the study. She has said that there is compelling evidence that domesticated dogs have developed an inner eyebrow muscle that wolves do not have. The study involved the behavior of both wolves and domesticated dogs and compared the boy language and behavior of the two groups when they were exposed to humans for a period of two minutes.
The findings revealed that domesticated dogs not only raised their inner eyebrows more frequently but also at higher intensities than wolves. It is possible that these findings indicate that dogs use expressive eyebrows because of the unconscious preferences of humans. This may have influenced selection during the domestication of dogs. Humans have a strong desire to look after dogs when they make these eye movements. Therefore, dogs that make the eye movements have a disadvantage over dogs that do not. This then gives them a selection advantage and reinforces the trait for ‘puppy dog eyes’ that is then passed on to future generations.
Another co-author of the study is Anne Burrows, an anatomist professor at Duquesne University. She discussed the study further, saying that they needed to determine whether the changes in eyebrow movement was the result of evolution or if other factors were involved. To do this, the researchers studied the behavior and facial anatomy of domesticated dogs and wolves. They discovered that wolves raised their eyebrows slightly due to a scant and irregular cluster of muscle fibers rather than a full muscle. Burrows explains that wolves are the closest living relatives to domestic dogs and that the muscle that drives the inner eyebrow movement in domestic dogs does not consistently exist in wolves.
Domestic dogs and wolves are species that were only separated 33,000 years ago. In evolutionary terms, this is a relatively short period of time. Despite this relatively short evolutionary period of separation, there is now a striking difference between wolves and domesticated dogs. The scientists involved in the study believe that these facial muscular and expression changes have occurred so fast because of the enhanced social interaction of domesticated dogs with humans. Interestingly, one of the domesticated dog breeds included in the study did not have the muscle above the inner eye that enables domesticated dogs to mimic the sad expression of humans. The Independent says that this dog breed is the Siberian Husky. This is interesting because the Siberian Husky is one of the most ancient breeds of dog, and one that it most closely related to wild wolves. An important point to note about the study is that the looked at the entire facial anatomy of domesticated dogs compared to that of wolves. In almost every other aspect of their facial anatomies, both groups had the same facial structure. The inner eyebrow muscle was the only significant subject noticed.
The study has attracted interest from scientists from many fields around the world, with many giving their opinions on the research. One such scientist is Adam Hartstone, an anatomist at North Carolina State University. He described how the tiny inner eye muscles are so thin that you can see through them. Despite the small size of the muscles, they have a powerful effect on the expressions a dog can make. Hartstone believes that this suggests there has been substantial evolutionary pressure. Hartstone goes on to say that the facial expressions made by domesticated dogs can make a remarkable difference and that it is possible that these changes to facial expressions may have influenced and defined the relationship between humans and early dogs.
Although the findings of this study have no immediate impact on the relationship that humans have with dogs, it could allow scientists to understand the evolutionary processes that take place during domestication and look to potential future evolutionary changes that may occur. It is also possible that they could apply their findings to other species of domesticated animals to understand any evolutionary changes. For example, scientists could research the evolutionary changes of domesticated cats compared to their wild counterparts. Regardless of the potential uses of the research, the findings are very interesting.